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That they are powered by networks. Food chains, food webs and trophic levels. The nature of the age structure of a population depends on the type of survival curve characteristic of a given population.

Biological taxonomy
10.07.2020

This is a set of food chains of a community, interconnected by common food links.

cabbage ^ caterpillar ^ titmouse ^ hawk ^ human

For example: carrot ^ hare ^ wolf
Species with a wide range of food can be included in food chains at different trophic levels. Only producers always occupy the first trophic level. Using solar energy and biogens, they form organic matter, which contains energy in the form of energy of chemical bonds. This organic matter, or biomass of producers, is consumed by organisms of the second trophic level. However, not all biomass of the previous level is consumed by organisms of the next level, therefore
that resources for the development of the ecosystem would disappear. During the transition from one trophic level to another, the transformation of matter and energy occurs. At each trophic level of the pasture food chain, not all of the eaten biomass goes to the formation of biomass of organisms of a given level. A significant part of it is spent on ensuring the vital activity of organisms: respiration, movement, reproduction, maintaining body temperature, etc. In addition, not all eaten biomass is digested. Undigested part of it in the form of excrement enters the environment. The percentage of digestibility depends on the composition of food and the biological characteristics of organisms, it ranges from 12 to 75%. The main part of the assimilated biomass is spent on maintaining the vital activity of organisms, and only a relatively small part of it is spent on building the body and growing. In other words, most of Substances and energy are lost during the transition from one trophic level to another, because only that part of them that was included in the biomass of the previous trophic level gets to the next consumer. It is estimated that about 90% is lost on average, and only 10% of matter and energy is transferred at each stage of the food chain. For example:
Producers ^ consumers I ^ consumers II ^ consumables III
1000 kJ ^ 100 kJ ^ 10 kJ ^ 1 kJ This pattern was formulated as the "10% law". It states that during the transition from one link to another in the pasture food chain, only 10% of matter and energy is transferred, and the rest is spent by the previous trophic level to maintain vital activity. If the amount of matter or energy at each trophic level is plotted in the form of a diagram and placed above each other, then an ecological pyramid of biomass or energy is obtained (Fig. 13). This pattern is called the "ecological pyramid rule". The number of organisms at trophic levels also obeys this rule, therefore it is possible to build an ecological pyramid of numbers (Fig. 13).
Boy 1 Calves 4.5 Alfalfa 2107



Energy pyramid

Thus, the supply of matter and energy accumulated by plants in pasture food chains is quickly consumed (eaten away), so food chains cannot be long. They usually include 4-5 links, but no more than 10. At each trophic level of the pasture food chain, dead organic matter and excrement are formed - detritus, from which detrital chains or decomposition chains begin. In terrestrial ecosystems, the process of detritus decomposition includes three stages:
The stage of mechanical destruction and partial transformation into saccharides. It is very short - 3-4 years. It is carried out by decomposers of the first order - macrobiota (worms, insect larvae, burrowing mammals, etc.). At this stage, there is practically no energy loss.
The stage of destruction of detritus to humic acids. It lasts 10-15 years and is still poorly understood. It is carried out by reducers of the II order - the mesobiota (fungi, protozoa, micro-
organisms larger than 0.1 mm). Humic acids are humus, half-destroyed organic matter, therefore, when they are formed, part of the chemical bonds are broken and heat energy is released, which is dissipated in outer space.
3. The stage of destruction of humic acids to inorganic substances - biogens. It proceeds very slowly, especially in our temperate zone (hundreds and thousands of years) and has hardly been studied yet. It is carried out by reducers of the III order - microbiota (microorganisms less than 0.1 mm). When humic acids are destroyed, all chemical bonds are broken and a large amount of thermal energy is released, which is lost in outer space. The biogens formed as a result of this process do not contain energy, later they are absorbed by producers and again are involved in the circulation of matter.
As can be seen from the above, there is a delay in life at the level of decomposers, but this should not be so. The soil has a supply of humic acids, which were formed a very long time ago, so there is no delay in life. In different ecosystems, the rate of destruction of humic acids is different. If it is less than the rate of their formation, then the soil fertility increases, if on the contrary, then it decreases. That is why, in the temperate zone, after the destruction of the biogeocenosis, the long-term use of soil fertility is possible. In the tropics, soil fertility is sufficient for 2-3 years, and then it turns into a desert. Here, the destruction of humic acids is rapid. High temperature, humidity and aeration contribute to this. In the temperate zone, the soil contains up to 55% of carbon, and in the tropics - only up to 25%. This is why rainforests should not be cut down to prevent desertification of the planet.
Thus, the energy flow entering the ecosystem is further divided into two main channels - pasture and detrital. At the end of each of them, energy is lost irretrievably, because plants cannot use thermal long-wave energy during photosynthesis.
The ratio of the amount of energy passing through the grazing and detrital chains is different in different types of ecosystems. The loss of energy in the food chain can only be replenished by the intake of new portions. This is done through the assimilation of solar energy by plants. Therefore, there cannot be a cycle of energy in an ecosystem, similar to the cycle of matter. The ecosystem functions only due to the directed flow of energy - its constant supply in the form of solar radiation, or in the form of ready-made organic matter.

