Nature is amazing and diverse, and everything in it is interconnected and balanced. The number of individuals of any species of animals, insects, fish is constantly regulated.
It is impossible to imagine that the number of any species of individuals is constantly increasing. To prevent this from happening, there is natural selection and many other environmental factors that constantly regulate this number. You have all probably heard the expression “ecological pyramid”. What it is? What types of ecological pyramids exist? What rules is it based on? You will receive answers to these and other questions below.
An ecological pyramid is... Definition
So, everyone knows that in biology there are food chains, when some animals, usually predators, feed on other animals.
The ecological pyramid is approximately the same system, but, in turn, much more global. What is she? An ecological pyramid is a certain system that reflects in its composition the number of creatures, the mass of individuals, and plus the energy embedded in them at each level. Another peculiarity is that as each level increases, the indicators decrease significantly. By the way, this is precisely what the rule of the ecological pyramid is connected with. Before we talk about it, it’s worth understanding what this scheme looks like.
Pyramid rule
If you imagine it schematically in the figure, it will be something similar to the Cheops pyramid: a quadrangular pyramid with a pointed top, where the smallest number of individuals is concentrated.
The ecological pyramid rule defines one very interesting pattern. It lies in the fact that the base of the ecological pyramid, namely the vegetation that forms the basis of nutrition, is about ten times greater than the mass of animals that eat plant foods.
Moreover, each next level is also ten times smaller than the previous one. So it turns out that the uppermost level contains the least mass and energy. What does this pattern give us?
The role of the pyramid rule
Based on the rule of the ecological pyramid, many problems can be solved. For example, how many eagles can grow when there is a certain amount of grain, when the food chain includes frogs, snakes, grasshoppers and the eagle.
Based on the fact that only 10% of energy is transferred to the highest level, such problems can be easily solved. We learned what ecological pyramids are and identified their rules and patterns. But now we’ll talk about what ecological pyramids exist in nature.
Types of ecological pyramids
There are three types of pyramids. Based on the initial definition, we can already conclude that they are related to the number of individuals, their biomass and the energy contained in them. In general, first things first.
Pyramid of numbers
The name speaks for itself. This pyramid reflects the number of individuals located at all levels separately. But it is worth noting that in ecology it is used quite rarely, since there are a very large number of individuals at one level, and it is quite difficult to give the complete structure of the biocenosis.
All this is much easier to imagine with one specific example. Let's say there are 1000 tons of green plants at the base of the pyramid. This vegetation is eaten by grasshoppers. Their number, for example, is somewhere around thirty million. Ninety thousand frogs can eat all these grasshoppers. The frogs themselves are the food of 300 trout. One person can eat this amount of fish in a year. What are we doing? What happens is that at the base of the pyramid there are millions of blades of grass, but at the top of the pyramid there is only one person.
It is here that we can observe how, when moving from one level to each subsequent level, the indicators decrease. The mass and number of individuals decreases, and the energy contained in them decreases. It should also be noted that there are exceptions. Let's say that sometimes there are inverted ecopyramids of numbers. Let's say insects live on a certain tree in the forest. All insectivorous birds feed on them.
Biomass pyramid
The second scheme is the biomass pyramid. It also represents a ratio. But in this case it is the mass ratio. As a rule, the mass at the base of the pyramid is always much greater than at the highest trophic level, and the mass of the second level is higher than the mass of the third level, and so on. If organisms at different trophic levels do not differ much in size, then in the figure it just looks like a quadrangular pyramid, tapering upward. One of the American scientists explained the structure of this pyramid using the following example: the weight of vegetation in a meadow is much greater than the mass of individuals consuming these plants, the weight of herbivores is higher than the weight of carnivores of the first level, the weight of the latter is higher than the weight of carnivores of the second level, and so on.
For example, one lion weighs quite a lot, but this individual is so rare that compared to the mass of other individuals, its own mass is negligible. Exceptions also occur in such pyramids, when the mass of producers is smaller compared to the mass of consumers. Let's consider this using the example of a water system. The mass of phytoplankton, even taking into account its high productivity, is less than the mass of consumers, such as whales. Such pyramids are called inverted or inverted.
Pyramid of Energy
And finally, the third type of ecological pyramid is the energy pyramid. It reflects the speed at which the mass of food passes through the chain, as well as the amount of energy given. This law was formulated by R. Lindeman. It was he who proved that with a change in the trophic level, only 10% of the energy that was at the previous level is transferred.
