Target: expand knowledge about biotic factors environment.

Equipment: herbarium plants, stuffed chordates (fish, amphibians, reptiles, birds, mammals), insect collections, wet preparations of animals, illustrations various plants and animals.

Work progress:

1. Use the equipment and make two power circuits. Remember that the chain always starts with a producer and ends with a reducer.

Plants → insects→lizard → bacteria

Plants → grasshopper→ frog → bacteria

Remember your observations in nature and make two food chains. Label producers, consumers (1st and 2nd orders), decomposers.

Violet → Springtails→predatory mites→predatory centipedes→ bacteria

Producer - consumer1 - consumer2 - consumer2 - decomposer

Cabbage→ slug→ frog →bacteria

Producer – consumer1 - consumer2 - decomposer

What is a food chain and what underlies it? What determines the stability of a biocenosis? State your conclusion.

Conclusion:

Food (trophic) chain- a series of species of plants, animals, fungi and microorganisms that are connected to each other by the relationship: food - consumer (a sequence of organisms in which a gradual transfer of matter and energy occurs from source to consumer). Organisms of the next 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, it is lost most(up to 80-90%) potential energy dissipated as heat. For this reason, the number of links (types) in the food chain is limited and usually does not exceed 4-5. The stability of a biocenosis is determined by its diversity species composition. Producers- organisms capable of synthesizing organic substances from inorganic ones, that is, all autotrophs. Consumers- heterotrophs, organisms that consume ready-made organic substances created by autotrophs (producers). Unlike decomposers

Consumers are not able to decompose organic substances into inorganic ones. Decomposers- microorganisms (bacteria and fungi) that destroy dead remains of living beings, turning them into inorganic and simple organic compounds.

3. Name the organisms that should be in the missing place in the following food chains.

1) Spider, fox

2) tree-eater-caterpillar, snake-hawk

3) caterpillar

4. From the proposed list of living organisms, create a trophic network:

grass, berry bush, fly, tit, frog, snake, hare, wolf, rotting bacteria, mosquito, grasshopper. Indicate the amount of energy that moves from one level to another.

1. Grass (100%) - grasshopper (10%) - frog (1%) - snake (0.1%) - rotting bacteria (0.01%).

2. Shrub (100%) - hare (10%) - wolf (1%) - rotting bacteria (0.1%).

3. Grass (100%) - fly (10%) - tit (1%) - wolf (0.1%) - rotting bacteria (0.01%).

4. Grass (100%) - mosquito (10%) - frog (1%) - snake (0.1%) - rotting bacteria (0.01%).

5. Knowing the rule of energy transfer from one trophic level on the other (about 10%), build a pyramid of biomass for the third food chain (task 1). Plant biomass is 40 tons.

Grass (40 tons) -- grasshopper (4 tons) -- sparrow (0.4 tons) -- fox (0.04).

6. Conclusion: what the rules reflect ecological pyramids?

The rule of ecological pyramids very conditionally conveys the pattern of energy transfer from one nutrition level to the next, in food chain. These graphic models were first developed by Charles Elton in 1927. According to this pattern, the total mass of plants should be an order of magnitude greater than that of herbivorous animals, and the total mass of herbivorous animals should be an order of magnitude greater than that of first-level predators, etc. to the very end of the food chain.

Laboratory work № 1

In nature, any species, population and even an 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, representing a stable system connected by numerous internal connections, with relatively permanent 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 people living together and interacting with each other and with inanimate nature, populations different types under 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 persist and function 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. Ecosystem sustainability is ensured by direct and feedback between its components, the internal circulation 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 characteristic features 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 - mirror image aboveground: the roots of trees go deepest; the underground parts of mosses are located near the surface of the soil.

By method of receipt and use nutrients all organisms are divided into autotrophs and heterotrophs. In nature there is a continuous cycle of nutrients necessary for life. Chemicals are extracted by autotrophs from the environment and return to it again through heterotrophs. This process takes very complex shapes. 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 in 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 is consistently decreasing, the number of victims more in number 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 )

Interconnected views, sequentially extracting 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 III 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. Detritus chains are also characteristic of deep ocean ecosystems, whose inhabitants feed on dead organisms that have sunk down from upper layers water.