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

The 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 cohabitants and interacting with each other and with inanimate nature, populations different types in relatively uniform environmental conditions.

Ecological systems

Functional systems that include communities of living organisms of different species and their habitat. The links between the components of the ecosystem arise primarily on the basis of food relationships and methods of obtaining energy.

Ecosystem

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

All organisms of the Earth and their habitats also represent the highest rank ecosystem - biosphere with stability and other properties of the ecosystem.

The existence of an ecosystem is possible due to a constant influx of energy from the outside - such a source of energy, as a rule, is the sun, although this is not true for all ecosystems. The sustainability of the ecosystem is provided by direct and feedback links between its components, 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. Tensley in 1935, the term" biogeocenosis"- Academician V.N. Sukachev in 1942. biogeocenosis the presence of the main link of the plant community (phytocenosis) is mandatory, which ensures the potential immortality of the biogeocenosis due to the energy produced by the plants. Ecosystems may not contain phytocenosis.

Phytocenosis

A plant community, historically formed as a result of a combination of interacting plants in a homogeneous area of \u200b\u200bthe territory.

It is characterized by:

- a certain species composition,

- life forms,

- tiered (aboveground and underground),

- abundance (frequency of occurrence of species),

- placement,

- aspect (appearance),

- vitality,

- seasonal changes,

- development (change of communities).

Tiered (number of storeys)

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

Above ground layering allows better use of light, and underground - water and minerals. Usually, up to five tiers can be distinguished in the forest: the upper (first) - tall trees, the second - low trees, the third - shrubs, the fourth - grasses, the fifth - mosses.

Underground tier - a mirror reflection of the aboveground: the roots of trees go deepest of all, underground parts of mosses are located near the soil surface.

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

Most biogeocenoses have a similar trophic structure... They are based on green plants - producers. Herbivorous and carnivorous animals must be present: consumers of organic matter - consumers and destroyers of organic residues - reducers.

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

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

Violation of any link in the food chain causes a violation of the biocenosis as a whole. For example, deforestation leads to a change in the species composition of insects, birds, and, consequently, animals. On a treeless area, other food chains will develop and another biocenosis will form, which will take more than a dozen years.

Food chain (trophic or food )

Interconnected species that sequentially extract organic matter and energy from the original food substance; while each previous link in the chain is food for the next.

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

Ecosystem components:

- Producers - autotrophic organisms (mainly green plants) are the only producers of organic matter on Earth. Energy-rich organic matter is synthesized during photosynthesis from energy-poor not organic matter (H 2 0 and C0 2).

- Consumptions - herbivorous and carnivorous animals, consumers of organic matter. Consumables can be herbivorous when they are used directly by producers, or carnivores when they feed on other animals. In the food chain, they most often have serial number from I to IV.

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

Trophic (food) level - a set of organisms united by the 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. the second - consumers of the first order (herbivorous animals),
  3. the third - consumers of the II order - predators feeding on herbivorous animals),
  4. the fourth - consumers of the III order (secondary predators).

There are the following types food chains:

IN pasture chain (grazing chains) the main food source is green plants. For example: grass -\u003e insects -\u003e amphibians -\u003e snakes -\u003e birds of prey.

