And directly or indirectly affects its vital activity, growth, development, reproduction.

Each organism lives in a specific habitat. Elements or properties of the environment are called environmental factors. On our planet there are four environments of life: ground-air, water, soil, and other organisms. Living organisms are adapted to exist in certain living conditions and in a certain environment.

Some organisms live on land, others in soil, and others in water. Some chose the bodies of other organisms as their place of residence. Thus, four living environments are distinguished: ground-air, aquatic, soil, and other organisms (Fig. 3). Each living environment is characterized by certain properties to which the organisms living in it are adapted.

Ground-air environment

The land-air environment is characterized by low air density, abundance of light, rapid temperature changes, and variable humidity. Therefore, organisms that live in the ground-air environment have well-developed supporting structures - the external or internal skeleton in animals, special structures in plants.

Many animals have organs of movement on the ground - limbs or wings for flight. Thanks to their developed visual organs, they see well. Land organisms have adaptations that protect them from fluctuations in temperature and humidity (for example, special body coverings, construction of nests, burrows). The plants have well-developed roots, stems, and leaves.

Water environment

The aquatic environment is characterized by a higher density compared to air, so water has a buoyant force. Many organisms “float” in the water column - small animals, bacteria, protists. Others are actively moving. To do this, they have locomotion organs in the form of fins or flippers (fish, whales, seals). Active swimmers, as a rule, have a streamlined body shape.

Many aquatic organisms (coastal plants, algae, coral polyps) lead an attached lifestyle, others are sedentary (some mollusks, starfish).

Water accumulates and retains heat, so there are no such sharp temperature fluctuations in water as on land. The amount of light in reservoirs varies depending on the depth. Therefore, autotrophs populate only that part of the reservoir where light penetrates. Heterotrophic organisms have mastered the entire water column.

Soil environment

There is no light in the soil environment, no sudden temperature changes, and high density. The soil is inhabited by bacteria, protists, fungi, and some animals (insects and their larvae, worms, moles, shrews). Soil animals have a compact body. Some of them have digging limbs, absent or underdeveloped organs of vision (mole).

The totality of environmental elements necessary for an organism, without which it cannot exist, is called the conditions of existence or living conditions.

On this page there is material on the following topics:

• shrew habitat terrestrial aerial aquatic soil or other

• organism as a habitat examples

• examples of organisms living in our environment

• what properties are characteristic of aquatic habitats

• organisms living in the body of other organisms

Questions for this article:

• What is habitat and living conditions?

• What are called environmental factors?

• What groups of environmental factors are distinguished?

• What properties are characteristic of the ground-air environment?

• Why is it believed that the land-air environment of life is more complex than the water or soil environment?

• What are the characteristics of organisms living inside other organisms?

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  4.1. Aquatic habitat. Specifics of adaptation of aquatic organisms

  Water as a habitat has a number of specific properties, such as high density, strong pressure drops, relatively low oxygen content, strong absorption of sunlight, etc. Reservoirs and their individual areas also differ in salt regime, speed of horizontal movements (currents) , content of suspended particles. For the life of benthic organisms, the properties of the soil, the mode of decomposition of organic residues, etc. are important. Therefore, along with adaptation to the general properties of the aquatic environment, its inhabitants must also be adapted to a variety of particular conditions. The inhabitants of the aquatic environment received a common name in ecology hydrobionts. They inhabit the World Ocean, continental reservoirs and groundwater. In any body of water, zones with different conditions can be distinguished.

  4.1.1. Ecological zones of the World Ocean

  In the ocean and its seas, there are primarily two ecological areas: the water column - pelagic and the bottom - benthal (Fig. 38). Depending on the depth, benthal is divided into sublittoral zone - an area of ​​gradual decline of land to a depth of approximately 200 m, bathyal– area of ​​steep slope and abyssal zone– an area of ​​the ocean floor with an average depth of 3–6 km. Even deeper benthic regions, corresponding to the depressions of the ocean floor, are called ultraabyssal. The edge of the shore that is flooded during high tides is called littoral Above the tide level, the part of the coast moistened by the spray of the surf is called supralittoral.

  Rice. 38. Ecological zones of the World Ocean

  
  

  Naturally, for example, the inhabitants of the sublittoral zone live in conditions of relatively low pressure, daytime sunlight, and often quite significant changes in temperature. The inhabitants of the abyssal and ultra-abyssal depths exist in darkness, at a constant temperature and monstrous pressure of several hundred, and sometimes about a thousand atmospheres. Therefore, just an indication of the benthic zone in which a particular species of organism lives already indicates what general ecological properties it should have. The entire population of the ocean floor was named benthos.

  Organisms that live in the water column, or pelagic zone, are classified as Pelagos. The pelagic zone is also divided into vertical zones corresponding in depth to the benthic zones: epipelagic, bathypelagic, abyssopelagic. The lower boundary of the epipelagic zone (no more than 200 m) is determined by the penetration of sunlight in an amount sufficient for photosynthesis. Photosynthetic plants cannot exist deeper than these zones. In the twilight bathyal and dark abyssal depths, only microorganisms and animals live. Different ecological zones are also distinguished in all other types of reservoirs: lakes, swamps, ponds, rivers, etc. The diversity of aquatic organisms that have mastered all these habitats is very great.

  4.1.2. Basic properties of the aquatic environment

  Density of water is a factor that determines the conditions for the movement of aquatic organisms and pressure at different depths. For distilled water, the density is 1 g/cm 3 at 4 °C. The density of natural waters containing dissolved salts can be greater, up to 1.35 g/cm 3 . Pressure increases with depth by an average of 1 × 10 5 Pa (1 atm) for every 10 m.

  Due to the sharp pressure gradient in water bodies, aquatic organisms are generally much more eurybathic compared to land organisms. Some species, distributed at different depths, tolerate pressure from several to hundreds of atmospheres. For example, holothurians of the genus Elpidia and worms Priapulus caudatus live from the coastal zone to the ultra-abyssal zone. Even freshwater inhabitants, such as slipper ciliates, suvoikas, swimming beetles, etc., can withstand up to 6 × 10 7 Pa (600 atm) in experiments.

  However, many inhabitants of the seas and oceans are relatively stenobatic and confined to certain depths. Stenobacy is most often characteristic of shallow- and deep-sea species. Only the littoral zone is inhabited by the annelids Arenicola and limpet mollusks (Patella). Many fish, for example from the group of anglers, cephalopods, crustaceans, pogonophora, starfish, etc., are found only at great depths at a pressure of at least 4 10 7 – 5 10 7 Pa (400–500 atm).

  The density of water provides the ability to lean on it, which is especially important for non-skeletal forms. The density of the environment serves as a condition for floating in water, and many aquatic organisms are adapted specifically to this way of life. Suspended organisms floating in water are combined into a special ecological group of aquatic organisms - plankton (“planktos” – soaring).

  
  
  
  

  Rice. 39. Increase in the relative body surface of planktonic organisms (according to S. A. Zernov, 1949):

  A – rod-shaped:

  1 – diatom Synedra;

  2 – cyanobacterium Aphanizomenon;

  3 – peridine alga Amphisolenia;

  4 – Euglena acus;

  5 – cephalopod Doratopsis vermicularis;

  6 – copepod Setella;

  7 – Porcellana larva (Decapoda)

  
  
  

  B – dissected forms:

  1 – mollusk Glaucus atlanticus;

  2 – worm Tomopetris euchaeta;

  3 – larva of Palinurus crayfish;

  4 – larva of the monkfish fish Lophius;

  5 – copepod Calocalanus pavo

  
  

  The plankton includes unicellular and colonial algae, protozoa, jellyfish, siphonophores, ctenophores, pteropods and keelfoot mollusks, various small crustaceans, larvae of bottom animals, fish eggs and fry, and many others (Fig. 39). Planktonic organisms have many similar adaptations that increase their buoyancy and prevent them from sinking to the bottom. Such adaptations include: 1) a general increase in the relative surface of the body due to reduction in size, flattening, elongation, development of numerous projections or bristles, which increases friction with water; 2) a decrease in density due to the reduction of the skeleton, the accumulation of fats, gas bubbles, etc. in the body. In diatoms, reserve substances are deposited not in the form of heavy starch, but in the form of fat drops. The night light Noctiluca is distinguished by such an abundance of gas vacuoles and fat droplets in the cell that the cytoplasm in it has the appearance of strands that merge only around the nucleus. Siphonophores, a number of jellyfish, planktonic gastropods, etc. also have air chambers.

  Seaweed (phytoplankton) They float in water passively, but most planktonic animals are capable of active swimming, but to a limited extent. Planktonic organisms cannot overcome currents and are transported by them over long distances. Many types zooplankton However, they are capable of vertical migrations in the water column for tens and hundreds of meters, both due to active movement and by regulating the buoyancy of their body. A special type of plankton is an ecological group Neuston (“nein” - swim) - inhabitants of the surface film of water at the border with the air.

  The density and viscosity of water greatly influence the possibility of active swimming. Animals capable of fast swimming and overcoming the force of currents are united in an ecological group nekton (“nektos” – floating). Representatives of nekton are fish, squid, and dolphins. Rapid movement in the water column is possible only if you have a streamlined body shape and highly developed muscles. The torpedo-shaped shape is developed in all good swimmers, regardless of their systematic affiliation and method of movement in the water: reactive, due to bending of the body, with the help of limbs.

  Oxygen regime. In oxygen-saturated water, its content does not exceed 10 ml per 1 liter, which is 21 times lower than in the atmosphere. Therefore, the breathing conditions of aquatic organisms are significantly complicated. Oxygen enters water mainly through the photosynthetic activity of algae and diffusion from the air. Therefore, the upper layers of the water column are, as a rule, richer in this gas than the lower ones. As the temperature and salinity of water increase, the concentration of oxygen in it decreases. In layers heavily populated by animals and bacteria, a sharp deficiency of O 2 can be created due to its increased consumption. For example, in the World Ocean, life-rich depths from 50 to 1000 m are characterized by a sharp deterioration in aeration - it is 7-10 times lower than in surface waters inhabited by phytoplankton. Conditions near the bottom of reservoirs can be close to anaerobic.

  Among aquatic inhabitants there are many species that can tolerate wide fluctuations in oxygen content in water, up to its almost complete absence (euryoxybionts – “oxy” – oxygen, “biont” – inhabitant). These include, for example, the freshwater oligochaete Tubifex tubifex and the gastropod Viviparus viviparus. Among fish, carp, tench, and crucian carp can withstand very low oxygen saturation of water. However, a number of types stenoxybiont – they can exist only with sufficiently high oxygen saturation of the water (rainbow trout, brown trout, minnow, eyelash worm Planaria alpina, larvae of mayflies, stoneflies, etc.). Many species are capable of falling into an inactive state when there is a lack of oxygen - anoxybiosis - and thus experience an unfavorable period.

  Respiration of aquatic organisms occurs either through the surface of the body or through specialized organs - gills, lungs, tracheas. In this case, the integument can serve as an additional respiratory organ. For example, the loach fish consumes an average of 63% of oxygen through its skin. If gas exchange occurs through the integuments of the body, they are very thin. Breathing is also made easier by increasing the surface area. This is achieved during the evolution of species by the formation of various outgrowths, flattening, elongation, and a general decrease in body size. Some species, when there is a lack of oxygen, actively change the size of the respiratory surface. Tubifex tubifex worms greatly elongate their body; hydra and sea anemone - tentacles; echinoderms - ambulacral legs. Many sessile and sedentary animals renew the water around them, either by creating a directed current or by oscillating movements, promoting its mixing. Bivalve mollusks use cilia lining the walls of the mantle cavity for this purpose; crustaceans - the work of the abdominal or thoracic legs. Leeches, bell mosquito larvae (bloodworms), and many oligochaetes sway their bodies, sticking out of the ground.

  In some species, a combination of water and air respiration occurs. These include lungfishes, siphonophores discophants, many pulmonary mollusks, crustaceans Gammarus lacustris, etc. Secondary aquatic animals usually retain the atmospheric type of respiration as it is more energetically favorable and therefore require contact with the air, for example, pinnipeds, cetaceans, water beetles, mosquito larvae, etc.

  Lack of oxygen in water sometimes leads to catastrophic phenomena - I'm dying, accompanied by the death of many aquatic organisms. Winter freezes often caused by the formation of ice on the surface of bodies of water and the cessation of contact with air; summer– an increase in water temperature and a resulting decrease in oxygen solubility.

  Frequent death of fish and many invertebrates in winter is characteristic, for example, of the lower part of the Ob River basin, the waters of which, flowing from the wetlands of the West Siberian Lowland, are extremely poor in dissolved oxygen. Sometimes death occurs in the seas.

  In addition to a lack of oxygen, death can be caused by an increase in the concentration of toxic gases in water - methane, hydrogen sulfide, CO 2, etc., formed as a result of the decomposition of organic materials at the bottom of reservoirs.

  Salt regime. Maintaining the water balance of aquatic organisms has its own specifics. If for terrestrial animals and plants it is most important to provide the body with water in conditions of its deficiency, then for hydrobionts it is no less important to maintain a certain amount of water in the body when there is an excess of it in the environment. Excessive amounts of water in cells leads to changes in osmotic pressure and disruption of the most important vital functions.

  Most aquatic life poikilosmotic: the osmotic pressure in their body depends on the salinity of the surrounding water. Therefore, the main way for aquatic organisms to maintain their salt balance is to avoid habitats with unsuitable salinity. Freshwater forms cannot exist in the seas, and marine forms cannot tolerate desalination. If the salinity of water is subject to changes, animals move in search of a favorable environment. For example, when the surface layers of the sea are desalinated after heavy rains, radiolarians, sea crustaceans Calanus and others descend to a depth of 100 m. Vertebrates, higher crustaceans, insects and their larvae living in water belong to homoiosmotic species, maintaining constant osmotic pressure in the body regardless of the concentration of salts in the water.

  In freshwater species, body juices are hypertonic in relation to the surrounding water. They are threatened by excessive watering if the flow of water is not prevented or excess water is not removed from the body. In protozoa this is achieved by the work of excretory vacuoles, in multicellular organisms - by removing water through the excretory system. Some ciliates secrete an amount of water equal to their body volume every 2–2.5 minutes. The cell expends a lot of energy to “pump out” excess water. With increasing salinity, the work of vacuoles slows down. Thus, in Paramecium slippers, at a water salinity of 2.5%o, the vacuole pulsates at intervals of 9 s, at 5%o - 18 s, at 7.5%o - 25 s. At a salt concentration of 17.5% o, the vacuole stops working, since the difference in osmotic pressure between the cell and the external environment disappears.