The relationships between species in ecological systems that have developed during the process of evolution, in which many components feed 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 obtain food through equal number links of these chains are located 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 it is always traceable main trend- reduction 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 . i.e. each subsequent nutritional 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 in at the moment and does not reflect the productivity of each trophic level (i.e., its ability to produce biomass over a 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 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. widely adapted to different environments habitat (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 defined 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 biocenoses- the total total productivity of photosynthesis, which is the result of the activity of autotrophs - green plants, for example, pine forest 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, possessing all necessary conditions to maintain its stability for a long time in 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 produce offspring) 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 in this type uniformly, 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. Characteristic of many species high mortality rate in the early stages of ontogenesis. In such species, the survival curve is characterized by a sharp drop in the region 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

The sex ratio has direct relation to population reproduction and its sustainability.

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

- Primary sex ratio determined genetic mechanisms- 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 may 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, different 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 more low 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 homogeneous environment and only in species that do not show any tendency to form groups (for example, the flour beetle).

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 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 heterosexual animals, 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 total mass received by a consumer of the 2nd order is equal to 10 kg, then what was the total mass of producers that became a 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

The main condition for the existence of an ecosystem is the maintenance of the circulation of substances and the transformation of energy. It is provided thanks to trophic (food) connections between species belonging to different functional groups. It is on the basis of these connections that organic substances synthesized by producers from mineral substances with absorption solar energy, are transmitted to consumers and undergo chemical transformations. As a result of the life activity of predominantly decomposers, the atoms of the main biogenic chemical elements pass from organic substances to inorganic ones (CO 2, NH 3, H 2 S, H 2 O). Then inorganic substances used by producers to create new organic substances from them. And they are again drawn into the cycle with the help of producers. If these substances were not reused, life on Earth would be impossible. After all, the reserves of substances absorbed by producers in nature are not unlimited. To carry out a full cycle of substances in the ecosystem, all three must be present. functional groups organisms. And between them there must be constant interaction in the form of trophic connections with the formation of trophic (food) chains, or food chains.

A food chain (food chain) is a sequence of organisms in which a gradual transfer of matter and energy occurs from the source (previous link) to the consumer (subsequent link).

In this case, one organism can eat another, feeding on its dead remains or waste products. Depending on the type of initial source of matter and energy, food chains are divided into two types: pasture (grazing chains) and detrital (decomposition chains).

Grazing chains (grazing chains)- food chains that begin with producers and include consumers of different orders. IN general view The pasture chain can be shown with the following diagram:

Producers -> First order consumers -> Second order consumers -> Third order consumers

For example: 1) food chain of a meadow: red clover - butterfly - frog - snake; 2) food chain of the reservoir: chlamydomonas - daphnia - gudgeon - pike perch. The arrows in the diagram show the direction of transfer of matter and energy in the power circuit.

Each organism in the food chain belongs to a specific trophic level.

Trophic level is a set of organisms that, depending on their method of nutrition and type of food, constitute a certain link in the food chain.

Trophic levels are usually numbered. The first trophic level consists of autotrophic organisms - plants (producers), at the second trophic level there are herbivorous animals (consumers of the 1st order), at the third and subsequent levels - carnivores (consumers of the 2nd, 3rd, etc. orders).

In nature, almost all organisms feed not on one, but on several types of food. Therefore, any organism can be at different trophic levels in the same food chain depending on the nature of the food. For example, a hawk, eating mice, occupies the third trophic level, and eating snakes, the fourth. In addition, the same organism can be a link in different food chains, connecting them with each other. Thus, a hawk can eat a lizard, a hare or a snake, which are part of different food chains.

In nature, pasture chains do not occur in their pure form. They are interconnected by common nutritional links and form food web, or power network. Its presence in the ecosystem contributes to the survival of organisms in the absence of certain type feed due to the ability to use other feed. And the wider species diversity individuals in an ecosystem, the more food chains there are in the food web and the more stable the ecosystem. The loss of one link from the food chain will not disrupt the entire ecosystem, since food sources from other food chains can be used.

Detrital chains (decomposition chains)- food chains that begin with detritus, include detritivores and decomposers, and end with minerals. In detrital chains, the matter and energy of detritus are transferred between detritivores and decomposers through the products of their vital activity.

For example: dead bird - fly larvae - mold fungi - bacteria - minerals. If detritus does not require mechanical destruction, then it immediately turns into humus with subsequent mineralization.

Thanks to detrital chains, the cycle of substances in nature is closed. Dead organic substances in detrital chains are converted into minerals, which enter the environment and are absorbed from it by plants (producers).

