Often, studying ecological pyramids causes great difficulties for students. In fact, even the most primitive and easy ecological pyramids begin to be studied by preschoolers and schoolchildren in primary school. Ecology as a science has begun to receive a lot of attention in recent years, since this science plays a significant role in the modern world. The ecological pyramid is part of ecology as a science. In order to understand what this is, you need to read this article.
What is an ecological pyramid?
An ecological pyramid is a graphic design that is most often depicted in the shape of a triangle. Such models depict the trophic structure of the biocenosis. This means that ecological pyramids display the number of individuals, their biomass, or the amount of energy contained in them. Each of them can demonstrate any one indicator. Accordingly, this means that ecological pyramids can be of several types: a pyramid that displays the number of individuals, a pyramid that reflects the amount of biomass of the individuals represented, and also the last ecological pyramid, which clearly demonstrates the amount of energy contained in these individuals.
What are number pyramids?
The pyramid of numbers (or numbers) shows the number of organisms at each trophic level. Such an ecological graphical model can be used in science, but it is extremely rare. The links in the ecological pyramid of numbers can be depicted almost indefinitely, that is, the structure of the biocenosis in one pyramid is extremely difficult to depict. In addition, at each trophic level there are many individuals, which makes it sometimes almost impossible to demonstrate the entire structure of the biocenosis on one full scale.
An example of constructing a pyramid of numbers
In order to understand the pyramid of numbers and its construction, it is necessary to find out which individuals and what interactions between them are included in this ecological pyramid. Let's look at the examples in detail now.
Let the base of the figure be 1000 tons of grass. This grass, say, in 1 year, will be able to feed about 26 million grasshoppers or other insects under natural survival conditions. In this case, grasshoppers will be located above the vegetation and constitute the second trophic level. The third trophic level will be 90 thousand frogs, which will consume the insects located below in a year. About 300 trout will be able to consume these frogs in a year, which means they will be located at the fourth trophic level in the pyramid. An adult will already be located at the top of the ecological pyramid; he will become the fifth and final link in this chain, that is, the last trophic level. This will happen because a person will be able to eat about 300 trout in a year. In turn, a person is the highest level in the world, and therefore no one can eat him. As shown in the example, missing links in the ecological pyramid of numbers are impossible.
It can have a wide variety of structures depending on the ecosystem. For example, this pyramid for terrestrial ecosystems may look almost identical to the energy pyramid. This means that the biomass pyramid will be built in such a way that the amount of biomass will decrease with each subsequent trophic level.
In general, biomass pyramids are studied mainly by students, because understanding them requires some knowledge in the fields of biology, ecology and zoology. This ecological pyramid is a graphical drawing that represents the relationship between producers (that is, producers of organic substances from inorganic ones) and consumers (consumers of these organic substances).
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In order to truly understand the principle of constructing a pyramid of biomass, it is necessary to understand who the consumers and producers are.
Producers are producers of organic substances from inorganic ones. These are plants. For example, plant leaves use carbon dioxide (inorganic matter) and produce organic matter through photosynthesis.
Consumers are consumers of these organic substances. In a terrestrial ecosystem these are animals and people, and in aquatic ecosystems they are various marine animals and fish.
Reversed pyramids of biomass
The inverted pyramid of biomass has the construction of an inverted downward triangle, that is, its base is narrower than the top. Such a pyramid is called inverted or inverted. The ecological pyramid has this structure if the biomass of producers (producers of organic substances) is less than the biomass of consumers (consumers of organic substances).
As we know, an ecological pyramid is a graphic model of a particular ecosystem. One of the important ecological models is the graphical construction of energy flow. A pyramid that reflects the speed and time of passage of food through is called a pyramid of energies. It was formulated thanks to the famous American scientist, who was an ecologist and zoologist, Raymond Lindeman. Raymond formulated a law (rule of the ecological pyramid), which stated that during the transition from the lowest trophic level to the next one, about 10% (more or less) of the energy that entered the previous level in the ecological pyramid passes through the food chains. And the remaining part of the energy, as a rule, is spent on the process of life, on the embodiment of this process. And as a result of the exchange process itself in each link, organisms lose about 90% of their energy.