  If water is hypertonic in relation to the body fluids of aquatic organisms, they are at risk of dehydration as a result of osmotic losses. Protection against dehydration is achieved by increasing the concentration of salts also in the body of aquatic organisms. Dehydration is prevented by the water-impermeable integument of homoiosmotic organisms - mammals, fish, higher crayfish, aquatic insects and their larvae.

  Many poikilosmotic species transition to an inactive state - suspended animation as a result of a lack of water in the body with increasing salinity. This is characteristic of species living in pools of sea water and in the littoral zone: rotifers, flagellates, ciliates, some crustaceans, the Black Sea polychaete Nereis divesicolor, etc. Salt suspended animation– a means to survive unfavorable periods in conditions of variable salinity of water.

  Truly euryhaline There are not many species among aquatic inhabitants that can live in an active state in both fresh and salt water. These are mainly species inhabiting river estuaries, estuaries and other brackish water bodies.

  Temperature reservoirs are more stable than on land. This is due to the physical properties of water, primarily its high specific heat capacity, due to which the receipt or release of a significant amount of heat does not cause too sudden changes in temperature. The evaporation of water from the surface of reservoirs, which consumes about 2263.8 J/g, prevents overheating of the lower layers, and the formation of ice, which releases the heat of fusion (333.48 J/g), slows down their cooling.

  The amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10–15 °C, in continental waters – 30–35 °C. Deep layers of water are characterized by constant temperature. In equatorial waters, the average annual temperature of surface layers is +(26–27) °C, in polar waters it is about 0 °C and below. In hot land-based springs, the water temperature can approach +100 °C, and in underwater geysers, at high pressure on the ocean floor, temperatures of +380 °C have been recorded.

  Thus, there is a fairly significant variety of temperature conditions in reservoirs. Between the upper layers of water with seasonal temperature fluctuations expressed in them and the lower ones, where the thermal regime is constant, there is a zone of temperature jump, or thermocline. The thermocline is more pronounced in warm seas, where the temperature difference between external and deep waters is greater.

  Due to the more stable temperature regime of water, stenothermy is common among aquatic organisms to a much greater extent than among the land population. Eurythermal species are found mainly in shallow continental reservoirs and in the littoral zone of seas of high and temperate latitudes, where daily and seasonal temperature fluctuations are significant.

  Light mode. There is much less light in water than in air. Some of the rays incident on the surface of a reservoir are reflected into the air. The lower the position of the Sun, the stronger the reflection, so the day under water is shorter than on land. For example, a summer day near the island of Madeira at a depth of 30 m - 5 hours, and at a depth of 40 m only 15 minutes. The rapid decrease in the amount of light with depth is associated with its absorption by water. Rays of different wavelengths are absorbed differently: red ones disappear close to the surface, while blue-green ones penetrate much deeper. The twilight in the ocean, which deepens with depth, is first green, then blue, indigo and blue-violet, finally giving way to constant darkness. Accordingly, green, brown and red algae, specialized in capturing light with different wavelengths, replace each other with depth.

  The color of animals changes with depth just as naturally. The inhabitants of the littoral and sublittoral zones are most brightly and variedly colored. Many deep organisms, like cave organisms, do not have pigments. In the twilight zone, red coloration is widespread, which is complementary to the blue-violet light at these depths. Rays of additional color are most completely absorbed by the body. This allows animals to hide from enemies, since their red color in blue-violet rays is visually perceived as black. Red coloring is characteristic of twilight zone animals such as sea bass, red coral, various crustaceans, etc.

  In some species that live near the surface of water bodies, the eyes are divided into two parts with different abilities to refract rays. One half of the eye sees in the air, the other in water. Such “four-eyedness” is characteristic of whirling beetles, the American fish Anableps tetraphthalmus, and one of the tropical species of blenny Dialommus fuscus. During low tides, this fish sits in recesses, exposing part of its head from the water (see Fig. 26).

  The absorption of light is stronger, the lower the transparency of the water, which depends on the number of particles suspended in it.

  Transparency is characterized by the maximum depth at which a specially lowered white disk with a diameter of about 20 cm (Secchi disk) is still visible. The clearest waters are in the Sargasso Sea: the disk is visible to a depth of 66.5 m. In the Pacific Ocean, the Secchi disk is visible up to 59 m, in the Indian Ocean - up to 50, in shallow seas - up to 5-15 m. The transparency of rivers is on average 1–1 .5 m, and in the muddiest rivers, for example in the Central Asian Amu Darya and Syr Darya, only a few centimeters. The boundary of the photosynthetic zone therefore varies greatly in different bodies of water. In the clearest waters euphotic zone, or zone of photosynthesis, extends to depths not exceeding 200 m, crepuscular, or dysphotic, the zone occupies depths of up to 1000–1500 m, and deeper, in aphotic zone, sunlight does not penetrate at all.

  The amount of light in the upper layers of reservoirs varies greatly depending on the latitude of the area and the time of year. Long polar nights severely limit the time available for photosynthesis in Arctic and Antarctic basins, and ice cover makes it difficult for light to reach all frozen bodies of water in winter.

  In the dark depths of the ocean, organisms use light emitted by living things as a source of visual information. The glow of a living organism is called bioluminescence. Luminous species are found in almost all classes of aquatic animals from protozoa to fish, as well as among bacteria, lower plants and fungi. Bioluminescence appears to have arisen multiple times in different groups at different stages of evolution.

  The chemistry of bioluminescence is now quite well understood. The reactions used to generate light are varied. But in all cases this is the oxidation of complex organic compounds (luciferins) using protein catalysts (luciferase). Luciferins and luciferases have different structures in different organisms. During the reaction, the excess energy of the excited luciferin molecule is released in the form of light quanta. Living organisms emit light in impulses, usually in response to stimuli coming from the external environment.

  Glow may not play a special ecological role in the life of a species, but may be a by-product of the vital activity of cells, as, for example, in bacteria or lower plants. It acquires ecological significance only in animals that have a sufficiently developed nervous system and visual organs. In many species, the luminescent organs acquire a very complex structure with a system of reflectors and lenses that enhance radiation (Fig. 40). A number of fish and cephalopods, unable to generate light, use symbiotic bacteria that multiply in the special organs of these animals.

  
  
  
  

  Rice. 40. Luminescence organs of aquatic animals (according to S. A. Zernov, 1949):

  1 – a deep-sea anglerfish with a flashlight over its toothed mouth;

  2 – distribution of luminous organs in fish of the family. Mystophidae;

  3 – luminous organ of the fish Argyropelecus affinis:

  a – pigment, b – reflector, c – luminous body, d – lens

  
  

  Bioluminescence has mainly a signaling value in the life of animals. Light signals can serve for orientation in a flock, attracting individuals of the opposite sex, luring victims, for camouflage or distraction. A flash of light can act as a defense against a predator by blinding or disorienting it. For example, deep-sea cuttlefish, fleeing from an enemy, release a cloud of luminous secretion, while species living in illuminated waters use dark liquid for this purpose. In some bottom worms - polychaetes - luminous organs develop during the period of maturation of reproductive products, and females glow brighter, and the eyes are better developed in males. In predatory deep-sea fish from the order of anglerfish, the first ray of the dorsal fin is shifted to the upper jaw and turned into a flexible “rod” carrying at the end a worm-shaped “bait” - a gland filled with mucus with luminous bacteria. By regulating the blood flow to the gland and, therefore, the supply of oxygen to the bacterium, the fish can voluntarily cause the “bait” to glow, imitating the movements of the worm and luring in prey.

  In a terrestrial environment, bioluminescence is developed only in a few species, most strongly in beetles from the family of fireflies, which use light signaling to attract individuals of the opposite sex during twilight or night time.

  4.1.3. Some specific adaptations of aquatic organisms

  Methods of orientation of animals in the aquatic environment. Living in constant twilight or darkness greatly limits your options visual orientation hydrobionts. Due to the rapid attenuation of light rays in water, even those with well-developed visual organs can only use them to navigate at close range.

  Sound travels faster in water than in air. Focus on sound In hydrobionts it is generally better developed than the visual one. A number of species detect even very low frequency vibrations (infrasounds), arising when the rhythm of waves changes, and descends from the surface layers to deeper ones in advance of the storm (for example, jellyfish). Many inhabitants of water bodies - mammals, fish, mollusks, crustaceans - make sounds themselves. Crustaceans do this by rubbing various body parts against each other; fish - using the swim bladder, pharyngeal teeth, jaws, pectoral fin rays and other means. Sound signaling most often serves for intraspecific relationships, for example, for orientation in a school, attracting individuals of the opposite sex, etc., and is especially developed among inhabitants of turbid waters and great depths, living in the dark.

  A number of hydrobionts find food and navigate using echolocation– perception of reflected sound waves (cetaceans). Many perceive reflected electrical impulses, producing discharges of different frequencies while swimming. About 300 species of fish are known to generate electricity and use it for orientation and signaling. The freshwater elephant fish (Mormyrus kannume) sends out up to 30 pulses per second, detecting invertebrates that it forages in liquid mud without the aid of vision. The discharge frequency of some marine fish reaches 2000 pulses per second. A number of fish also use electric fields for defense and attack (electric stingray, electric eel, etc.).

  For orientation in depth it is used perception of hydrostatic pressure. It is carried out using statocysts, gas chambers and other organs.

  The most ancient method of orientation, characteristic of all aquatic animals, is perception of environmental chemistry. The chemoreceptors of many aquatic organisms are extremely sensitive. In the thousand-kilometer migrations that are typical for many species of fish, they navigate mainly by smell, finding spawning or feeding grounds with amazing accuracy. It has been experimentally proven, for example, that salmon artificially deprived of their sense of smell do not find the mouth of their river when returning to spawn, but they are never mistaken if they can perceive odors. The subtlety of the sense of smell is extremely high in fish that make especially long migrations.

  Specifics of adaptations to life in drying up water bodies. On Earth there are many temporary, shallow reservoirs that appear after river floods, heavy rains, snow melting, etc. In these reservoirs, despite the brevity of their existence, a variety of aquatic organisms settle.

  Common features of the inhabitants of drying up pools are the ability to give birth to numerous offspring in a short time and endure long periods without water. Representatives of many species bury themselves in the silt, going into a state of reduced vital activity - hypobiosis. This is how scale insects, cladocerans, planarians, oligochaete worms, mollusks and even fish behave like loaches, African protopterus and the South American lepidosiren from lungfishes. Many small species form cysts that can withstand drought, such as sunflowers, ciliates, rhizopods, a number of copepods, turbellarians, and nematodes of the genus Rhabditis. Others experience an unfavorable period in the highly resistant egg stage. Finally, some small inhabitants of drying up reservoirs have a unique ability to dry out to a film state, and when moistened, resume growth and development. The ability to tolerate complete dehydration of the body has been revealed in rotifers of the genera Callidina, Philodina, etc., tardigrades Macrobiotus, Echiniscus, nematodes of the genera Tylenchus, Plectus, Cephalobus, etc. These animals inhabit micro-reservoirs in the cushions of mosses and lichens and are adapted to sudden changes in humidity conditions.

  Filtration as a type of nutrition. Many hydrobionts have a special feeding pattern - this is the filtering or sedimentation of particles of organic origin suspended in water and numerous small organisms (Fig. 41).

  
  
  

  Rice. 41. Composition of planktonic food of ascidians from the Barents Sea (according to S. A. Zernov, 1949)

  
  

  This method of feeding, which does not require large amounts of energy to search for prey, is characteristic of elasmobranch mollusks, sessile echinoderms, polychaetes, bryozoans, ascidians, planktonic crustaceans, etc. (Fig. 42). Filter-feeding animals play a vital role in the biological purification of water bodies. Mussels living on an area of ​​1 m2 can drive 150–280 m3 of water per day through the mantle cavity, precipitating suspended particles. Freshwater daphnia, cyclops, or the most abundant crustacean in the ocean, Calanus finmarchicus, filter up to 1.5 liters of water per individual per day. The littoral zone of the ocean, especially rich in accumulations of filter-feeding organisms, works as an effective purification system.

  
  
  
  

  Rice. 42. Filtering devices of hydrobionts (according to S. A. Zernov, 1949):

  1 – Simulium midge larvae on the stone (a) and their filter appendages (b);

  2 – filter leg of the crustacean Diaphanosoma brachyurum;

  3 – gill slits of the ascidian Phasullia;

  4 – Bosmina crustacean with filtered intestinal contents;

  5 – food current of the ciliate Bursaria

  
  

  The properties of the environment largely determine the ways of adaptation of its inhabitants, their lifestyle and methods of using resources, creating chains of cause-and-effect dependencies. Thus, the high density of water makes the existence of plankton possible, and the presence of organisms floating in water is a prerequisite for the development of a filtration type of nutrition, in which a sedentary lifestyle of animals is also possible. As a result, a powerful mechanism for self-purification of water bodies of biosphere significance is formed. It involves a huge number of hydrobionts, both benthic and pelagic, from single-celled protozoa to vertebrates. According to calculations, all the water in the lakes of the temperate zone is passed through the filtration apparatus of animals from several to dozens of times during the growing season, and the entire volume of the World Ocean is filtered within a few days. Disruption of the activity of filter feeders by various anthropogenic influences poses a serious threat to maintaining water purity.

  4.2. Ground-air environment of life

  The ground-air environment is the most complex in terms of environmental conditions. Life on land required adaptations that turned out to be possible only with a sufficiently high level of organization of plants and animals.

  4.2.1. Air as an environmental factor for terrestrial organisms

  The low density of air determines its low lifting force and low air mobility. Inhabitants of the air must have their own support system that supports the body: plants - with a variety of mechanical tissues, animals - with a solid or, much less frequently, hydrostatic skeleton. In addition, all inhabitants of the air are closely connected with the surface of the earth, which serves them for attachment and support. Life suspended in the air is impossible.

  True, many microorganisms and animals, spores, seeds, fruits and pollen of plants are regularly present in the air and are carried by air currents (Fig. 43), many animals are capable of active flight, but in all these species the main function of their life cycle - reproduction - is carried out on the surface of the earth. For most of them, staying in the air is associated only with settling or searching for prey.