The initial energy percentage is always 100%. But if only a tenth of it moves to the next trophic level, then where does most of the energy go? The main part of it, namely 90%, is spent by individuals to ensure all life processes. Thus, there is a certain pattern here too. A significantly smaller portion of energy also flows through the upper trophic levels, where there is less mass and number of individuals, than it passes through the lower levels. This is what can explain the fact that there are not such a large number of predators.
Disadvantages and advantages of ecological pyramids
Despite the number of different types, almost each of them has a number of disadvantages. These are, for example, pyramids of numbers and biomass. What is their disadvantage? The fact is that constructing the first one causes some difficulties if the dispersion of the numbers of different levels is too large. But the whole difficulty lies not only in this.
The Energy Pyramid is able to compare productivity because it takes into account the most important time factor. And, of course, it is worth saying that such a pyramid never turns out to be upside down. Thanks to this, it is a kind of standard.
The role of the ecological pyramid
The ecological pyramid is what helps us understand the structure of the biocenosis and describe the state of the system. These schemes also help in determining the permissible amount of fish caught and the number of animals to be shot.
All this is necessary in order not to violate the overall integrity and sustainability of the environment. The pyramid, in turn, helps us understand the organization of functional communities, as well as compare different ecosystems based on their productivity.
Ecological pyramid as a ratio of characteristics
Based on the above types, we can conclude that the ecological pyramid is a certain ratio of indicators related to numbers, mass and energy. The levels of the ecological pyramid are different in all respects. Higher levels have lower levels and vice versa. Don't forget about inverted diagrams. Here consumers outnumber producers. But this is not surprising. Nature has its own laws, exceptions can be anywhere.
The energy pyramid is the simplest and most reliable, as it takes into account the most important time factor. Due to this, it is considered to be a kind of standard. The role of ecological pyramids is very important in maintaining the balance of natural ecosystems and ensuring their sustainability.
One type of relationship between organisms in ecosystems is trophic relationships. They show how energy moves through food chains in ecosystems. A model that demonstrates changes in the amount of energy in the links of food chains is the ecological pyramid.
Pyramid structure
A pyramid is a graphical model. Its image is divided into horizontal levels. The number of levels corresponds to the number of links in the power circuits.
All food chains begin with producers - autotrophic organisms that form organic substances. The totality of autotrophs in an ecosystem is what is at the base of the ecological pyramid.
Rice. 1. Ecological pyramid of numbers
Typically, the food pyramid contains from 3 to 5 levels.
The last links in food chains are always large predators or humans. Thus, the number of individuals and biomass at the last level of the pyramid are the lowest.
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The essence of the ecological pyramid is to depict the progressive decrease in biomass in food chains.
Model convention
It should be understood that the model shows reality in a general way. Everything in life is more complicated. Any large organism, including humans, can be eaten and its energy will be used in an atypical way in the ecological pyramid.
Part of the biomass of an ecosystem always comes from decomposers - organisms that decompose dead organic matter. Decomposers are eaten by consumers, partially returning energy to the ecosystem.
Omnivorous animals such as the brown bear act both as a consumer of the first order (eats plants), and as a decomposer (feeds on carrion), and as a large predator.
Kinds
Depending on what quantitative characteristic of levels is used, There are three types of ecological pyramids:
- numbers;
- biomass;
- energy.
10% rule
According to calculations by ecologists, 10% of the biomass or energy of the previous level goes to each subsequent level of the ecological pyramid. The remaining 90% is spent on the vital processes of organisms and is dissipated in the form of thermal radiation.
This pattern is called the rule of the ecological pyramid of energy and biomass.
Let's look at examples. One ton of green plants produces about 100 kg of herbivorous animal body weight. When small predators consume herbivores, their weight increases by 10 kg. If small predators are eaten by large ones, then the body weight of the latter increases by 1 kg.
Rice. 2. Ecological pyramid of biomass
Food chain: phytoplankton - zooplankton - small fish - large fish - humans. There are already 5 levels and in order for a person’s mass to increase by 1 kg, it is necessary that the first level contains 10 tons of phytoplankton.
Rice. 3. Ecological pyramid of energy
Benefits of the summit
Species at the top of the ecological pyramid have a much greater chance of evolving. In ancient times, it was the animals that occupied the highest level in trophic relationships that developed faster.
