Phytophagous and carnivorous
The structure of living matter in an ecosystem. Biotic structure. Autotrophs and heterotrophs
Ecosystem. Signs of an ecosystem
Ecosystem homeostasis. Ecological succession. Types of natural and anthropogenic successions. Concepts of climax, stability and variability of ecosystems.
Populations in an ecosystem.
Producers. Consumers of the 1st and 2nd order. Detritivores. Decomposers.
Phytophagous and carnivorous.
The structure of living matter in an ecosystem. Biotic structure. Autotrophs and heterotrophs.
Ecosystem. Signs of an ecosystem.
Topic 3. Ecosystem. Ecosystem structure
Bioconsumption. Population and stability of the biosphere
Concepts of noosphere and technosphere
The term “ecosystem” was proposed by the English ecologist A. Tansley in 1935.
Ecosystem is any set of interacting living organisms and environmental conditions.
“Any unit (biosystem) that includes all the co-functioning organisms (biotic community) in a given area and interacts with the physical environment in such a way that the flow of energy creates well-defined biotic structures and the circulation of substances between living and inanimate parts, represents ecological system, or ecosystem"(Y. Odum, 1986).
Ecosystems are, for example, anthills, a forest plot, a farm area, a cabin spaceship, a geographical landscape or even the entire globe.
Ecologists also use the term “biogeocenosis”, proposed by the Russian scientist V.N. Sukachev. This term refers to the collection of plants, animals, microorganisms, soil and atmosphere on a homogeneous land area. Biogeocenosis is one of the variants of an ecosystem.
Between ecosystems, as well as between biogeocenoses, there are usually no clear boundaries, and one ecosystem gradually passes into another. Large ecosystems are made up of smaller ecosystems.
Rice. "Matryoshka" of ecosystems
In Fig. a “matryoshka” of ecosystems is shown. How smaller size ecosystem, the more closely its constituent organisms interact. An organized group of ants lives in an anthill, in which all responsibilities are distributed. There are ants-hunters, guards, builders.
The anthill ecosystem is part of the forest biogeocenosis, and the forest biogeocenosis is part of the geographical landscape. The composition of the forest ecosystem is more complex; representatives of many species of animals, plants, fungi, and bacteria live together in the forest. The connections between them are not as close as those of ants in an anthill. Many animals spend only part of their time in the forest ecosystem.
Within the landscape, different biogeocenoses are connected by aboveground and underground movement of water in which minerals are dissolved. Water with minerals moves most intensively within drainage basin– a reservoir (lakes, rivers) and adjacent slopes from which above-ground and underground waters flow into this reservoir. The ecosystem of the drainage basin includes several different ecosystems - forest, meadow, and arable land. The organisms of all these ecosystems may not have direct relationships and are connected through underground and aboveground water flows that move to the reservoir.
Within the landscape, plant seeds are transferred and animals move. A fox's hole or a wolf's lair are located in one biogeocenosis, and these predators hunt over a large territory consisting of several biogeocenoses.
Landscapes are united into physical-geographical regions (for example, the Russian Plain, the West Siberian Lowland), where different biogeocenoses are connected by a common climate, geological structure territory and the possibility of settlement of animals and plants. Connections between organisms, including humans, in the ecosystems of a physical-geographical region and the biosphere are carried out through changes in the gas composition of the atmosphere and chemical composition reservoirs.
Finally, all ecosystems globe are connected through the atmosphere and the World Ocean, into which the waste products of organisms enter, and form a single whole - biosphere.
The ecosystem includes:
1) living organisms (their totality can be called a biocenosis or biota of an ecosystem);
2) non-living (abiotic) factors - atmosphere, water, nutrients, light;
3) dead organic matter - detritus.
Special meaning to highlight ecosystems have trophic , i.e. food relationships between organisms that regulate the entire energy of biotic communities and the entire ecosystem as a whole.
First of all, all organisms are divided into two large groups - autotrophs and heterotrophs.
Autotrophic organisms use inorganic sources for their existence, thereby creating organic matter from inorganic matter. Such organisms include photosynthetic green plants of land and aquatic environments, blue-green algae, some bacteria due to chemosynthesis, etc.
Since organisms are quite diverse in types and forms of nutrition, they enter into complex trophic interactions with each other, thereby performing the most important ecological functions in biotic communities. Some of them produce products, others consume them, and others convert them into inorganic form. They are called accordingly: producers, consumers and decomposers.
Producers- producers of products that all other organisms then feed on - these are terrestrial green plants, microscopic sea and freshwater algae, producing organic substances from inorganic compounds.
Consumers are consumers of organic substances. Among them there are animals that eat only plant foods - herbivores(cow) or eating only the meat of other animals – carnivores(predators), as well as those who use both – “ omnivores"(man, bear).
Reducers (destructors)– reducing agents. They return substances from dead organisms back to inanimate nature, decomposing organic matter into simple inorganic compounds and elements (for example, CO 2, NO 2 and H 2 O). Returning to the soil or aquatic environment biogenic elements, they thereby complete the biochemical cycle. This is done mainly by bacteria, most other microorganisms and fungi. Functionally, decomposers are the same consumers, which is why they are often called micro-consumers.
A.G. Bannikov (1977) believes that insects also play important role in the processes of decomposition of dead organic matter and in soil-forming processes.
Microorganisms, bacteria and other more complex forms, depending on their habitat, are divided into aerobic, i.e. living in the presence of oxygen, and anaerobic– living in an oxygen-free environment.
All living organisms are divided into two groups according to their feeding method:
autotrophs(from Greek autos– himself and tropho- nutrition);
heterotrophs(from Greek heteros- another).
Autotrophs use inorganic carbon ( inorganic energy sources) and synthesize organic substances from inorganic ones; these are the producers of the ecosystem. According to the source (used) energy, they, in turn, are also divided into two groups:
Photoautotrophs– used for the synthesis of organic substances solar energy. These are green plants that have chlorophyll (and other pigments) and absorb sunlight. The process by which its absorption occurs is called photosynthesis.
(Chlorophyll is a green pigment that causes the color of plant chloroplasts in green color. With its participation, the process of photosynthesis is carried out.
Choroplasts are green plastids that are found in the cells of plants and some bacteria. With their help, photosynthesis occurs.)
Chemoautotrophs– chemical energy is used to synthesize organic substances. These are sulfur bacteria and iron bacteria that obtain energy from the oxidation of sulfur and iron compounds (chemosynthesis). Chemoautotrophs play a significant role only in ecosystems groundwater. Their role in terrestrial ecosystems is relatively small.
Heterotrophs They use carbon from organic substances that are synthesized by producers, and together with these substances they obtain energy. Heterotrophs are consumers(from lat. consumo– consume), consuming organic matter, and decomposers, decomposing it into simple compounds.
Phytophagous(herbivores). These include animals that feed on living plants. Among the phytophages there are small animals, such as aphids or grasshoppers, and giants, such as the elephant. Almost all farm animals are phytophages: cows, horses, sheep, rabbits. There are phytophages among aquatic organisms, for example, the grass carp fish, which eats plants that overgrow irrigation canals. An important phytophage is the beaver. It feeds on tree branches, and from the trunks it builds dams that regulate water regime territories.
Zoophagi(predators, carnivores). Zoophages are diverse. These are small animals that feed on amoebas, worms or crustaceans. And big ones, like a wolf. Predators that feed on smaller predators are called second-order predators. There are predator plants (sundew, bladderwort) that use insects as food.