Pasture chains are predominantly located in the above-ground, and decomposition chains - in the underground layers of ecosystems. The relationship between pasture chains and detrital chains occurs through detritus entering the soil. Detrital chains are connected with pasture chains through mineral substances extracted from the soil by producers. Thanks to the interconnection of pasture and detritus chains, a complex food network is formed in the ecosystem, ensuring the constancy of the processes of transformation of matter and energy.

Ecological pyramids

The process of converting matter and energy into pasture chains has certain patterns. At each trophic level of the pasture chain, not all of the consumed biomass goes to the formation of consumer biomass this level. A significant part of it is spent on the vital processes of organisms: movement, reproduction, maintaining body temperature, etc. In addition, part of the feed is not digested and ends up in the body in the form of waste products. environment. In other words, most of the matter and the energy it contains is lost during the transition from one trophic level to another. The percentage of digestibility varies greatly and depends on the composition of the food and biological features organisms. Numerous studies have shown that at each trophic level of the food chain, on average, about 90% of energy is lost, and only 10% passes to the next level. American environmentalist R. Lindeman in 1942 formulated this pattern as 10% rule. Using this rule, it is possible to calculate the amount of energy at any trophic level of the food chain, if its indicator is known at one of them. With some degree of assumption, this rule is also used to determine the transition of biomass between trophic levels.

If at each trophic level of a food chain we determine the number of individuals, or their biomass, or the amount of energy contained in it, then a decrease in these quantities will become obvious as we move towards the end of the food chain. This pattern was first established by the English ecologist C. Elton in 1927. He called it rule of the ecological pyramid and suggested expressing it graphically. If any of the above characteristics of trophic levels are depicted in the form of rectangles with the same scale and placed on top of each other, then the result will be ecological pyramid.

There are three types of ecological pyramids. Pyramid of numbers reflects the number of individuals in each link of the food chain. However, in the ecosystem the second trophic level ( consumers of the first order) may be numerically richer than the first trophic level ( producers). In this case, the result is an inverted pyramid of numbers. This is explained by the participation in such pyramids of individuals that are not equal in size. An example is a pyramid of numbers consisting of a deciduous tree, leaf-eating insects, small insectivores and large birds of prey. Biomass pyramid reflects the amount of organic matter accumulated at each trophic level of the food chain. Biomass pyramid terrestrial ecosystems correct. And in the pyramid of biomass for aquatic ecosystems, the biomass of the second trophic level, as a rule, is greater than the biomass of the first when it is determined at a particular moment. But since aquatic producers (phytoplankton) have high speed formation of products, then ultimately their biomass during the season will still be greater than the biomass of consumers of the first order. And this means that in aquatic ecosystems The rule of the ecological pyramid is also observed. Pyramid of Energy reflects patterns of energy expenditure at different trophic levels.

Thus, the supply of matter and energy accumulated by plants in pasture food chains is quickly consumed (eaten away), so these chains cannot be long. They usually include three to five trophic levels.

In an ecosystem, producers, consumers and decomposers are connected by trophic links and form food chains: grazing and detritus. In grazing chains, the 10% rule and the ecological pyramid rule apply. Three types of ecological pyramids can be built: numbers, biomass and energy.

Food chain structure

food chain represents a connected linear structure from links, each of which is connected with neighboring links by the “food-consumer” relationship. Groups of organisms, for example, specific biological species, act as links in the chain. A connection between two links is established if one group of organisms acts as food for another group. The first link of the chain has no predecessor, that is, organisms from this group do not use other organisms as food, being producers. Most often, plants, mushrooms, and algae are found in this place. Organisms in the last link in the chain do not act as food for other organisms.

Each organism has a certain amount of energy, that is, we can say that each link in the chain has its own potential energy. During the feeding process, the potential energy of food is transferred to its consumer. When transferring potential energy from link to link, up to 80-90% is lost in the form of heat. This fact limits the length of the food chain, which in nature usually does not exceed 4-5 links. The longer the trophic chain, the lower the production of its last link in relation to the production of the initial one.

Trophic network

Usually, for each link in the chain, you can specify not one, but several other links connected to it by the “food-consumer” relationship. So, not only cows, but also other animals eat grass, and cows are food not only for humans. Establishing such connections turns the food chain into a more complex structure - food web.

Trophic level

A trophic level is a set of organisms that, depending on their method of nutrition and type of food, constitute a certain link in the food chain.

In some cases, in a trophic network, it is possible to group individual links into levels in such a way that links at one level act only as food for the next level. This grouping is called a trophic level.