In the Mesozoic, mammals occupied the middle levels of the ecological pyramid and were actively exterminated by predatory reptiles. Only thanks to the extinction of dinosaurs were they able to rise to the top level and occupy a dominant position in all ecosystems.
Ecological pyramid - graphic representations of the relationship between producers and consumers of all levels (herbivores, predators, species that feed on other predators) in the ecosystem.
The American zoologist Charles Elton suggested schematically depicting these relationships in 1927.
In a schematic representation, each level is shown as a rectangle, the length or area of which corresponds to the numerical values of a link in the food chain (Elton’s pyramid), their mass or energy. Rectangles arranged in a certain sequence create pyramids of various shapes.
The base of the pyramid is the first trophic level - the level of producers; subsequent floors of the pyramid are formed by the next levels of the food chain - consumers of various orders. The height of all blocks in the pyramid is the same, and the length is proportional to the number, biomass or energy at the corresponding level.
Ecological pyramids are distinguished depending on the indicators on the basis of which the pyramid is built. At the same time, the basic rule has been established for all pyramids, according to which in any ecosystem there are more plants than animals, herbivores than carnivores, insects than birds.
Based on the rule of the ecological pyramid, it is possible to determine or calculate the quantitative ratios of different species of plants and animals in natural and artificially created ecological systems. For example, 1 kg of mass of a sea animal (seal, dolphin) requires 10 kg of eaten fish, and these 10 kg already need 100 kg of their food - aquatic invertebrates, which, in turn, need to eat 1000 kg of algae and bacteria to form such a mass. In this case, the ecological pyramid will be sustainable.
However, as you know, there are exceptions to every rule, which will be considered in each type of ecological pyramid.
Types of ecological pyramids
Pyramids of numbers - at each level the number of individual organisms is plotted
The pyramid of numbers displays a clear pattern discovered by Elton: the number of individuals making up a sequential series of links from producers to consumers is steadily decreasing (Fig. 3).
For example, to feed one wolf, he needs at least several hares for him to hunt; To feed these hares, you need a fairly large variety of plants. In this case, the pyramid will look like a triangle with a wide base tapering upward.
However, this form of a pyramid of numbers is not typical for all ecosystems. Sometimes they can be reversed, or upside down. This applies to forest food chains, where trees serve as producers and insects serve as primary consumers. In this case, the level of primary consumers is numerically richer than the level of producers (a large number of insects feed on one tree), therefore the pyramids of numbers are the least informative and least indicative, i.e. the number of organisms of the same trophic level largely depends on their size.
Biomass pyramids - characterizes the total dry or wet mass of organisms at a given trophic level, for example, in units of mass per unit area - g/m2, kg/ha, t/km2 or per volume - g/m3 (Fig. 4)
Usually in terrestrial biocenoses the total mass of producers is greater than each subsequent link. In turn, the total mass of first-order consumers is greater than that of second-order consumers, etc.
In this case (if the organisms do not differ too much in size) the pyramid will also have the appearance of a triangle with a wide base tapering upward. However, there are significant exceptions to this rule. For example, in the seas, the biomass of herbivorous zooplankton is significantly (sometimes 2-3 times) greater than the biomass of phytoplankton, represented mainly by unicellular algae. This is explained by the fact that algae are very quickly eaten by zooplankton, but they are protected from being completely eaten away by the very high rate of division of their cells.
In general, terrestrial biogeocenoses, where producers are large and live relatively long, are characterized by relatively stable pyramids with a wide base. In aquatic ecosystems, where producers are small in size and have short life cycles, the pyramid of biomass can be inverted or inverted (with the tip pointing down). Thus, in lakes and seas, the mass of plants exceeds the mass of consumers only during the flowering period (spring), and during the rest of the year the opposite situation can occur.
Pyramids of numbers and biomass reflect the statics of the system, that is, they characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of an ecosystem, although they allow solving a number of practical problems, especially related to maintaining the sustainability of ecosystems.
The pyramid of numbers allows, for example, to calculate the permissible amount of fish catch or shooting of animals during the hunting season without consequences for their normal reproduction.
Energy pyramids - shows the amount of energy flow or productivity at successive levels (Fig. 5).
In contrast to the pyramids of numbers and biomass, which reflect the statics of the system (the number of organisms at a given moment), the pyramid of energy, reflecting the picture of the speed of passage of food mass (amount of energy) through each trophic level of the food chain, gives the most complete picture of the functional organization of communities.
