Ecological pyramid rule

The amount of plant matter that serves as the basis of the food chain is about 10 times greater than the mass of herbivorous animals, and each subsequent food level also has a mass 10 times less.

Pyramid of numbers (numbers) reflects the number of individual organisms at each level. For example, to feed one wolf, you need at least a few hares that he could hunt; to feed these hares, you need a fairly large number of various plants. Sometimes pyramids of numbers can be inverted, or inverted. This applies to forest food chains, when trees serve as producers, and insects 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).

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 second-order consumers, and so on. If the organisms do not differ too much in size, then the graph usually shows a stepped pyramid with a tapering top. So, for the formation of 1 kg of beef, 70-90 kg of fresh grass is needed.

In aquatic ecosystems, it is also possible to obtain an inverted or inverted biomass pyramid, when the biomass of producers is less than that of consumers, and sometimes 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, mollusks).

Pyramids of numbers and biomass reflect the statics of the system, 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 the ecosystem, although they allow solving a number of practical problems, especially those related to maintaining the stability of ecosystems. The pyramid of numbers makes it possible, for example, to calculate the allowable amount of catching fish or shooting animals during the hunting period without consequences for their normal reproduction.

energy pyramid reflects the magnitude of the energy flow, the speed of passage of the mass of food through the food chain. The structure of the biocenosis is largely influenced 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 at best. In many biocenoses, food chains, the value of the transferred energy can be only 1%.

In 1942, the American ecologist R. Lindeman formulated energy pyramid law(law of 10 percent), according to which, on average, about 10% of the energy received by 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 about 90% of all energy in each link of the food chain, which is spent on maintaining their vital functions.

The concept of trophic levels

Trophic level A group of organisms occupying a certain position in a 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 is a 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 the community reflects the ratio 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.

The 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 (numbers) reflects the number of individual organisms at each level. For example, to feed one wolf, you need at least a few hares that he could hunt; to feed these hares, you need a fairly large number of various plants. Sometimes pyramids of numbers can be inverted, or inverted. This applies to forest food chains, when trees serve as producers, and insects 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 second-order consumers, and so on. If the organisms do not differ too much in size, then the graph usually shows a stepped pyramid with a tapering top. So, for the formation of 1 kg of beef, 70-90 kg of fresh grass is needed.

In aquatic ecosystems, it is also possible to obtain an inverted or inverted biomass pyramid, when the biomass of producers is less than that of consumers, and sometimes 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, mollusks).

Pyramids of numbers and biomass reflect static systems, i.e., characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of the ecosystem, although they allow solving a number of practical problems, especially those related to maintaining the stability of ecosystems. The pyramid of numbers makes it possible, for example, to calculate the allowable amount of catching fish or shooting animals during the hunting period without consequences for their normal reproduction.

3. Pyramid of energy reflects the magnitude of the energy flow, the speed of passage of the mass of food through the food chain. The structure of the biocenosis is largely influenced 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 at best. In many biocenoses, food chains, the value of the transferred energy can be only 1%.

In 1942, the American ecologist R. Lindeman formulated the law of the pyramid of energies (the law of 10 percent) , according to which, on average, about 10% of the energy received by 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 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 could increase by 1 kg. A fox or a wolf, eating 1 kg of hare, 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 algae, this value is much higher, since they do not have hard-to-digest tissues. However, the general regularity of the process of energy transfer remains: much less energy passes through the upper trophic levels than through the lower ones.

That 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. To the final link of the food chain, as well as to the top floor of the ecological pyramid, there will be so little energy that it will not be enough if the number of organisms increases.

This statement can be explained by looking at where the energy of the consumed food is spent: part of it goes to building new cells, i.e. for growth, part of the energy of food is spent on ensuring energy metabolism or on breathing. 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.

That is why large predatory animals are always rare. Therefore, there are also no predators that would feed on wolves. In this case, they simply would not feed themselves, since the wolves are not numerous.

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 graphical models, express the quantitative ratios of organisms that differ in the way they feed: producers, consumers and decomposers.

1. What is a food web?

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

2. What organisms are producers?

Answer. Producers - organisms capable of synthesizing organic substances from inorganic, that is, all autotrophs. These are mainly green plants (they synthesize organic substances from inorganic substances in 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 to 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 or 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 consumers of the second order (predators). And so on to 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 the pyramids of numbers and energy?

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

Pyramids of abundance, which reflect the abundance of individual organisms; biomass pyramids characterizing the total mass of individuals of 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 abundance of organisms of the same 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.

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

Pyramids of biomass express the relationships between different trophic levels of an ecosystem much better. 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, which is represented mainly by unicellular algae. This is explained by the fact that algae are very quickly eaten away by zooplankton, but the very high rate of division of their cells protects them from complete eating.

The most complete picture of the functional organization of ecosystems is provided by the pyramids of productions. At the same time, it is better to represent the production values ​​of each trophic level in common units of measurement, best of all in energy units. In this case, the pyramids of productions will be the pyramids of energies.

In contrast to the pyramids of abundance and biomass, which reflect the statics of the system (i.e., characterize the number of organisms at a given moment in time), the pyramids of production characterize the rates of passage of food energy along the 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 maintain 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 on it.