Types of food chains

There are 2 main types of trophic chains - pasture And detrital.

In the pasture trophic chain (grazing chain), the basis is made up of autotrophic organisms, then there are herbivorous animals consuming them (consumers) (for example, zooplankton feeding on phytoplankton), then 1st order predators (for example, fish consuming zooplankton), 2nd order predators order (for example, pike feeding on other fish). The trophic chains are especially long in the ocean, where many species (for example, tuna) occupy the place of fourth-order consumers.

In detrital trophic chains (decomposition chains), most common in forests, most plant production is not consumed directly by herbivores, but dies, then undergoes decomposition by saprotrophic organisms and mineralization. Thus, detrital trophic chains start from detritus (organic remains), go to microorganisms that feed on it, and then to detritivores and their consumers - predators. In aquatic ecosystems (especially in eutrophic reservoirs and at great depths of the ocean), part of the production of plants and animals also enters detrital trophic chains.

Terrestrial detrital food chains are more energy intensive, since most of the organic mass created by autotrophic organisms remains unclaimed and dies off, forming detritus. On a planetary scale, grazing chains account for about 10% of the energy and substances stored by autotrophs, while 90% is included in the cycle through decomposition chains.

See also

Literature

• Trophic chain / Biological encyclopedic dictionary / chapter. ed. M. S. Gilyarov. - M.: Soviet Encyclopedia, 1986. - P. 648-649.

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See what “Food chain” is in other dictionaries:

- (food chain, trophic chain), relationships between organisms in which groups of individuals (bacteria, fungi, plants, animals) are connected to each other by relationships: food consumer. The food chain usually includes from 2 to 5 links: photos and... ... Modern encyclopedia

- (food chain, trophic chain), a series of organisms (plants, animals, microorganisms), in which each previous link serves as food for the next. Connected to each other by relationships: food consumer. The food chain usually includes from 2 to 5... ... Big Encyclopedic Dictionary

FOOD CHAIN, a system of energy transfer from organism to organism, in which each previous organism is destroyed by the next. IN simplest form energy transfer begins with plants (PRIMARY PRODUCERS). The next link in the chain is... ... Scientific and technical encyclopedic dictionary

See Trophic chain. Ecological encyclopedic dictionary. Chisinau: Main editorial office of Moldavian Soviet encyclopedia. I.I. Dedu. 1989 ... Ecological dictionary

food chain- — EN food chain A sequence of organisms on successive trophic levels within a community, through which energy is transferred by feeding; energy enters the food chain during fixation… Technical Translator's Guide

- (food chain, trophic chain), a series of organisms (plants, animals, microorganisms), in which each previous link serves as food for the next. Connected to each other by relationships: food consumer. The food chain usually includes from 2 to... ... Encyclopedic Dictionary

food chain- mitybos grandinė statusas T sritis ekologija ir aplinkotyra apibrėžtis Augalų, gyvūnų ir mikroorganizmų mitybos ryšiai, dėl kurių pirminė augalų energija maisto pavidalu perduodama vartotojams ir skaidytojams. Vienam organizmui pasimaitinus kitu… Ekologijos terminų aiškinamasis žodynas

- (food chain, trophic chain), a number of organisms (plants, animals, microorganisms), in which each previous link serves as food for the next one. Connected to each other by relationships: food consumer. P. c. usually includes from 2 to 5 links: photo and... ... Natural science. Encyclopedic Dictionary

- (trophic chain, food chain), the relationship of organisms through food-consumer relationships (some serve as food for others). In this case, a transformation of matter and energy occurs from producers (primary producers) through consumers... ... Biological encyclopedic dictionary

See Power Circuit... Large medical dictionary

Books

• The omnivore's dilemma. A shocking study of the modern diet, Pollan Michael. Have you ever thought about how food gets to our table? Did you buy your groceries at the supermarket or farmers market? Or maybe you grew your own tomatoes or brought a goose with...

Energy transfer in an ecosystem occurs through the so-called food chains. In turn, a food chain is the transfer of energy from its original source (usually autotrophs) through a number of organisms, by eating some by others. Food chains are divided into two types:

Scots pine => Aphids => Ladybugs=> Spiders => Insectivores

birds => Birds of prey.

Grass => Herbivorous mammals => Fleas => Flagellates.