Symbiotrophs. These are bacteria and fungi that feed on plant root secretions. Symbiotrophs are very important for the life of the ecosystem. Fungal threads entangling plant roots help absorb water and minerals. Symbiotrophic bacteria absorb nitrogen gas from the atmosphere and bind it into compounds available to plants (ammonia, nitrates). This nitrogen is called biological (as opposed to nitrogen from mineral fertilizers).
Symbiotrophs also include microorganisms (bacteria, single-celled animals) that live in the digestive tract of phytophagous animals and help them digest food. Animals such as a cow, without the help of symbiotrophs, are not able to digest the grass they eat.
Detritivores are organisms that feed on dead organic matter. These are centipedes, earthworms, dung beetles, crayfish, crabs, jackals and many others.
Some organisms use both plants and animals and even detritus for food, and are classified as euryphages (omnivores) - bear, fox, pig, rat, chicken, crow, cockroaches. Man is also a euryphage.
Decomposers- organisms that, in their position in the ecosystem, are close to detritivores, since they also feed on dead organic matter. However, decomposers - bacteria and fungi - break down organic matter into mineral compounds, which are returned to the soil solution and used again by plants.
Reducers need time to process corpses. Therefore, there is always detritus in the ecosystem - a supply of dead organic matter. Detritus is leaf litter on the surface of forest soil (preserved for 2–3 years), the trunk of a fallen tree (preserved for 5–10 years), soil humus (preserved for hundreds of years), deposits of organic matter at the bottom of the lake - sapropel - and peat in the swamp ( lasts for thousands of years). The longest-lasting detritus is coal and oil.
In Fig. shows the structure of an ecosystem, the basis of which is plants - photoautotrophs, and the table shows examples of representatives of different trophic groups for some ecosystems.
Rice. Ecosystem structure
Organic substances created by autotrophs serve as food and a source of energy for heterotrophs: phytophagous consumers eat plants, first-order predators eat phytophages, second-order predators eat first-order predators, etc. This sequence of organisms is called food chain, its links are located at different trophic levels (representing different trophic groups).
The trophic level is the location of each link in the food chain. First trophic level- these are producers, all the rest are consumers. The second trophic level is herbivorous consumers; the third is carnivorous consumers, feeding on herbivorous forms; the fourth are consumers who consume other carnivores, etc. therefore, consumers can be divided into levels: consumers of the first, second, third, etc. orders (Fig.).
Rice. Food relationships of organisms in biogeocenosis
Only consumers specializing in a certain type of food are clearly divided into levels. However, there are species that eat meat and plant foods(human, bear, etc.), which can be included in food chains at any level.
In Fig. Five examples of food chains are given.
Rice. Some food chains in ecosystems
The first two food chains represent natural ecosystems– land and water. In the terrestrial ecosystem, predators such as foxes, wolves, and eagles that feed on mice or gophers complete the chain. In an aquatic ecosystem, solar energy, absorbed mainly by algae, passes to small consumers - daphnia crustaceans, then to small fish (roach) and, finally, to large predators - pike, catfish, pike perch. In agricultural ecosystems, the food chain can be complete when raising farm animals (third example), or shortened when plants are grown that are directly used by humans for food (fourth example).
The given examples simplify the actual picture, since the same plant can be eaten by different herbivores, and they, in turn, become victims of different predators. A plant leaf can be eaten by a caterpillar or slug, the caterpillar can become a victim of a beetle or an insectivorous bird, which can also peck the beetle itself. A beetle can also become a victim of a spider. Therefore, in real nature, it is not food chains that form, but food webs.
During the transition of energy from one trophic level to another (from plants to phytophages, from phytophages to first-order predators, from first-order predators to second-order predators) approximately 90% of the energy is lost through excrement and respiration. In addition, phytophages eat only about 10% of plant biomass, the rest replenishes the supply of detritus and is then destroyed by decomposers. Therefore, secondary biological products are 20–50 times less than primary ones.
Rice. Main types of ecosystems
Topic No. 4 BIOCENOSIS
The concept of biocenosis
Trophic structure of biocenosis
Spatial structure of the biocenosis
The concept of biocenosis
In nature, populations of different species are integrated into macrosystems of a higher rank - into so-called communities, or biocenoses.
Biocenosis (from the Greek bios - life, koinos - general) is an organized group of interconnected populations of plants, animals, fungi and microorganisms living together in the same environmental conditions.
The concept of “biocenosis” was proposed in 1877 by the German zoologist K. Mobius. Moebius, studying oyster banks, came to the conclusion that each of them represents a community of living beings, all members of which are closely interconnected. Biocenosis is a product natural selection. Its survival, stable existence in time and space depends on the nature of the interaction of the constituent populations and is possible only with the obligatory supply of radiant energy from the Sun from outside.
Each biocenosis has a certain structure, species composition and territory; it is characterized by a certain organization of food connections and a certain type of metabolism
But no biocenosis can develop on its own, outside and independently of the environment. As a result, certain complexes, collections of living and nonliving components, develop in nature. The complex interactions of their individual parts are supported on the basis of versatile mutual adaptability.
A space with more or less homogeneous conditions, inhabited by one or another community of organisms (biocenosis), is called a biotope.
In other words, a biotope is a place of existence, habitat, biocenosis. Therefore, a biocenosis can be considered as a historically established complex of organisms, characteristic of a specific biotope.
Any biocenosis forms a dialectical unity with a biotope, a biological macrosystem of an even higher rank - a biogeocenosis. The term “biogeocenosis” was proposed in 1940 by V. N. Sukachev. It is almost identical to the term “ecosystem”, widely used abroad, which was proposed in 1935 by A. Tansley. There is an opinion that the term “biogeocoenosis” to a much greater extent reflects the structural characteristics of the macrosystem being studied, while the concept of “ecosystem” primarily includes its functional essence. In fact, there is no difference between these terms. Undoubtedly, V.N. Sukachev, formulating the concept of “biogeocoenosis”, combined in it not only the structural, but also the functional significance of the macrosystem. According to V.N. Sukachev, biogeocenosis- This a set of homogeneous natural phenomena over a known area of the earth's surface- atmosphere, rock, hydrological conditions, vegetation, fauna, microorganisms and soil. This set is distinguished by the specific interactions of its components, their special structure and a certain type of exchange of substances and energy among themselves and with other natural phenomena.
Biogeocenoses can be of very different sizes. In addition, they are characterized by great complexity - it is sometimes difficult to take into account all the elements, all the links. These are, for example, such natural groups as a forest, lake, meadow, etc. An example of a relatively simple and clear biogeocenosis is a small reservoir or pond. Its non-living components include water, substances dissolved in it (oxygen, carbon dioxide, salts, organic compounds) and soil - the bottom of a reservoir, which also contains a large number of various substances. The living components of a reservoir are divided into primary producers - producers (green plants), consumers - consumers (primary - herbivores, secondary - carnivores, etc.) and destroyers - destructors (microorganisms), which decompose organic compounds to inorganic ones. Any biogeocenosis, regardless of its size and complexity, consists of these main links: producers, consumers, destroyers and components of inanimate nature, as well as many other links. Connections of the most varied orders arise between them - parallel and intersecting, entangled and intertwined, etc.