The shape of this pyramid is not affected by changes in the size and metabolic rate of individuals, and if all energy sources are taken into account, the pyramid will always have a typical appearance with a wide base and a tapering apex. When constructing a pyramid of energy, a rectangle is often added to its base to show the influx of solar energy.
In 1942, the American ecologist R. Lindeman formulated the law of the energy pyramid (the law of 10 percent), according to which, on average, about 10% of the energy received at the previous level of the ecological pyramid passes from one trophic level through food chains to another trophic level. The rest of the energy is lost in the form of thermal radiation, movement, etc. As a result of metabolic processes, organisms lose about 90% of all energy in each link of the food chain, which is spent on maintaining their vital functions.
If a hare ate 10 kg of plant matter, then its own weight may increase by 1 kg. A fox or wolf, eating 1 kg of hare meat, increases its mass by only 100 g. In woody plants, this proportion is much lower due to the fact that wood is poorly absorbed by organisms. For grasses and seaweeds, this value is much greater, since they do not have difficult-to-digest tissues. However, the general pattern of the process of energy transfer remains: much less energy passes through the upper trophic levels than through the lower ones.
Let's consider the transformation of energy in an ecosystem using the example of a simple pasture trophic chain, in which there are only three trophic levels.
level - herbaceous plants,
level - herbivorous mammals, for example, hares
level - predatory mammals, for example, foxes
Nutrients are created during the process of photosynthesis by plants, which form organic substances and oxygen, as well as ATP, from inorganic substances (water, carbon dioxide, mineral salts, etc.) using the energy of sunlight. Part of the electromagnetic energy of solar radiation is converted into the energy of chemical bonds of synthesized organic substances.
All organic matter created during photosynthesis is called gross primary production (GPP). Part of the energy of gross primary production is spent on respiration, resulting in the formation of net primary production (NPP), which is the very substance that enters the second trophic level and is used by hares.
Let the runway be 200 conventional units of energy, and the costs of plants for respiration (R) - 50%, i.e. 100 conventional units of energy. Then net primary production will be equal to: NPP = WPP - R (100 = 200 - 100), i.e. At the second trophic level, the hares will receive 100 conventional units of energy.
However, for various reasons, hares are able to consume only a certain share of NPP (otherwise the resources for the development of living matter would disappear), while a significant part of it is in the form of dead organic remains (underground parts of plants, hard wood of stems, branches, etc. .) is not capable of being eaten by hares. It enters detrital food chains and/or is decomposed by decomposers (F). The other part goes to the construction of new cells (population size, growth of hares - P) and ensuring energy metabolism or respiration (R).
In this case, according to the balance approach, the balance equality of energy consumption (C) will look like this: C = P + R + F, i.e. The energy received at the second trophic level will be spent, according to Lindemann's law, on population growth - P - 10%, the remaining 90% will be spent on respiration and removal of undigested food.
Thus, in ecosystems, with an increase in the trophic level, there is a rapid decrease in the energy accumulated in the bodies of living organisms. From here it is clear why each subsequent level will always be less than the previous one and why food chains usually cannot have more than 3-5 (rarely 6) links, and ecological pyramids cannot consist of a large number of floors: to the final link of the food chain is the same as to the top floor of the ecological pyramid will receive so little energy that it will not be enough if the number of organisms increases.
Such a sequence and subordination of groups of organisms connected in the form of trophic levels represents the flows of matter and energy in the biogeocenosis, the basis of its functional organization.
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Ministry of Education and Scienceyouth and sports of Ukraine
NTU "KhPI"
Department of Labor and Environment Sciences
Essay
on the topic: “Ecological pyramids”
Completed: Art. gr. MT-30b
Mazanova Daria
Checked by: Prof. Dreval A. N.
Harkov city
Introduction
1. Pyramids of numbers
2. Biomass pyramids
3. Pyramids of energy
Conclusion
Bibliography
Introduction
Ecological pyramid - graphic representations of the relationship between producers and consumers of all levels (herbivores, predators, species that feed on other predators) in the ecosystem. The pyramid effect in the form of graphic models was developed in 1927 by C. Elton.
The rule of the ecological pyramid is that the amount of plant matter that serves as the basis of the food chain is approximately 10 times greater than the mass of herbivorous animals, and each subsequent food level also has a mass 10 times less. This rule is known as Lindemann's rule or the 10% rule.
A chain of interconnected species that successively extract organic matter and energy from the original food substance. Each previous link in the food chain is food for the next link.