2) Detrital food chain. It originates from dead organic matter (the so-called detritus), which is either consumed by small, mainly invertebrate animals, or decomposed by bacteria or fungi. Organisms that consume dead organic matter are called detritivores, decomposing it - destructors.

Grassland and detrital food chains usually exist together in ecosystems, but one type of food chain almost always dominates the other. In some specific environments (for example, underground), where the vital activity of green plants is impossible due to the lack of light, only detrital food chains exist.

In ecosystems, food chains are not isolated from each other, but are closely intertwined. They constitute the so-called food webs. This happens because each producer has not one, but several consumers, which, in turn, can have several food sources. The relationships within a food web are clearly illustrated by the diagram below.

Food web diagram.

In food chains, so-called trophic levels. Trophic levels classify organisms in the food chain according to their types of life activity or sources of energy. Plants occupy the first trophic level (the level of producers), herbivores (consumers of the first order) belong to the second trophic level, predators that eat herbivores form the third trophic level, secondary predators form the fourth, etc. first order.

Flow of energy in an ecosystem

As we know, energy transfer in an ecosystem occurs through food chains. But not all the energy from the previous trophic level is transferred to the next one. An example is the following situation: net primary production in an ecosystem (that is, the amount of energy accumulated by producers) is 200 kcal/m^2, secondary productivity (energy accumulated by first-order consumers) is 20 kcal/m^2 or 10% from the previous trophic level, the energy of the next level is 2 kcal/m^2, which is equal to 20% of the energy of the previous level. As can be seen from this example, with each transition to a higher level, 80-90% of the energy of the previous link in the food chain is lost. Such losses are due to the fact that a significant part of the energy during the transition from one stage to another is not absorbed by representatives of the next trophic level or is converted into heat, unavailable for use by living organisms.

Universal model of energy flow.

Energy intake and expenditure can be viewed using universal energy flow model. It applies to any living component of an ecosystem: plant, animal, microorganism, population or trophic group. Such graphical models, connected to each other, can reflect food chains (when the energy flow patterns of several trophic levels are connected in series, a diagram of the energy flow in the food chain is formed) or bioenergetics in general. The energy entering the biomass in the diagram is designated I. However, part of the incoming energy does not undergo transformation (in the figure indicated as NU). For example, this occurs when some of the light passing through plants is not absorbed by them, or when some of the food passing through the digestive tract of an animal is not absorbed by its body. Assimilated (or assimilated) energy (denoted by A) is used for various purposes. It is spent on breathing (in the diagram - R) i.e. to maintain the vital activity of biomass and to produce organic matter ( P). Products, in turn, take different forms. It is expressed in energy costs for biomass growth ( G), in various secretions of organic matter in external environment (E), in the body's energy reserves ( S) (an example of such a reserve is fat accumulation). The stored energy forms the so-called working loop, since this part of the production is used to provide energy in the future (for example, a predator uses its energy reserve to search for new victims). The remaining part of the production is biomass ( B).

The universal energy flow model can be interpreted in two ways. Firstly, it can represent a population of a species. In this case, the channels of energy flow and connections of the species in question with other species represent a diagram of the food chain. Another interpretation treats the energy flow model as an image of some energy level. The biomass rectangle and energy flow channels then represent all populations supported by the same energy source.

In order to clearly show the difference in approaches to interpreting the universal model of energy flow, we can consider an example with a population of foxes. Part of the foxes' diet consists of vegetation (fruits, etc.), while the other part consists of herbivores. To emphasize the aspect of intrapopulation energetics (the first interpretation of the energetic model), the entire fox population should be depicted as a single rectangle, if metabolism is to be distributed ( metabolism- metabolism, metabolic rate) fox populations into two trophic levels, that is, to display the relationship between the roles of plant and animal food in metabolism, it is necessary to construct two or more rectangles.

Knowing the universal model of energy flow, it is possible to determine the ratio of energy flow values ​​at different points of the food chain. Expressed as a percentage, these ratios are called environmental efficiency. There are several groups of environmental efficiencies. The first group of energy relations: B/R And P/R. The proportion of energy spent on respiration is large in populations of large organisms. When exposed to stress from the external environment R increases. Magnitude P significant in active populations of small organisms (for example algae), as well as in systems that receive energy from the outside.