In general, biogeocenosis represents an internal contradictory dialectical unity, in constant movement and change. “Biogeocenosis is not the sum of biocenosis and environment,” points out N.V. Dylis, “but a holistic and qualitatively isolated phenomenon of nature, acting and developing according to its own laws, the basis of which is the metabolism of its components.”
The living components of biogeocenosis, i.e., balanced animal-plant communities (biocenoses), are the highest form of existence of organisms. They are characterized by a relatively stable composition of fauna and flora and have a typical set of living organisms that retain their basic characteristics in time and space. The stability of biogeocenoses is supported by self-regulation, i.e. all elements of the system exist together, never completely destroying each other, but only limiting the number of individuals of each species to a certain limit. That is why such relationships have historically developed between species of animals, plants and microorganisms that ensure development and maintain their reproduction at a certain level. Overpopulation of one of them may arise for some reason as an outbreak of mass reproduction, and then the existing relationship between the species is temporarily disrupted.
To simplify the study of biocenosis, it can be conditionally divided into separate components: phytocenosis - vegetation, zoocenosis - animal world, microbiocenosis - microorganisms. But such fragmentation leads to an artificial and actually incorrect separation from a single natural complex of groups that cannot exist independently. In no habitat can there be dynamic system, which would consist only of plants or only of animals. Biocenosis, phytocenosis and zoocenosis must be considered as biological unities of different types and stages. This view objectively reflects the real situation in modern ecology.
In the conditions of scientific and technological progress, human activity transforms natural biogeocenoses (forests, steppes). They are being replaced by sowing and planting of cultivated plants. This is how special secondary agrobiogeocenoses, or agrocenoses, are formed, the number of which on Earth is constantly increasing. Agrocenoses are not only agricultural fields, but also shelterbelts, pastures, artificially regenerated forests in cleared areas and fires, ponds and reservoirs, canals and drained swamps. Agrobiocenoses in their structure are characterized by a small number of species, but their high abundance. Although there are many specific features in the structure and energy of natural and artificial biocenoses, there are no sharp differences between them. In a natural biogeocenosis, the quantitative ratio of individuals of different species is mutually determined, since mechanisms regulating this ratio operate in it. As a result, a stable state is established in such biogeocenoses, maintaining the most favorable quantitative proportions of its constituent components. In artificial agrocenoses there are no such mechanisms; there, man has completely taken upon himself the responsibility for regulating the relationships between species. Much attention is paid to the study of the structure and dynamics of agrocenoses, since in the foreseeable future there will be practically no primary, natural, biogeocenoses left.
Trophic structure of biocenosis
The main function of biocenoses - maintaining the cycle of substances in the biosphere - is based on the nutritional relationships of species. It is on this basis that organic substances synthesized by autotrophic organisms undergo multiple chemical transformations and ultimately return to the environment in the form of inorganic waste products, again involved in the cycle. Therefore, with all the diversity of species that make up various communities, each biocenosis necessarily includes representatives of all three fundamental ecological groups of organisms - producers, consumers and decomposers . The completeness of the trophic structure of biocenoses is an axiom of biocenology.
Groups of organisms and their relationships in biocenoses
Based on their participation in the biogenic cycle of substances in biocenoses, three groups of organisms are distinguished:
1) Producers(producers) - autotrophic organisms that create organic substances from inorganic ones. The main producers in all biocenoses are green plants. The activities of producers determine the initial accumulation of organic substances in the biocenosis;
ConsumersIorder.
This trophic level is composed of direct consumers of primary production. In the most typical cases, when the latter is created by photoautotrophs, these are herbivores (phytophagous). The species and ecological forms representing this level are very diverse and adapted to nutrition different types plant food. Due to the fact that plants are usually attached to the substrate, and their tissues are often very strong, many phytophages have evolved a gnawing type of mouthparts and various types of adaptations for grinding and grinding food. These are the dental systems of the gnawing and grinding type in various herbivorous mammals, the muscular stomach of birds, especially well expressed in granivores, etc. n. The combination of these structures determines the ability to grind solid food. Gnawing mouthparts are characteristic of many insects and others.
Some animals are adapted to feeding on plant sap or flower nectar. This food is rich in high-calorie, easily digestible substances. Oral apparatus in species that feed in this way, it is arranged in the form of a tube through which liquid food is absorbed.
Adaptations to feeding on plants are also found at the physiological level. They are especially pronounced in animals that feed on the rough tissues of the vegetative parts of plants, containing large amounts of fiber. In the body of most animals, cellulolytic enzymes are not produced, and the breakdown of fiber is carried out by symbiotic bacteria (and some protozoa of the intestinal tract).
Consumers partially use food to support life processes (“respiration costs”), and partially build their own body on its basis, thus carrying out the first, fundamental stage of transformation of organic matter synthesized by producers. The process of creation and accumulation of biomass at the level of consumers is designated as , secondary products.
ConsumersIIorder.
This level unites animals with a carnivorous type of nutrition (zoophagous). Usually, all predators are considered in this group, since their specific features practically do not depend on whether the prey is a phytophage or a carnivore. But strictly speaking, only predators that feed on herbivores and, accordingly, represent the second stage of transformation of organic matter in food chains should be considered second-order consumers. The chemical substances from which the tissues of an animal organism are built are quite homogeneous, therefore the transformation during the transition from one level of consumers to another is not as fundamental as the transformation of plant tissues into animals.
With a more careful approach, the level of consumers of the second order should be divided into sublevels according to the direction of flow of matter and energy. For example, in the trophic chain “cereals - grasshoppers - frogs - snakes - eagles”, frogs, snakes and eagles constitute successive sublevels of consumers of the second order.
Zoophages are characterized by their specific adaptations to their feeding patterns. For example, their mouthparts are often adapted to grasp and hold live prey. When feeding on animals that have dense protective coverings, adaptations are developed to destroy them.
At the physiological level, adaptations of zoophages are expressed primarily in the specificity of the action of enzymes “tuned” to digest food of animal origin.
ConsumersIIIorder.
Most important in biocenoses they have trophic connections. Based on these connections of organisms in each biocenosis, so-called food chains are distinguished, which arise as a result of complex food relationships between plant and animal organisms. Power circuits are connected directly or indirectly large group organisms into a single complex, connected to each other by the relationship: food - consumer. The food chain usually consists of several links. The organisms of the subsequent link eat the organisms of the previous link, and thus a chain transfer of energy and matter occurs, which underlies the cycle of substances in nature. With each transfer from link to link, a large part (up to 80 - 90%) of the potential energy is lost, dissipated in the form of heat. For this reason, the number of links (types) in the food chain is limited and usually does not exceed 4-5.
A schematic diagram of the food chain is shown in Fig. 2.
Here, the basis of the food chain is made up of species - producers - autotrophic organisms, mainly green plants that synthesize organic matter (they build their body from water, inorganic salts and carbon dioxide, assimilating energy solar radiation), as well as sulfur, hydrogen and other bacteria that use the energy of oxidation of chemicals to synthesize organic substances. The next links in the food chain are occupied by consumer species—heterotrophic organisms that consume organic substances. Primary consumers are herbivorous animals that feed on grass, seeds, fruits, underground parts of plants - roots, tubers, bulbs and even wood (some insects). Secondary consumers include carnivores. Carnivores, in turn, are divided into two groups: those that feed on mass small prey and active predators that often attack prey larger than the predator itself. At the same time, both herbivores and carnivores have a mixed feeding pattern. For example, even with the abundance of mammals and birds, martens and sables also eat fruits, seeds and pine nuts, and herbivores consume some amount of animal food, thus obtaining the essential amino acids of animal origin they need. Starting from the producer level, there are two new ways to use energy. Firstly, it is used by herbivores (phytophages), which directly eat living plant tissue; secondly, they consume saprophages in the form of already dead tissue (for example, during the decomposition of forest litter). Organisms called saprophages, mainly fungi and bacteria, obtain the necessary energy by decomposing dead organic matter. In accordance with this, there are two types of food chains: chains of consumption and chains of decomposition, Fig. 3.