Here is a simple example of an ecological pyramid:
Let one person be fed with 300 trout for a year. They require 90 thousand frog tadpoles to feed them. To feed these tadpoles, 27,000,000 insects are needed, which consume 1,000 tons of grass per year. If a person eats plant foods, then all the intermediate steps of the pyramid can be thrown out and then 1,000 tons of plant biomass can feed 1,000 times more people.
1. Pyramidsnumber
To study the relationships between organisms in an ecosystem and to graphically represent these relationships, it is more convenient to use ecological pyramids rather than food web diagrams. In this case, the number of different organisms in a given territory is first counted, grouping them by trophic levels.
After such calculations, it becomes obvious that the number of animals progressively decreases during the transition from the second trophic level to subsequent ones. The number of plants at the first trophic level also often exceeds the number of animals that make up the second level. This can be depicted as a pyramid of numbers.
For convenience, the number of organisms at a given trophic level can be represented as a rectangle, the length (or area) of which is proportional to the number of organisms living in a given area (or in a given volume, if it is an aquatic ecosystem
2. Pyramidsbiomass
The inconveniences associated with the use of population pyramids can be avoided by constructing biomass pyramids, which take into account the total mass of organisms (biomass) of each trophic level.
Determining biomass involves not only counting numbers, but also weighing individual individuals, so it is a more labor-intensive process that requires more time and special equipment.
Thus, the rectangles in the biomass pyramids represent the mass of organisms at each trophic level per unit area or volume.
When sampling, in other words, at a given point in time, the so-called standing biomass, or standing yield, is always determined. It is important to understand that this value does not contain any information about the rate of biomass production (productivity) or its consumption; otherwise errors may occur for two reasons:
1. If the rate of biomass consumption (loss due to consumption) approximately corresponds to the rate of its formation, then the standing crop does not necessarily indicate productivity, i.e., the amount of energy and matter transferred from one trophic level to another over a given period of time, e.g. in a year.
Thus, on a fertile, intensively used pasture, the yield of standing grass may be lower, and productivity higher, than on a less fertile, but little used for grazing.
2. Small-sized producers, such as algae, are characterized by a high rate of renewal, that is, a high rate of growth and reproduction, balanced by their intensive consumption as food by other organisms and natural death.
Thus, although standing biomass may be small compared to large producers (such as trees), productivity may not be less because trees accumulate biomass over long periods of time.
In other words, phytoplankton with the same productivity as a tree will have much less biomass, although it could support the same mass of animals.
In general, populations of large and long-lived plants and animals have a lower renewal rate compared to small and short-lived ones, and accumulate matter and energy over a longer period of time.
Zooplankton have greater biomass than the phytoplankton on which they feed. This is typical for planktonic communities of lakes and seas at certain times of the year; the biomass of phytoplankton exceeds the biomass of zooplankton during the spring “blooming”, but in other periods the opposite relationship is possible. Such apparent anomalies can be avoided by using energy pyramids.
3. Pyramidsenergy
ecosystem population biomass
Organisms in an ecosystem are connected by a commonality of energy and nutrients. The entire ecosystem can be likened to a single mechanism that consumes energy and nutrients to do work. Nutrients initially originate from the abiotic component of the system, to which they are ultimately returned either as waste products or after the death and destruction of organisms. Thus, a nutrient cycle occurs in the ecosystem, in which both living and nonliving components participate. The driving force behind these cycles is ultimately the energy of the Sun. Photosynthetic organisms directly use the energy of sunlight and then transfer it to other representatives of the biotic component.
The result is a flow of energy and nutrients through the ecosystem. Energy can exist in various convertible forms, such as mechanical, chemical, thermal and electrical energy. The transition from one form to another is called energy conversion. Unlike the cyclical flow of substances in an ecosystem, the flow of energy is like a one-way street. Energy enters ecosystems from the Sun and, gradually moving from one form to another, is dissipated in the form of heat, lost in endless outer space.
It should also be noted that climatic factors of the abiotic component, such as temperature, atmospheric movement, evaporation and precipitation, are also regulated by the supply of solar energy. Thus, all living organisms are energy converters, and every time energy is converted, part of it is lost in the form of heat. Ultimately, all energy entering the biotic component of an ecosystem is dissipated as heat. In 1942, R. Lindemann formulated the law of the pyramid of energies, or the law (rule) of 10%, according to which from one trophic level of the ecological pyramid moves to another, higher level (along the “ladder”: producer consumer decomposer) on average about 10 % of energy received at the previous level of the ecological pyramid.