The pattern of the energy pyramid
In fact, the pattern is that much less energy (several times) passes through the upper trophic levels than through the lower ones. It is for this reason that there are much fewer large predatory animals than, for example, frogs or insects.
Let us consider, for example, such a predatory animal as a bear. It may be at the top, that is, at the very last trophic level, because it is difficult to find an animal that would feed on it. If there were large numbers of animals that consumed bears as food, they would have already died out, because they would not be able to feed themselves, since bears are few in number. This is what the pyramid of energies proves.
Pyramid of natural balances
Schoolchildren begin to study it in the 1st or 2nd grades, because it is quite easy to understand, but at the same time very important as a component of the science of ecology. The pyramid of natural balance operates in different ecosystems, both in terrestrial and underwater nature. It is often used to introduce schoolchildren to the importance of every creature on earth. In order to understand the pyramid of natural balances, it is necessary to consider examples.
Examples of constructing a pyramid of natural balances
The pyramid of natural balances can be clearly demonstrated by the interaction of a river and a forest. For example, a graphical drawing might show the following interaction of natural resources: on the bank of a river there was a forest that went far into the depths. The river was very deep, and flowers, mushrooms, and shrubs grew on its banks. There were a lot of fish in its waters. In this example, there is an ecological balance. The river gives its moisture to the trees, but the trees create shade and do not allow the water from the river to evaporate. Let's consider the opposite example of natural balance. If something happens to the forest, the trees burn or are cut down, the river can dry up without receiving protection. This is an example of destruction
The same can happen with animals and plants. Consider owls, and acorns. Acorns are the basis of natural balance in the ecological pyramid, because they do not feed on anything, but at the same time they feed rodents. The second component in the next trophic level will be wood mice. They feed on acorns. There will be owls at the top of the pyramid because they eat mice. If the acorns that grow on the tree disappear, then the mice will have nothing to eat and they will most likely die. But then the owls will have no one to eat, and their entire species will die. This is the pyramid of natural balance.
Thanks to these pyramids, ecologists can monitor the state of nature and the animal world and draw appropriate conclusions.
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.
The ecological pyramid is a graphical representation of energy losses in food chains.
Food chains are stable chains of interconnected species that successively extract materials and energy from the original food substance that have developed during the evolution of living organisms and the biosphere as a whole. They constitute the trophic structure of any biocenosis, through which energy transfer and substance cycles are carried out. A food chain consists of a number of trophic levels, the sequence of which corresponds to the flow of energy.
The primary source of energy in power supply circuits is solar energy. The first trophic level - producers (green plants) - use solar energy in the process of photosynthesis, creating the primary production of any biocenosis. However, only 0.1% of solar energy is used in the process of photosynthesis. The efficiency with which green plants assimilate solar energy is assessed by the value of primary productivity. More than half of the energy associated with photosynthesis is immediately consumed by plants during respiration; the rest of the energy is transferred further along food chains.
In this case, there is an important pattern associated with the efficiency of use and conversion of energy in the nutrition process. Its essence is as follows: the amount of energy spent on maintaining one’s own vital functions in food chains increases from one trophic level to another, and productivity decreases.
Phytobiomass is used as a source of energy and material to create biomass of second-order organisms
trophic level of first-order consumers - herbivores. Typically, the productivity of the second trophic level is no more than 5 - 20% (10%) of the previous level. This is reflected in the ratio of plant and animal biomass on the planet. The amount of energy required to ensure the vital functions of the body grows with an increase in the level of morphofunctional organization. Accordingly, the amount of biomass created at higher trophic levels decreases.
Ecosystems are highly variable in the relative rates of creation and consumption of both net primary production and net secondary production at each trophic level. However, all ecosystems without exception are characterized by certain ratios of primary and secondary production. The amount of plant matter that serves as the basis of the food chain is always several times (about 10 times) greater than the total mass of herbivorous animals, and the mass of each subsequent link in the food chain changes proportionally accordingly.
The progressive decrease in assimilated energy in a number of trophic levels is reflected in the structure of ecological pyramids.