It should be emphasized that food chains of decomposition are no less important than chains of grazing. On land, these chains begin with dead organic matter (leaves, bark, branches), in water - dead algae, fecal matter and other organic debris. Organic residues can be completely consumed by bacteria, fungi and small animals - saprophages; This releases gas and heat.
Each biocenosis usually has several food chains, which in most cases are complexly intertwined.
Ecological pyramid
All species that form the food chain exist on organic matter created by green plants. In this case, there is an important pattern associated with the efficiency of use and conversion of energy in the nutrition process. Its essence is as follows.
Only about 0.1% of the energy received from the Sun is bound through the process of photosynthesis. However, due to this energy, several thousand grams of dry organic matter per 1 m2 per year can be synthesized. More than half of the energy associated with photosynthesis is immediately consumed in the process of respiration of the plants themselves. The other part is transported through food chains by a number of organisms. But when animals eat plants, most of the energy contained in food is spent on various vital processes, turning into heat and dissipating. Only 5 - 20% of food energy passes into the newly built substance of the animal's body. The amount of plant matter that serves as the basis of the food chain is always several times greater than the total mass of herbivorous animals, and the mass of each of the subsequent links in the food chain also decreases. This very important pattern is called rule of the ecological pyramid. An ecological pyramid representing a food chain: cereals - grasshoppers - frogs - snakes - eagle is shown in Fig. 6.
The height of the pyramid corresponds to the length of the food chain.
The transition of biomass from a lower trophic level to a higher one is associated with losses of matter and energy. On average, it is believed that only about 10% of the biomass and its associated energy moves from each level to the next. Because of this, total biomass, production and energy, and often the number of individuals, progressively decrease as they ascend through trophic levels. This pattern was formulated by Ch. Elton (Ch. Elton, 1927) in the form of a rule ecological pyramids
(Fig. 4) and acts as main limiter length of food chains. 
Biomass And biocenosis productivity
The amount of living matter of all groups of plant and animal organisms is called biomass. The rate of biomass production is characterized by the productivity of the biocenosis. There is a distinction between primary productivity - plant biomass formed per unit time during photosynthesis, and secondary - biomass produced by animals (consumers) consuming primary products. Secondary products are formed as a result of the use of energy stored by autotrophs by heterotrophic organisms.
Productivity is usually expressed in units of mass per year on a dry matter basis per unit area or volume, which varies considerably among different plant communities. For example, 1 hectare of pine forest produces 6.5 tons of biomass per year, and a sugar cane plantation produces 34-78 tons. In general, the primary productivity of the world's forests is the highest compared to other formations. A biocenosis is a historically established complex of organisms and is part of a more general natural complex - an ecosystem.
Spatial structure of biocenoses.
The definition of a biocenosis as a system of interacting species that carries out a cycle of biogenic circulation provides for the minimum spatial volume of this level of biosystems. Thus, it is incorrect to talk about “biocenosis of a stump”, “biocenosis of a gopher hole”, etc., since a complex of organisms of this level does not provide the possibility of a complete cycle of circulation. But this approach does not limit the “upper threshold” of the concept of biocenosis: the complete circulation of substances can take place within spatial boundaries of different scales. R. Hesse (R. Hesse, 1925) gave practically the first system of dividing the biosphere into subordinate zones of life. As the largest unit, he identified biocycles: land, sea bodies and sandy waters. They are divided into biochores- large spatial areas of the biocycle, covering a series of homogeneous landscape systems (desert, tundra, etc.). Later, this term was almost completely replaced by the one introduced by L.S. Berg (1913, 1931) concept "landscape zone". Both of these divisions meet the formal criteria of a biocenosis, but are not considered as such. The spatial boundaries of the biocenosis correspond to the concept biotope- a division of a biochore (landscape zone), characterized by a single type of vegetation cover (phytocenosis). In this regard, the most clear approach is manifested in the formulation introduced by V.N. Sukachev’s concept of “biogeocenosis”: “Biogeocenosis is an ecosystem within the boundaries of a phytocenosis” (E.M. Lavrenko, N.V. Dylis, 1968, p. 159). In most cases, the idea of a biocenosis (ecosystem) is associated with precisely this spatial scale.
Species populations within a biocenosis are naturally located not only in area, but also vertically in accordance with the biological characteristics of each species. Thanks to this, the ecosystem always occupies a certain three-dimensional space; Accordingly, interspecific relationships have not only a functional, but also a spatial orientation.
In aquatic ecosystems, large-scale vertical structure is determined primarily by external conditions. In the pelagic zone, the determining factors are gradients of illumination, temperature, concentration of nutrients, etc. At great depths, the factor of hydrostatic pressure operates; in bottom biocenoses, the heterogeneity of soils and the hydrodynamics of near-bottom water layers are added to this. Features of the vertical structure are expressed in the specificity of species composition, changes in dominant species, biomass and production indicators. Thus, in the northwestern part of the Pacific Ocean, a vertical change in dominance in hydromedusa species is clearly visible: in the surface layer (50-300 m) Aglantha digitate, in a layer of 500-1000 m - Crossota brunea, and even deeper - Bottynema bruceu. In freshwater bodies of water, populations of mosquito larvae of the genus Chaoborus, and to the superficial - kind Sikh. Photosynthetic algae are confined to the upper, better illuminated horizons, which forms vertical flows of matter and energy, connecting communities of the euphotic zone with deep-sea biocenoses, the life of which is based on allochthonous (brought from outside) organic matter (A.S. Konstantinov, 1986).
In terrestrial ecosystems, the main factor creating vertical structure is biological in nature and is associated with the division of plant communities by height. This is especially clearly expressed in forest phytocenoses, the vertical structure of which is expressed in the form Tiering. The upper tier is represented by tree species, followed by tiers of shrubs, dwarf shrubs, herbaceous plants and ground moss cover. IN different types In forests this scheme is expressed differently. So, in deciduous forests several tree layers are distinguished, composed of species with different heights trees, as well as the undergrowth layer (shrubs and low-growing trees); herbaceous vegetation can also form 2-3 tiers. The growth of young trees forms groups that change in height as they grow. The underground parts of plants, in turn, form several tiers.
From the perspective of biogeocenology, a layer is a complex material and energy system, on the basis of which a number of elementary vertical components are differentiated (N.V. Dylis et al., 1964).
Tiering is also expressed in herbaceous phytocenoses, determining the vertical differentiation of the distribution of animals and microorganisms in the above-ground part of the community. It has already been noted that the vertical structure of terrestrial ecosystems is closely related to their functional activity: pasture chains are concentrated mainly in the aboveground part of biocenoses, and decomposition chains are concentrated in their underground part.