The reverse flow associated with the consumption of substances and the energy produced by the upper level of the ecological pyramid to its lower levels, for example, from animals to plants, is much weaker, no more than 0.5% (even 0.25%) of its total flow, and therefore we talk about a cycle there is no energy in the biocenosis. If energy is lost tenfold during the transition to a higher level of the ecological pyramid, then the accumulation of a number of substances, including toxic and radioactive ones, increases in approximately the same proportion.
This fact is fixed in the rule of biological enhancement. It is true for all cenoses. Given a constant energy flow in a food web or chain, smaller terrestrial organisms with high specific metabolism produce relatively less biomass than larger ones.
Therefore, due to anthropogenic disturbance of nature, the “average” individual living on land is shredded; large animals and birds are exterminated; in general, all large representatives of the plant and animal kingdom are increasingly becoming rarities. This should inevitably lead to a general decrease in the relative productivity of terrestrial organisms and thermodynamic disorder in biosystems, including communities and biocenoses.
The disappearance of species composed of large individuals changes the material and energy structure of cenoses. Since the energy flow passing through the biocenosis and ecosystem as a whole practically does not change (otherwise there would be a change in the type of cenosis), mechanisms of biocenotic, or ecological, duplication are activated: organisms of the same trophic group and level of the ecological pyramid naturally replace each other. Moreover, a small species takes the place of a large one, an evolutionarily lower organized one displaces a more highly organized one, a more genetically mobile one replaces a less genetically variable one. Thus, when ungulates are exterminated in the steppe, they are replaced by rodents, and in some cases, herbivorous insects.
In other words, it is in the anthropogenic disruption of the energy balance of natural steppe ecosystems that one should look for one of the reasons for the increasing frequency of locust invasions. In the absence of predators in the watersheds of Southern Sakhalin, the gray rat plays their role in the bamboo forests.
Perhaps this is the same mechanism for the emergence of new human infectious diseases. In some cases, a completely new ecological niche arises, while in others, the fight against diseases and the destruction of their pathogens frees up such a niche in human populations. Even 13 years before the discovery of HIV, the likelihood of the emergence of a “flu-like disease with high mortality” was predicted.
Conclusion
It is obvious that systems that contradict natural principles and laws are unstable. Attempts to preserve them are becoming increasingly expensive and difficult, and in any case are doomed to failure.
When studying the laws of functioning of ecosystems, we are dealing with the flow of energy passing through a particular ecosystem. The rate of accumulation of energy in the form of organic matter, which can be used for food, is an important parameter, since it determines the total flow of energy through the biotic component of the ecosystem, and therefore the number (biomass) of animal organisms that can exist in the ecosystem.
“Harvesting” means removing from the ecosystem those organisms or parts thereof that are used for food (or other purposes). At the same time, it is desirable that the ecosystem produces edible products as efficiently as possible. Rational use of natural resources is the only way out of the situation.
The general task of rational management of natural resources is to select the best, or optimal, ways to exploit natural and artificial (for example, in agriculture) ecosystems. Moreover, exploitation means not only harvesting, but also the impact of certain types of economic activity on the conditions of existence of natural biogeocenoses. Consequently, the rational use of natural resources involves the creation of balanced agricultural production that does not deplete soil and water resources and does not pollute the land and food; preserving natural landscapes and ensuring a clean environment, maintaining the normal functioning of ecosystems and their complexes, maintaining the biological diversity of natural communities on the planet.
Listliterature
1. Reimers N. F. Ecology. M., 1994.
2. Reimers N. F. Popular biological dictionary.
3. Nebel B. Environmental Science: How the World Works. In 2 volumes. M.: Mir, 1993.
4. Goldfein M.D., Kozhevnikov N.V. et al. Problems of life in the environment.
5. Revvel P., Revvel Ch. Our habitat. M., 1994.
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The concept of trophic levels
Trophic level is a collection of organisms that occupy a certain position in the overall food chain. Organisms that receive their energy from the Sun through the same number of steps belong to the same trophic level.
Such a sequence and subordination of groups of organisms connected in the form of trophic levels represents the flow of matter and energy in an ecosystem, the basis of its organization.