A decrease in the amount of available energy at each subsequent trophic level is accompanied by a decrease in biomass and number of individuals. The pyramids of biomass and the number of organisms for a given biocenosis repeat in general terms the configuration of the productivity pyramid.
Graphically, the ecological pyramid is depicted as several rectangles of the same height but different lengths. The length of the rectangle decreases from lower to upper, corresponding to a decrease in productivity at subsequent trophic levels. The lower triangle is the largest in length and corresponds to the first trophic level - producers, the second is approximately 10 times smaller and corresponds to the second trophic level - herbivores, first-order consumers, etc.
The rate of creation of organic matter does not determine its total reserves, i.e. the total mass of organisms at each trophic level. The available biomass of producers and consumers in specific ecosystems depends on the relationship between the rates of accumulation of organic matter at a certain trophic level and its transfer to a higher level, i.e. How severe is the consumption of the formed reserves? An important role here is played by the speed of reproduction of the main generations of producers and consumers.
In most terrestrial ecosystems, as already mentioned, the rule of biomass also applies, i.e. the total mass of plants turns out to be greater than the biomass of all herbivores, and the mass of herbivores exceeds the mass of all predators.
It is necessary to distinguish quantitatively between productivity, namely the annual growth of vegetation, and biomass. The difference between the primary production of the biocenosis and biomass determines the scale of grazing of plant mass. Even for communities with a predominance of herbaceous forms, in which the rate of biomass reproduction is quite high, animals use up to 70% of the annual growth of plants.
In those trophic chains where the transfer of energy is carried out through predator-prey connections, pyramids in the number of individuals are often observed: the total number of individuals participating in the food chain decreases with each link. This is also due to the fact that predators are usually larger than their prey. An exception to the rules of the population pyramid is when small predators live by group hunting large animals.
All three rules of the pyramid - productivity, biomass and abundance - express energy relationships in ecosystems. At the same time, the productivity pyramid has a universal character, and the pyramids of biomass and abundance appear in communities with a certain trophic structure.
Knowledge of the laws of ecosystem productivity and the ability to quantify energy flow are of great practical importance. Primary production of agrocenoses and human exploitation of natural communities is the main source of food for humans. Secondary products of biocenoses obtained from industrial and farm animals are also important as a source of animal protein. Knowledge of the laws of energy distribution, flows of energy and matter in biocenoses, patterns of plant and animal productivity, understanding of the limits of permissible removal of plant and animal biomass from natural systems allows us to correctly build relationships in the “society - nature” system.
Relationships in which some organisms eat other organisms or their remains or excretions (excrement) are called trophic (trophe - nutrition, food, gr.). At the same time, food relationships between members of the ecosystem are expressed through trophic (food) chains . Examples of such circuits include:
· moss → deer → wolf (tundra ecosystem);
· grass → cow → human (anthropogenic ecosystem);
· microscopic algae (phytoplankton) → bugs and daphnia (zooplankton) → roach → pike → seagulls (aquatic ecosystem).
Influencing food chains in order to optimize them and obtain more or better quality products is not always successful. The example of the importation of cows to Australia is widely known from the literature. Before this, natural pastures were used mainly by kangaroos, whose excrement was successfully mastered and processed by the Australian dung beetle. The Australian beetle did not digest cow excrement, resulting in gradual degradation of pastures. To stop this process, the European dung beetle had to be brought to Australia.
Trophic or food chains can be presented in the form pyramids. The numerical value of each step of such a pyramid can be expressed by the number of individuals, their biomass or the energy accumulated in it.
In accordance with law of the energy pyramid R. Lindeman and ten percent rule , from each stage approximately 10% (from 7 to 17%) of energy or matter in energy terms passes to the next stage (Fig. 3.7). Note that at each subsequent level, as the amount of energy decreases, its quality increases, i.e. the ability to do work per unit of animal biomass is a corresponding number of times higher than the same amount of plant biomass.
A striking example is the food chain of the open sea, represented by plankton and whales. The mass of plankton is dispersed in ocean water and, with the bioproductivity of the open sea less than 0.5 g/m2 day-1, the amount of potential energy in a cubic meter of ocean water is infinitesimal compared to the energy of a whale, whose mass can reach several hundred tons. As you know, whale oil is a high-calorie product that was even used for lighting.
