Ecosystem is an informationally self-developing, thermodynamically open set of biotic ecological components and abiotic sources of matter and energy, the unity and functional connection of which within the time and space characteristic of a certain area of ​​the biosphere (including the biosphere as a whole) ensures that internal regular movements of matter and energy are exceeded in this area and information over external exchange (and between neighboring similar populations) and on the basis of this indefinitely long self-regulation and development of the whole under the controlling influence of biotic and biogenic components.

The composition of ecosystems largely depends on their functional “purpose” and vice versa. This remark comes from the principle of ecological complementarity (complementarity): no functional part of the ecosystem (ecological component, element, etc.) can exist without other functionally complementary parts.

Figure 1. - Classification of natural ecosystems

The law of ecosystem formation: the long-term existence of organisms is possible only within the framework of ecological systems, where their components and elements complement each other and are accordingly adapted to each other. This ensures the reproduction of the habitat of each species and the relatively unchanged existence of all environmental components.

The second ecological law, according to Yu. N. Kurazhskovsky: “the law of conservation of life: life can only exist in the process of moving a flow of matter, energy and information through a living body. Stopping movement in this flow ends life.” This principle is also true for any ecological formations and, in general, many natural systems, even those not directly related to living things.

In the early 70s. Reimers N.F. formulated the law of internal dynamic equilibrium, and then four main consequences from it. Statement of the law: matter, energy, information and dynamic qualities of individual natural systems (including ecosystems) and their hierarchy are so interconnected that any change in one of these indicators causes accompanying functional-structural quantitative and qualitative changes that preserve the total amount of material-energy, informational and dynamic qualities of the systems where these changes occur, or in their hierarchy. Important consequences from the law of internal dynamic equilibrium:

1. Any change in the environment (matter, energy, information, dynamic qualities of ecosystems) inevitably leads to the development of natural chain reactions that go towards neutralizing the change or the formation of new natural systems, the formation of which, with significant changes in the environment, can become irreversible;

2. The interaction of material-energy environmental components (energy, gases, liquids, substrates, producer organisms, consumers and decomposers), information and dynamic qualities of natural systems is quantitatively nonlinear, i.e. a weak impact or change in one of the indicators can cause strong deviations in others (and in the entire system as a whole);

3. The changes made in large ecosystems are relatively irreversible - passing through their hierarchy from the bottom up, from the place of impact to the biosphere as a whole, they change global processes and thereby transfer them to a new evolutionary level;

4. Any local transformation of nature causes responses in the global totality of the biosphere and in its largest divisions, leading to the relative constancy of the ecological and economic potential (the “Trishkin caftan” rule), the increase of which is possible only through a significant increase in energy investments.

Based on the data accumulated by ecology, taking into account the above generalizations, it is possible to formulate the principle of ecological (operational) reliability: the effectiveness of an ecosystem, its ability to self-heal and self-regulate (within natural fluctuations) depends on its position in the hierarchy of natural formations, the degree of interaction of its components and elements , as well as from the private adaptations of organisms that make up the biota of the ecosystem. The diversity, complexity and other morphological features of an ecosystem are of varying importance and are dependent on the degree of its evolutionary and successional maturity. If a decrease in diversity leads to a sharp imbalance in the “hardness” of parts of the ecosystem, and this happens quite often, then simplifying the system is fraught with a noticeable decrease in its reliability.

By shifting the dynamic equilibrium state of natural systems with the help of significant investments of energy (through agricultural techniques), people disrupt the ratio of environmental components, achieving an increase in useful products (harvest) or a state of the environment favorable for human life. If these shifts “extinguish” in the hierarchy of natural systems and do not cause thermodynamic disorder, the situation is favorable. However, excessive investment of energy and the resulting material-energy discord lead to a decrease in natural resource potential up to the desertification of the territory, which occurs without compensation: instead of blooming gardens, deserts appear.

Ecosystem structure

Ecosystems exist everywhere - in water and on land, in dry and wet areas, in cold and hot areas. They look different and include different types of plants and animals. However, the “behavior” of all ecosystems also has common aspects associated with the fundamental similarity of the energy processes occurring in them. One of the fundamental rules that all ecosystems obey is the Le Chatelier-Brown principle: when an external influence takes the system out of a state of stable equilibrium, this equilibrium shifts in the direction in which the effect of the external influence is weakened.

The largest natural ecosystem on Earth is the biosphere. The boundary between a large ecosystem and the biosphere is as arbitrary as between many concepts in ecology. The difference mainly lies in such characteristics of the biosphere as globality and greater conditional closedness (with thermodynamic openness). Other ecosystems of the Earth are practically not closed in material terms.

Biomes are the largest terrestrial ecosystems corresponding to the main climatic zones of the Earth (desert, grassy, ​​forest); aquatic ecosystems are the main ecosystems existing in the aquatic sphere (hydrosphere).

