Ecological pyramids are graphic models that reflect 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.

There are three types of ecological pyramids: energy, biomass and numbers. We talked about the energy pyramid in the previous section, “Energy Transfer in Ecosystems.” The ratio of living matter at different levels generally obeys the same rule as the ratio of incoming energy: the higher the level, the lower the total biomass and the number of its constituent organisms.

Biomass pyramid

Pyramids of biomass, as well as numbers, can be not only straight, but also inverted, characteristic of aquatic ecosystems.

An ecological (trophic) pyramid is a graphic representation of the quantitative relationships between the trophic levels of a biocenosis - producers, consumers (each level separately) and decomposers, expressed in their numbers (pyramid of numbers), biomass (pyramid of biomass) or the rate of growth of biomass (pyramid of energies).

The pyramid of biomass is the relationship between producers, consumers and decomposers in an ecosystem, expressed in their mass and depicted in the form of a trophic model.

Pyramids of biomass, as well as numbers, can be not only straight, but also inverted (Fig. 12.38). Inverted pyramids of biomass are characteristic of aquatic ecosystems, in which primary producers, for example, phytoplanktonic algae, divide very quickly, and their consumers - zooplanktonic crustaceans - are much larger, but have a long reproduction cycle. In particular, this applies to freshwater environments, where primary productivity is provided by microscopic organisms whose metabolic rates are increased, i.e., biomass is low, productivity is high.

Biomass pyramids are of more fundamental interest, since they eliminate the “physical” factor and clearly show the quantitative relationships of biomass. If organisms do not vary too much in size, then by designating the total mass of individuals at trophic levels, we can obtain a stepped pyramid. But if organisms of lower levels are on average smaller than organisms of higher levels, then an inverted pyramid of biomass takes place. For example, in ecosystems with very small producers and large consumers, the total mass of the latter may at any given moment be higher than the total mass of the producers. Several generalizations can be made for biomass pyramids.

The pyramid of biomass shows the change in biomass at each subsequent trophic level: for terrestrial ecosystems, the pyramid of biomass narrows upward, for the ocean ecosystem it is inverted (narrows downward), which is associated with the rapid consumption of phytoplankton by consumers.

Number pyramid

The population pyramid is an ecological pyramid that reflects the number of individuals at each nutritional level. The pyramid of numbers does not always give a clear idea of ​​the structure of food chains, since it does not take into account the size and mass of individuals, life expectancy, and metabolic rate, but the main tendency - a decrease in the number of individuals from link to link - is observed in most cases.

Thus, in the steppe ecosystem the following number of individuals was established: producers - 150,000, herbivorous consumers - 20,000, carnivorous consumers - 9000 individuals/ar (Odum, 1075), which in terms of per hectare amounts to figures 100 times larger. The biocenosis of the meadow is characterized by the following number of individuals on an area of ​​4 thousand m2: producers - 5,842,424, herbivorous consumers of the first order - 708,024, carnivorous consumers of the second order - 35,490, carnivorous consumers of the third order - 3.

Inverted pyramids

If the reproduction rate of the prey population is high, then even with low biomass such a population can be a sufficient source of food for predators that have a higher biomass but a low reproduction rate. For this reason, population pyramids can be inverted, i.e. The density of organisms at a given point in time at a low trophic level may be lower than the density of organisms at a high level. For example, many insects can live and feed on one tree (an inverted population pyramid).

The inverted pyramid of biomass is characteristic of marine ecosystems, where the primary producers (phytoplanktonic algae) divide very quickly (have a high reproductive potential and a rapid change of generations). In the ocean, up to 50 generations of phytoplankton can change in a year. Phytoplankton consumers are much larger, but reproduce much more slowly. During the time until predatory fish (and even more so walruses and whales) accumulate their biomass, many generations of phytoplankton will change, the total biomass of which is much greater.

Biomass pyramids do not take into account the duration of existence of generations of individuals at different trophic levels and the rate of formation and consumption of biomass. That is why a universal way of expressing the trophic structure of ecosystems is the pyramid of rates of formation of living matter, i.e. productivity. They are usually called pyramids of energies, referring to the energetic expression of the products.

1. What is a food web?

Answer. Food (trophic) chain - a series of species of plants, animals, fungi and microorganisms that are connected to each other by the relationship: food - consumer. A food web is a system of relationships between food chains.

2. What organisms are producers?

Answer. Producers are organisms capable of synthesizing organic substances from inorganic ones, that is, all autotrophs. This is basically green plants(synthesize organic substances from inorganic substances during the process of photosynthesis), however, some types of chemotrophic bacteria are capable of purely chemical synthesis of organic matter without sunlight.

3. How do consumers differ from producers?

Questions after § 85

1. What is an ecological pyramid? What processes in the community does it reflect?

Answer. The drop in the amount of energy during the transition from one trophic level to another (higher) determines the number of these levels and the ratio of predators and prey. It is estimated that any given trophic level receives about 10% (or slightly more) of the energy of the previous level. Therefore, the total number of trophic levels is rarely more than four to six.