Fig.3.7. Pyramid of energy transfer along the food chain (according to Yu. Odum)
A corresponding sequence is also observed in the destruction of organic matter: about 90% of the energy of pure primary production is released by microorganisms and fungi, less than 10% by invertebrate animals and less than 1% by vertebrate animals, which are the final cosumentors. In accordance with the last figure it is formulated one percent rule : for the stability of the biosphere as a whole, the share of possible final consumption of net primary production in energy terms should not exceed 1%.
Relying on the food chain as the basis for the functioning of the ecosystem, it is also possible to explain cases of accumulation in the tissues of certain substances (for example, synthetic poisons), which, as they move along the food chain, do not participate in the normal metabolism of organisms. According to rules of biological enhancement There is an approximately tenfold increase in the concentration of the pollutant when moving to a higher level of the ecological pyramid.
In particular, a seemingly insignificant increase in the content of radionuclides in river water at the first level of the trophic chain is assimilated by microorganisms and plankton, then concentrated in the tissues of fish and reaches maximum values in gulls. Their eggs have a level of radionuclides 5000 times higher than background contamination.
The species composition of organisms is usually studied at the level populations .
Let us recall that a population is a collection of individuals of the same species inhabiting one territory, having a common gene pool and the ability to interbreed freely. In general, a particular population may be located within a certain ecosystem, but it can also spread beyond its borders. For example, the population of the black-capped marmot of the Tuora-Sis ridge, listed in the Red Book, is known and protected. This population is not limited to this ridge, but extends further south into the Verkhoyansk Mountains in Yakutia.
The environment in which the species being studied is usually found is called its habitat.
As a rule, an ecological niche is occupied by one species or its population. With coinciding requirements for the environment and food resources, two species invariably enter into competition, which usually ends with the displacement of one of them. A similar situation is known in systems ecology as G.F. principle Gause , which states that two species cannot exist in the same area if their ecological needs are identical, i.e. if they occupy the same niche. Accordingly, a system of interacting populations differentiated by ecological niches, complementing each other to a greater extent than competing with each other for the use of space, time and resources, is called a community (cenosis).
The polar bear cannot live in taiga ecosystems, just like the brown bear in the polar regions.
Speciation is always adaptive, so axiom of Charles Darwin each species is adapted to a strictly defined, specific set of living conditions. In this case, organisms reproduce with an intensity that ensures their maximum possible number ( rule of maximum "life pressure"" ).
For example, oceanic plankton organisms quickly cover an area of thousands of square kilometers in the form of a film. V.I. Vernadsky calculated that the speed of advancement of a Fischer bacterium measuring 10-12 cm3 by reproduction in a straight line would be equal to about 397,200 m/hour - the speed of an airplane! However, excessive reproduction of organisms is limited by limiting factors and correlates with the amount of food resources in their habitat.
When species disappear, primarily composed of large individuals, the material-energy structure of the census changes as a result. If the energy flow passing through the ecosystem does not change, then the mechanisms ecological duplication according to the principle: an endangered or destroyed species within one level of the ecological pyramid replaces another functionally coenotic, similar one. The replacement of a species proceeds according to the following scheme: a small one replaces a large one, which is evolutionarily lower organized, with a more highly organized one, more genetically labile, and less genetically variable. Since an ecological niche in a biocenosis cannot be empty, ecological duplication necessarily occurs.
A successive change of biocenoses that successively arises in the same territory under the influence of natural factors or human influence is called succession (succession - continuity, lat.). For example, after a forest fire, the burnt forest is inhabited for many years first by grasses, then by shrubs, then by deciduous trees and ultimately by coniferous forest. In this case, successive communities replacing each other are called series or stages. The end result of succession will be the state of a stabilized ecosystem - menopause (climax - staircase, "mature step", gr.).
Succession that begins in an area that was not previously occupied is called primary . These include settlements of lichens on stones, which will subsequently replace mosses, grasses and shrubs (Fig. 3.8). If a community develops on the site of an existing one (for example, after a fire or uprooting, the construction of a pond or reservoir), then we speak of secondary succession. Of course, the speed of succession will vary. Primary successions can take hundreds or thousands of years, but secondary successions occur more quickly.