3. Why can the pyramid of numbers be straight and inverted?

Answer. If the reproduction rate of the prey population is high, then even with a low biomass, such a population can be a sufficient food source for predators with 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 pyramid of numbers). An inverted pyramid of biomass is characteristic of marine ecosystems, where primary producers (phytoplankton algae) divide very quickly, and their consumers (zooplankton crustaceans) are much larger, but multiply much more slowly. Marine vertebrates have an even greater mass and a long reproduction 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.

An ecological pyramid is a graphic representation of energy losses in food chains.

Food chains are stable chains of interconnected species that consistently 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 make up the trophic structure of any biocenosis, through which energy transfer and substance cycling are carried out. The food chain consists of a series of trophic levels, the sequence of which corresponds to the flow of energy.

The primary source of energy in food chains 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. At the same time, only 0.1% of solar energy is used in the process of photosynthesis. The efficiency with which green plants assimilate solar energy is estimated by the value of primary productivity. More than half of the energy associated with photosynthesis is immediately consumed by plants in the process of respiration, the rest of the energy is transferred further along the food chains.

At the same time, there is an important regularity associated with the efficiency of the use and conversion of energy in the process of nutrition. Its essence is as follows: the amount of energy spent on maintaining one's own life activity in food chains grows from one trophic level to another, while productivity decreases.

Phytobiomass is used as a source of energy and material to create the biomass of organisms of the second

trophic level consumers of the first order - herbivores. Usually 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 volume of energy necessary to ensure the vital activity of the organism grows with an increase in the level of morphofunctional organization. Accordingly, the amount of biomass created at higher trophic levels is reduced.

Ecosystems are highly variable in the relative rates of creation and expenditure 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, accordingly, changes proportionally.

The progressive decline of assimilated energy in a series 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 the number of individuals. Pyramids of biomass and abundance 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 the bottom to the top, 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 - herbivorous animals, 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 how the rates of accumulation of organic matter at a certain trophic level and its transfer to a higher one, i.e., correlate with each other. how strong the consumption of the formed reserves is. An important role is played by the speed of reproduction of the main generations of producers and consumers.

In most terrestrial ecosystems, as already mentioned, the biomass rule 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 the biomass determines the extent of the grazing of the plant mass. Even for communities with a predominance of herbaceous forms, whose biomass reproduction rate is quite high, animals use up to 70% of the annual plant growth.

In those trophic chains where energy transfer is carried out through “predator-prey” connections, pyramids of the number of individuals are often observed: the total number of individuals participating in food chains decreases with each link. This is also due to the fact that predators, as a rule, are larger than their victims. An exception to the rules of the pyramid of numbers are cases when small predators live by group hunting for 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, while the pyramids of biomass and abundance appear in communities with a certain trophic structure.

Knowledge of the laws of ecosystem productivity, the ability to quantify the flow of energy are of great practical importance. The primary production of agrocenoses and human exploitation of natural communities is the main source of food for humans. The secondary production of biocenoses, obtained from industrial and agricultural animals, is also important as a source of animal protein. Knowledge of the laws of distribution of energy, flows of energy and matter in biocenoses, the laws of productivity of plants and animals, understanding the limits of permissible withdrawal of plant and animal biomass from natural systems allow us to correctly build relationships in the "society - nature" system.

Relationships in which some organisms eat other organisms or their remains or secretions (excrement) are called trophic (trophe - nutrition, food, gr.). At the same time, nutritional relationships between members of the ecosystem are expressed through trophic (food) chains . Examples of such circuits are:

Moss moss → deer → wolf (tundra ecosystem);

Grass → cow → human (anthropogenic ecosystem);

microscopic algae (phytoplankton) → bugs and daphnia (zooplankton) → roach → pike → gulls (aquatic ecosystem).

Influencing food chains with the aim of optimizing them and obtaining more or better products in quality is not always successful. So widely known from the literature is the example of the importation of cows to Australia. Prior to this, natural pastures were used mainly by kangaroos, whose excrement was successfully developed and processed by the Australian dung beetle. Cow dung was not used by the Australian beetle, as a result of which the gradual degradation of pastures began. To stop this process, the European dung beetle had to be brought to Australia.

Trophic or food chains can be represented 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 energy pyramid law R. Lindemann and ten percent rule , approximately 10% (from 7 to 17%) of energy or matter in energy terms passes from each stage to the next stage (Fig. 3.7). Note that at each subsequent level, with a decrease in the amount of energy, its quality increases, i.e. the ability to do the work of a unit of animal biomass is a corresponding number of times higher than the same plant biomass.

A striking example is the high seas food chain, 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 infinitely small 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 Y. Odum)

In the destruction of organics, a corresponding sequence is also observed: for example, about 90% of the energy of pure primary production is released by microorganisms and fungi, less than 10% by invertebrates, and less than 1% by vertebrates, which are final cosuments. In accordance with the last digit, 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%.