  
  
  
  

  Rice. 43. Distribution of aerial plankton arthropods by height (according to Dajo, 1975)

  
  

  Low air density causes low resistance to movement. Therefore, during the course of evolution, many terrestrial animals used the ecological benefits of this property of the air environment, acquiring the ability to fly. 75% of the species of all terrestrial animals are capable of active flight, mainly insects and birds, but flyers are also found among mammals and reptiles. Land animals fly mainly with the help of muscular efforts, but some can also glide using air currents.

  Thanks to the mobility of air and the vertical and horizontal movements of air masses existing in the lower layers of the atmosphere, passive flight of a number of organisms is possible.

  Anemophilia - the oldest method of pollinating plants. All gymnosperms are pollinated by wind, and among angiosperms, anemophilous plants make up approximately 10% of all species.

  Anemophily is observed in the families of beech, birch, walnut, elm, hemp, nettle, casuarina, goosefoot, sedge, cereals, palms and many others. Wind-pollinated plants have a number of adaptations that improve the aerodynamic properties of their pollen, as well as morphological and biological features that ensure pollination efficiency.

  The life of many plants is completely dependent on the wind, and dispersal occurs with its help. Such a double dependence is observed in spruce, pine, poplar, birch, elm, ash, cotton grass, cattail, saxaul, dzhuzgun, etc.

  Many species have developed anemochory– settlement using air currents. Anemochory is characteristic of spores, seeds and fruits of plants, protozoan cysts, small insects, spiders, etc. Organisms passively transported by air currents are collectively called aeroplankton by analogy with planktonic inhabitants of the aquatic environment. Special adaptations for passive flight are very small body sizes, an increase in its area due to outgrowths, strong dissection, a large relative surface of the wings, the use of a web, etc. (Fig. 44). Anemochorous seeds and fruits of plants also have either very small sizes (for example, orchid seeds) or a variety of wing-like and parachute-like appendages that increase their ability to plan (Fig. 45).

  
  
  
  

  Rice. 44. Adaptations for transport by air currents in insects:

  1 – mosquito Cardiocrepis brevirostris;

  2 – gall midge Porrycordila sp.;

  3 – Hymenoptera Anargus fuscus;

  4 – Hermes Dreyfusia nordmannianae;

  5 – gypsy moth larva Lymantria dispar

  
  
  
  

  Rice. 45. Adaptations to wind transfer in fruits and seeds of plants:

  1 – linden Tilia intermedia;

  2 – maple Acer monspessulanum;

  3 – birch Betula pendula;

  4 – cotton grass Eriophorum;

  5 – dandelion Taraxacum officinale;

  6 – cattail Typha scuttbeworhii

  
  

  In the dispersal of microorganisms, animals and plants, the main role is played by vertical convection air currents and weak winds. Strong winds, storms and hurricanes also have significant environmental impacts on terrestrial organisms.

  Low air density causes relatively low pressure on land. Normally it is 760 mmHg. Art. As altitude increases, pressure decreases. At an altitude of 5800 m it is only half normal. Low pressure may limit the distribution of species in the mountains. For most vertebrates, the upper limit of life is about 6000 m. A decrease in pressure entails a decrease in oxygen supply and dehydration of animals due to an increase in respiration rate. The limits of advancement of higher plants into the mountains are approximately the same. Somewhat more hardy are arthropods (springtails, mites, spiders), which can be found on glaciers above the vegetation line.

  In general, all terrestrial organisms are much more stenobatic than aquatic ones, since normal pressure fluctuations in their environment amount to fractions of the atmosphere and, even for birds rising to great heights, do not exceed 1/3 of normal.

  Gas composition of air. In addition to the physical properties of the air, its chemical properties are extremely important for the existence of terrestrial organisms. The gas composition of air in the surface layer of the atmosphere is quite homogeneous in terms of the content of the main components (nitrogen - 78.1%, oxygen - 21.0, argon - 0.9, carbon dioxide - 0.035% by volume) due to the high diffusivity of gases and constant mixing convection and wind currents. However, various impurities of gaseous, droplet-liquid and solid (dust) particles entering the atmosphere from local sources can have significant environmental significance.

  The high oxygen content contributed to an increase in metabolism in terrestrial organisms compared to primary aquatic ones. It was in a terrestrial environment, on the basis of the high efficiency of oxidative processes in the body, that animal homeothermy arose. Oxygen, due to its constantly high content in the air, is not a factor limiting life in the terrestrial environment. Only in places, under specific conditions, is a temporary deficiency created, for example in accumulations of decomposing plant residues, reserves of grain, flour, etc.

  The carbon dioxide content can vary in certain areas of the surface layer of air within fairly significant limits. For example, in the absence of wind in the center of large cities, its concentration increases tens of times. There are regular daily changes in the carbon dioxide content in the surface layers associated with the rhythm of plant photosynthesis. Seasonal are caused by changes in the intensity of respiration of living organisms, mainly the microscopic population of soils. Increased saturation of air with carbon dioxide occurs in areas of volcanic activity, near thermal springs and other underground outlets of this gas. In high concentrations, carbon dioxide is toxic. In nature, such concentrations are rare.

  In nature, the main source of carbon dioxide is the so-called soil respiration. Soil microorganisms and animals breathe very intensively. Carbon dioxide diffuses from the soil into the atmosphere, especially vigorously during rain. It is abundant in soils that are moderately moist, well heated, and rich in organic residues. For example, the soil of a beech forest emits CO 2 from 15 to 22 kg/ha per hour, and unfertilized sandy soil emits only 2 kg/ha.

  In modern conditions, human activity in burning fossil fuel reserves has become a powerful source of additional amounts of CO 2 entering the atmosphere.

  Air nitrogen is an inert gas for most inhabitants of the terrestrial environment, but a number of prokaryotic organisms (nodule bacteria, Azotobacter, clostridia, blue-green algae, etc.) have the ability to bind it and involve it in the biological cycle.

  
  
  
  

  Rice. 46. A mountainside with destroyed vegetation due to sulfur dioxide emissions from surrounding industrial enterprises

  
  

  Local pollutants entering the air can also significantly affect living organisms. This especially applies to toxic gaseous substances - methane, sulfur oxide, carbon monoxide, nitrogen oxide, hydrogen sulfide, chlorine compounds, as well as dust particles, soot, etc., that pollute the air in industrial areas. The main modern source of chemical and physical pollution of the atmosphere is anthropogenic: the work of various industrial enterprises and transport, soil erosion, etc. Sulfur oxide (SO 2), for example, is toxic to plants even in concentrations from one fifty-thousandth to one millionth of the volume of air. Around industrial centers that pollute the atmosphere with this gas, almost all vegetation dies (Fig. 46). Some plant species are particularly sensitive to SO 2 and serve as a sensitive indicator of its accumulation in the air. For example, many lichens die even with traces of sulfur oxide in the surrounding atmosphere. Their presence in forests around large cities indicates high air purity. The resistance of plants to impurities in the air is taken into account when selecting species for landscaping in populated areas. Sensitive to smoke, for example, common spruce and pine, maple, linden, birch. The most resistant are thuja, Canadian poplar, American maple, elderberry and some others.

  4.2.2. Soil and relief. Weather and climatic features of the ground-air environment

  Edaphic environmental factors. Soil properties and terrain also affect the living conditions of terrestrial organisms, primarily plants. The properties of the earth's surface that have an ecological impact on its inhabitants are collectively called edaphic environmental factors (from the Greek “edaphos” - foundation, soil).

  The nature of the plant root system depends on the hydrothermal regime, aeration, composition, composition and structure of the soil. For example, the root systems of tree species (birch, larch) in areas with permafrost are located at shallow depths and spread out wide. Where there is no permafrost, the root systems of these same plants are less widespread and penetrate deeper. In many steppe plants, the roots can reach water from great depths; at the same time, they also have many surface roots in the humus-rich soil horizon, from where the plants absorb elements of mineral nutrition. On waterlogged, poorly aerated soil in mangroves, many species have special respiratory roots - pneumatophores.

  A number of ecological groups of plants can be distinguished in relation to different soil properties.

  So, according to the reaction to soil acidity, they distinguish: 1) acidophilic species - grow on acidic soils with a pH less than 6.7 (plants of sphagnum bogs, white grass); 2) neutrophilic – gravitate towards soils with a pH of 6.7–7.0 (most cultivated plants); 3) basophilic– grow at a pH of more than 7.0 (mordovnik, forest anemone); 4) indifferent – can grow on soils with different pH values ​​(lily of the valley, sheep fescue).

  In relation to the gross composition of the soil there are: 1) oligotrophic plants that are content with a small amount of ash elements (Scots pine); 2) eutrophic, those that need a large amount of ash elements (oak, common gooseberry, perennial woodweed); 3) mesotrophic, requiring a moderate amount of ash elements (common spruce).

  Nitrophils– plants that prefer soils rich in nitrogen (nettle).

  Plants of saline soils form a group halophytes(soleros, sarsazan, kokpek).

  Some plant species are confined to different substrates: petrophytes grow on rocky soils, and psammophytes inhabit shifting sands.

  The terrain and the nature of the soil affect the specific movement of animals. For example, ungulates, ostriches, and bustards living in open spaces need hard ground to enhance repulsion when running fast. In lizards that live on shifting sands, the toes are fringed with a fringe of horny scales, which increases the support surface (Fig. 47). For terrestrial inhabitants that dig holes, dense soils are unfavorable. The nature of the soil in some cases influences the distribution of terrestrial animals that dig burrows, burrow into the soil to escape heat or predators, or lay eggs in the soil, etc.

  
  
  
  

  Rice. 47. Fan-toed gecko - inhabitant of the sands of the Sahara: A - fan-toed gecko; B – gecko leg

  
  

  Weather features. Living conditions in the ground-air environment are complicated, in addition, weather changes. Weather - this is a continuously changing state of the atmosphere at the earth's surface up to an altitude of approximately 20 km (the boundary of the troposphere). Weather variability is manifested in a constant variation in the combination of environmental factors such as temperature and humidity, cloudiness, precipitation, wind strength and direction, etc. Weather changes, along with their natural alternation in the annual cycle, are characterized by non-periodic fluctuations, which significantly complicates the conditions of existence terrestrial organisms. The weather affects the life of aquatic inhabitants to a much lesser extent and only on the population of the surface layers.

  Climate of the area. The long-term weather regime characterizes climate of the area. The concept of climate includes not only the average values ​​of meteorological phenomena, but also their annual and daily cycle, deviations from it and their frequency. The climate is determined by the geographical conditions of the area.

  The zonal diversity of climates is complicated by the action of monsoon winds, the distribution of cyclones and anticyclones, the influence of mountain ranges on the movement of air masses, the degree of distance from the ocean (continentality) and many other local factors. In the mountains there is a climatic zonation, much similar to the change of zones from low latitudes to high latitudes. All this creates an extraordinary diversity of living conditions on land.

  For most terrestrial organisms, especially small ones, it is not so much the climate of the area that is important as the conditions of their immediate habitat. Very often, local environmental elements (relief, exposure, vegetation, etc.) change the regime of temperature, humidity, light, air movement in a particular area in such a way that it differs significantly from the climatic conditions of the area. Such local climate modifications that develop in the surface layer of air are called microclimate. Each zone has very diverse microclimates. Microclimates of arbitrarily small areas can be identified. For example, a special regime is created in the corollas of flowers, which is used by the insects living there. Differences in temperature, air humidity and wind strength are widely known in open space and in forests, in grass stands and over bare areas of soil, on slopes of northern and southern exposures, etc. A special stable microclimate occurs in burrows, nests, hollows, caves and other closed places.

  Precipitation. In addition to providing water and creating moisture reserves, they can play other ecological roles. Thus, heavy rainfall or hail sometimes have a mechanical effect on plants or animals.

  The ecological role of snow cover is especially diverse. Daily temperature fluctuations penetrate into the snow depth only up to 25 cm; deeper the temperature remains almost unchanged. With frosts of -20-30 °C under a layer of snow of 30-40 cm, the temperature is only slightly below zero. Deep snow cover protects renewal buds and protects green parts of plants from freezing; many species go under the snow without shedding their foliage, for example, hairy grass, Veronica officinalis, hoofed grass, etc.

  
  
  

  Rice. 48. Scheme of telemetric study of the temperature regime of hazel grouse located in a snow hole (according to A.V. Andreev, A.V. Krechmar, 1976)

  
  

  Small land animals also lead an active lifestyle in winter, creating entire galleries of tunnels under the snow and in its thickness. A number of species that feed on snow-covered vegetation are even characterized by winter reproduction, which is noted, for example, in lemmings, wood and yellow-throated mice, a number of voles, water rats, etc. Grouse birds - hazel grouse, black grouse, tundra partridge - burrow in the snow for the night ( Fig. 48).

  Winter snow cover makes it difficult for large animals to obtain food. Many ungulates (reindeer, wild boars, musk oxen) feed exclusively on snow-covered vegetation in winter, and deep snow cover, and especially the hard crust on its surface that occurs during icy conditions, doom them to starvation. During nomadic cattle breeding in pre-revolutionary Russia, a huge disaster in the southern regions was jute – mass mortality of livestock as a result of icy conditions, depriving animals of food. Movement on loose deep snow is also difficult for animals. Foxes, for example, in snowy winters prefer areas in the forest under dense spruce trees, where the layer of snow is thinner, and almost never go out into open glades and forest edges. Snow depth may limit the geographic distribution of species. For example, real deer do not penetrate north into those areas where the snow thickness in winter is more than 40–50 cm.

  The whiteness of the snow cover reveals dark animals. Selection for camouflage to match the background color apparently played a major role in the occurrence of seasonal color changes in the ptarmigan and tundra partridge, mountain hare, ermine, weasel, and arctic fox. On the Commander Islands, along with white foxes, there are many blue foxes. According to the observations of zoologists, the latter stay mainly near dark rocks and ice-free surf strips, while the white ones prefer areas with snow cover.