PRIMARY CONSUMER - an organism, for example a rabbit or deer, that feeds mainly or exclusively on green plants, their fruits or seeds.[...]
These are primary consumers that feed on algae, bacteria and detritus. They reproduce sexually (although crustaceans and rotifers can reproduce in other ways) and therefore reproduce more slowly than phytoplankton. The feeding process of zooplankton occurs through filtration and grazing of phytoplankton; in mesotrophic water bodies, consumption can be comparable to the rate of primary production. Most are 0.5-1mm long, but some may be less than 0.1mm. Zooplankton includes both plant and predatory organisms. In lakes they migrate during daylight hours to deeper waters; the almost transparent outer shell protects them from death (eaten by fish). [...]
Against the background of primary zoning, based mainly on physical factors, secondary zoning is clearly visible - both vertical and horizontal; this secondary zonation is evident in the distribution of communities. The communities of each primary zone, with the exception of the euphotic one, are divided into two fairly clear vertical components - benthic, or bottom (benthos), and pelagic. In the sea, as well as in large lakes, plant producers are represented by microscopic phytoplankton, although large multicellular algae(macrophytes) may be significant in some coastal areas. Primary consumers, therefore, primarily include zooplankton. Medium-sized animals feed on either plankton or detritus formed from plankton, while large animals are mainly predators. There are only a small number of large animals that, like large land animals such as deer, cows and horses, feed exclusively on plant foods.[...]
Primary macroconsumers, or plant-telivores (see Fig. 2.3, IIA and IIB), feed directly on living plants or their parts. There are two types of primary macroconsumers in the pond: zooplankton (animal plankton) and benthos (bottom forms), corresponding to two types of producers. In a grassland ecosystem, herbivores are also divided into two size groups: small - herbivorous insects and other invertebrates, and large - herbivorous rodents and ungulate mammals. Another important type of consumers is represented by detritivores (IIIA and IIIB), which exist due to the “rain” of organic detritus falling from the upper autotrophic layers. Together with herbivores, detritivores serve as food for carnivores. Many, and perhaps even all, detritivores receive most food, digesting microorganisms that have colonized detritus particles. [...]
P - producers C, - primary consumers. D. Soil arthropods - according to Engeliann (1968).[...]
Then the primary consumers are connected - herbivorous animals (T) and, finally, carnivorous consumers (X). They all take specific place in the hierarchy of participants in the biotic cycle and perform their functions of transforming the branches of energy flow that they receive and transferring biomass. But everyone is united, their substances are depersonalized and the general circle is closed by a system of single-cell destructors. They return to the abiotic environment of the biosphere all the elements necessary for new and new turns of the cycle.[...]
The second group is represented by consumers, i.e. consumers (from Latin consumo - to consume) - heterotrophic organisms, mainly animals, eating other organisms. There are primary consumers (animals that eat green plants, herbivores), and secondary consumers (predators, carnivores that eat herbivores). A secondary consumer can serve as a source of food for another predator - a third-order consumer, etc. [...]
A person, eating cow meat, is a secondary consumer at the third trophic level, and eating plants, he is a primary consumer at the second trophic level. Each person requires about 1 million kcal of energy received through food per year for the physiological functioning of the body. Humanity produces about 810 5 kcal (with a population of over 6 billion people), but this energy is distributed extremely unevenly. For example, in the city energy consumption per person reaches 80 million kcal per year, i.e. For all types of activities (transport, household, industry), a person spends 80 times more energy than is necessary for his body.[...]
All producers belong to the first trophic level, all primary consumers, regardless of whether they feed on living or dead producers, belong to the second trophic level, respectively, consumers of the 2nd order belong to the third, etc. As a rule, the number of trophic levels does not exceeds three or four. B. Nebel (1993) confirms this conclusion with the following: the total mass of organisms (their biomass) at each trophic level can be calculated by collecting (or capturing) and then weighing the corresponding samples of plants and animals. Thus, it was established that at each trophic level the biomass is 90-99% less than at the previous one. From this it is not difficult to imagine that the existence of a large number of trophic levels is impossible due to the fact that biomass will very quickly approach zero. Graphically this is represented in the form of a biomass pyramid (Fig. 47).[...]
The amount of detritus produced also increases. Corresponding changes also occur in trophic networks. Detritus becomes the main source of nutrients.[...]
| 3.15 |
In the case of pasture forest food chains, when trees are producers and insects are primary consumers, the level of primary consumers is numerically richer in individuals of the producer level. Thus, pyramids of numbers can be reversed. For example in Fig. 9.7 shows pyramids of numbers for steppe and forest ecosystems temperate zone.[ ...]
Fish pond - good example how secondary production depends on 1) the length of the food chain, 2) primary productivity, and 3) the nature and amount of external energy introduced into the pond system. As shown in table. 3.11, large lakes and seas produce 1 m2 less fish than small productive fertilized ponds with intensive farming, and the point is not only that in large reservoirs primary productivity is lower and food chains are longer, but also that in these In large bodies of water, a person collects only part of the population of consumers, namely the part that is beneficial to him. In addition, the production yield is several times higher when breeding herbivorous species (for example, carp) than when breeding predatory species (perch, etc.); the latter, of course, need a longer food chain. High product yields indicated in table. 3.11. Therefore, when calculating production per unit area in such cases, it would be necessary to include the area of the land from which additional food comes. Many people incorrectly assess the high productivity of reservoirs in Eastern countries by comparing it with the productivity of fish ponds in the United States, which usually does not receive additional food. Naturally, the method of conducting pond farming depends on the population density in the area.[...]
It is argued that in the upper reaches of rivers, communities are shaded by tree canopy and receive little light. Consumers depend mainly on leaf litter and other allochthonous organic matter. The fauna of the river is represented mainly by primary consumers, classified as mechanical destroyers.[...]
Despite the diversity of food chains, they have common patterns: from green plants to primary consumers, from them to secondary consumers, etc., then to detritivores. On last place There are always detritivores, they close the food chain.[...]
Lakes contain fish that can consume large quantities of phytoplankton. They are classified as primary consumers, since they feed on ready-made organic matter and cannot create food on their own. Other animals, mainly insect larvae, but also some fish, feed on zooplankton; they are secondary consumers. Fish use various inhabitants of the reservoir as food (Fig. 2.22).[...]
The biotic communities of each of these zones, except for the euphotic, are divided into benthic and pelagic. In them, the primary consumers include zooplankton; insects in the sea are ecologically replaced by crustaceans. The overwhelming majority of large animals are predators. The sea is characterized by a very important group of animals called sessile (attached). They are not found in freshwater systems. Many of them resemble plants and hence their names, for example, sea lilies. Mutualism and commensalism are widely developed here. All benthic animals in their life cycle pass through the pelagic stage in the form of larvae.[...]
Each link in the food chain is called a trophic level. The first trophic level is occupied by autotrophs, otherwise called primary producers. Organisms of the second trophic level are called primary consumers, the third - secondary consumers, etc. There are usually four or five trophic levels and rarely more than six (Fig. 5.1).[...]
A deer that eats buds and young bark from trees will already be the first consumer of these substances and the energy contained in them, or the primary consumer. Moving from tree to tree, he loses energy, but at the same time receives much more than he expends. Large predator, for example, a wolf, is a secondary consumer, since, by eating a deer, it receives energy, so to speak, second-hand.[...]
[ ...]