- detrital chains (decomposition chains) begin with detritus - dead biomass. For example: leaf litter -\u003e earthworms -\u003e bacteria. A feature of detrital chains is also the fact that in them the products of plants are often not consumed directly by herbivorous animals, but die off and are mineralized by saprophytes. Detrital chains are also characteristic of ecosystems of the ocean depths, whose inhabitants feed on dead organisms that have descended from the upper layers of water.

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

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

Ecological pyramid

The way to graphically display the ratio of different trophic levels in an ecosystem is of 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 that has passed through each trophic level during a certain period of time.

The ecological pyramid rule

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

The pyramid of numbers

An ecological pyramid representing the number of individuals at each food level. The pyramid of numbers does not take into account the size and weight of individuals, life expectancy, metabolic rate, but the main trend is always traced - a decrease in the number of individuals from link to link. For example, in the steppe ecosystem, the number of individuals is distributed as follows: producers - 150,000, herbivorous consumers - 20,000, carnivorous consumers - 9,000 individuals / are. The biocenosis of the meadow is characterized by the following number of individuals on an area of \u200b\u200b4000 m 2: producers - 5,842,424, herbivorous consumers of the 1st order - 708,624, carnivorous consumers of the 2nd order - 35,490, carnivorous consumers of the 3rd order - 3.

Biomass pyramid

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

Energy pyramid

expresses the pattern according to which the flow of energy gradually decreases and depreciates during the transition 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; Consumers of the II order, using the food of consumers of the I order, create their own biomass containing 5.46 kJ / cm 2. The loss of energy in the transition from 1st order consumers to 2nd order consumers, if they 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 raising a calf and a perch, then the same amount of consumed food energy will give 7 kg of beef and only 1 kg of fish, since the calf feeds on grass, and the predator perch feeds on fish.

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

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

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

Environmental plasticity

The degree of hardiness of organisms or their communities (biocenoses) to the effects of environmental factors. Ecologically plastic species have a wide reaction rate , that is, they are widely adapted to different habitats (stickleback fish and eel, some protozoa live in both fresh and salt waters). Highly specialized species can exist only in a certain environment: sea 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,

The density of species populations,

Biomass.

Biomass

The total amount of organic matter of all individuals of the biocenosis or a species with energy contained in it. Biomass is usually expressed in units of mass in terms of dry matter unit area or volume. Biomass can be determined separately for animals, plants, or individual species. So, 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 , vertebrates - 0.001-0.015 t / ha.

In biogeocenoses are distinguished primary and secondary biological productivity :

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

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

Populations. The structure and dynamics of the population.

Each species on Earth occupies a certain area, since it is able to exist only under certain environmental conditions. However, the 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 a species (with relatively uniform habitat conditions), freely interbreeding with each other (having a common gene pool) and isolated from other populations of this species, having all the necessary conditions to maintain their stability for a long time in changing environmental conditions. The most important characteristics population are its structure (age, sex composition) and population dynamics.

Under the demographic structure the population understands its sex and age composition.

Spatial structure populations are the features of the distribution of individuals of 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 combined into cohorts - age groups.

IN age structure of plant populations allocate next periods:

Latent - the state of the seed;

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

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

Postgenerative (includes the state of subsenile, senile plants and the phase of withering away).

Belonging to a certain age condition is determined by biological age - the severity of certain morphological (for example, the degree of dissection of a complex leaf) and physiological (for example, the ability to give offspring) characters.

In animal populations, various age stages... For example, insects that develop with complete metamorphosis go through the stages:

Larvae,

Pupae,

Imago (adult insect).

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

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

  1. If the mortality rate does not depend on the age of individuals, the death of individuals in this type occurs evenly, the mortality rate remains constant throughout life ( type I ). Such a survival curve is characteristic of species that develop without metamorphosis with sufficient stability of the nascent offspring. This type is usually called type of hydra - it has 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 a sharp drop occurs due to natural (physiological) mortality ( type II ). The nature of the survival curve is similar to this type in humans (although the human survival curve is somewhat flatter and is something in 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. Very many species are characterized by high mortality in the early stages of ontogenesis. In such species, the survival curve is characterized by a sharp drop in the area of \u200b\u200byounger ages. Individuals that have survived the "critical" age demonstrate low mortality and live to an older age. The type is named oyster type (type III ).