  4.3. Soil as a habitat

  4.3.1. Soil Features

  The soil is a loose thin surface layer of land in contact with the air. Despite its insignificant thickness, this shell of the Earth plays a vital role in the spread of life. The soil is not just a solid body, like most rocks of the lithosphere, but a complex three-phase system in which solid particles are surrounded by air and water. It is permeated with cavities filled with a mixture of gases and aqueous solutions, and therefore extremely diverse conditions develop in it, favorable for the life of many micro- and macroorganisms (Fig. 49). In the soil, temperature fluctuations are smoothed out compared to the surface layer of air, and the presence of groundwater and the penetration of precipitation create moisture reserves and provide a humidity regime intermediate between the aquatic and terrestrial environments. The soil concentrates reserves of organic and mineral substances supplied by dying vegetation and animal corpses. All this determines the greater saturation of the soil with life.

  The root systems of terrestrial plants are concentrated in the soil (Fig. 50).

  
  
  

  Rice. 49. Underground passages of the Brandt's vole: A – top view; B – side view

  
  
  

  Rice. 50. Placement of roots in steppe chernozem soil (according to M. S. Shalyt, 1950)

  
  

  On average, per 1 m 2 of soil layer there are more than 100 billion protozoan cells, millions of rotifers and tardigrades, tens of millions of nematodes, tens and hundreds of thousands of mites and springtails, thousands of other arthropods, tens of thousands of enchytraeids, tens and hundreds of earthworms, mollusks and other invertebrates . In addition, 1 cm 2 of soil contains tens and hundreds of millions of bacteria, microscopic fungi, actinomycetes and other microorganisms. In the illuminated surface layers, hundreds of thousands of photosynthetic cells of green, yellow-green, diatoms and blue-green algae live in every gram. Living organisms are just as characteristic of the soil as its nonliving components. Therefore, V.I. Vernadsky classified the soil as a bio-inert body of nature, emphasizing its saturation with life and its inextricable connection with it.

  The heterogeneity of soil conditions is most pronounced in the vertical direction. With depth, a number of the most important environmental factors affecting the life of soil inhabitants change dramatically. First of all, this relates to the structure of the soil. It contains three main horizons, differing in morphological and chemical properties: 1) the upper humus-accumulative horizon A, in which organic matter accumulates and is transformed and from which some of the compounds are carried down by washing waters; 2) the inwash horizon, or illuvial B, where the substances washed out from above settle and are transformed, and 3) the parent rock, or horizon C, the material of which is transformed into soil.

  Within each horizon, more subdivided layers are distinguished, which also differ greatly in properties. For example, in a temperate climate zone under coniferous or mixed forests the horizon A consists of litter (A 0)– a layer of loose accumulation of plant residues, a dark-colored humus layer (A 1), in which particles of organic origin are mixed with mineral ones, and a podzolic layer (A 2)– ash-gray in color, in which silicon compounds predominate, and all soluble substances are washed into the depths of the soil profile. Both the structure and chemistry of these layers are very different, and therefore plant roots and soil inhabitants, moving just a few centimeters up or down, find themselves in different conditions.

  The sizes of cavities between soil particles suitable for animals to live in usually decrease rapidly with depth. For example, in meadow soils the average diameter of cavities at a depth of 0–1 cm is 3 mm, at 1–2 cm – 2 mm, and at a depth of 2–3 cm – only 1 mm; deeper the soil pores are even smaller. Soil density also changes with depth. The loosest layers are those containing organic matter. The porosity of these layers is determined by the fact that organic substances glue mineral particles into larger aggregates, the volume of cavities between which increases. The illuvial horizon is usually the densest IN, cemented by colloidal particles washed into it.

  Moisture in the soil is present in various states: 1) bound (hygroscopic and film) firmly held by the surface of soil particles; 2) capillary occupies small pores and can move along them in different directions; 3) gravitational fills larger voids and slowly seeps down under the influence of gravity; 4) vaporous is contained in the soil air.

  Water content varies in different soils and at different times. If there is too much gravitational moisture, then the soil regime is close to the regime of reservoirs. In dry soil, only bound water remains and conditions approach those found on land. However, even in the driest soils, the air is moister than the ground air, so the inhabitants of the soil are much less susceptible to the threat of drying out than on the surface.

  The composition of soil air is variable. With depth, the oxygen content in it decreases greatly and the concentration of carbon dioxide increases. Due to the presence of decomposing organic substances in the soil, the soil air may contain a high concentration of toxic gases such as ammonia, hydrogen sulfide, methane, etc. When the soil is flooded or intensive rotting of plant residues, completely anaerobic conditions may occur in some places.

  Fluctuations in cutting temperature only on the soil surface. Here they can be even stronger than in the surface layer of air. However, with each centimeter in depth, daily and seasonal temperature changes become less and less and at a depth of 1–1.5 m they are practically no longer traceable (Fig. 51).

  
  
  

  Rice. 51. Decrease in annual fluctuations in soil temperature with depth (according to K. Schmidt-Nilsson, 1972). The shaded part is the range of annual temperature fluctuations

  
  

  All these features lead to the fact that, despite the great heterogeneity of environmental conditions in the soil, it acts as a fairly stable environment, especially for mobile organisms. The steep gradient of temperature and humidity in the soil profile allows soil animals to provide themselves with a suitable ecological environment through minor movements.

  4.3.2. Soil inhabitants

  The heterogeneity of the soil leads to the fact that for organisms of different sizes it acts as a different environment. For microorganisms, the huge total surface of soil particles is of particular importance, since the overwhelming majority of the microbial population is adsorbed on them. The complexity of the soil environment creates a wide variety of conditions for a wide variety of functional groups: aerobes and anaerobes, consumers of organic and mineral compounds. The distribution of microorganisms in the soil is characterized by fine focality, since even within a few millimeters different ecological zones can change.

  For small soil animals (Fig. 52, 53), which are combined under the name microfauna (protozoa, rotifers, tardigrades, nematodes, etc.), soil is a system of micro-reservoirs. Essentially, these are aquatic organisms. They live in soil pores filled with gravitational or capillary water, and part of life can, like microorganisms, be in an adsorbed state on the surface of particles in thin layers of film moisture. Many of these species also live in ordinary bodies of water. However, soil forms are much smaller than freshwater ones and, in addition, are distinguished by their ability to remain in an encysted state for a long time, waiting out unfavorable periods. While freshwater amoebas are 50-100 microns in size, soil amoebas are only 10-15. Representatives of flagellates are especially small, often only 2–5 microns. Soil ciliates also have dwarf sizes and, moreover, can greatly change their body shape.

  
  
  
  

  Rice. 52. Testate amoebas feeding on bacteria on decaying leaves of the forest floor

  
  
  
  

  Rice. 53. Soil microfauna (according to W. Dunger, 1974):

  1–4 – flagella; 5–8 – naked amoebas; 9-10 – testate amoebas; 11–13 – ciliates; 14–16 – roundworms; 17–18 – rotifers; 19–20 – tardigrades

  
  

  To slightly larger air-breathing animals, the soil appears as a system of small caves. Such animals are grouped under the name mesofauna (Fig. 54). The sizes of soil mesofauna representatives range from tenths to 2–3 mm. This group includes mainly arthropods: numerous groups of mites, primary wingless insects (collembolas, proturus, two-tailed insects), small species of winged insects, symphila centipedes, etc. They do not have special adaptations for digging. They crawl along the walls of soil cavities using their limbs or wriggling like a worm. Soil air saturated with water vapor allows breathing through the covers. Many species do not have a tracheal system. Such animals are very sensitive to drying out. The main means of escape from fluctuations in air humidity is to move deeper. But the possibility of deep migration through soil cavities is limited by a rapid decrease in pore diameter, so movement through soil holes is accessible only to the smallest species. Larger representatives of the mesofauna have some adaptations that allow them to tolerate a temporary decrease in soil air humidity: protective scales on the body, partial impermeability of the integument, a solid thick-walled shell with an epicuticle in combination with a primitive tracheal system that ensures respiration.

  
  
  
  

  Rice. 54. Soil mesofauna (no W. Danger, 1974):

  1 - false scorion; 2 – gama new bell-bottom; 3–4 oribatid mites; 5 – centipede pauroioda; 6 – chironomid mosquito larva; 7 - beetle from this family. Ptiliidae; 8–9 springtails

  
  

  Representatives of the mesofauna survive periods of soil flooding in air bubbles. Air is retained around the body of animals due to their non-wettable integument, which is also equipped with hairs, scales, etc. The air bubble serves as a kind of “physical gill” for a small animal. Respiration is carried out due to oxygen diffusing into the air layer from the surrounding water.

  Representatives of micro- and mesofauna are able to tolerate winter freezing of the soil, since most species cannot move down from layers exposed to negative temperatures.

  Larger soil animals, with body sizes from 2 to 20 mm, are called representatives macrofauna (Fig. 55). These are insect larvae, centipedes, enchytraeids, earthworms, etc. For them, the soil is a dense medium that provides significant mechanical resistance when moving. These relatively large forms move in the soil either by expanding natural wells by pushing apart soil particles, or by digging new tunnels. Both methods of movement leave an imprint on the external structure of animals.

  
  
  
  

  Rice. 55. Soil macrofauna (no W. Danger, 1974):

  1 - earthworm; 2 – woodlice; 3 – centipede; 4 – two-legged centipede; 5 – ground beetle larva; 6 – click beetle larva; 7 – mole cricket; 8 - Khrushchev larva

  
  

  The ability to move through thin holes, almost without resorting to digging, is inherent only in species that have a body with a small cross-section, capable of bending strongly in winding passages (centipedes - drupes and geophiles). Moving apart soil particles due to the pressure of the body walls, earthworms, larvae of long-legged mosquitoes, etc. move. Having fixed the rear end, they thin and lengthen the front, penetrating into narrow soil crevices, then secure the front part of the body and increase its diameter. In this case, in the expanded area, due to the work of the muscles, a strong hydraulic pressure of the non-compressible intracavitary fluid is created: in worms - the contents of the coelomic sacs, and in tipulids - the hemolymph. Pressure is transmitted through the body walls to the soil, and thus the animal expands the well. At the same time, the rear passage remains open, which threatens to increase evaporation and persecution of predators. Many species have developed adaptations to an ecologically more advantageous type of movement in the soil - digging and blocking the passage behind them. Digging is carried out by loosening and raking away soil particles. The larvae of various insects use for this the anterior end of the head, mandibles and forelimbs, expanded and strengthened by a thick layer of chitin, spines and outgrowths. At the rear end of the body, devices for strong fixation develop - retractable supports, teeth, hooks. To close the passage on the last segments, a number of species have a special depressed platform framed by chitinous sides or teeth, a kind of wheelbarrow. Similar areas are formed on the back of the elytra and in bark beetles, which also use them to clog the passages with drill flour. Closing the passage behind them, the animals that inhabit the soil are constantly in a closed chamber, saturated with the vapors of their own bodies.

  Gas exchange of most species of this ecological group is carried out with the help of specialized respiratory organs, but at the same time it is supplemented by gas exchange through the integument. It is even possible that exclusively cutaneous respiration is possible, for example in earthworms and enchytraeids.

  Burrowing animals can leave layers where unfavorable conditions arise. During drought and winter, they concentrate in deeper layers, usually several tens of centimeters from the surface.

  Megafauna soils are large shrews, mainly mammals. A number of species spend their entire lives in the soil (mole rats, mole rats, zokora, Eurasian moles, golden moles

  Africa, marsupial moles of Australia, etc.). They create entire systems of passages and burrows in the soil. The appearance and anatomical features of these animals reflect their adaptability to a burrowing underground lifestyle. They have underdeveloped eyes, a compact, ridged body with a short neck, short thick fur, strong digging limbs with strong claws. Mole rats and mole rats loosen the ground with their incisors. Soil megafauna also includes large oligochaetes, especially representatives of the family Megascolecidae, living in the tropics and the Southern Hemisphere. The largest of them, the Australian Megascolides australis, reaches a length of 2.5 and even 3 m.

  In addition to the permanent inhabitants of the soil, a large ecological group can be distinguished among large animals burrow inhabitants (gophers, marmots, jerboas, rabbits, badgers, etc.). They feed on the surface, but reproduce, hibernate, rest, and escape danger in the soil. A number of other animals use their burrows, finding in them a favorable microclimate and shelter from enemies. Burrowers have structural features characteristic of terrestrial animals, but have a number of adaptations associated with the burrowing lifestyle. For example, badgers have long claws and strong muscles on the forelimbs, a narrow head, and small ears. Compared to hares that do not dig holes, rabbits have noticeably shortened ears and hind legs, a more durable skull, more developed bones and muscles of the forearms, etc.

  For a number of ecological features, soil is a medium intermediate between aquatic and terrestrial. The soil is similar to the aquatic environment due to its temperature regime, low oxygen content in the soil air, its saturation with water vapor and the presence of water in other forms, the presence of salts and organic substances in soil solutions, and the ability to move in three dimensions.

  The soil is brought closer to the air environment by the presence of soil air, the threat of drying out in the upper horizons, and rather sharp changes in the temperature regime of the surface layers.

  The intermediate ecological properties of soil as a habitat for animals suggest that soil played a special role in the evolution of the animal world. For many groups, in particular arthropods, soil served as a medium through which initially aquatic inhabitants were able to transition to a terrestrial lifestyle and conquer land. This path of arthropod evolution was proven by the works of M. S. Gilyarov (1912–1985).

  4.4. Living organisms as habitat

  Many types of heterotrophic organisms, throughout their entire life or part of their life cycle, live in other living beings, whose bodies serve as an environment for them, significantly different in properties from the external one.

  Rice. 56. Aphids infecting aphids

  Rice. 57. Cut gall on a beech leaf with a larva of the gall midge Mikiola fagi

  General characteristics. In the course of evolution, the land-air environment was mastered much later than the aquatic environment. Life on land required adaptations that became possible only with a relatively high level of organization in both plants and animals. A feature of the land-air environment of life is that the organisms that live here are surrounded by air and a gaseous environment characterized by low humidity, density and pressure, and high oxygen content. Typically, animals in this environment move on the soil (hard substrate) and plants take root in it.

  In the ground-air environment, the operating environmental factors have a number of characteristic features: higher light intensity compared to other environments, significant temperature fluctuations, changes in humidity depending on the geographical location, season and time of day (Table 3).