HERBIVORE - an organism, such as a rabbit or deer, that feeds primarily on green plants or their fruits and seeds.[...]
TROPHIC LEVEL - the stage of movement of solar energy (as part of food) through the ecosystem. Green plants are on the first trophic level, primary consumers are on the second, secondary consumers are on the third, etc. [...]
The location of each link in the food chain is a trophic level. The first trophic level, as noted earlier, is occupied by autotrophs, or so-called primary producers. Organisms of the second trophic. level are called primary consumers, the third - secondary consumers, etc. [...]
The metabolism of the system is carried out due to solar energy, and the intensity of metabolism and the relative stability of the pond system depend on the intensity of the supply of substances with precipitation and runoff from the drainage basin.[...]
Complex forms of interdependence between plants and animals were also formed on the basis of direct trophic connections. The balance of plant biomass removed by phytophages, which determines the stable relationship between the populations of producers and primary consumers, is largely determined by the adaptations of plants to limit their consumption by animals. Such adaptations often include the formation of hard bark, various kinds of thorns, prickles, etc. Without ensuring complete inaccessibility for phytophages (they develop adaptations of the opposite nature), these formations still reduce the range of possible consumers, and accordingly increase the likelihood of sufficient for effective reproduction of the number and density of populations of the species.[...]
First, multicellular plants (P) develop - higher producers. Together with unicellular organisms, they create organic matter through the process of photosynthesis, using the energy of solar radiation. Subsequently, primary consumers are involved - herbivorous animals (T), and then carnivorous consumers. We examined the biotic cycle of land. This fully applies to the biotic cycle of aquatic ecosystems, for example, the ocean (Fig. 12.17).[...]
At the ecosystem “step” there is a shift in the relationship between the links of the ecological (in this case, energy) pyramid. For example, the overall energy balance of two similar (say, meadow) ecosystems, in one of which the dominant primary consumers are large ungulates, and in the other small invertebrate phytophages (after large herbivorous mammals, most of the rodents and even a significant proportion of arthropods) may be similar.[...]
Due to a certain sequence of food relationships, individual trophic levels of transfer of substances and energy in the ecosystem associated with nutrition are distinguished certain group organisms. Thus, the first trophic level in all ecosystems is formed by producers - plants; the second - primary consumers - phytophages, the third - secondary consumers - zoophages, etc. As already noted, many animals feed not at one, but at several trophic levels (an example is the diet of the gray rat, brown bear and human).[...]
Analysis of trophic relationships between fish larvae and food invertebrates allows one to imagine the complexity of these relationships. Fish larvae at different stages of development consume food items of different energy significance and thereby determine their distribution among trophic levels from consumers of the second to consumers of the fourth and fifth orders, and at the same stage of development they can simultaneously occupy different trophic levels. Pike perch larvae, for example, move through all links of the trophic chain from primary consumers to n-order predators, occupying two, sometimes three, trophic levels at once. The transition of larvae at one or another stage of development to feeding on organisms of lower energy levels, reducing the length of the food chain, can be considered as an adaptation leading to a balanced supply of energy through food during the period of their larval development. This is especially important in the years with unfavorable condition food supply in the reservoir. Of the three trophic complexes of larvae in reservoirs - coastal-phytophilic, coastal-pelagic and pelagic) - the most significant with a large number of species is coastal-phytophilic. The larvae of this complex live in protected shallow waters, forming common schools, and do not travel long distances throughout the entire larval development period, since different depths, islands, flooded shrubs, and different densities of coastal aquatic vegetation create conditions for the ecological isolation of individual areas of the littoral zone. Larvae of perch and pike perch also come here from open coastal areas, which, starting from stages D1 and Dg, form significant accumulations at night. Based on this, the protected coastal area should be considered not only a breeding ground for phytophilic fish, but also a feeding area for the larvae of the main commercial species, requiring special treatment and protection.[...]
In the case of acidification of a watercourse, the changes occurring in its ecosystem largely have a different direction. Although biological diversity ecosystem decreases, the general structure of the river continuum is preserved. At the same time, the processes of destruction of organic matter by bacteria are suppressed and the biomass of primary consumers is significantly reduced, which often leads to an increase in biomass and complication of spatial structure periphyton. The role of secondary consumers, among which predatory larvae of aquatic insects dominate, is sharply increasing. Many of them have a long life cycle and can be classified as r-strategists. In general, acidification leads to the predominance of pasture food chains, a decrease in the rate of destruction of organic matter and an increase in the P/R and K2 ratio of the ecosystem and, therefore, causes a shift in the functioning of the ecological system of the watercourse to an equilibrium state. [...]
The distance of an organism in a food chain from its producers is called its food or trophic level. Organisms that receive energy from the Sun through the same number of steps in the food chain are considered to belong to the same trophic level. So. green plants occupy the first trophic level (level of producers), herbivores occupy the second (level of primary consumers), primary predators eating herbivores occupy the third (level of secondary consumers), and secondary predators occupy the fourth (level of tertiary consumers). An organism of a given species can occupy one or more trophic levels, depending on what energy sources it uses.[...]
There are calculations showing that 1 hectare of some forest receives an average of 2.1 109 kJ of solar energy annually. However, if everything stored in a year plant matter burn, then as a result we get only 1.1 106 kJ, which is less than 0.5% of the energy received. This means that the actual productivity of photosynthetics (green plants), or primary productivity, does not exceed 0.5%. Secondary productivity is extremely low: during the transfer from each previous link of the trophic chain to the next, 90-99% of energy is lost. If, for example, on 1 m2 of soil surface, plants create an amount of substance equivalent to approximately 84 kJ per day, then the production of primary consumers will be 8.4 kJ, and that of secondary consumers will not exceed 0.8 kJ. There are specific calculations that to produce 1 kg of beef, for example, you need 70-90 kg of fresh grass.[...]
Secondary production is defined as the rate of formation of new biomass by heterotrophic organisms. Unlike plants, bacteria, fungi and animals are not able to synthesize the complex, energy-rich compounds they need from simple molecules. They grow and obtain energy by consuming plant matter either directly or indirectly by eating other heterotrophs. Plants, the primary producers, constitute the first trophic level in the community. The second contains primary consumers; on the third - secondary consumers (predators), etc. [...]
The concept of energy flow not only allows ecosystems to be compared among themselves, but also provides a means for assessing the relative roles of populations within them. In table Figure 14 shows estimates of density, biomass and energy flow rate for 6 populations that differ in the size of individuals and habitat. The numbers in this series vary by 17 orders of magnitude (1017 times), biomass by about 5 orders of magnitude (10° times), and energy flow by only about 5 times. This comparative uniformity of energy flows indicates that all 6 populations belong to the same trophic level in their communities (primary consumers), although this cannot be assumed either by numbers or biomass. It is possible to formulate a certain “ecological rule”: data on numbers lead to an exaggeration of the importance of small organisms, and data on biomass lead to an exaggeration of the role of large organisms; Consequently, these criteria are unsuitable for comparing the functional role of populations that differ greatly in the ratio of metabolic intensity to the size of individuals, although, as a rule, biomass is still a more reliable criterion than abundance. At the same time, energy flow (i.e. P-Y) serves as a more suitable indicator for comparing any component with another and all components of the ecosystem with each other. [...]