Any ecosystem can first of all be divided into a set of organisms and a set of inanimate (abiotic) environmental factors (Fig. 2).

In turn, the ecotope consists of climate in all its diverse manifestations and the geological environment (soils and soils), called edaphotope. The edaphotope is where the biocenosis draws its means for subsistence and where it releases waste products.

The structure of the living part of the biogeocenosis is determined by trophoenergetic connections and relationships, according to which three main functional components are distinguished: a complex of autotrophic producer organisms that provide organic matter and, therefore, energy to other organisms (phytocenosis (green plants), as well as photo- and chemosynthetic bacteria ); a complex of heterotrophic consumer organisms living off nutrients created by producers; firstly, this is a zoocenosis (animals), secondly, chlorophyll-free plants; a complex of decomposer organisms that decompose organic compounds to a mineral state (microbiocenosis, as well as fungi and other organisms that feed on dead organic matter).

Figure 2. - Ecosystem structure

Examples of ecosystems: a piece of forest, a pond, a rotting stump, an individual inhabited by microbes or helminths are ecosystems. The concept of an ecosystem is thus applicable to any collection of living organisms and their habitats.

The structure of an ecosystem is usually called the totality of its system-forming connections. Taking into account the nature of the interactions between the biotic and abiotic components, several aspects of the unified internal structure of the ecosystem can be identified:

Energy (the totality of energy flows in the ecosystem);

Material (a set of flows of matter);

Information (a set of intra-ecosystem information flows);

Spatial (characterizing the spatial distribution of energy, matter and information flows within the ecosystem);

Dynamic (determining changes in intra-ecosystem flows over time).

From point of view trophic structure the ecosystem can be divided into two tiers - autotrophic and heterotrophic (according to Yu. Odum, 1986).

1. Upper autotrophic layer, or "green belt", including plants or parts thereof containing chlorophyll, where the fixation of light energy, the use of simple inorganic compounds and the accumulation of complex organic compounds predominate.

2. Lower heterotrophic tier, or "brown belt" of soils and sediments, decaying matter, roots, etc., in which the use, transformation and decomposition of complex compounds predominate.

From a biological point of view, it is convenient to distinguish the following components in the composition of the ecosystem (according to Yu. Odum, 1986):

1) inorganic substances;

2) organic compounds;

3) air, water and substrate environment;

4) producers;

5) macroconsumers;

6) micro-consumers.

1.Inorganic substances (C0 2, H 2 0, N 2, 0 2, mineral salts, etc.) included in the cycles.

2.Organic matter (proteins, carbohydrates, lipids, humic substances, etc.) connecting the biotic and abiotic parts.

3.Air, water And substrate environment, including abiotic factors.

4.Producers - autotrophic organisms capable of producing organic substances from inorganic ones using photosynthesis or chemosynthesis (plants and autotrophic bacteria).

5. Consumers (macroconsumers, phagotrophs) - heterotrophic organisms that consume organic matter from producers or other consumers (animals, heterotrophic plants, some microorganisms). Consumers are of the first order (phytophages, saprophages), second order (zoophages, necrophages), etc.

6.Reducetes (microconsumers, destructors, saprotrophs, osmotrophs) - heterotrophic organisms that feed on organic residues and decompose them into mineral substances (saprotrophic bacteria and fungi).

It should be taken into account that both producers and consumers partially perform the functions of decomposers, releasing mineral substances into the environment - the products of their metabolism.

Thus, as a rule, in any ecosystem three functional groups of organisms can be distinguished: producers, consumers and decomposers. In ecosystems formed only by microorganisms, there are no consumers. Each group includes many populations inhabiting the ecosystem.

In an ecosystem, food and energy connections go in the direction: producers -> consumers -> decomposers.

Any ecosystem is characterized by the circulation of substances and the passage of energy flow through it.

In an ecosystem, organic substances are synthesized by autotrophs from inorganic substances. They are then consumed by heterotrophs. Organic substances released during life or after the death of organisms (both autotrophs and heterotrophs) undergo mineralization, i.e. transformation into inorganic substances. These inorganic substances can be reused by autotrophs for the synthesis of organic substances. This is how it works biological cycle of substances.

At the same time, energy cannot circulate within the ecosystem. Energy flow(transfer of energy) contained in food in the ecosystem is carried out unidirectionally from autotrophs to heterotrophs.

Nature is a tireless conjugation
verbs “to eat” and “to be eaten.”
William Inge

What are the main components of ecosystems? What are food chains and food networks? What is the trophic structure of the ecosystem?