Gender structure populations

The sex ratio is directly related to the reproduction of the population and its stability.

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

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

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

- Tertiary sex ratio - the sex ratio among adult animals.

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

Allocate three main types of distribution of individuals in space:

- uniform or uniform (individuals are evenly distributed in space, at equal distances from each other); occurs rarely 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 frequently. It is associated with the characteristics of the microenvironment or behavior of animals;

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

Population size denoted by the letter N. The ratio of the increment N per unit time dN / dt expressesinstant speed changes in the size of the population, i.e. change in the size at time t.Population growth depends on two factors - fertility and mortality in the absence of emigration and immigration (such a population is called isolated). The difference between fertility b and mortality 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 - the population also changes. Internal diversity is one of the most important conditions for sustainability. In relation to the population, these are the mechanisms for maintaining a certain population density.

Allocate 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 provided by various mechanisms. For example, many bird species are characterized by a decrease in fertility (fertility) with an increase in population density; an increase in mortality, a decrease in the resistance of organisms with an increased population density; change in the age of onset of puberty depending on population density.

The third type ( III ) characteristic of populations in which the "group effect" is noted, that is, 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, for the resumption of populations of heterosexual animals, at least density is necessary, providing a sufficient probability of a meeting between a male and a female.

Thematic tasks

A1. Biogeocenosis formed

1) plants and animals

2) animals and bacteria

3) plants, animals, bacteria

4) territory and organisms

A2. The consumers of organic matter in the 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 self-regulation process in the 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. Reducers include

2) lichens

4) ferns

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

A8. Indicate 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 the biocenosis is energy

1) organic compounds

2) inorganic compounds

4) chemosynthesis

1) hares

2) bees

3) field thrush

4) wolves

A11. In one ecosystem you can find oak and

1) gopher

3) lark

4) blue cornflower

A12. Power supply networks are:

1) communication between parents and offspring

2) family (genetic) ties

3) metabolism in the cells of the body

4) ways of transferring substances and energy in the ecosystem

A13. The ecological pyramid of numbers reflects:

1) the ratio of biomasses at each trophic level

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

3) food chain structure

4) diversity of species at different trophic levels

In ecosystems, producers, consumers and decomposers are united by complex processes of transfer of substances and energy, which is contained in food, created mainly by plants.

The transfer of the potential energy of food created by plants through a number of organisms by eating some species by others is called the trophic (food) chain, and each of its links is called the trophic level.

All organisms using one type of food belong to the same trophic level.

Figure 4. the diagram of the trophic chain is presented.

Fig. 4. Food chain diagram.

Fig. 4. Food chain diagram.

First trophic level form producers (green plants) that accumulate solar energy and create organic matter in the process of photosynthesis.

At the same time, more than half of the energy stored in organic substances is consumed in the life processes of plants, turning into heat and dissipating in space, and the rest enters the food chains and can be used by heterotrophic organisms of subsequent trophic levels during nutrition.

Second trophic level form consumers of the 1st order - these are herbivorous organisms (phytophages) that feed on producers.

First-order consumables spend most of the energy contained in food to support their life processes, and use the rest of the energy to build their own body, thereby transforming plant tissues into animals.

Thus , 1st order consumers carry out the first, fundamental stage in the transformation of organic matter synthesized by producers.

Primary consumers can serve as a food source for consumers of the 2nd order.

Third trophic level form consumers of the 2nd order - these are carnivorous organisms (zoophages) that feed exclusively on herbivorous organisms (phytophages).

Second order consumables carry out the second stage of transformation of organic matter in food chains.

However, the chemical substances from which the tissues of animal organisms are built are rather homogeneous and therefore the transformation of organic matter during the transition from the second trophic level of consumers to the third does not have such a fundamental character as during the transition from the first trophic level to the second, where the transformation of plant tissues into animals.

Secondary consumers can serve as a source of food for consumers of the 3rd order.

Fourth trophic level form consumers of the third order - these are carnivores that feed only on carnivores.

The last level of the food chain are occupied by reducers (destructors and detritivores).