Based on the food chain as the basis for the functioning of the ecosystem, it is also possible to explain the cases of accumulation in the tissues of certain substances (for example, synthetic poisons), which, as they move along the trophic chain, do not participate in the normal metabolism of organisms. According to biological amplification rules 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 it is concentrated in fish tissues and reaches maximum values ​​in gulls. Their eggs have a level of radionuclides 5000 times higher than background pollution.

The species composition of organisms is usually studied at the level populations .

Recall that a population is a set of individuals of the same species inhabiting the same territory, having a common gene pool and the ability to interbreed freely. In general, one or another population can be within a certain ecosystem, but it can also spread beyond the 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 range, but also extends further south to the Verkhoyansk mountains in Yakutia.

The environment in which the species under study usually occurs is called its habitat.

As a rule, an ecological niche is occupied by one species or its population. With identical requirements for the environment and food resources, the two species invariably enter into a competitive struggle, which usually ends in the displacement of one of them. This situation is known in systems ecology as G.F. principle Gause , which states that two species cannot exist in the same locality if their ecological needs are identical, i.e. if they occupy the same niche. Accordingly, the 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 (coenosis).

The polar bear cannot live in taiga ecosystems, just like the brown bear in the polar regions.

Speciation is always adaptive, so Ch. Darwin's axiom each species is adapted to a strictly defined set of conditions of existence specific to it. At the same time, organisms reproduce with an intensity that provides the maximum possible number of them ( rule of maximum "life pressure"" ).

For example, organisms of oceanic plankton quite 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 Fisher bacterium with a size of 10-12 cm3 by reproduction in a straight line would be equal to about 397,200 m/h - the speed of an airplane! However, excessive reproduction of organisms is limited by limiting factors and correlates with the amount of food resources of their habitat.

When species disappear, primarily composed of large individuals, as a result, the material-energy structure of qualifications changes. 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 functional-coenotic, similar one. The substitution of a species proceeds according to the scheme: a small one replaces a large one, evolutionarily lower organized, more highly organized, more genetically labile, less genetically variable. Since an ecological niche in a biocenosis cannot be empty, ecological duplication necessarily occurs.

A successive change of biocenoses, successively arising in the same territory under the influence of natural factors or human impact, is called succession (succession - continuity, lat.). For example, after a forest fire, for many years the burnt area is first populated with grasses, then with shrubs, then with deciduous trees, and finally with coniferous forests. In this case, successive communities that replace each other are called series or stages. The end result of succession will be the state of a stabilized ecosystem - menopause (climax - stairs, "mature step", gr.).

A succession that begins in a previously unoccupied area is called primary . These include lichen settlements on stones, which will later replace mosses, grasses and shrubs (Fig. 3.8). If a community develops on the site of an already existing one (for example, after a fire or uprooting, a pond or reservoir device), then they talk about secondary successions. Of course, succession rates will vary. Primary successions may take hundreds or thousands of years, while secondary successions are faster.

All populations of producers, consumers and heterotrophs closely interact 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 whole set of bodies of living organisms inhabiting the Earth is physically and chemically one, regardless of their systematic affiliation, and is called living matter ( the law of physico-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 get a layer of only one and a half centimeters. According to VI Vernadsky, this "film of life", which is less than 10-6 masses of other shells of the Earth, is "one of the most powerful geochemical forces of our planet."

One of the types of relationships between organisms in ecosystems are trophic relationships. They show how energy moves through food chains in ecosystems. A model that demonstrates the change in the amount of energy in the links of food chains is the ecological pyramid.

The structure of the pyramid

The pyramid is a graphic model. Her image is divided into horizontal levels. The number of levels corresponds to the number of links in the food chains.

All food chains begin with producers - autotrophic organisms that form organic substances. The totality of ecosystem autotrophs is what is at the base of the ecological pyramid.

Rice. 1. Ecological pyramid of population

Usually the food pyramid contains from 3 to 5 levels.

The last links in the food chain are always large predators or humans. Thus, the number of individuals and biomass at the last level of the pyramid are the lowest.

TOP 2 articleswho read along with this

The essence of the ecological pyramid is in the image of a progressive decrease in biomass in food chains.

Model conditionality

It should be understood that the model shows the reality in a generalized way. Everything is more difficult in life. Any large organism, including humans, can be eaten and its energy will be used in the ecological pyramid in an atypical way.

Part of the biomass of an ecosystem is always accounted for by decomposers - organisms that decompose dead organic matter. Reducers 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 (eats carrion), and as a large predator.

Kinds

Depending on what quantitative characteristic of the levels is used, There are three types of ecological pyramids:

• numbers;
• biomass;
• energy.

10% rule

According to ecologists' calculations, 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 dissipated in the form of thermal radiation.

This pattern is called the rule of the ecological pyramid of energy and biomass.

Consider examples. About 100 kg of body weight of herbivores is formed from one ton of green plants. When herbivores are consumed by small predators, 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 - man. There are already 5 levels here, and in order for a person's mass to increase by 1 kg, it is necessary that there are 10 tons of phytoplankton on the first level.

Rice. 3. Ecological pyramid of energy

Apex Benefits

Species at the top of the ecological pyramid are much more likely to evolve. 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. It was only thanks to the extinction of the dinosaurs that they were able to rise to the top level and take a dominant position in all ecosystems.