Lesson-lecture

MAIN ECOSYSTEM COMPONENTS. Ecosystems are an elementary functional unit of living nature, in which interactions take place between all its components and the circulation of substances and energy occurs. The composition of the ecosystem includes inorganic substances (water, carbon dioxide, nitrogen compounds, etc.), which are included in the cycle, and organic compounds (proteins, carbohydrates, fats, etc.), connecting biotic (living) and abiotic (non-living or inert) its parts. Each ecosystem is characterized by a certain environment (air, water, land), including a climate regime and a certain set of parameters of the physical environment (temperature, humidity, etc.). Based on the role played by organisms in the ecosystem, they are divided into three groups:

• producers- autotrophic organisms, mainly green plants, which are capable of creating organic substances from inorganic ones;
• consumers- heterotrophic organisms, mainly animals that feed on other organisms or particles of organic matter;
• decomposers- heterotrophic organisms, mainly bacteria and fungi, ensuring the decomposition of organic compounds.

The environment and living organisms are interconnected by the processes of circulation of matter and energy.

Producers capture sunlight and convert its energy into the energy of chemical bonds of the organic compounds they synthesize. Consumers, eating producers, use the energy released during the breakdown of these chemical bonds to build their own body. Decomposers behave in a similar way, but use either dead bodies or products released during the life processes of organisms as a food source. At the same time, decomposers decompose complex organic molecules into simple inorganic compounds - carbon dioxide, nitrogen oxides, water, ammonium salts, etc. As a result, they return substances removed from it by plants to the environment, and these substances can again be utilized by producers. The cycle is completed. It should be noted that all living beings are decomposers to a certain extent. During their metabolism, they extract the energy they need by breaking down organic compounds, releasing carbon dioxide and water as end products.

In ecosystems, living components are arranged in chains - food or trophic chains, in which each previous link serves as food for the next one. At the base of the trophic chain there are producers who, from inorganic matter and light energy, create living matter - primary biomass. The second link consists of animal phytophages that consume this primary biomass - these are consumers of the first order. They, in turn, serve as food for the organisms that make up the next trophic level - second-order consumers. Next come consumers of the third order, etc. Let's give an example of a simple chain:

Here is an example of a more complex circuit:

In natural ecosystems, food chains are not isolated from one another, but are closely intertwined. They form food webs, the principle of their formation is that each producer can serve as food not for one, but for many phytophagous animals, which, in turn, can be eaten by different types of second-order consumers, etc. (Fig. 49).

Rice. 49. Herring food web

Food webs form the framework of ecosystems, and disruptions to them can have unpredictable consequences. Particularly vulnerable are ecosystems with relatively simple food chains, i.e. those in which the range of food items for a particular species is narrow (for example, many Arctic ecosystems). The loss of one of the links can lead to the collapse of the entire trophic network and degradation of the ecosystem as a whole.

TROPHIC STRUCTURE OF ECOSYSTEM AND ENERGY. Green plants capture 1-2% of the solar energy falling on them, converting it into the energy of chemical bonds. First order consumers absorb about 10% of the total energy contained in the plants they eat. At each subsequent level, 10-20% of the energy of the previous one is lost. This pattern is in full accordance with the second law of thermodynamics. According to this law, during any transformation of energy, a significant part of it is dissipated in the form of thermal energy unavailable for use. Thus, energy decreases rapidly in food chains, limiting their length. This is also associated with a decrease at each subsequent level in the number and biomass (the amount of living matter expressed in units of mass or calories) of living organisms. However, this rule, as we will see below, has a number of exceptions.

The stability of each ecosystem is based on a certain trophic structure, which can be expressed in the form of pyramids of numbers, biomass and energy. When constructing them, the values ​​of the corresponding parameter for each trophic level are depicted in the form of rectangles placed on top of each other.

The shape of population pyramids (Fig. 50) largely depends on the size of organisms at each trophic level, especially producers. For example, the number of trees in a forest is much lower than that of grass in a meadow.

Starting with consumers of the first order, the rule is more or less observed, according to which the size of living creatures increases at each subsequent trophic level. Although there are exceptions here: a pack of wolves can drive a deer or elk - prey much larger than each wolf individually.

Biomass pyramids better reflect the actual structure of the ecosystem. If the sizes of living creatures at different trophic levels do not differ too much, then a stepped pyramid can be obtained (see Fig. 50). However, in ecosystems with very small producers (phytoplankton) and large consumers, the total mass of the latter will be higher, and we will get an inverted pyramid. This picture is typical for most marine and freshwater ecosystems.

Rice. 50. Ecological pyramids

Energy pyramids provide the most complete picture of the functional organization of an ecosystem. The number and mass of organisms at each trophic level depend on the abundance of food at the previous level at a given time. Therefore, pyramids of numbers and biomass reflect the statics of the ecosystem, i.e., they characterize the number of organisms at the time of the study. The energy pyramid reflects the speed at which food passes through the trophic chain. Each step symbolizes the amount of energy (calculated per unit area or volume) that has passed through a certain trophic level over a certain period. Therefore, the shape of the energy pyramid is not affected by changes in size, population and biomass. It always has the shape of a triangle with the apex facing upward, which is associated with the loss of energy during the transition from one trophic level to another (see Fig. 50).