  Table 3

  Living conditions for organisms in the air and water environment (according to D.F. Mordukhai-Boltovsky, 1974)

  Living conditions	The importance of conditions for organisms
  air environment	aquatic environment
  Humidity	Very important (often in short supply)	Does not have (always in excess)
  Medium density	Minor (except for soil)	Large compared to its role for the inhabitants of the air
  Pressure	Almost none	Large (can reach 1000 atmospheres)
  Temperature	Significant (varies within very wide limits (from -80 to +100 °C and more)	Less than the value for the inhabitants of the air (varies much less, usually from -2 to +40°C)
  Oxygen	Non-essential (mostly in excess)	Essential (often in short supply)
  Suspended solids	Unimportant; not used for food (mainly minerals)	Important (food source, especially organic matter)
  Dissolved substances in the environment	To some extent (only relevant in soil solutions)	Important (certain quantities required)

  The impact of the above factors is inextricably linked with the movement of air masses - wind. In the process of evolution, living organisms of the land-air environment have developed characteristic anatomical, morphological, physiological, behavioral and other adaptations. For example, organs have appeared that provide direct absorption of atmospheric oxygen during respiration (the lungs and trachea of ​​animals, the stomata of plants). Skeletal formations (animal skeleton, mechanical and supporting tissues of plants) have received strong development, which support the body in conditions of low environmental density. Adaptations have been developed to protect against unfavorable factors, such as the periodicity and rhythm of life cycles, the complex structure of the integument, mechanisms of thermoregulation, etc. A close connection with the soil has formed (animal limbs, plant roots), the mobility of animals in search of food has developed, and air currents have appeared. seeds, fruits and pollen of plants, flying animals.

  Let us consider the features of the impact of basic environmental factors on plants and animals in the ground-air environment of life.

  Low air density determines its low lifting force and insignificant controversy. All inhabitants of the air are closely connected with the surface of the earth, which serves them for attachment and support. The density of the air does not provide high resistance to the body when moving along the surface of the earth, but it makes it difficult to move vertically. For most organisms, staying in the air is associated only with settling or searching for prey.

  The low lifting force of air determines the maximum mass and size of terrestrial organisms. The largest animals on the surface of the earth are smaller than the giants of the aquatic environment. Large mammals (the size and mass of a modern whale) could not live on land, as they would be crushed by their own weight. Giant Mesozoic dinosaurs led a semi-aquatic lifestyle. Another example: tall, erect redwood plants (Sequoja sempervirens), reaching 100 m, have powerful supporting wood, while in the thalli of the giant brown algae Macrocystis, growing up to 50 m, the mechanical elements are only very weakly isolated in the core part of the thallus.

  Low air density creates little resistance to movement. The ecological benefits of this property of the air environment were used by many land animals during evolution, acquiring the ability to fly. 75% of all species of land animals are capable of active flight. These are mostly insects and birds, but there are also mammals and reptiles. Land animals fly mainly with the help of muscular efforts. Some animals can glide using air currents.

  Due to the mobility of air, which exists in the lower layers of the atmosphere, vertical and horizontal movement of air masses, passive flight of certain types of organisms is possible, developed anemochory -- dispersal by air currents. Organisms passively transported by air currents are collectively called aeroplankton, by analogy with planktonic inhabitants of the aquatic environment. For passive flight along N.M. Chernova, A.M. Bylova (1988) organisms have special adaptations - small body size, an increase in its area due to outgrowths, strong dismemberment, a large relative surface of the wings, the use of a web, etc.

  Anemochorous seeds and fruits of plants also have very small sizes (for example, fireweed seeds) or various wing-shaped (maple Acer pseudoplatanum) and parachute-shaped (dandelion Taraxacum officinale) appendages

  Wind-pollinated plants have a number of adaptations that improve the aerodynamic properties of pollen. Their floral integument is usually reduced and the anthers are not protected from the wind in any way.

  In the dispersal of plants, animals and microorganisms, the main role is played by vertical conventional air flows and weak winds. Storms and hurricanes also have a significant environmental impact on terrestrial organisms. Quite often, strong winds, especially blowing in one direction, bend tree branches and trunks to the leeward side and cause the formation of flag-shaped crowns.

  In areas where strong winds constantly blow, the species composition of small flying animals is usually poor, since they are not able to resist powerful air currents. Thus, a honey bee flies only when the wind force is up to 7 - 8 m/s, and aphids fly only when the wind is very weak, not exceeding 2.2 m/s. Animals in these places develop dense integuments that protect the body from cooling and loss of moisture. On oceanic islands with constant strong winds, birds and especially insects predominate, having lost the ability to fly, they lack wings, since those who are able to rise into the air are blown out to sea by the wind and die.

  The wind causes a change in the intensity of transpiration in plants and is especially pronounced during dry winds, which dry out the air and can lead to the death of plants. The main ecological role of horizontal air movements (winds) is indirect and consists in strengthening or weakening the impact on terrestrial organisms of such important environmental factors as temperature and humidity. Winds increase the release of moisture and heat from animals and plants.

  When there is wind, heat is easier to bear and frost is more difficult, and desiccation and cooling of organisms occurs faster.

  Terrestrial organisms exist in conditions of relatively low pressure, which is caused by low air density. In general, terrestrial organisms are more stenobatic than aquatic ones, because normal pressure fluctuations in their environment amount to fractions of the atmosphere, and for those that rise to high altitudes, for example, birds, do not exceed 1/3 of normal.

  Gas composition of air, as already discussed earlier, in the ground layer of the atmosphere it is quite homogeneous (oxygen - 20.9%, nitrogen - 78.1%, m.g. gases - 1%, carbon dioxide - 0.03% by volume) due to its high diffusion capacity and constant mixing by convection and wind flows. At the same time, various impurities of gaseous, droplet-liquid, dust (solid) particles entering the atmosphere from local sources often have significant environmental significance.

  Oxygen, due to its constantly high content in the air, is not a factor limiting life in the terrestrial environment. The high oxygen content contributed to an increase in metabolism in terrestrial organisms, and animal homeothermy arose on the basis of the high efficiency of oxidative processes. Only in places, under specific conditions, is a temporary oxygen deficiency created, for example, in decomposing plant debris, grain reserves, flour, etc.

  In certain areas of the surface air layer, the carbon dioxide content can vary within fairly significant limits. Thus, in the absence of wind in large industrial centers and cities, its concentration can increase tenfold.

  There are regular daily changes in the content of carbon dioxide in the ground layers, determined by the rhythm of plant photosynthesis (Fig. 17).

  Rice. 17. Daily changes in the vertical profile of CO 2 concentration in forest air (from W. Larcher, 1978)

  Using the example of daily changes in the vertical profile of CO 2 concentration in forest air, it is shown that during the day, at the level of tree crowns, carbon dioxide is spent on photosynthesis, and in the absence of wind, a zone poor in CO 2 (305 ppm) is formed here, into which CO comes from the atmosphere and soil (soil respiration). At night, a stable air stratification is established with an increased concentration of CO 2 in the soil layer. Seasonal fluctuations in carbon dioxide are associated with changes in the respiration rate of living organisms, mostly soil microorganisms.

  In high concentrations, carbon dioxide is toxic, but such concentrations are rare in nature. Low CO 2 content inhibits the process of photosynthesis. To increase the rate of photosynthesis in the practice of greenhouse and greenhouse farming (in closed ground conditions), the concentration of carbon dioxide is often artificially increased.

  For most inhabitants of the terrestrial environment, air nitrogen is an inert gas, but microorganisms such as nodule bacteria, azotobacteria, and clostridia have the ability to bind it and involve it in the biological cycle.

  The main modern source of physical and chemical pollution of the atmosphere is anthropogenic: industrial and transport enterprises, soil erosion, etc. Thus, sulfur dioxide is toxic to plants in concentrations from one fifty-thousandth to one millionth of the volume of air. Lichens die when there are traces of sulfur dioxide in the environment. Therefore, plants that are particularly sensitive to SO 2 are often used as indicators of its content in the air. Common spruce and pine, maple, linden, and birch are sensitive to smoke.

  Light mode. The amount of radiation reaching the Earth's surface is determined by the geographic latitude of the area, the length of the day, the transparency of the atmosphere and the angle of incidence of the sun's rays. Under different weather conditions, 42-70% of the solar constant reaches the Earth's surface. Passing through the atmosphere, solar radiation undergoes a number of changes not only in quantity, but also in composition. Short-wave radiation is absorbed by the ozone shield and oxygen in the air. Infrared rays are absorbed in the atmosphere by water vapor and carbon dioxide. The rest reaches the Earth's surface in the form of direct or diffuse radiation.

  The combination of direct and diffuse solar radiation makes up from 7 to 7„ of the total radiation, while on cloudy days the diffuse radiation is 100%. At high latitudes, diffuse radiation predominates, while in the tropics, direct radiation predominates. Scattered radiation contains up to 80% of yellow-red rays at noon, direct radiation - from 30 to 40%. On clear sunny days, solar radiation reaching the Earth's surface consists of 45% visible light (380 - 720 nm) and 45% infrared radiation. Only 10% comes from ultraviolet radiation. The radiation regime is significantly influenced by atmospheric dust. Due to its pollution, in some cities the illumination may be 15% or less of the illumination outside the city.

  Illumination on the Earth's surface varies widely. It all depends on the height of the Sun above the horizon or the angle of incidence of the sun’s rays, the length of the day and weather conditions, and the transparency of the atmosphere (Fig. 18).

  
  

  Rice. 18. Distribution of solar radiation depending on the height of the Sun above the horizon (A 1 - high, A 2 - low)

  Depending on the season and time of day, the light intensity also fluctuates. In certain regions of the Earth, the quality of light is also unequal, for example, the ratio of long-wave (red) and short-wave (blue and ultraviolet) rays. Short-wave rays are known to be absorbed and scattered by the atmosphere more than long-wave rays. In mountainous areas there is therefore always more short-wave solar radiation.

  Trees, shrubs, and plant crops shade the area and create a special microclimate, weakening radiation (Fig. 19).

  
  

  Rice. 19.

  A - in a rare pine forest; B - in corn crops Of the incoming photosynthetically active radiation, 6--12% is reflected (R) from the surface of the planting

  Thus, in different habitats, not only the intensity of radiation differs, but also its spectral composition, the duration of illumination of plants, the spatial and temporal distribution of light of different intensities, etc. Accordingly, the adaptations of organisms to life in a terrestrial environment under one or another light regime are also varied. . As we noted earlier, in relation to light there are three main groups of plants: photophilous(heliophytes), shade-loving(sciophytes) and shade-tolerant. Light-loving and shade-loving plants differ in the position of their ecological optimum.

  In light-loving plants it is located in the area of ​​full sunlight. Strong shading has a depressing effect on them. These are plants of open areas of land or well-lit steppe and meadow grasses (the upper tier of the grass stand), rock lichens, early spring herbaceous plants of deciduous forests, most cultivated plants of open ground and weeds, etc. Shade-loving plants have an optimum in the area of ​​low light and cannot tolerate strong light. These are mainly the lower shaded layers of complex plant communities, where shading is the result of the “interception” of light by taller plants and co-inhabitants. This includes many indoor and greenhouse plants. For the most part, these come from the herbaceous cover or epiphyte flora of tropical forests.

  The ecological curve of the relationship to light in shade-tolerant plants is somewhat asymmetrical, since they grow and develop better in full light, but adapt well to low light. They are a common and highly flexible group of plants in terrestrial environments.

  Plants in the terrestrial-air environment have developed adaptations to various light conditions: anatomical-morphological, physiological, etc.

  A clear example of anatomical and morphological adaptations is a change in appearance in different light conditions, for example, the unequal size of leaf blades in plants related in systematic position, but living in different lighting (meadow bell - Campanula patula and forest - C. trachelium, field violet -- Viola arvensis, growing in fields, meadows, forest edges, and forest violets -- V. mirabilis), fig. 20.

  

  Rice. 20. Distribution of leaf sizes depending on plant living conditions: from wet to dry and from shaded to sunny

  Note. The shaded area corresponds to conditions prevailing in nature

  Under conditions of excess and lack of light, the spatial arrangement of leaf blades in plants varies significantly. In heliophyte plants, the leaves are oriented to reduce the influx of radiation during the most “dangerous” daytime hours. The leaf blades are located vertically or at a large angle to the horizontal plane, so during the day the leaves receive mostly sliding rays (Fig. 21).

  This is especially pronounced in many steppe plants. An interesting adaptation to the weakening of the received radiation is in the so-called “compass” plants (wild lettuce - Lactuca serriola, etc.). The leaves of wild lettuce are located in the same plane, oriented from north to south, and at noon the arrival of radiation to the leaf surface is minimal.

  In shade-tolerant plants, the leaves are arranged so as to receive the maximum amount of incident radiation.

  
  

  Rice. 21.

  1,2 -- leaves with different angles of inclination; S 1, S 2 - direct radiation reaching them; Stot -- its total intake to the plant

  Often, shade-tolerant plants are capable of protective movements: changing the position of leaf blades when exposed to strong light. Areas of grass cover with folded oxalis leaves coincide relatively precisely with the location of large sun flares. A number of adaptive features can be noted in the structure of the leaf as the main receiver of solar radiation. For example, in many heliophytes, the leaf surface helps to reflect sunlight (shiny - in laurel, covered with a light hairy coating - in cactus, euphorbia) or weaken their effect (thick cuticle, dense pubescence). The internal structure of the leaf is characterized by the powerful development of palisade tissue and the presence of a large number of small and light chloroplasts (Fig. 22).

  One of the protective reactions of chloroplasts to excess light is their ability to change orientation and move within the cell, which is clearly expressed in light plants.

  In bright light, chloroplasts occupy a wall position in the cell and become an “edge” towards the direction of the rays. In low light, they are distributed diffusely in the cell or accumulate in its lower part.

  

  Rice. 22.

  1 - yew; 2- larch; 3 - hoof; 4 - spring clearweed (According to T.K. Goryshina, E.G. Spring, 1978)

  Physiological adaptations plants to the light conditions of the ground-air environment cover various vital functions. It has been established that in light-loving plants, growth processes react more sensitively to a lack of light compared to shady plants. As a result, there is an increased elongation of stems, which helps plants break through to the light and into the upper tiers of plant communities.

  The main physiological adaptations to light lie in the area of ​​photosynthesis. In general terms, the change in photosynthesis depending on light intensity is expressed by the “photosynthesis light curve.” Its following parameters are of ecological significance (Fig. 23).