All populations of producers, consumers and heterotrophs interact closely through trophic chains and thus maintain the structure and integrity of biocenoses, coordinate the flows of energy and matter, and determine the regulation of their environment. The entire set of bodies of living organisms inhabiting the Earth is physical and chemically unified, regardless of their systematic affiliation and is called living matter ( law of physical and chemical unity of living matter by V.I. Vernadsky). The mass of living matter is relatively small and is estimated at 2.4-3.6 * 1012 tons (in dry weight). If it is distributed over the entire surface of the planet, you will get a layer of only one and a half centimeters. According to V.I. Vernadsky, this “film of life”, which is less than 10-6 of the mass of other shells of the Earth, is “one of the most powerful geochemical forces of our planet.”
The trophic structure of a biocenosis is usually displayed by graphic models in the form of ecological pyramids. Such models were developed in 1927 by the English zoologist C. Elton.
Ecological pyramids- these are graphic models (usually in the form of triangles) reflecting the number of individuals (pyramid of numbers), the amount of their biomass (pyramid of biomass) or the energy contained in them (pyramid of energy) at each trophic level and indicating a decrease in all indicators with increasing trophic level level.
There are three types of ecological pyramids.
Pyramid of numbers
Pyramid of numbers(abundance) reflects the number of individual organisms at each level. In ecology, the population pyramid is rarely used, since due to the large number of individuals at each trophic level it is very difficult to display the structure of the biocenosis on one scale.
To understand what a pyramid of numbers is, let's give an example. Suppose that at the base of the pyramid there are 1000 tons of grass, the mass of which is hundreds of millions of individual blades of grass. This vegetation will be able to feed 27 million grasshoppers, which, in turn, can be eaten by about 90 thousand frogs. The frogs themselves can serve as food for 300 trout in the pond. And this is the amount of fish one person can eat in a year! Thus, at the base of the pyramid there are several hundred million blades of grass, and at its top there is one person. This is a clear loss of matter and energy during the transition from one trophic level to another.
Sometimes there are exceptions to the pyramid rule, and then we have to deal with inverted pyramid of numbers. This can be observed in the forest, where insects live on one tree, which insectivorous birds feed on. Thus, the number of producers is less than that of consumers.
Biomass pyramid
Biomass pyramid - the ratio between producers and consumers, expressed in their mass (total dry weight, energy content or other measure of total living matter). Typically, in terrestrial biocenoses, the total weight of producers is greater than that of consumers. In turn, the total weight of first-order consumers is greater than that of second-order consumers, etc. If the organisms do not vary too much in size, the graph will usually form a stepped pyramid with a tapering top.
The American ecologist R. Ricklefs explained the structure of the biomass pyramid as follows: “In most terrestrial communities, the biomass pyramid is similar to the productivity pyramid. If you collect all the organisms living in some meadow, then the weight of the plants will be much greater than the weight of all the orthoptera and ungulates that feed on these plants. The weight of these herbivorous animals, in turn, will be greater than the weight of birds and cats, which constitute the level of primary carnivores, and these latter will also exceed in weight the predators that feed on them, if any. One lion weighs quite a lot, but lions are so rare that their weight, expressed in grams per 1 m2, will be insignificant.”
As in the case of pyramids of numbers, you can get the so-called inverted (inverted) pyramid of biomass, when the biomass of producers turns out to be less than consumers, and sometimes decomposers, and at the base of the pyramid there are not plants, but animals. This applies mainly to aquatic ecosystems. 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 zooplankton and the final consumer (whales, large fish, shellfish).
Pyramid of Energy
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.
All ecological pyramids are built according to one rule, namely: at the base of any pyramid there are green plants, and when constructing pyramids, the natural decrease from its base to the top in the number of individuals (pyramid of numbers), their biomass (pyramid of biomass) and energy passing through food prices is taken into account (energy pyramid).