The study of the trophic structure of ecosystems, especially the laws of energy conversion, is of paramount importance for understanding the mechanisms that underlie their stability. Without this, it is impossible to correctly calculate the permissible limits of impact on the environment, beyond which it will cause irreparable damage.

Trophic connections between organisms form the basis of an ecosystem. In any ecosystem there are certainly primary producers of organic matter - producers, and organisms that consume and process this substance - consumers and decomposers. These main components of the ecosystem form food chains and networks through which the flow of matter and energy passes. According to the second law of thermodynamics, at each trophic level there is a significant loss of energy in the form of heat, which limits the length of trophic chains. The ecosystem functions as a single, developing system with self-regulation.

• Explain why it is possible to identify common components in any ecosystem.
• What constitutes the basis for the interaction of ecosystem components?
• What is the importance of the diversity of its components for the sustainability of an ecosystem?

Main components of the ecosystem. Ecosystems are an elementary functional unit of living nature, in which interactions take place between all its components and the circulation of substances and energy occurs. The composition of the ecosystem includes inorganic substances (C, N, CO 2, H 2 O, etc.), which are included in the cycle, and organic compounds (proteins, carbohydrates, fats, etc.), connecting biotic (living) and abiotic (non-living) ) its parts. Each ecosystem is characterized by a certain environment (air, water, land), including a climate regime and a certain set of parameters of the physical environment (temperature, humidity, etc.). Based on the role played by organisms in the ecosystem, they are divided into three groups:

producers - autotrophic organisms, mainly green plants, which are capable of creating organic substances from inorganic ones;

consumers are heterotrophic organisms, mainly animals, that feed on other organisms or particles of organic matter;

decomposers are heterotrophic organisms, mainly bacteria and fungi, that ensure the decomposition of organic compounds.

The environment and living organisms are interconnected by the processes of circulation of matter and energy.

Producers capture sunlight and convert its energy into the energy of chemical bonds of the organic compounds they synthesize. Consumers, eating producers, break these bonds and use the energy released to build their own bodies. Decomposers behave in a similar way, but use either dead bodies or products released during the life processes of organisms as a food source. At the same time, decomposers decompose complex organic molecules into simple inorganic compounds - carbon dioxide, nitrogen oxides, water, ammonia salts, etc. As a result, they return substances removed from it by plants to the environment, and these substances can again be utilized by producers. The cycle is completed. It should be noted that all living beings are decomposers to a certain extent. During their metabolism, they extract the energy they need by breaking down organic compounds, releasing carbon dioxide and water as end products.

In ecosystems, living components are arranged in chains (food or trophic(*) chains), in which each previous link serves as food for the next. Each such link represents a certain trophic level, since the organisms located on it receive energy through the same number of intermediaries. At the base of the trophic chain there are producers who create living matter from inorganic matter and light energy - primary biomass. The second link consists of those who consume this primary biomass phytophagous animals- These are consumers of the first order. They, in turn, serve as food for organisms that make up the next trophic level - second-order consumers. Next come consumers of the third order, etc. Let's give an example of a simple chain:

Here is an example of a more complex circuit:

In natural ecosystems, food chains are not isolated from one another, but are closely intertwined. They form food networks, the principle of which is that each producer can serve as food not for one, but for many phytophagous animals, which, in turn, can be eaten by different types of second-order consumers, etc.

Food webs form the framework of ecosystems, and disruptions to them can have unpredictable consequences. Particularly vulnerable are ecosystems with relatively simple food chains, i.e. those in which the range of food items for a particular species is narrow (for example, many Arctic ecosystems). The loss of one of the links can lead to the collapse of the entire trophic network and degradation of the ecosystem as a whole.

A clear example of the complexity of connections between organisms in ecosystems can be seen in the unexpected consequences that resulted from an attempt to combat malaria in Kalimantan (one of the Indonesian islands) in the 50s of the 20th century. To destroy the malaria mosquito (the carrier of the malaria pathogen), the island was sprayed with the insecticide DDT containing organochlorine compounds. The mosquitoes died, as expected, but complications arose. DDT also entered the body of cockroaches, which turned out to be more resistant to it. The cockroaches did not die, but became so slow that they were eaten by lizards in much larger quantities than usual. The insecticide that got into the lizards' bodies along with the cockroaches caused them nervous disorders and weakened reflexes. Therefore, lizards became easy prey for cats, and their numbers fell sharply. Lizards are predators, feeding, among other things, on caterpillars that eat away the thatched roofs of local residents’ houses. The caterpillars multiplied in huge numbers and the roofs began to collapse. But that was only half the story. Cats began to die from DDT poisoning, which entered the body while feeding on poisoned lizards. This led to the villages being overrun by rats that came from the forest and carried fleas infected with the plague bacillus. So, we fought malaria, but got the plague. This is what events carried out without proper environmental assessment lead to. The people of Kalimantan preferred the plague to malaria. Therefore, spraying with insecticide was stopped, and a large batch of cats were parachuted into the jungle to fight rats.