Trophic structure of the ecosystem
As a result of the sequence of energy transformations in food chains, each community of living organisms in an ecosystem acquires a certain trophic structure. The trophic structure of a community reflects the relationship between producers, consumers (separately of the first, second, etc. orders) and decomposers, expressed either by the number of individuals of living organisms, or their biomass, or the energy contained in them, calculated per unit area per unit time.
Trophic structure is usually depicted as ecological pyramids. This graphic model was developed in 1927 by the American zoologist Charles Elton. The base of the pyramid is the first trophic level - the level of producers, and the next floors of the pyramid are formed by subsequent levels - consumers of various orders. The height of all blocks is the same, and the length is proportional to the number, biomass or energy at the corresponding level. There are three ways to build ecological pyramids.
1. Pyramid of numbers (abundance) reflects the number of individual organisms at each level. For example, to feed one wolf, he needs at least several hares for him to hunt; To feed these hares, you need a fairly large variety of plants. Sometimes pyramids of numbers can be reversed, or upside down. This applies to forest food chains, where trees serve as producers and insects serve as primary consumers. In this case, the level of primary consumers is numerically richer than the level of producers (a large number of insects feed on one tree).
2. Pyramid of biomass - the ratio of the masses of organisms of different trophic levels. Usually in terrestrial biocenoses the total mass of producers is greater than each subsequent link. In turn, the total mass of first-order consumers is greater than that of second-order consumers, etc. If the organisms do not differ too much in size, the graph usually results in a stepped pyramid with a tapering tip. So, to produce 1 kg of beef you need 70-90 kg of fresh grass.
In aquatic ecosystems, you can also get an inverted, or inverted, pyramid of biomass, when the biomass of producers is less than that of consumers, and sometimes of decomposers. For example, in the ocean, with a fairly high productivity of phytoplankton, its total mass at a given moment may be less than that of consumer consumers (whales, large fish, shellfish).
Pyramids of numbers and biomass reflect static systems, i.e., they characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of an ecosystem, although they allow solving a number of practical problems, especially related to maintaining the sustainability of ecosystems. The pyramid of numbers allows, for example, to calculate the permissible amount of fish catch or shooting of animals during the hunting season without consequences for their normal reproduction.
3. Pyramid of Energy reflects the amount of energy flow, the speed of passage of food mass through the food chain. The structure of the biocenosis is influenced to a greater extent not by the amount of fixed energy, but by the rate of food production.
It has been established that the maximum amount of energy transferred to the next trophic level can in some cases be 30% of the previous one, and this is in the best case. In many biocenoses and food chains, the amount of energy transferred can be only 1%.
In 1942, the American ecologist R. Lindeman formulated law of the pyramid of energies (law of 10 percent) , according to which, on average, about 10% of the energy received at the previous level of the ecological pyramid passes from one trophic level through food chains to another trophic level. The rest of the energy is lost in the form of thermal radiation, movement, etc. As a result of metabolic processes, organisms lose about 90% of all energy in each link of the food chain, which is spent on maintaining their vital functions.
If a hare ate 10 kg of plant matter, then its own weight may increase by 1 kg. A fox or wolf, eating 1 kg of hare meat, increases its mass by only 100 g. In woody plants, this proportion is much lower due to the fact that wood is poorly absorbed by organisms. For grasses and seaweeds, this value is much greater, since they do not have difficult-to-digest tissues. However, the general pattern of the process of energy transfer remains: much less energy passes through the upper trophic levels than through the lower ones.
This is why food chains usually cannot have more than 3-5 (rarely 6) links, and ecological pyramids cannot consist of a large number of floors. The final link of the food chain, just like the top floor of the ecological pyramid, will receive so little energy that it will not be enough if the number of organisms increases.
This statement can be explained by tracing where the energy of consumed food is spent: part of it goes to the construction of new cells, i.e. growth, part of the food energy is spent on energy metabolism or respiration. Since the digestibility of food cannot be complete, i.e. 100%, then part of the undigested food in the form of excrement is removed from the body.
Considering that the energy spent on respiration is not transferred to the next trophic level and leaves the ecosystem, it becomes clear why each subsequent level will always be less than the previous one.
This is why large predatory animals are always rare. Therefore, there are also no predators that feed on wolves. In this case, they simply would not have enough food, since wolves are few in number.
The trophic structure of an ecosystem is expressed in complex food relationships between its constituent species. Ecological pyramids of numbers, biomass and energy, depicted in the form of graphic models, express the quantitative relationships of organisms with different feeding methods: producers, consumers and decomposers.