This phenomenon, depicted graphically, is called the ecological pyramid. There are a pyramid of numbers (individuals), a pyramid of biomass and a pyramid of energy.

The base of the pyramid is formed by producers (plants). Above them are consumers of the first order (herbivores). The next level is represented by second-order consumers (predators). And so on until the top of the pyramid, which is occupied by the largest predators. The height of the pyramid usually corresponds to the length of the food chain.

The biomass pyramid shows the ratio of the biomass of organisms of different trophic levels, depicted graphically in such a way that the length or area of ​​the rectangle corresponding to a certain trophic level is proportional to its biomass

2. What is the difference between pyramids of numbers and energy?

Answer. Ecological pyramids can be classified into three main types:

Pyramids of numbers, which reflect the number of individual organisms; pyramids of biomass characterizing the total mass of individuals at each trophic level; production pyramids characterizing the production of each trophic level.

Population pyramids, as a rule, are the least informative and indicative, since the number of organisms of one trophic level in an ecosystem largely depends on their size. For example, the mass of one fox is equal to the mass of several hundred mice.

Typically, the number of heterotrophic organisms in an ecosystem is higher than autotrophic ones. One tree (first trophic level) can feed up to several thousand insects (second trophic level). With an increase in the trophic level of heterotrophic organisms, the average size of the individuals located on it usually increases, and their numbers decrease. Therefore, population pyramids in ecosystems often look like a “Christmas tree.”

Biomass pyramids much better express the relationships between different trophic levels of an ecosystem. In general, the biomass of lower levels exceeds that of higher levels. 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 very high speed their cell divisions.

The most complete picture of the functional organization of ecosystems is provided by product pyramids. In this case, it is better to represent the production values ​​of each trophic level in single units of measurement, preferably in energy units. In this case, the pyramids of products will be pyramids of energies.

In contrast to the pyramids of numbers and biomass, which reflect the statics of the system (i.e., characterizing the number of organisms at a given time), the pyramids of production characterize the rate of passage of food energy through trophic chains. If all values ​​of energy intake and expenditure in the trophic chain are correctly taken into account, then, in accordance with the second law of thermodynamics, the product pyramids will always have the correct shape.

The number and biomass of organisms that can be maintained by any level under certain conditions does not depend on the amount of fixed energy currently available at the previous level (i.e., on the biomass of the latter), but on the rate of food production at it.

3. Why can a population pyramid be straight or inverted?

Answer. If the reproduction rate of the prey population is high, then even with low biomass such a population can be a sufficient source of food for predators that have a higher biomass but a low reproduction rate. For this reason, pyramids of abundance or biomass may be inverted, i.e., low trophic levels may have lower density and biomass than higher levels.

For example, many insects can live and feed on one tree (an inverted population pyramid). The inverted pyramid of biomass is characteristic of marine ecosystems, where the primary producers (phytoplanktonic algae) divide very quickly, and their consumers (zooplanktonic crustaceans) are much larger, but reproduce much more slowly. Marine vertebrates also have large mass and a long reproductive cycle.

Calculate the share of energy received at the 5th trophic level, provided that its total amount at the 1st level was 500 units.

Answer. The first level is 500, the second is 50, the third is 5, the fourth is 0.5, the fifth is 0.05 units.

The main process that occurs in all ecosystems is the transfer and circulation of matter or energy. At the same time, losses are inevitable. The magnitude of these losses from level to level is what the rules of ecological pyramids reflect.

Some academic terms

Metabolism of matter and energy is a directed flow in the chain of producers - consumers. Simply put, the eating of some organisms by others. In this case, a chain or sequence of organisms is built, which, like links in a chain, are connected by the “food - consumer” relationship. This sequence is called the trophic or food chain. And the links in it are trophic levels. The first level of the chain is producers (plants), because only they can form organic substances from inorganic ones. The next links are consumers (animals) of various orders. Herbivores are consumers of the 1st order, and predators that feed on herbivores will be consumers of the 2nd order. The next link in the chain will be decomposers - organisms whose food is the remains of vital activity or the corpses of living organisms.

Graphic pyramids

British ecologist Charles Elton (1900-1991) in 1927, based on an analysis of quantitative changes in trophic chains, introduced into biology the concept of ecological pyramids as a graphic illustration of the relationships in the ecosystem of producers and consumers. Elton's pyramid is depicted as a triangle divided by the number of links in the chain. Or in the form of rectangles standing on top of each other.

Pyramid patterns

C. Elton analyzed the number of organisms in chains and found that there are always more plants than animals. Moreover, the ratio of levels in quantitative terms is always the same - a decrease occurs at each subsequent level, and this is an objective conclusion, which is reflected by the rules of ecological pyramids.