Trophic structure of the ecosystem and energy. Green plants capture 1–2% of the sun's energy falling on them, converting it into the energy of chemical bonds. First-order consumers absorb about 10% of the total energy contained in the plants they eat. At each subsequent level, 10–20% of the energy of the previous one is lost. Such a pattern is in full accordance with the second law (law) (for more details on thermodynamics, see § 00). According to this law, during any transformation of energy, a significant part of it is dissipated in the form of thermal energy unavailable for use. Thus, energy decreases rapidly in food chains, limiting their length. This is also associated with a decrease at each subsequent level in the number and biomass (the amount of living matter expressed in units of mass or calories) of living organisms. However, this rule, as we will see below, has a number of exceptions.

The stability of each ecosystem is based on a certain trophic structure, which can be expressed in the form of pyramids of numbers, biomass and energy. When constructing them, the values ​​of the corresponding parameter for each trophic level are depicted in the form of rectangles placed on top of each other.

The shape of population pyramids depends largely on the size of organisms at each trophic level, especially producers.

For example, the number of trees in a forest is much lower than that of grass in a meadow or phytoplankton (microscopic planktonic photosynthetic organisms) in a pond.

In nature, any species, population and even individual do not live in isolation from each other and their habitat, but, on the contrary, experience numerous mutual influences. Biotic communities or biocenoses - communities of interacting living organisms, which are a stable system connected by numerous internal connections, with a relatively constant structure and an interdependent set of species.

Biocenosis is characterized by certain structures: species, spatial and trophic.

The organic components of the biocenosis are inextricably linked with the inorganic ones - soil, moisture, atmosphere, forming together with them a stable ecosystem - biogeocenosis .

Biogenocenosis– a self-regulating ecological system formed by populations of different species living together and interacting with each other and with inanimate nature in relatively homogeneous environmental conditions.

Ecological systems

Functional systems, including communities of living organisms of different species and their habitat. Connections between ecosystem components arise primarily on the basis of food relationships and methods of obtaining energy.

Ecosystem

A set of species of plants, animals, fungi, microorganisms that interact with each other and with the environment in such a way that such a community can survive and function for an indefinitely long time. Biotic community (biocenosis) consists of a plant community ( phytocenosis), animals ( zoocenosis), microorganisms ( microbiocenosis).

All organisms of the Earth and their habitat also represent an ecosystem of the highest rank - biosphere , possessing stability and other properties of the ecosystem.

The existence of an ecosystem is possible thanks to a constant flow of energy from the outside - such an energy source is usually the sun, although this is not true for all ecosystems. The stability of an ecosystem is ensured by direct and feedback connections between its components, the internal cycle of substances and participation in global cycles.

The doctrine of biogeocenoses developed by V.N. Sukachev. The term " ecosystem"introduced into use by the English geobotanist A. Tansley in 1935, the term " biogeocenosis" - Academician V.N. Sukachev in 1942 biogeocenosis It is necessary to have a plant community (phytocenosis) as the main link, ensuring the potential immortality of the biogeocenosis due to the energy generated by plants. Ecosystems may not contain phytocenosis.

Phytocenosis

A plant community formed historically as a result of a combination of interacting plants in a homogeneous area of ​​territory.

He is characterized:

- a certain species composition,

- life forms,

- tiering (aboveground and underground),

- abundance (frequency of occurrence of species),

- accommodation,

- aspect (appearance),

- vitality,

- seasonal changes,

- development (change of communities).

Tiering (number of floors)

One of the characteristic features of a plant community, which consists, as it were, in its floor-by-floor division in both above-ground and underground space.

Aboveground tiering allows better use of light, and underground - water and minerals. Typically, up to five tiers can be distinguished in a forest: the upper (first) - tall trees, the second - short trees, the third - shrubs, the fourth - grasses, the fifth - mosses.

Underground tiering - a mirror image of the above-ground: the roots of trees go deepest, the underground parts of mosses are located near the surface of the soil.

According to the method of obtaining and using nutrients all organisms are divided into autotrophs and heterotrophs. In nature there is a continuous cycle of nutrients necessary for life. Chemical substances are extracted by autotrophs from the environment and returned to it through heterotrophs. This process takes very complex forms. Each species uses only part of the energy contained in organic matter, bringing its decomposition to a certain stage. Thus, in the process of evolution, ecological systems have developed chains And power supply network .

Most biogeocenoses have similar trophic structure. They are based on green plants - producers. Herbivores and carnivores are necessarily present: consumers of organic matter - consumers and destroyers of organic residues - decomposers.