In 1942, the American ecologist R. Lindeman formulated energy pyramid law, according to which, on average, about 10% of the energy received at the previous level of the ecological pyramid passes from one trophic level to another through food prices. The rest of the energy is spent on supporting vital processes. As a result of metabolic processes, organisms lose about 90% of all energy in each link of the food chain. Therefore, to obtain, for example, 1 kg of perch, approximately 10 kg of juvenile fish, 100 kg of zooplankton and 1000 kg of phytoplankton must be consumed.
The general pattern of the energy transfer process is as follows: significantly less energy passes through the upper trophic levels than through the lower ones. This is why large predatory animals are always rare, and there are no predators that feed on, for example, wolves. In this case, they simply would not be able to feed themselves, as wolves are so few in number.
Trophic chains can theoretically consist of a large number of links, but practically do not exceed 5–6 links, since as a result of the action second law of thermodynamics the energy quickly dissipates.
The second law of thermodynamics is also known as the law of increase entropy(Greek entropia turn, transformation). According to this law, energy cannot be created or destroyed - it is transferred from one system to another and transformed from one form to another.
In trophic chains, 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 pattern is called the 10% rule: on average, no more than 1/10 of the energy received from the previous level is transferred to the next trophic level. Therefore, if about one percent of solar energy accumulates in plants, then, for example, at the 4th trophic level its share will be only 0.001%.
Trophic chains represent very unstable systems , since the accidental loss of any link destroys the entire chain. Sustainability of natural communities are ensured by the presence of complex branched multi-species trophic networks . In such networks, when any link falls out, energy begins to move along bypass paths. The more species there are in a biogeocenosis, the more reliable and stable it is.
To visualize the magnitude of the energy transfer coefficient from level to level in the food chains of ecosystems, ecological pyramids of several types are used.
Ecological pyramid –is a graphical (or diagrammatic) representation of the relationship between volumes of organic matter or energy at adjacent levels in a food chain.
The graphic model of the pyramid was developed in 1927 by an 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
The most widespread types of ecological pyramids are:
Elton's Number Pyramids;
Pyramids of biomass;
Pyramids of energy.
Lindemann's principle. In 1942, based on a generalization of extensive empirical material, the American ecologist Lindeman formulated the principle of transformation of biochemical energy in ecosystems, which was called in environmental literature law 10%.
Lindemann's principle - 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.
Elton's number pyramids are presented in the form average number of individuals , required for nutrition of organisms located at subsequent trophic levels.
Pyramid of numbers(abundance) reflects the number of individual organisms at each level (Fig. 35).
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.
For example, to represent the food chain:
OAK LEAF – CATERPILLAR – TIT
The pyramid of numbers for one tit (third level) depicts the number of caterpillars (second level) that it eats in a certain time, for example, in one day of light. At the first level of the pyramid, as many oak leaves are depicted as are required to feed the number of caterpillars that are shown at the second level of the pyramid.
Pyramids of biomass and energy express the ratios of the amount of biomass or energy at each trophic level.
The biomass pyramid is based on displaying the results of weighing the dry mass of organic matter at each level, and the energy pyramid is based on calculations of biochemical energy transferred from the underlying to the upper level. These levels on the biomass (or energy) pyramid graph are depicted as rectangles of equal height, the width of which is proportional to the amount of biomass transferred to each subsequent (overlying) level of the trophic chain under study.
GRASS (809) – HERBIVORES (37) – CARNIVORES-1 (11) – CARNIVORES-2 (1.5),
where the values of dry biomass (g/sq. m) are indicated in parentheses.
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 rate of food production (Fig. 37).
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%.
Rice. 37. Energy Pyramid: energy flow through the grazing food chain (all figures are in kilojoules per meter squared times the year)
Note that ecological pyramids are a clear illustration of the Lindemann principle and with their help reflect an essential feature of energy processes in ecosystems, namely: due to the relatively small share of energy (on average approximately a tenth) transferred to the next level, very little energy remains in ecosystem, and the rest returns to the geosphere. Thus, with a 4-level trophic chain, only ten thousandth of the biochemical energy remains in the ecosystem. The negligible fraction of energy remaining in the ecosystem explains why in real natural ecosystems food chains have no more than 5–6 levels.
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