The following group of relations: A/I And P/A. The first of them is called efficiency of assimilation(i.e., the efficiency of using the supplied energy), the second - efficiency of tissue growth. Assimilation efficiency can vary from 10 to 50% or higher. It can either reach a small value (with the assimilation of light energy by plants), or have large values(when assimilation of food energy by animals). Typically, the efficiency of assimilation in animals depends on their food. In herbivorous animals, it reaches 80% when eating seeds, 60% when eating young foliage, 30-40% when eating older leaves, 10-20% when eating wood. In carnivorous animals, the efficiency of assimilation is 60-90%, since animal food is much more easily absorbed by the body than plant food.

The efficiency of tissue growth also varies widely. It reaches its greatest values ​​in cases where organisms are small in size and the conditions of their habitat do not require large energy expenditures to maintain the temperature optimal for the growth of organisms.

The third group of energy relations: P/B. If we consider P as the rate of increase in production, P/B represents the ratio of production at a particular point in time to biomass. If products are calculated for a certain period of time, the value of the ratio P/B is determined based on the average biomass over this period of time. IN in this case P/B is a dimensionless quantity and shows how many times the production is more or less than biomass.

It should be noted that the energy characteristics of an ecosystem are influenced by the size of the organisms inhabiting the ecosystem. A relationship has been established between the size of an organism and its specific metabolism (metabolism per 1 g of biomass). The smaller the organism, the higher its specific metabolism and, therefore, the lower the biomass that can be supported at a given trophic level of the ecosystem. With the same amount of energy used, organisms large sizes accumulate more biomass than small ones. For example, when equal value energy consumed, the biomass accumulated by bacteria will be much lower than the biomass accumulated by large organisms (for example, mammals). A different picture emerges when considering productivity. Since productivity is the rate of biomass growth, it is greater in small animals, which have higher rates of reproduction and biomass renewal.

Due to the loss of energy within food chains and the dependence of metabolism on the size of individuals, each biological community acquires a certain trophic structure, which can serve as a characteristic of the ecosystem. The trophic structure is characterized either by the standing crop or by the amount of energy fixed per unit area per unit time by each subsequent trophic level. The trophic structure can be depicted graphically in the form of pyramids, the base of which is the first trophic level (the level of producers), and subsequent trophic levels form the “floors” of the pyramid. There are three types of ecological pyramids.

1) Number pyramid (indicated by number 1 in the diagram) It displays the number of individual organisms at each trophic level. The number of individuals at different trophic levels depends on two main factors. The first one is more high level specific metabolism in small animals compared to large ones, which allows them to have a numerical superiority over large species and higher rates of reproduction. Another of the above factors is the existence of upper and lower limits on the size of their prey among predatory animals. If the prey is much larger in size than the predator, then it will not be able to defeat it. Small prey will not be able to satisfy the energy needs of the predator. Therefore, for each predatory species there is an optimal size of prey. However, for of this rule there are exceptions (for example, snakes use venom to kill animals larger than themselves). Pyramids of numbers can be pointed downward if the producers are much larger than the primary consumers in size (an example is a forest ecosystem, where the producers are trees and the primary consumers are insects).

2) Biomass pyramid (2 in the diagram). With its help, you can clearly show the ratios of biomass at each of the trophic levels. It can be direct if the size and lifespan of producers reaches relatively large values ​​(terrestrial and shallow-water ecosystems), and reversed when producers are small in size and have a short life cycle (open and deep water bodies).

3) Pyramid of energy (3 in the diagram). Reflects the amount of energy flow and productivity at each trophic level. Unlike pyramids of numbers and biomass, the pyramid of energy cannot be reversed, since the transition of food energy to higher trophic levels occurs with large energy losses. Consequently, the total energy of each previous trophic level cannot be higher than the energy of the next one. The above reasoning is based on the use of the second law of thermodynamics, so the pyramid of energy in an ecosystem serves as a clear illustration of it.

Of all the trophic characteristics of an ecosystem mentioned above, only the energy pyramid provides the most complete picture of the organization of biological communities. In the population pyramid, the role of small organisms is greatly exaggerated, and in the biomass pyramid, the importance of large ones is overestimated. In this case, 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. For this reason, it is energy flow that serves as the most suitable criterion for comparing individual components of an ecosystem with each other, as well as for comparing two ecosystems with each other.

Knowledge of the basic laws of energy transformation in an ecosystem contributes to a better understanding of the functioning processes of the ecosystem. This is especially important due to the fact that human intervention in its natural “work” can lead to the destruction of the ecological system. In this regard, he must be able to predict the results of his activities in advance, and an understanding of energy flows in the ecosystem can provide greater accuracy of these predictions.