The number of individuals in the food chain consistently decreases, the number of victims is greater than the number of their consumers, since in each link of the food chain, with each transfer of energy, 80-90% of it is lost, dissipating in the form of heat. Therefore, the number of links in the chain is limited (3-5).

Species diversity of biocenosis represented by all groups of organisms - producers, consumers and decomposers.

Violation of any link in the food chain causes disruption of the biocenosis as a whole. For example, deforestation leads to a change in the species composition of insects, birds, and, consequently, animals. In a treeless area, other food chains will develop and a different biocenosis will form, which will take several decades.

Food chain (trophic or food )

Interrelated species that sequentially extract organic matter and energy from the original food substance; Moreover, each previous link in the chain is food for the next one.

The food chains in each natural area with more or less homogeneous conditions of existence are composed of complexes of interconnected species that feed on each other and form a self-sustaining system in which the circulation of substances and energy occurs.

Ecosystem components:

- Producers - autotrophic organisms (mostly green plants) are the only producers of organic matter on Earth. Energy-rich organic matter is synthesized during photosynthesis from energy-poor inorganic substances (H 2 0 and C0 2).

- Consumers - herbivores and carnivores, consumers of organic matter. Consumers can be herbivores, when they directly use producers, or carnivores, when they feed on other animals. In the food chain they most often can have serial number from I to IV.

- Decomposers - heterotrophic microorganisms (bacteria) and fungi - destroyers of organic residues, destructors. They are also called the Earth's orderlies.

Trophic (nutritional) level - a set of organisms united by a type of nutrition. The concept of the trophic level allows us to understand the dynamics of energy flow in an ecosystem.

1. the first trophic level is always occupied by producers (plants),
2. second - consumers of the first order (herbivorous animals),
3. third - consumers of the second order - predators that feed on herbivorous animals),
4. fourth - consumers of the third order (secondary predators).

The following types are distinguished: food chains:

IN pasture chain (eating chains) the main source of food is green plants. For example: grass -> insects -> amphibians -> snakes -> birds of prey.

- detrital chains (chains of decomposition) begin with detritus - dead biomass. For example: leaf litter -> earthworms -> bacteria. Another feature of detrital chains is that plant products in them are often not consumed directly by herbivorous animals, but die off and are mineralized by saprophytes. Detrital chains are also characteristic of deep ocean ecosystems, whose inhabitants feed on dead organisms that have sunk down from the upper layers of water.

The relationships between species in ecological systems that have developed during the process of evolution, in which many components feed on different objects and themselves serve as food for various members of the ecosystem. In simple terms, a food web can be represented as intertwined food chain system.

Organisms of different food chains that receive food through an equal number of links in these chains are on same trophic level. At the same time, different populations of the same species, included in different food chains, may be located on different trophic levels. The relationship between different trophic levels in an ecosystem can be depicted graphically as ecological pyramid.

Ecological pyramid

A method of graphically displaying the relationship between different trophic levels in an ecosystem - there are three types:

The population pyramid reflects the number of organisms at each trophic level;

The biomass pyramid reflects the biomass of each trophic level;

The energy pyramid shows the amount of energy passing through each trophic level over a specified period of time.

Ecological pyramid rule

A pattern reflecting a progressive decrease in mass (energy, number of individuals) of each subsequent link in the food chain.

Number pyramid

An ecological pyramid showing the number of individuals at each nutritional level. The pyramid of numbers does not take into account the size and mass of individuals, life expectancy, metabolic rate, but the main trend is always visible - a decrease in the number of individuals from link to link. For example, in a steppe ecosystem the number of individuals is distributed as follows: producers - 150,000, herbivorous consumers - 20,000, carnivorous consumers - 9,000 individuals/area. The meadow biocenosis is characterized by the following number of individuals on an area of ​​4000 m2: producers - 5,842,424, herbivorous consumers of the first order - 708,624, carnivorous consumers of the second order - 35,490, carnivorous consumers of the third order - 3.

Biomass pyramid

The pattern according to which the amount of plant matter that serves as the basis of the food chain (producers) is approximately 10 times greater than the mass of herbivorous animals (consumers of the first order), and the mass of herbivorous animals is 10 times greater than that of carnivores (consumers of the second order), t That is, each subsequent food level has a mass 10 times less than the previous one. On average, 1000 kg of plants produce 100 kg of herbivore body. Predators that eat herbivores can build 10 kg of their biomass, secondary predators - 1 kg.

Pyramid of Energy

expresses a pattern according to which the flow of energy gradually decreases and depreciates when moving from link to link in the food chain. Thus, in the biocenosis of the lake, green plants - producers - create a biomass containing 295.3 kJ/cm 2, consumers of the first order, consuming plant biomass, create their own biomass containing 29.4 kJ/cm 2; Second order consumers, using first order consumers for food, create their own biomass containing 5.46 kJ/cm2. The loss of energy during the transition from consumers of the first order to consumers of the second order, if these are warm-blooded animals, increases. This is explained by the fact that these animals spend a lot of energy not only on building their biomass, but also on maintaining a constant body temperature. If we compare the raising of a calf and a perch, then the same amount of food energy expended will yield 7 kg of beef and only 1 kg of fish, since the calf eats grass, and the predatory perch eats fish.