  • 1. The point of intersection of the curve with the ordinate axis (Fig. 23, A) corresponds to the magnitude and direction of gas exchange in plants in complete darkness: photosynthesis is absent, respiration takes place (not absorption, but release of CO 2), therefore point a lies below the x-axis.
  • 2. The point of intersection of the light curve with the abscissa axis (Fig. 23, b) characterizes the “compensation point,” i.e., the light intensity at which photosynthesis (CO 2 absorption) balances respiration (CO 2 release).
  • 3. The intensity of photosynthesis with increasing light increases only up to a certain limit, then remains constant - the light curve of photosynthesis reaches a “saturation plateau”.
  

  Rice. 23.

  A - general diagram; B -- curves for light-loving (1) and shade-tolerant (2) plants

  In Fig. 23, the inflection area is conventionally designated by a smooth curve, the break of which corresponds to a point V. The projection of point c onto the x-axis (point d) characterizes the “saturated” light intensity, i.e., the value above which light no longer increases the intensity of photosynthesis. Projection onto the ordinate axis (point e) corresponds to the highest intensity of photosynthesis for a given species in a given ground-air environment.

  4. An important characteristic of the light curve is the angle of inclination (a) to the abscissa, which reflects the degree of increase in photosynthesis with increasing radiation (in the region of relatively low light intensity).

  Plants exhibit seasonal dynamics in their response to light. Thus, in the hairy sedge (Carex pilosa), in early spring in the forest, newly emerged leaves have a plateau of light saturation of photosynthesis at 20 - 25 thousand lux; with summer shading in these same species, the curves of the dependence of photosynthesis on light become corresponding to the “shadow” parameters, that is, the leaves acquire the ability to use weak light more efficiently; these same leaves, after overwintering under the canopy of a leafless spring forest, again display the “light” features of photosynthesis.

  A peculiar form of physiological adaptation during a sharp lack of light is the loss of the plant’s ability to photosynthesize and the transition to heterotrophic nutrition with ready-made organic substances. Sometimes such a transition became irreversible due to the loss of chlorophyll by plants, for example, orchids of shady spruce forests (Goodyera repens, Weottia nidus avis), orchids (Monotropa hypopitys). They live off dead organic matter obtained from trees and other plants. This method of nutrition is called saprophytic, and plants are called saprophytes.

  For the vast majority of terrestrial animals with day and night activity, vision is one of the methods of orientation and is important for searching for prey. Many animal species also have color vision. In this regard, animals, especially victims, developed adaptive features. These include protective, camouflage and warning coloring, protective similarity, mimicry, etc. The appearance of brightly colored flowers of higher plants is also associated with the characteristics of the visual apparatus of pollinators and, ultimately, with the light regime of the environment.

  Water mode. Moisture deficiency is one of the most significant features of the ground-air environment of life. The evolution of terrestrial organisms took place through adaptation to obtaining and preserving moisture. The humidity regimes of the environment on land are varied - from complete and constant saturation of the air with water vapor, where several thousand millimeters of precipitation falls per year (regions of equatorial and monsoon-tropical climates) to their almost complete absence in the dry air of deserts. Thus, in tropical deserts the average annual precipitation is less than 100 mm per year, and at the same time, rain does not fall every year.

  The annual amount of precipitation does not always make it possible to assess the water supply of organisms, since the same amount can characterize a desert climate (in the subtropics) and a very humid one (in the Arctic). An important role is played by the ratio of precipitation and evaporation (total annual evaporation from the free water surface), which also varies in different regions of the globe. Areas where this value exceeds the annual amount of precipitation are called arid(dry, arid). Here, for example, plants experience lack of moisture during most of the growing season. Areas in which plants are provided with moisture are called humid, or wet. Transition zones are often identified - semi-arid(semiarid).

  The dependence of vegetation on average annual precipitation and temperature is shown in Fig. 24.

  
  

  Rice. 24.

  1 -- tropical forest; 2 -- deciduous forest; 3 - steppe; 4 - desert; 5 -- coniferous forest; 6 -- arctic and mountain tundra

  The water supply of terrestrial organisms depends on the precipitation regime, the presence of reservoirs, soil moisture reserves, the proximity of groundwater, etc. This has contributed to the development of many adaptations in terrestrial organisms to various water supply regimes.

  In Fig. 25 from left to right shows the transition from lower algae living in water with cells without vacuoles to primary poikilohydric terrestrial algae, the formation of vacuoles in aquatic green and charophytes, the transition from thallophytes with vacuoles to homoyohydric cormophytes (the distribution of mosses - hydrophytes is still limited to habitats with high humidity air, in dry habitats mosses become secondary poikilohydric); among ferns and angiosperms (but not among gymnosperms) there are also secondary poikilohydric forms. Most leafy plants are homoyohydric due to the presence of cuticular protection against transpiration and strong vacuolation of their cells. It should be noted that xerophilicity of animals and plants is characteristic only of the ground-air environment.

  
  

  Rice. 2

  Precipitation (rain, hail, snow), in addition to providing water and creating moisture reserves, often plays another environmental role. For example, during heavy rains, the soil does not have time to absorb moisture, the water quickly flows in strong streams and often carries weakly rooted plants, small animals and fertile soil into lakes and rivers. In floodplains, rain can cause floods and thus have adverse effects on the plants and animals living there. In periodically flooded places, unique floodplain fauna and flora are formed.

  Hail also has a negative effect on plants and animals. Agricultural crops in individual fields are sometimes completely destroyed by this natural disaster.

  The ecological role of snow cover is diverse. For plants whose renewal buds are located in the soil or near its surface, and for many small animals, snow plays the role of a heat-insulating cover, protecting them from low winter temperatures. When frosts are above -14°C under a 20 cm layer of snow, the soil temperature does not fall below 0.2°C. Deep snow cover protects the green parts of plants from freezing, such as Veronica officinalis, hoofed grass, etc., which go under the snow without shedding their leaves. Small land animals lead an active lifestyle in winter, creating numerous galleries of passages under the snow and in its thickness. In the presence of fortified food, rodents (wood and yellow-throated mice, a number of voles, water rats, etc.) can breed there in snowy winters. During severe frosts, hazel grouse, partridges, and black grouse hide under the snow.

  Winter snow cover often prevents large animals from obtaining food and moving, especially when an ice crust forms on the surface. Thus, moose (Alces alces) freely overcome a layer of snow up to 50 cm deep, but this is inaccessible to smaller animals. Often during snowy winters, the death of roe deer and wild boars is observed.

  Large amounts of snow also have a negative impact on plants. In addition to mechanical damage in the form of snow chips or snow blowers, a thick layer of snow can lead to damping off of plants, and when the snow melts, especially in a long spring, to soaking of plants.

  

  Rice. 26.

  Plants and animals suffer from low temperatures and strong winds in winters with little snow. Thus, in years when there is little snow, mouse-like rodents, moles and other small animals die. At the same time, in latitudes where precipitation falls in the form of snow in winter, plants and animals have historically adapted to life in snow or on its surface, developing various anatomical, morphological, physiological, behavioral and other characteristics. For example, in some animals the supporting surface of their legs increases in winter by overgrowing them with coarse hair (Fig. 26), feathers, and horny scutes.

  Others migrate or fall into an inactive state - sleep, hibernation, diapause. A number of animals switch to feeding on certain types of feed.

  

  Rice. 5.27.

  The whiteness of the snow cover reveals dark animals. The seasonal change in color in the ptarmigan and tundra partridge, ermine (Fig. 27), mountain hare, weasel, and arctic fox is undoubtedly associated with selection for camouflage to match the background color.

  Precipitation, in addition to its direct impact on organisms, determines one or another air humidity, which, as already noted, plays an important role in the life of plants and animals, as it affects the intensity of their water metabolism. Evaporation from the surface of the body of animals and transpiration in plants are more intense, the less the air is saturated with water vapor.

  Absorption by the above-ground parts of droplet-liquid moisture falling in the form of rain, as well as vaporous moisture from the air, in higher plants is found in epiphytes of tropical forests, which absorb moisture over the entire surface of the leaves and aerial roots. The branches of some shrubs and trees, for example saxauls - Halaxylon persicum, H. aphyllum, can absorb vaporous moisture from the air. In higher spore plants and especially lower plants, the absorption of moisture by above-ground parts is a common method of water nutrition (mosses, lichens, etc.). With a lack of moisture, mosses and lichens are able to survive for a long time in a state close to air-dry, falling into suspended animation. But as soon as it rains, these plants quickly absorb moisture with all ground parts, acquire softness, restore turgor, and resume the processes of photosynthesis and growth.

  In plants in highly humid terrestrial habitats, there is often a need to remove excess moisture. As a rule, this happens when the soil is well warmed up and the roots actively absorb water, and there is no transpiration (in the morning or during fog, when the air humidity is 100%).

  Excess moisture is removed by guttation -- this is the release of water through special excretory cells located along the edge or at the tip of the leaf (Fig. 28).

  

  Rice. 28.

  1 - in cereals, 2 - in strawberries, 3 - in tulips, 4 - in milkweed, 5 - in Sarmatian bellevalia, 6 - in clover

  Not only hygrophytes, but also many mesophytes are capable of guttation. For example, in the Ukrainian steppes, guttation was found in more than half of all plant species. Many meadow grasses humidify so much that they wet the soil surface. This is how animals and plants adapt to the seasonal distribution of precipitation, its quantity and nature. This determines the composition of plants and animals, the timing of certain phases in their development cycle.

  Humidity is also affected by the condensation of water vapor, which often occurs in the surface layer of air when the temperature changes. Dew appears when the temperature drops in the evening. Often dew falls in such quantities that it abundantly wets plants, flows into the soil, increases air humidity and creates favorable conditions for living organisms, especially when there is little other precipitation. Plants contribute to the deposition of dew. Cooling at night, they condense water vapor on themselves. The humidity regime is significantly affected by fogs, thick clouds and other natural phenomena.

  When quantitatively characterizing the plant habitat based on the water factor, indicators are used that reflect the content and distribution of moisture not only in the air, but also in the soil. Soil water, or soil moisture, is one of the main sources of moisture for plants. Water in the soil is in a fragmented state, interspersed with pores of different sizes and shapes, has a large interface with the soil, and contains a number of cations and anions. Hence, soil moisture is heterogeneous in physical and chemical properties. Not all the water contained in the soil can be used by plants. Based on its physical state, mobility, availability and importance for plants, soil water is divided into gravitational, hygroscopic and capillary.

  The soil also contains vaporous moisture, which occupies all water-free pores. This is almost always (except in desert soils) saturated water vapor. When the temperature drops below 0°C, soil moisture turns into ice (initially free water, and with further cooling - part of the bound water).

  The total amount of water that can be held by soil (determined by adding excess water and then waiting until it stops dripping out) is called field moisture capacity.

  Consequently, the total amount of water in the soil cannot characterize the degree of moisture supply to plants. To determine it, it is necessary to subtract the wilting coefficient from the total amount of water. However, physically accessible soil water is not always physiologically available to plants due to low soil temperature, lack of oxygen in soil water and soil air, soil acidity, and high concentration of mineral salts dissolved in soil water. The discrepancy between the absorption of water by the roots and its release by the leaves leads to wilting of plants. The development of not only the above-ground parts, but also the root system of plants depends on the amount of physiologically available water. In plants growing on dry soils, the root system, as a rule, is more branched and more powerful than on wet soils (Fig. 29).

  
  

  Rice. 29.

  1 -- with a lot of precipitation; 2 - at average; 3 -- at low

  One of the sources of soil moisture is groundwater. When their level is low, capillary water does not reach the soil and does not affect its water regime. Moistening the soil due to precipitation alone causes strong fluctuations in its humidity, which often negatively affects plants. Too high a groundwater level is also harmful, because it leads to waterlogging of the soil, depletion of oxygen and enrichment in mineral salts. Constant soil moisture, regardless of the vagaries of the weather, ensures an optimal groundwater level.

  Temperature conditions. A distinctive feature of the land-air environment is the large range of temperature fluctuations. In most land areas, daily and annual temperature ranges are tens of degrees. Changes in air temperature are especially significant in deserts and subpolar continental regions. For example, the seasonal temperature range in the deserts of Central Asia is 68-77°C, and the daily temperature range is 25-38°C. In the vicinity of Yakutsk, the average January temperature is 43°C, the average July temperature is +19°C, and the annual range is from -64 to +35°C. In the Trans-Urals, the annual variation in air temperature is sharp and is combined with great variability in the temperatures of the winter and spring months in different years. The coldest month is January, the average air temperature ranges from -16 to -19°C, in some years it drops to -50°C, the warmest month is July with temperatures from 17.2 to 19.5°C. Maximum positive temperatures are 38--41°C.

  Temperature fluctuations at the soil surface are even more significant.

  Terrestrial plants occupy a zone adjacent to the soil surface, i.e., to the “interface”, on which the transition of incident rays from one medium to another or, in another way, from transparent to opaque, takes place. A special thermal regime is created on this surface: during the day there is strong heating due to the absorption of heat rays, at night there is strong cooling due to radiation. From here, the ground layer of air experiences the sharpest daily temperature fluctuations, which are most pronounced over bare soil.

  The thermal regime of plant habitats, for example, is characterized based on temperature measurements directly in the vegetation cover. In herbaceous communities, measurements are taken inside and on the surface of the grass stand, and in forests, where there is a certain vertical temperature gradient, at a number of points at different heights.

  Resistance to temperature changes in the environment in terrestrial organisms varies and depends on the specific habitat where their life takes place. Thus, terrestrial leafy plants for the most part grow in a wide temperature range, i.e. they are eurythermic. Their life span in the active state extends, as a rule, from 5 to 55°C, while these plants are productive between 5 and 40°C. Plants in continental regions, which are characterized by a clear diurnal temperature variation, develop best when the night is 10-15°C colder than the day. This applies to most plants in the temperate zone - with a temperature difference of 5-10 ° C, and tropical plants with an even smaller amplitude - about 3 ° C (Fig. 30).

  

  Rice. thirty.

  In poikilothermic organisms, with increasing temperature (T), the duration of development (t) decreases more and more rapidly. The development rate Vt can be expressed by the formula Vt = 100/t.

  To achieve a certain stage of development (for example, in insects - from an egg), i.e. pupation, the imaginal stage, always requires a certain amount of temperature. The product of the effective temperature (temperature above the zero point of development, i.e. T - To) by the duration of development (t) gives a species-specific thermal constant development c=t(T--To). Using this equation, you can calculate the time of onset of a certain stage of development, for example, of a plant pest, at which its control is effective.