Reducers-destructors (bacteria, fungi, protozoa) in the course of their vital activity decompose organic residues of all trophic levels of producers and consumers to mineral substances, which again return to producers.

All links of the trophic chain are interconnected and interdependent.

Between them, from the first to the last link, substances and energy are transferred. However, it should be noted that when energy is transferred from one trophic level to another, its loss occurs. As a result, the power supply chain cannot be long and most often consists of 4-6 links.

However, such food chains do not usually occur in their pure form in nature, since each organism has several food sources, i.e. uses several types of food, and itself is used as a food product by numerous other organisms from the same trophic chain or even from different food chains.

For example:

    omnivorous organisms consume as food both producers and consumers, i.e. are simultaneously consumers of the first, second, and sometimes third order;

    a mosquito that feeds on the blood of humans and predatory animals is at a very high trophic level. But the marsh sundew plant feeds on mosquitoes, which, therefore, is both a producer and a consumer of a high order.

Therefore, almost any organism that is part of one trophic chain can simultaneously be part of other trophic chains.

Thus, trophic chains can branch and intertwine many times, forming complex food webs or trophic (food) webs , in which the multiplicity and diversity of food links acts as an important mechanism for maintaining the integrity and functional stability of ecosystems.

Figure 5. a simplified terrestrial ecosystem food network diagram is shown.

Human intervention in natural communities of organisms through the intentional or unintentional elimination of any species often has unpredictable negative consequences and leads to a violation of the stability of ecosystems.

Fig. 5. The scheme of the food web.

There are two main types of food chains:

    grazing chains (grazing or consumption chains);

    detrital chains (decomposition chains).

Pasture chains (grazing chains or consumption chains) are the processes of synthesis and transformation of organic substances in trophic chains.

Pasture chains begin with producers. Living plants are eaten by phytophages (consumers of the first order), and the phytophages themselves are food for carnivores (consumers of the second order), which can be eaten by consumers of the third order, etc.

Examples of grazing chains for terrestrial ecosystems:

3 links: aspen → hare → fox; plant → sheep → human.

4 links: plants → grasshoppers → lizards → hawk;

plant flower nectar → fly → insectivorous bird →

predatory bird.

5 links: plants → grasshoppers → frogs → snakes → eagle.

Examples of grazing chains for aquatic ecosystems: →

3 links: phytoplankton → zooplankton → fish;

5 links: phytoplankton → zooplankton → fish → predatory fish →

predator birds.

Detrital chains (decomposition chains) are the processes of stepwise destruction and mineralization of organic matter in trophic chains.

Detrital chains begin with the gradual destruction of dead organic matter by detritus feeders, which successively replace each other in accordance with a specific type of nutrition.

At the last stages of destructive processes, decomposers-destructors function, mineralizing the remains of organic compounds to simple inorganic substances, which are again used by producers.

For example, when decomposing dead wood, they successively replace each other: beetles → woodpeckers → ants and termites → fungi-destructors.

Detrital chains are most common in forests, where most (about 90%) of the annual increase in plant biomass is not consumed directly by herbivorous animals, but dies off and enters these chains in the form of leaf litter, then undergoes decomposition and mineralization.

In aquatic ecosystems, most of the matter and energy is incorporated into grazing chains, while in terrestrial ecosystems, detritus chains are of greatest importance.

Thus, at the consumer level, the flow of organic matter is divided into different groups of consumers:

    living organic matter follows pasture chains;

    dead organic matter travels along detrital chains.

The species in the biocenosis are interconnected by the processes of exchange of matter and energy, that is, by food relationships. By tracing the nutritional relationship between members of the biocenosis (“who eats whom and how much”), it is possible to build food chains and webs.

Trophic chains (from the Greek trophe - food) - food chains are the sequential transfer of matter and energy. For example, the food chain of animals of the Arctic sea: microalgae (phytoplankton) → small herbivorous crustaceans (zooplankton) → carnivorous plankton-phages (worms, molluscs, crustaceans) → fish (2-4 links in the sequence of predatory fish are possible) → seals → polar bears. This food chain is long, the food chains of terrestrial ecosystems are shorter, as there is more energy loss on land. There are several types terrestrial food webs .