In Fig. Figure 4.11 presents a graphical model of the “lower” part of the water cycle, showing how biotic communities adapt to changing conditions in the so-called river continuum (gradient from small to large rivers; see Wannoe et al., 1980). In the upper reaches, rivers are small and often completely shaded, so that the aquatic community receives little light. Consumers depend mainly on leaf and other organic detritus brought from the drainage basin. The detritus is dominated by large organic particles, such as leaf fragments, and the fauna is represented mainly by aquatic insects and other primary consumers, which ecologists who study river ecosystems classify as mechanical destroyers. The upper reaches ecosystem is heterotrophic; the P/I ratio is much less than one.[...]
Precipitations formed during atomic explosions, differ from radioactive waste in that they are generated by an explosion radioactive isotopes combine with iron, silicon, dust and anything else that happens to be nearby, resulting in relatively insoluble particles. The sizes of these particles often resemble tiny marbles under a microscope different colors, vary from several hundred microns to almost colloidal sizes. The smallest of them stick tightly to plant leaves, causing radioactive damage to leaf tissue; If such leaves are eaten by any herbivorous animal, the radioactive particles dissolve in its digestive juices. Thus, this type of sediment can directly enter the food chain at the trophic level of herbivores, or primary consumers.[...]
The transfer of food energy from its source - plants - through a number of organisms, occurring by eating some organisms by others, is called a food chain. With each successive transfer, most (80-90%) of the potential energy is lost, turning into heat. This limits the possible number of steps, or “links,” in the chain, usually to four or five. The shorter the food chain (or the closer the organism is to the beginning), the more quantity available energy. Food chains can be divided into two main types: grazing chains, which start with a green plant and go further to grazing, herbivorous (that is, organisms that eat green plants) and carnivores (organisms that eat animals), and detrital chains , which start from dead organic matter, go to microorganisms that feed on it, and then detritivores and their predators. Food chains are not isolated from one another, but are closely intertwined. Their network is often called a food web. In a complex natural community, organisms that obtain their food from plants through the same number of stages are considered to belong to the same trophic level. Thus, green plants occupy the first trophic level (the level of producers), herbivores occupy the second (the level of primary consumers), predators that eat herbivores occupy the third (the level of secondary consumers), and secondary predators occupy the fourth level (the level of tertiary consumers). It must be emphasized that this trophic classification divides into groups not the species themselves, but their types of life activity; a population of one species can occupy one or more trophic levels, depending on what energy sources it uses. The flow of energy through a trophic level is equal to the total assimilation (L) at that level, and the total assimilation in turn is equal to biomass production (P) plus respiration (/?).
Natural community is a collection of plants, animals, microorganisms adapted to living conditions in a certain territory, influencing each other and the environment. The circulation of substances is carried out and maintained in it.
We can distinguish natural communities of different scales, for example, continents, oceans, forests, meadows, taiga, steppes, deserts, ponds, and lakes. Smaller natural communities are part of larger ones. Man creates artificial communities, such as fields, gardens, aquariums, and spaceships.
Each natural community is characterized by various relationships - food, habitat, etc.
The main form of connections between organisms in a natural community is food connections. The initial, main link in any natural community, creating a supply of energy in it, are plants. Only plants, using solar energy, can create organic substances from minerals and carbon dioxide found in soil or water. Herbivorous invertebrates and vertebrates feed on plants. They, in turn, feed on carnivores - predators. So in natural communities Ah, food connections arise, a food chain: plants - herbivores - carnivores (predators - website note). Sometimes this chain becomes more complicated: the first predators can feed on others, and they, in turn, feed on others. For example, caterpillars eat plants, and caterpillars are eaten by predatory insects, which, in turn, serve as food for insectivorous birds, which feed on birds of prey.
Finally, the natural community also includes various organisms that feed on waste: dead plants or their parts (branches, leaves), as well as the corpses of dead animals or their excrement. They can be some animals - gravedigger beetles, earthworms. But the main role in the process of decomposition of organic substances is played by molds and bacteria. It is they who bring the decomposition of organic substances to mineral ones, which can again be used by plants. In total, the circulation of substances occurs in natural communities.
Changes in natural communities can occur under the influence of biotic, abiotic factors and man. The change of communities under the influence of the vital activity of organisms lasts hundreds and thousands of years. Plants play the main role in these processes. An example of a change in community under the influence of the vital activity of organisms is the process of overgrowing of water bodies. Most lakes gradually become shallow and decrease in size. Over time, the remains of aquatic and coastal plants and animals, as well as soil particles washed away from the slopes, accumulate at the bottom of the reservoir. Gradually, a thick layer of silt forms at the bottom. As the lake becomes shallower, its shores become overgrown with reeds and reeds, then with sedges. Organic residues accumulate even faster and form peaty deposits. Many plants and animals are replaced by species whose representatives are more adapted to life in new conditions. Over time, a different community forms in place of the lake - a swamp. But the change of communities does not stop there. Shrubs and trees that are unpretentious to the soil may appear in the swamp, and ultimately the swamp may be replaced by a forest.
Thus, a change in communities occurs because, as a result of changes in the species composition of communities of plants, animals, fungi, and microorganisms, the habitat gradually changes and conditions favorable for the habitat of other species are created.
Change of communities under the influence of human activity. If the change of communities under the influence of the life activity of the organisms themselves is a gradual and long process, covering a period of tens, hundreds and even thousands of years, then the change of communities caused by human activity occurs quickly, over several years.
So if they get into water bodies wastewater, fertilizers from fields, household waste, then oxygen dissolved in water is spent on their oxidation. As a result, it decreases species diversity, various aquatic plants(salvinia floating, amphibian knotweed) are replaced by duckweed, algae are replaced by blue-green algae, and a “water bloom” occurs. Valuable commercial fish are being replaced by low-value ones, shellfish and many species of insects are disappearing. A rich aquatic ecosystem turns into an ecosystem of a decaying reservoir.
If the human impact that caused a change in communities stops, then, as a rule, natural process self-healing. Plants continue to play a leading role in it. Thus, after the cessation of grazing, tall grasses appear on pastures, typical forest plants appear in the forest, and the lake is cleared of dominance unicellular algae and blue-green, fish, shellfish, and crustaceans reappear in it.
If the species and trophic structure are simplified so much that the process of self-healing can no longer occur, then man is again forced to intervene in this natural community, but now for good purposes: grass is sown in pastures, new trees are planted in the forest, water bodies are cleaned and juveniles are released there fish
The community is capable of self-healing only with partial violations. Therefore the influence economic activity a person should not exceed the threshold after which self-regulation processes cannot take place.
Change of communities under the influence of abiotic factors. For the development and change of communities big influence have had and are having drastic climate changes, fluctuations in solar activity, mountain-building processes, and volcanic eruptions. These factors are called abiotic - factors of inanimate nature. They disrupt the stability of the habitat of living organisms.
Unfortunately, the ability of natural communities to self-heal is not unlimited: if the external impact exceeds a certain limit, the ecosystem will collapse, and the territory where it was located will itself become a source of ecological imbalance. Even if restoration of the ecosystem is possible, it will cost much more than timely measures to preserve it.
The ability of natural communities to self-regulate is achieved thanks to the natural diversity of living beings that have adapted to each other as a result of long-term joint evolution. When the number of one of the species decreases, its partially vacated ecological niche is temporarily occupied by an ecologically close species of the same community, preventing the development of certain destabilizing processes.