  Plants, as poikilothermic organisms, do not have their own stable body temperature. Their temperature is determined by the thermal balance, i.e., the ratio of energy absorption and release. These values ​​depend on many properties of both the environment (the size of the radiation arrival, the temperature of the surrounding air and its movement) and the plants themselves (the color and other optical properties of the plant, the size and location of the leaves, etc.). The primary role is played by the cooling effect of transpiration, which prevents severe overheating of plants in hot habitats. As a result of the above reasons, the temperature of plants usually differs (often quite significantly) from the ambient temperature. There are three possible situations here: the plant temperature is higher than the ambient temperature, lower than it, equal to or very close to it. The excess of plant temperature over air temperature occurs not only in highly heated, but also in colder habitats. This is facilitated by the dark color or other optical properties of plants, which increase the absorption of solar radiation, as well as anatomical and morphological features that help reduce transpiration. Arctic plants can heat up quite noticeably (Fig. 31).

  Another example is the dwarf willow - Salix arctica in Alaska, whose leaves are 2--11 °C warmer than the air during the day and even at night during the polar “24-hour day” - by 1--3 °C.

  For early spring ephemeroids, the so-called “snowdrops,” heating of the leaves provides the opportunity for fairly intense photosynthesis on sunny but still cold spring days. For cold habitats or those associated with seasonal temperature fluctuations, an increase in plant temperature is ecologically very important, since physiological processes thereby become independent, to a certain extent, from the surrounding thermal background.

  
  

  Rice. 31.

  On the right is the intensity of life processes in the biosphere: 1 - the coldest layer of air; 2 -- upper limit of shoot growth; 3, 4, 5 - zone of greatest activity of life processes and maximum accumulation of organic matter; 6 -- permafrost level and lower rooting limit; 7 -- area of ​​lowest soil temperatures

  A decrease in the temperature of plants compared to the surrounding air is most often observed in highly illuminated and heated areas of the terrestrial sphere (desert, steppe), where the leaf surface of plants is greatly reduced, and increased transpiration helps remove excess heat and prevents overheating. In general terms, we can say that in hot habitats the temperature of the above-ground parts of plants is lower, and in cold habitats it is higher than the air temperature. The coincidence of plant temperature with the ambient air temperature is less common - in conditions that exclude a strong influx of radiation and intense transpiration, for example, in herbaceous plants under the canopy of forests, and in open areas - in cloudy weather or during rain.

  In general, terrestrial organisms are more eurythermic than aquatic ones.

  In the ground-air environment, living conditions are complicated by the existence weather changes. Weather is the continuously changing state of the atmosphere at the earth's surface, up to approximately an altitude of 20 km (the boundary of the troposphere). Weather variability is manifested in constant variations in the combination of environmental factors such as air temperature and humidity, cloudiness, precipitation, wind strength and direction, etc. (Fig. 32).

  
  

  Rice. 32.

  Weather changes, along with their regular alternation in the annual cycle, are characterized by non-periodic fluctuations, which significantly complicate the conditions for the existence of terrestrial organisms. In Fig. 33, using the example of the codling moth caterpillar Carpocapsa pomonella, shows the dependence of mortality on temperature and relative humidity.

  

  Rice. 33.

  It follows from this that equal mortality curves have a concentric shape and that the optimal zone is limited by relative humidity of 55 and 95% and temperature of 21 and 28 ° C.

  Light, temperature and air humidity usually determine not the maximum, but the average degree of opening of stomata in plants, since the coincidence of all conditions promoting their opening rarely happens.

  The long-term weather regime characterizes climate of the area. The concept of climate includes not only the average values ​​of meteorological phenomena, but also their annual and daily variations, deviations from them, and their frequency. The climate is determined by the geographical conditions of the area.

  The main climatic factors are temperature and humidity, measured by the amount of precipitation and the saturation of air with water vapor. Thus, in countries remote from the sea, there is a gradual transition from a humid climate through a semiarid intermediate zone with occasional or periodic dry periods to an arid territory, which is characterized by prolonged drought, salinization of soil and water (Fig. 34).

  
  

  Rice. 34.

  Note: where the precipitation curve intersects the ascending evapotranspiration line, the boundary between humid (left) and arid (right) climates is located. The humus horizon is shown in black, the illuvial horizon is shown in shading.

  Each habitat is characterized by a certain ecological climate, i.e., the climate of the ground layer of air, or ecoclimate.

  Vegetation has a great influence on climatic factors. Thus, under the forest canopy, air humidity is always higher, and temperature fluctuations are less than in the clearings. The light regime of these places is also different. Different plant associations form their own regime of light, temperature, humidity, i.e. phytoclimate.

  Ecoclimate or phytoclimate data are not always sufficient to fully characterize the climatic conditions of a particular habitat. Local environmental elements (relief, exposure, vegetation, etc.) very often change the regime of light, temperature, humidity, air movement in a particular area in such a way that it can differ significantly from the climatic conditions of the area. Local climate modifications that develop in the surface layer of air are called microclimate. For example, the living conditions surrounding insect larvae living under the bark of a tree are different than in the forest where the tree grows. The temperature of the southern side of the trunk can be 10 - 15°C higher than the temperature of its northern side. Burrows, tree hollows, and caves inhabited by animals have a stable microclimate. There are no clear differences between ecoclimate and microclimate. It is believed that ecoclimate is the climate of large areas, and microclimate is the climate of individual small areas. Microclimate influences living organisms of a particular territory or locality (Fig. 35).

  
  

  Rice. 3

  at the top is a well-warmed slope of southern exposure;

  below - a horizontal section of the plakor (the floristic composition in both sections is the same)

  The presence of many microclimates in one area ensures the coexistence of species with different requirements for the external environment.

  Geographical zonality and zonality. The distribution of living organisms on Earth is closely related to geographic zones and zones. The belts have a latitudinal extension, which, naturally, is primarily due to radiation boundaries and the nature of atmospheric circulation. There are 13 geographic zones on the surface of the globe, spread across continents and oceans (Fig. 36).

  

  Rice. 36.

  These are like arctic, antarctic, subarctic, subantarctic, north and south moderate, north and south subarctic, north and south tropical, north and south subequatorial And equatorial. Inside the belts there are geographical zones, where, along with radiation conditions, the moisture of the earth's surface and the ratio of heat and moisture characteristic of a given zone are taken into account. Unlike the ocean, where the supply of moisture is complete, on the continents the ratio of heat and moisture can have significant differences. From here, geographic zones extend to continents and oceans, and geographic zones only to continents. Distinguish latitudinal And meridial or longitudinal natural zones. The former stretch from west to east, the latter from north to south. In the longitudinal direction, latitudinal zones are divided into subzones, and in the latitude - on provinces.

  The founder of the doctrine of natural zonality is V.V. Dokuchaev (1846-1903), who substantiated zonality as a universal law of nature. All phenomena within the biosphere are subject to this law. The main reasons for zonation are the shape of the Earth and its position relative to the sun. In addition to latitude, the distribution of heat on Earth is influenced by the nature of the relief and the altitude of the area above sea level, the ratio of land and sea, sea currents, etc.

  Subsequently, the radiation foundations for the formation of zonality of the globe were developed by A. A. Grigoriev and M. I. Budyko. To establish a quantitative characteristic of the relationship between heat and moisture for various geographical zones, they determined some coefficients. The ratio of heat and moisture is expressed by the ratio of the surface radiation balance to the latent heat of evaporation and the amount of precipitation (radiation dryness index). A law was established, called the law of periodic geographical zoning (A. A. Grigorieva - M. I. Budyko), which states: that with the change of geographical zones, similar geographical(landscape, natural) zones and some of their general properties are repeated periodically.

  Each zone is confined to a certain range of indicator values: a special nature of geomorphological processes, a special type of climate, vegetation, soil and animal life. The following geographical zones were noted on the territory of the former USSR: icy, tundra, forest-tundra, taiga, mixed forests. Russian plain, monsoon mixed forests of the Far East, forest-steppes, steppes, semi-deserts, temperate deserts, subtropical deserts, Mediterranean and humid subtropics.

  One of the important conditions for the variability of organisms and their zonal distribution on earth is the variability of the chemical composition of the environment. In this regard, the teaching of A.P. Vinogradov about biogeochemical provinces, which are determined by the zonality of the chemical composition of soils, as well as the climatic, phytogeographical and geochemical zonality of the biosphere. Biogeochemical provinces are areas on the Earth's surface that differ in the content (in soils, waters, etc.) of chemical compounds, which are associated with certain biological reactions on the part of the local flora and fauna.

  Along with horizontal zoning in the terrestrial environment, high-rise or vertical zonality.

  The vegetation of mountainous countries is richer than on the adjacent plains, and is characterized by an increased distribution of endemic forms. Thus, according to O. E. Agakhanyants (1986), the flora of the Caucasus includes 6,350 species, of which 25% are endemic. The flora of the mountains of Central Asia is estimated at 5,500 species, of which 25-30% are endemic, while on the adjacent plains of the southern deserts there are 200 plant species.

  When climbing mountains, the same change of zones is repeated as from the equator to the poles. At the foot there are usually deserts, then steppes, deciduous forests, coniferous forests, tundra and, finally, ice. However, there is still no complete analogy. As you climb the mountains, the air temperature decreases (the average air temperature gradient is 0.6 °C per 100 m), evaporation decreases, ultraviolet radiation and illumination increase, etc. All this forces plants to adapt to dry or wet conditions. The dominant plants here are cushion-shaped life forms and perennials, which have developed adaptation to strong ultraviolet radiation and reduced transpiration.

  The fauna of the high mountain regions is also unique. Low air pressure, significant solar radiation, sharp fluctuations in day and night temperatures, and changes in air humidity with altitude contributed to the development of specific physiological adaptations in the body of mountain animals. For example, in animals the relative volume of the heart increases, the content of hemoglobin in the blood increases, which allows more intensive absorption of oxygen from the air. Rocky soil complicates or almost eliminates the burrowing activity of animals. Many small animals (small rodents, pikas, lizards, etc.) find refuge in rock crevices and caves. Among the birds typical for mountainous regions are mountain turkeys (sulars), mountain finches, larks, and large birds - bearded vultures, vultures, and condors. Large mammals in the mountains are inhabited by rams, goats (including snow goats), chamois, yaks, etc. Predators are represented by species such as wolves, foxes, bears, lynxes, snow leopards (irbis), etc.

  A habitat is the immediate environment in which a living organism (animal or plant) exists. It can contain both living organisms and inanimate objects and any number of varieties of organisms from several species to several thousand, coexisting in a certain living space. The air-ground habitat includes such areas of the earth's surface as mountains, savannas, forests, tundra, polar ice and others.

  Habitat - planet Earth

  Different parts of planet Earth are home to a huge biological diversity of living organisms. There are certain types of animal habitats. Hot, arid areas are often covered by hot deserts. Warm, humid regions contain humid

  There are 10 main types of land habitats on Earth. Each of them has many varieties, depending on where in the world it is located. Animals and plants that are typical of a particular habitat adapt to the conditions in which they live.

  

  African savannas

  This tropical herbaceous aerial-terrestrial community habitat is found in Africa. It is characterized by long dry periods following wet seasons with heavy rainfall. African savannas are home to a huge number of herbivores, as well as powerful predators that feed on them.

  Mountains

  The tops of high mountain ranges are very cold and few plants grow there. Animals living in these high places are adapted to cope with low temperatures, lack of food and steep, rocky terrain.

  Evergreen forests

  Coniferous forests are often found in cooler areas of the globe: Canada, Alaska, Scandinavia and regions of Russia. Dominated by evergreen spruce trees, these areas are home to animals such as elk, beaver and wolf.

  

  Deciduous trees

  In cold, damp areas, many trees grow rapidly in the summer but lose their leaves in the winter. The number of wildlife in these areas varies seasonally as many migrate to other areas or hibernate during the winter.

  Temperate zone

  It is characterized by dry grassy prairies and steppes, grasslands, hot summers and cold winters. This terrestrial-air habitat is home to gregarious herbivores such as antelope and bison.

  Mediterranean zone

  The lands around the Mediterranean Sea have a hot climate, but there is more rainfall here than in desert areas. These areas are home to shrubs and plants that can only survive if they have access to water and are often filled with many different types of insects.

  Tundra

  An air-terrestrial habitat such as the tundra is covered with ice most of the year. Nature comes to life only in spring and summer. Deer live here and birds nest.

  

  Rainforests

  These dense green forests grow close to the equator and are home to the richest biological diversity of living organisms. No other habitat can boast as many inhabitants as the rainforest area.

  polar ice

  Cold regions near the North and South Poles are covered with ice and snow. Here you can meet penguins, seals and polar bears, who forage for food in the icy waters of the ocean.

  Animals of the land-air habitat

  Habitats are scattered across a vast area of ​​planet Earth. Each is characterized by a certain biological and plant world, representatives of which unevenly populate our planet. In colder parts of the world, such as the polar regions, there are not many species of fauna that inhabit these areas and are specially adapted to living in low temperatures. Some animals are distributed throughout the world depending on the plants they eat, for example, the giant panda inhabits areas where

  

  Air-ground habitat

  Every living organism needs a home, shelter or environment that can provide security, ideal temperature, food and reproduction - all the things necessary for survival. One of the important functions of a habitat is to provide the ideal temperature, since extreme changes can destroy an entire ecosystem. An important condition is also the availability of water, air, soil and sunlight.

  

  The temperature on Earth is not the same everywhere; in some corners of the planet (North and South Poles) the thermometer can drop to -88°C. In other places, especially in the tropics, it is very warm and even hot (up to +50°C). Temperature plays an important role in the processes of adaptation of the land-air habitat; for example, animals adapted to low temperatures cannot survive in heat.

  

  A habitat is the natural environment in which an organism lives. Animals require different amounts of space. The habitat can be large and occupy an entire forest or small, like a mink. Some inhabitants have to defend and defend a huge territory, while others need a small area of ​​​​space where they can coexist relatively peacefully with neighbors living nearby.

  The ground-air environment is the most complex in terms of environmental conditions. Life on land required adaptations that turned out to be possible only with a sufficiently high level of organization of plants and animals.