Thus, the first two types of pyramids have a number of significant disadvantages:

The biomass pyramid reflects the state of the ecosystem at the time of sampling and therefore shows the ratio of biomass at a given moment and does not reflect the productivity of each trophic level (i.e. its ability to produce biomass over a certain period of time). Therefore, in the case when the number of producers includes fast-growing species, the biomass pyramid may turn out to be inverted.

The energy pyramid allows you to compare the productivity of different trophic levels because it takes into account the time factor. In addition, it takes into account the difference in energy value of various substances (for example, 1 g of fat provides almost twice as much energy as 1 g of glucose). Therefore, the pyramid of energy always narrows upward and is never inverted.

Ecological plasticity

The degree of endurance of organisms or their communities (biocenoses) to the influence of environmental factors. Ecologically plastic species have a wide range of reaction norm , i.e., they are widely adapted to different habitats (fish stickleback and eel, some protozoa live in both fresh and salt waters). Highly specialized species can exist only in a certain environment: marine animals and algae - in salt water, river fish and lotus plants, water lilies, duckweed live only in fresh water.

Generally ecosystem (biogeocenosis) characterized by the following indicators:

Species diversity

Density of species populations,

Biomass.

Biomass

The total amount of organic matter of all individuals of a biocenosis or species with the energy contained in it. Biomass is usually expressed in units of mass in terms of dry matter per unit area or volume. Biomass can be determined separately for animals, plants or individual species. Thus, the biomass of fungi in the soil is 0.05-0.35 t/ha, algae - 0.06-0.5, roots of higher plants - 3.0-5.0, earthworms - 0.2-0.5 , vertebrate animals - 0.001-0.015 t/ha.

In biogeocenoses there are primary and secondary biological productivity :

ü Primary biological productivity of biocenoses- the total total productivity of photosynthesis, which is the result of the activity of autotrophs - green plants, for example, a pine forest of 20-30 years of age produces 37.8 t/ha of biomass per year.

ü Secondary biological productivity of biocenoses- the total total productivity of heterotrophic organisms (consumers), which is formed through the use of substances and energy accumulated by producers.

Populations. Structure and dynamics of numbers.

Each species on Earth occupies a specific range, since it is able to exist only in certain environmental conditions. However, living conditions within the range of one species can differ significantly, which leads to the disintegration of the species into elementary groups of individuals - populations.

Population

A set of individuals of the same species, occupying a separate territory within the range of the species (with relatively homogeneous living conditions), freely interbreeding with each other (having a common gene pool) and isolated from other populations of this species, having all the necessary conditions to maintain their stability for a long time in a changing environmental conditions. The most important characteristics populations are its structure (age, sex composition) and population dynamics.

Under the demographic structure populations understand its sex and age composition.

Spatial structure Populations are the characteristics of the distribution of individuals in a population in space.

Age structure population is associated with the ratio of individuals of different ages in the population. Individuals of the same age are grouped into cohorts - age groups.

IN age structure of plant populations allocate following periods:

Latent - state of the seed;

Pregenerative (includes the states of seedling, juvenile plant, immature and virginal plants);

Generative (usually divided into three subperiods - young, mature and old generative individuals);

Postgenerative (includes the states of subsenile, senile plants and the dying phase).

Belonging to a certain age status is determined by biological age- the degree of expression of certain morphological (for example, the degree of dissection of a complex leaf) and physiological (for example, the ability to give birth) characteristics.

In animal populations it is also possible to distinguish different age stages. For example, insects developing with complete metamorphosis go through the stages:

Larvae,

dolls,

Imago (adult insect).

The nature of the age structure of the populationdepends on the type of survival curve characteristic of a given population.

Survival curvereflects the mortality rate in different age groups and is a decreasing line:

1. If the mortality rate does not depend on the age of individuals, the death of individuals occurs evenly in a given type, the mortality rate remains constant throughout life ( type I ). Such a survival curve is characteristic of species whose development occurs without metamorphosis with sufficient stability of the born offspring. This type is usually called type of hydra- it is characterized by a survival curve approaching a straight line.
2. In species for which the role of external factors in mortality is small, the survival curve is characterized by a slight decrease until a certain age, after which there is a sharp drop due to natural (physiological) mortality ( type II ). The nature of the survival curve close to this type is characteristic of humans (although the human survival curve is somewhat flatter and is something between types I and II). This type is called Drosophila type: This is what fruit flies demonstrate in laboratory conditions (not eaten by predators).
3. Many species are characterized by high mortality in the early stages of ontogenesis. In such species, the survival curve is characterized by a sharp drop in the younger ages. Individuals that survive the “critical” age exhibit low mortality and live to older ages. The type is called type of oyster (type III ).