The situation is completely different if a species has dropped out of the community. In this case, the system of “mutual insurance” of ecologically similar species is disrupted, and part of the resources they consume is not used, that is, an ecological imbalance arises. As the natural species composition of the community further depletes, conditions are created for excessive accumulation of organic matter, outbreaks of insect numbers, the introduction of alien species, etc.
Usually, the so-called rare species are the first to drop out of the natural community, since their rarity is due to the fact that they are the most demanding of living conditions and sensitive to their changes. In a stable community, rare species should be present among all groups of living organisms. Therefore, the presence of various rare species serves as an indicator of the preservation of natural biodiversity as a whole and, thus, the ecological usefulness of the natural community.
As is known, the biotic cycle of substances is provided by species occupying different trophic levels:
Producers that produce organic matter from inorganic matter are, first of all, green plants;
First-order consumers who consume phytomass are herbivores, both vertebrates and invertebrates;
consumers of the second and higher orders that feed on other consumers, for example, predatory insects and spiders, predatory fish, amphibians and reptiles, insectivores and birds of prey and mammals;
decomposers that decompose dead organic matter - this process is provided primarily by a variety of microorganisms, fungi, as well as rain annelids and some other soil invertebrates.
The study of full-fledged natural communities shows that rare species are present in them at all trophic levels. The most significant thing is the presence in the community of viable populations of consumers of higher orders: they are at the top of the trophic pyramid and, thus, their condition is most dependent on the state of the trophic pyramid as a whole.
An important characteristic of any species is the size of the territory, the minimum necessary for the existence of its viable population. For conservation purposes, several size classes of territories necessary for the existence of a viable population of a species can be distinguished.
In the size range from an individual plant association to the biogeocenosis inclusive, it is advisable to identify areas of the following size classes:
1 - microbiotopes, individual areas of plant associations, necessary, for example, for fungi, many plants and invertebrate animals;
2 - a combination of certain microbiotopes and plant associations, necessary, for example, for some plants, amphibians, reptiles, dragonflies, and many butterflies;
3 - biogeocenosis as a whole, necessary for small birds and mammals, the largest and most mobile insects, and among plants - for forest-forming tree species.
For the existence of populations of medium and large birds and mammals, territories are usually required that significantly exceed the area occupied by one biogeocenosis. For such territories we distinguish the following size classes:
4 - a group of similar biocenoses or their combinations;
5 - natural massifs consisting of various biotopes;
6 - natural massifs and their complexes at the regional level.
Under conditions of transformation natural areas The most vulnerable species are those that require territories of higher (IV-VI) size classes, especially since most of these species belong to consumers of higher orders.
Thus, an indicator of the qualitative usefulness of an ecosystem is the presence of all trophic levels, and within each trophic level there are species whose populations occupy significantly different ecological niches and territories of different size classes.
The condition for preserving the environment-forming functions of natural communities is inter-ecosystem connections that make possible the natural restoration of disturbed areas due to the migration of living organisms from neighboring areas that are better preserved. Then they protect each other in the same way as populations of similar species within the same community. Being functionally interconnected within the region, natural communities form a natural framework on which regional environmental stability rests. Therefore, preserving a system of interconnected natural communities capable of self-healing is the only real way maintaining human habitat.
Within an ecosystem, energy-containing organic substances are created by autotrophic organisms and serve as food (a source of matter and energy) for heterotrophs. A typical example: an animal eats plants. This animal, in turn, can be eaten by another animal, and in this way energy can be transferred through a number of organisms - each subsequent one feeds on the previous one, which supplies it with raw materials and energy. This sequence is called food chain, and each of its links is trophic level(Greek trophos - food). The first trophic level is occupied by autotrophs, or so-called primary producers. Organisms of the second trophic level are called primary consumers, third - secondary consumers etc. There are usually four or five trophic levels and rarely more than six - for reasons described in Sect. 12.3.7 and obvious from Fig. 12.12. Below is a description of each link in the food chain, and their sequence is shown in Fig. 12.4.
Primary producers
The primary producers are autotrophic organisms, mainly green plants. Some prokaryotes, namely blue-green algae and a few species of bacteria, also photosynthesize, but their contribution is relatively small. Photosynthetics convert solar energy (light energy) into chemical energy contained in the organic molecules that make up their tissues. Chemosynthetic bacteria, which extract energy from inorganic compounds, also make a small contribution to the production of organic matter.
IN aquatic ecosystems the main producers are algae - often small unicellular organisms that make up the phytoplankton of the surface layers of oceans and lakes. On land, most of the primary production is supplied by more highly organized forms related to gymnosperms and angiosperms. They form forests and meadows.
Primary consumers
Primary consumers feed on primary producers, i.e. herbivores. On land, typical herbivores include many insects, reptiles, birds and mammals. Most important groups Herbivorous mammals are rodents and ungulates. The latter include grazing animals such as horses, sheep, and cattle, which are adapted to running on their toes.
In aquatic ecosystems (freshwater and marine), herbivorous forms are usually represented by mollusks and small crustaceans. Most of these organisms are cladocera and copepods, crab larvae, barnacles And bivalves(for example, mussels and oysters) - feed by filtering the smallest primary producers from the water, as described in section. 10.2.2. Together with protozoa, many of them form the bulk of the zooplankton that feed on phytoplankton. Life in oceans and lakes depends almost entirely on plankton, since almost all food chains begin with it.
Consumers of the second third order
In typical carnivore food chains, carnivores are larger at each trophic level:
Plant material (eg nectar) fly → spider → shrew owl
Rosebush sap → aphid → ladybug→ spider → insectivorous bird → bird of prey
Decomposers and detritivores (detritus food chains)
There are two main types of food chains - grazing and detrital. We gave examples above pasture chains, in which the first trophic level is occupied by green plants, the second by grazing animals (the term "grazing" is used in a broad sense and includes all organisms that feed on plants), and the third by carnivores. The bodies of dead plants and animals still contain energy and " construction material", as well as intravital excretions, such as urine and feces. These organic materials are decomposed by microorganisms, namely fungi and bacteria, living as saprophytes on organic debris. Such organisms are called decomposers. They secrete digestive enzymes into dead bodies or waste products and absorb the products of their digestion. The rate of decomposition may vary. Organic matter from urine, feces and animal carcasses is consumed within weeks, while fallen trees and branches can take many years to decompose. A very significant role in the decomposition of wood (and other plant debris) is played by fungi, which secrete the enzyme cellulase, which softens the wood, and this allows small animals to penetrate and absorb the softened material.
Pieces of partially decomposed material are called detritus, and many small animals ( detritivores) feed on it, accelerating the decomposition process. Since both true decomposers (fungi and bacteria) and detritivores (animals) are involved in this process, both are sometimes called decomposers, although in reality this term refers only to saprophytic organisms.
Larger organisms can, in turn, feed on detritivores, and then a different type of food chain is created - a chain starting with detritus:
Detritus → detritivore → predator
Some detritivores of forest and coastal communities are shown in Fig. 12.5.
Here are two typical detrital food chains in our forests:
Leaf litter → Earthworm → Lumbricus sp. → Blackbird → Sparrowhawk Turdus merula Accipiter nisus Dead animal → Carrion fly larvae → Calliphora vomitoria, etc. → Common frog → Common grass snake Rana temporaria Natrix natrix
Some typical terrestrial detritivores are earthworms, woodlice, bipeds and smaller ones (
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