  4.2.1. Air as an environmental factor for terrestrial organisms

  The low density of air determines its low lifting force and low air mobility. Inhabitants of the air must have their own support system that supports the body: plants - with a variety of mechanical tissues, animals - with a solid or, much less frequently, hydrostatic skeleton. In addition, all inhabitants of the air are closely connected with the surface of the earth, which serves them for attachment and support. Life suspended in the air is impossible.

  True, many microorganisms and animals, spores, seeds, fruits and pollen of plants are regularly present in the air and are carried by air currents (Fig. 43), many animals are capable of active flight, but in all these species the main function of their life cycle - reproduction - is carried out on the surface of the earth. For most of them, staying in the air is associated only with settling or searching for prey.

  Rice. 43. Distribution of aerial plankton arthropods by height (according to Dajo, 1975)

  Low air density causes low resistance to movement. Therefore, during the course of evolution, many terrestrial animals used the ecological benefits of this property of the air environment, acquiring the ability to fly. 75% of the species of all terrestrial animals are capable of active flight, mainly insects and birds, but flyers are also found among mammals and reptiles. Land animals fly mainly with the help of muscular efforts, but some can also glide using air currents.

  Thanks to the mobility of air and the vertical and horizontal movements of air masses existing in the lower layers of the atmosphere, passive flight of a number of organisms is possible.

  Anemophilia - the oldest method of pollinating plants. All gymnosperms are pollinated by wind, and among angiosperms, anemophilous plants make up approximately 10% of all species.

  Anemophily is observed in the families of beech, birch, walnut, elm, hemp, nettle, casuarina, goosefoot, sedge, cereals, palms and many others. Wind-pollinated plants have a number of adaptations that improve the aerodynamic properties of their pollen, as well as morphological and biological features that ensure pollination efficiency.

  The life of many plants is completely dependent on the wind, and dispersal occurs with its help. Such a double dependence is observed in spruce, pine, poplar, birch, elm, ash, cotton grass, cattail, saxaul, dzhuzgun, etc.

  Many species have developed anemochory– settlement using air currents. Anemochory is characteristic of spores, seeds and fruits of plants, protozoan cysts, small insects, spiders, etc. Organisms passively transported by air currents are collectively called aeroplankton by analogy with planktonic inhabitants of the aquatic environment. Special adaptations for passive flight are very small body sizes, an increase in its area due to outgrowths, strong dissection, a large relative surface of the wings, the use of a web, etc. (Fig. 44). Anemochorous seeds and fruits of plants also have either very small sizes (for example, orchid seeds) or a variety of wing-like and parachute-like appendages that increase their ability to plan (Fig. 45).

  

  Rice. 44. Adaptations for transport by air currents in insects:

  1 – mosquito Cardiocrepis brevirostris;

  2 – gall midge Porrycordila sp.;

  3 – Hymenoptera Anargus fuscus;

  4 – Hermes Dreyfusia nordmannianae;

  5 – gypsy moth larva Lymantria dispar

  

  Rice. 45. Adaptations to wind transfer in fruits and seeds of plants:

  1 – linden Tilia intermedia;

  2 – maple Acer monspessulanum;

  3 – birch Betula pendula;

  4 – cotton grass Eriophorum;

  5 – dandelion Taraxacum officinale;

  6 – cattail Typha scuttbeworhii

  In the dispersal of microorganisms, animals and plants, the main role is played by vertical convection air currents and weak winds. Strong winds, storms and hurricanes also have significant environmental impacts on terrestrial organisms.

  Low air density causes relatively low pressure on land. Normally it is 760 mmHg. Art. As altitude increases, pressure decreases. At an altitude of 5800 m it is only half normal. Low pressure may limit the distribution of species in the mountains. For most vertebrates, the upper limit of life is about 6000 m. A decrease in pressure entails a decrease in oxygen supply and dehydration of animals due to an increase in respiration rate. The limits of advancement of higher plants into the mountains are approximately the same. Somewhat more hardy are arthropods (springtails, mites, spiders), which can be found on glaciers above the vegetation line.

  In general, all terrestrial organisms are much more stenobatic than aquatic ones, since normal pressure fluctuations in their environment amount to fractions of the atmosphere and, even for birds rising to great heights, do not exceed 1/3 of normal.

  Gas composition of air. In addition to the physical properties of the air, its chemical properties are extremely important for the existence of terrestrial organisms. The gas composition of air in the surface layer of the atmosphere is quite homogeneous in terms of the content of the main components (nitrogen - 78.1%, oxygen - 21.0, argon - 0.9, carbon dioxide - 0.035% by volume) due to the high diffusivity of gases and constant mixing convection and wind currents. However, various impurities of gaseous, droplet-liquid and solid (dust) particles entering the atmosphere from local sources can have significant environmental significance.

  The high oxygen content contributed to an increase in metabolism in terrestrial organisms compared to primary aquatic ones. It was in a terrestrial environment, on the basis of the high efficiency of oxidative processes in the body, that animal homeothermy arose. Oxygen, due to its constantly high content in the air, is not a factor limiting life in the terrestrial environment. Only in places, under specific conditions, is a temporary deficiency created, for example in accumulations of decomposing plant residues, reserves of grain, flour, etc.

  The carbon dioxide content can vary in certain areas of the surface layer of air within fairly significant limits. For example, in the absence of wind in the center of large cities, its concentration increases tens of times. There are regular daily changes in the carbon dioxide content in the surface layers associated with the rhythm of plant photosynthesis. Seasonal are caused by changes in the intensity of respiration of living organisms, mainly the microscopic population of soils. Increased saturation of air with carbon dioxide occurs in areas of volcanic activity, near thermal springs and other underground outlets of this gas. In high concentrations, carbon dioxide is toxic. In nature, such concentrations are rare.

  In nature, the main source of carbon dioxide is the so-called soil respiration. Soil microorganisms and animals breathe very intensively. Carbon dioxide diffuses from the soil into the atmosphere, especially vigorously during rain. It is abundant in soils that are moderately moist, well heated, and rich in organic residues. For example, the soil of a beech forest emits CO 2 from 15 to 22 kg/ha per hour, and unfertilized sandy soil emits only 2 kg/ha.

  In modern conditions, human activity in burning fossil fuel reserves has become a powerful source of additional amounts of CO 2 entering the atmosphere.

  Air nitrogen is an inert gas for most inhabitants of the terrestrial environment, but a number of prokaryotic organisms (nodule bacteria, Azotobacter, clostridia, blue-green algae, etc.) have the ability to bind it and involve it in the biological cycle.

  

  Rice. 46. A mountainside with destroyed vegetation due to sulfur dioxide emissions from surrounding industrial enterprises

  Local pollutants entering the air can also significantly affect living organisms. This especially applies to toxic gaseous substances - methane, sulfur oxide, carbon monoxide, nitrogen oxide, hydrogen sulfide, chlorine compounds, as well as dust particles, soot, etc., that pollute the air in industrial areas. The main modern source of chemical and physical pollution of the atmosphere is anthropogenic: the work of various industrial enterprises and transport, soil erosion, etc. Sulfur oxide (SO 2), for example, is toxic to plants even in concentrations from one fifty-thousandth to one millionth of the volume of air. Around industrial centers that pollute the atmosphere with this gas, almost all vegetation dies (Fig. 46). Some plant species are particularly sensitive to SO 2 and serve as a sensitive indicator of its accumulation in the air. For example, many lichens die even with traces of sulfur oxide in the surrounding atmosphere. Their presence in forests around large cities indicates high air purity. The resistance of plants to impurities in the air is taken into account when selecting species for landscaping in populated areas. Sensitive to smoke, for example, common spruce and pine, maple, linden, birch. The most resistant are thuja, Canadian poplar, American maple, elderberry and some others.

  4.2.2. Soil and relief. Weather and climatic features of the ground-air environment

  Edaphic environmental factors. Soil properties and terrain also affect the living conditions of terrestrial organisms, primarily plants. The properties of the earth's surface that have an ecological impact on its inhabitants are collectively called edaphic environmental factors (from the Greek “edaphos” - foundation, soil).

  The nature of the plant root system depends on the hydrothermal regime, aeration, composition, composition and structure of the soil. For example, the root systems of tree species (birch, larch) in areas with permafrost are located at shallow depths and spread out wide. Where there is no permafrost, the root systems of these same plants are less widespread and penetrate deeper. In many steppe plants, the roots can reach water from great depths; at the same time, they also have many surface roots in the humus-rich soil horizon, from where the plants absorb elements of mineral nutrition. On waterlogged, poorly aerated soil in mangroves, many species have special respiratory roots - pneumatophores.

  A number of ecological groups of plants can be distinguished in relation to different soil properties.

  So, according to the reaction to soil acidity, they distinguish: 1) acidophilic species - grow on acidic soils with a pH less than 6.7 (plants of sphagnum bogs, white grass); 2) neutrophilic – gravitate towards soils with a pH of 6.7–7.0 (most cultivated plants); 3) basophilic– grow at a pH of more than 7.0 (mordovnik, forest anemone); 4) indifferent – can grow on soils with different pH values ​​(lily of the valley, sheep fescue).

  In relation to the gross composition of the soil there are: 1) oligotrophic plants that are content with a small amount of ash elements (Scots pine); 2) eutrophic, those that need a large amount of ash elements (oak, common gooseberry, perennial woodweed); 3) mesotrophic, requiring a moderate amount of ash elements (common spruce).

  Nitrophils– plants that prefer soils rich in nitrogen (nettle).

  Plants of saline soils form a group halophytes(soleros, sarsazan, kokpek).

  Some plant species are confined to different substrates: petrophytes grow on rocky soils, and psammophytes inhabit shifting sands.

  The terrain and the nature of the soil affect the specific movement of animals. For example, ungulates, ostriches, and bustards living in open spaces need hard ground to enhance repulsion when running fast. In lizards that live on shifting sands, the toes are fringed with a fringe of horny scales, which increases the support surface (Fig. 47). For terrestrial inhabitants that dig holes, dense soils are unfavorable. The nature of the soil in some cases influences the distribution of terrestrial animals that dig burrows, burrow into the soil to escape heat or predators, or lay eggs in the soil, etc.

  

  Rice. 47. Fan-toed gecko - inhabitant of the sands of the Sahara: A - fan-toed gecko; B – gecko leg

  Weather features. Living conditions in the ground-air environment are complicated, in addition, weather changes.Weather - this is a continuously changing state of the atmosphere at the earth's surface up to an altitude of approximately 20 km (the boundary of the troposphere). Weather variability is manifested in a constant variation in the combination of environmental factors such as temperature and humidity, cloudiness, precipitation, wind strength and direction, etc. Weather changes, along with their natural alternation in the annual cycle, are characterized by non-periodic fluctuations, which significantly complicates the conditions of existence terrestrial organisms. The weather affects the life of aquatic inhabitants to a much lesser extent and only on the population of the surface layers.

  Climate of the area. The long-term weather regime characterizes climate of the area. The concept of climate includes not only the average values ​​of meteorological phenomena, but also their annual and daily cycle, deviations from it and their frequency. The climate is determined by the geographical conditions of the area.

  The zonal diversity of climates is complicated by the action of monsoon winds, the distribution of cyclones and anticyclones, the influence of mountain ranges on the movement of air masses, the degree of distance from the ocean (continentality) and many other local factors. In the mountains there is a climatic zonation, much similar to the change of zones from low latitudes to high latitudes. All this creates an extraordinary diversity of living conditions on land.

  For most terrestrial organisms, especially small ones, it is not so much the climate of the area that is important as the conditions of their immediate habitat. Very often, local environmental elements (relief, exposure, vegetation, etc.) change the regime of temperature, humidity, light, air movement in a particular area in such a way that it differs significantly from the climatic conditions of the area. Such local climate modifications that develop in the surface layer of air are called microclimate. Each zone has very diverse microclimates. Microclimates of arbitrarily small areas can be identified. For example, a special regime is created in the corollas of flowers, which is used by the insects living there. Differences in temperature, air humidity and wind strength are widely known in open space and in forests, in grass stands and over bare areas of soil, on slopes of northern and southern exposures, etc. A special stable microclimate occurs in burrows, nests, hollows, caves and other closed places.

  Precipitation. In addition to providing water and creating moisture reserves, they can play other ecological roles. Thus, heavy rainfall or hail sometimes have a mechanical effect on plants or animals.

  The ecological role of snow cover is especially diverse. Daily temperature fluctuations penetrate into the snow depth only up to 25 cm; deeper the temperature remains almost unchanged. With frosts of -20-30 °C under a layer of snow of 30-40 cm, the temperature is only slightly below zero. Deep snow cover protects renewal buds and protects green parts of plants from freezing; many species go under the snow without shedding their foliage, for example, hairy grass, Veronica officinalis, hoofed grass, etc.

  

  Rice. 48. Scheme of telemetric study of the temperature regime of hazel grouse located in a snow hole (according to A.V. Andreev, A.V. Krechmar, 1976)

  Small land animals also lead an active lifestyle in winter, creating entire galleries of tunnels under the snow and in its thickness. A number of species that feed on snow-covered vegetation are even characterized by winter reproduction, which is noted, for example, in lemmings, wood and yellow-throated mice, a number of voles, water rats, etc. Grouse birds - hazel grouse, black grouse, tundra partridge - burrow in the snow for the night ( Fig. 48).

  Winter snow cover makes it difficult for large animals to obtain food. Many ungulates (reindeer, wild boars, musk oxen) feed exclusively on snow-covered vegetation in winter, and deep snow cover, and especially the hard crust on its surface that occurs during icy conditions, doom them to starvation. During nomadic cattle breeding in pre-revolutionary Russia, a huge disaster in the southern regions was jute – mass mortality of livestock as a result of icy conditions, depriving animals of food. Movement on loose deep snow is also difficult for animals. Foxes, for example, in snowy winters prefer areas in the forest under dense spruce trees, where the layer of snow is thinner, and almost never go out into open glades and forest edges. Snow depth may limit the geographic distribution of species. For example, real deer do not penetrate north into those areas where the snow thickness in winter is more than 40–50 cm.

  The whiteness of the snow cover reveals dark animals. Selection for camouflage to match the background color apparently played a major role in the occurrence of seasonal color changes in the ptarmigan and tundra partridge, mountain hare, ermine, weasel, and arctic fox. On the Commander Islands, along with white foxes, there are many blue foxes. According to the observations of zoologists, the latter stay mainly near dark rocks and ice-free surf strips, while the white ones prefer areas with snow cover.