Sexual structure populations

Sex ratio has a direct bearing on population reproduction and sustainability.

There are primary, secondary and tertiary sex ratios in the population:

- Primary sex ratio determined by genetic mechanisms - the uniformity of divergence of sex chromosomes. For example, in humans, XY chromosomes determine the development of the male sex, and XX chromosomes determine the development of the female sex. In this case, the primary sex ratio is 1:1, i.e. equally probable.

- Secondary sex ratio is the sex ratio at the time of birth (among newborns). It can differ significantly from the primary one for a number of reasons: the selectivity of eggs to sperm carrying the X or Y chromosome, the unequal ability of such sperm to fertilize, and various external factors. For example, zoologists have described the effect of temperature on the secondary sex ratio in reptiles. A similar pattern is typical for some insects. Thus, in ants, fertilization is ensured at temperatures above 20 ° C, and at lower temperatures unfertilized eggs are laid. The latter hatch into males, and those that are fertilized predominantly into females.

- Tertiary sex ratio - sex ratio among adult animals.

Spatial structure populations reflects the nature of the distribution of individuals in space.

Highlight three main types of distribution of individuals in space:

- uniform or uniform(individuals are distributed evenly in space, at equal distances from each other); is rare in nature and is most often caused by acute intraspecific competition (for example, in predatory fish);

- congregational or mosaic(“spotted”, individuals are located in isolated clusters); occurs much more often. It is associated with the characteristics of the microenvironment or behavior of animals;

- random or diffuse(individuals are randomly distributed in space) - can only be observed in a homogeneous environment and only in species that do not show any tendency to form groups (for example, a beetle in flour).

Population size denoted by the letter N. The ratio of the increase in N to a unit of time dN / dt expressesinstantaneous speedchanges in population size, i.e. change in number at time t.Population growthdepends on two factors - fertility and mortality in the absence of emigration and immigration (such a population is called isolated). The difference between the birth rate b and death rate d isisolated population growth rate:

Population stability

This is its ability to be in a state of dynamic (i.e., mobile, changing) equilibrium with the environment: environmental conditions change, and the population also changes. One of the most important conditions for sustainability is internal diversity. In relation to a population, these are mechanisms for maintaining a certain population density.

Highlight three types of dependence of population size on its density .

First type (I) - the most common, characterized by a decrease in population growth with an increase in its density, which is ensured by various mechanisms. For example, many bird species are characterized by a decrease in fertility (fertility) with increasing population density; increased mortality, decreased resistance of organisms with increased population density; change in age at puberty depending on population density.

Third type ( III ) is characteristic of populations in which a “group effect” is noted, i.e. a certain optimal population density contributes to better survival, development, and vital activity of all individuals, which is inherent in most group and social animals. For example, to renew populations of animals of different sexes, at a minimum, a density is required that provides a sufficient probability of meeting a male and a female.

Thematic assignments

A1. Biogeocenosis formed

1) plants and animals

2) animals and bacteria

3) plants, animals, bacteria

4) territory and organisms

A2. Consumers of organic matter in forest biogeocenosis are

1) spruce and birch

2) mushrooms and worms

3) hares and squirrels

4) bacteria and viruses

A3. Producers in the lake are

2) tadpoles

A4. The process of self-regulation in biogeocenosis affects

1) sex ratio in populations of different species

2) the number of mutations occurring in populations

3) predator-prey ratio

4) intraspecific competition

A5. One of the conditions for the sustainability of an ecosystem can be

1) her ability to change

2) variety of species

3) fluctuations in the number of species

4) stability of the gene pool in populations

A6. Decomposers include

2) lichens

4) ferns

A7. If the total mass received by a 2nd order consumer is 10 kg, then what was the total mass of the producers that became the source of food for this consumer?

A8. Indicate the detrital food chain

1) fly – spider – sparrow – bacteria

2) clover – hawk – bumblebee – mouse

3) rye – tit – cat – bacteria

4) mosquito - sparrow - hawk - worms

A9. The initial source of energy in a biocenosis is energy

1) organic compounds

2) inorganic compounds

4) chemosynthesis

1) hares

2) bees

3) fieldfare thrushes

4) wolves

A11. In one ecosystem you can find oak and

1) gopher

3) lark

4) blue cornflower

A12. Power networks are:

1) connections between parents and offspring

2) family (genetic) connections

3) metabolism in body cells

4) ways of transferring substances and energy in the ecosystem

A13. The ecological pyramid of numbers reflects:

1) the ratio of biomass at each trophic level

2) the ratio of the masses of an individual organism at different trophic levels

3) structure of the food chain

4) diversity of species at different trophic levels