Elton's Rule

This rule states that the number of individuals in a sequence decreases from level to level. The rules of the ecological pyramid are the quantitative ratio of the products of all levels of a particular food chain. It says that the chain level indicator will be approximately 10 times less than that at the previous level.

The following is a simple example that will dot the i's. Let's consider the trophic chain of algae - invertebrate crustaceans - herring - dolphin. A forty-kilogram dolphin needs to eat 400 kilograms of herring to survive. And in order for these 400 kilograms of fish to exist, about 4 tons of their food - invertebrate crustaceans - are needed. To produce 4 tons of crustaceans, 40 tons of algae are needed. This is what the rules of the ecological pyramid reflect. And only in this ratio will this ecological structure be sustainable.

Types of ecopyramids

Based on the criterion that will be taken into account when evaluating the pyramids, the following are distinguished:

• Numerical.
• Biomass estimates.
• Energy consumption.

In all cases, the rule of the ecological pyramid reflects a decrease in the main evaluation criterion by 10 times.

Number of individuals and trophic levels

The pyramid of numbers takes into account the number of organisms, which is reflected in the rule of the ecological pyramid. And the example with the dolphin fully suits the characteristics of this type of pyramid. But there are exceptions here - a forest ecosystem with a chain of plants - insects. The pyramid will become upside down (a huge number of insects feeding on one tree). That is why the pyramid of numbers is considered not the most informative and indicative.

What's left?

The biomass pyramid uses the dry (less often wet) mass of individuals of the same level as an evaluation criterion. Units of measurement are gram/square meter, kilogram/hectare, or gram/cubic meter. But there are exceptions here too. The rules of ecological pyramids, which reflect a decrease in the biomass of consumers in relation to the biomass of producers, are fulfilled for biocenoses where both are large and have a long lifespan. life cycle. But for water systems, the pyramid may again be inverted. For example, in the seas, the biomass of zooplankton feeding on algae is sometimes 3 times greater than the biomass of plant plankton itself. saves the high rate of reproduction of phytoplankton.

Energy flow is the most accurate indicator

Energy pyramids show the rate of passage of food (its mass) through trophic levels. The law of the energy pyramid was formulated by the outstanding American ecologist Raymond Lindeman (1915-1942); after his death in 1942, he entered biology as a rule of ten percent. According to it, 10% of the energy from the previous one passes to each subsequent level, the remaining 90% are losses that go to support the vital functions of the body (breathing, thermoregulation).

The meaning of the pyramids

We have analyzed what the rules of ecological pyramids reflect. But why do we need this knowledge? Pyramids of numbers and biomass allow us to solve some practical problems, since they describe the static and stable state of the system. For example, they are used when calculating permissible fish catch values ​​or counting the number of animals for shooting, so as not to disrupt the stability of the ecosystem and determine maximum size a particular population of individuals for a given ecosystem in its entirety. And the pyramid of energies gives a clear idea of ​​the organization of functional communities and allows us to compare different ecosystems according to their productivity.

Now the reader will not be confused when given a task like “describe what the rules of ecological pyramids reflect,” and will boldly answer that these are losses of matter and energy in a specific trophic chain.

As a result of complex nutritional relationships between different organisms, trophic (food) connections or food chains. The food chain usually consists of several links:

producers – consumers – decomposers.

Ecological pyramid – the amount of plant matter that serves as the basis for nutrition is several times greater than the total mass of herbivorous animals, and the mass of each of the subsequent links in the food chain is less than the previous one (Fig. 54).

Ecological pyramid - graphic representations of the relationship between producers, consumers and decomposers in an ecosystem.

Rice. 54. Simplified diagram of the ecological pyramid

or pyramids of numbers (according to Korobkin, 2006)

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.

1. Pyramid of numbers (abundance) reflects the number of individual organisms at each level (see Fig. 55). For example, to feed one wolf, he needs at least several hares for him to hunt; to feed these hares you need quite a large number of 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. Biomass pyramid – 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 turns out to be 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) (Fig. 55).

Rice. 55. Pyramids of biomass of some biocenoses (according to Korobkin, 2004):

P – producers; RK – herbivorous consumers; PC – carnivorous consumers;

F – phytoplankton; 3 – zooplankton (the rightmost pyramid of biomass has an inverted appearance)

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 (Fig. 56).

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. 56. Pyramid of energy (law of 10% or 10:1),

(according to Tsvetkova, 1999)

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. Organisms, as a result of metabolic processes, lose in each link of the food chain about 90% of all the energy that 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. woody plants this share is much lower due to the fact that wood is poorly absorbed by organisms. For herbs and seaweed 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 levels.

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.

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 factors. environment, constantly regulating 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 highest level Only 10% of the energy is transferred, 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 on 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 in this case this 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 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. Through the upper trophic levels, where there is less mass and number of individuals, a significantly smaller portion of energy also flows than it passes through 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 various 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 great. 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 inverted. 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 certain standard. The role of ecological pyramids is very important in maintaining the balance of natural ecosystems and ensuring their sustainability.