1. Pasture food chains (exploiters' chains) begin with producers. With the transition from one trophic level to another, an increase in the size of individuals occurs, while the density of populations, the rate of reproduction and productivity by weight decrease.

Grass → voles → fox

Grass → insects → frog → heron → kite

Apple tree → scale insect → rider

Cow → horsefly → bacteria → phages

    Detrital chains. Include decomposers only.

Fallen leaves → molds → bacteria

Any member of a food chain is simultaneously a link in another food chain: it is consumed and consumed by several types of other organisms. This is how food webs. For example, in the food of the meadow coyote wolf, there are up to 14 thousand species of animals and plants. In the sequence of transfer of substances and energy from one group of organisms to another, a distinction is made between trophic levels... Usually the chains do not exceed 5-7 levels. The first trophic level is made by producers, since only they can feed on solar energy. At all other levels - herbivores (phytophages), primary predators, secondary predators, etc. - the initially accumulated energy is expended to maintain metabolic processes.

It is convenient to represent food relations in the form trophic pyramids(numbers, biomasses, energies). Number pyramid - displaying the number of individuals at each trophic level in units (pieces).

It has a very wide base and a sharp taper towards the end consumers. This is a common type of pyramid for grass communities - meadow and steppe biocenoses. If we consider the forest community, the picture may be distorted: thousands of phytophages can feed on one tree, or aphids and an elephant (different phytophages) will appear at the same trophic level. Then the number of consumers may be greater than the number of producers. To overcome possible distortions, a biomass pyramid is used. It is expressed in units of dry or wet weight tonnage: kg, t, etc.

In terrestrial ecosystems, plant biomass is always greater than animal biomass. The biomass pyramid looks different for aquatic, especially marine ecosystems. The biomass of animals is much larger than the biomass of plants. This inaccuracy is due to the fact that the biomass pyramids do not take into account the duration of the existence of generations of individuals at different trophic levels and the rate of formation and consumption of biomass. The main producer of marine ecosystems is phytoplankton. Up to 50 phytoplankton generations can change in the ocean per year. During the time that predatory fish (and even more so whales) accumulate their biomass, many generations of phytoplankton will change and its total biomass will be much larger. Therefore, a universal way of expressing the trophic structure of ecosystems is the productivity pyramids, usually they are called energy pyramids, meaning the energy expression of production.

The absorbed solar energy is converted into the energy of chemical bonds between carbohydrates and other organic substances. Some of the substances are oxidized in the process of plant respiration and release energy. This energy is eventually dissipated as heat. The remaining energy determines the growth of biomass. The total biomass of a stable ecosystem is relatively constant. Thus, during the transition from one trophic level to another, part of the available energy is not perceived, part is given off in the form of heat, part is spent on breathing. On average, when passing from one trophic level to another, the total energy decreases by about 10 times. This pattern is called the rule of the Lindemann pyramid of energies (1942) orthe rule of 10%. The longer the food chain, the less energy is available towards the end, so the number of trophic levels is never too large.

If the energy and the bulk of organic matter decrease during the transition to the next stage of the ecological pyramid, then the accumulation of substances that enter the body that do not participate in normal metabolism (synthetic poisons) increases in approximately the same proportion. This phenomenon is called biological amplification rule.

Basic principles of the functioning of ecological systems

    A constant supply of solar energy – necessary condition the existence of the ecosystem.

    Nutrient cycle. The driving forces of the circulation of substances are the flows of energy from the sun and the activity of living matter. Thanks to the circulation of biogenic elements, a stable organization of all ecosystems and the biosphere as a whole is created, their normal functioning is carried out.

    Decrease in biomass at higher trophic levels: a decrease in the amount of available energy is usually accompanied by a decrease in biomass and the number of individuals at each trophic level (remember the pyramids of energy, abundance and biomass).

We have already covered these principles in detail during the lecture.

The food chain is made up of different types of organisms. At the same time, organisms of the same species can be part of different food chains. Therefore, food chains intertwine, forming complex food webs that span all ecosystems of the planet. [...]

The food (trophic) chain is the transfer of energy from its source - producers - through a number of organisms. Food chains can be divided into two main types: the grazing chain, which begins with a green plant and continues on to grazing herbivorous animals and predators, and the detrital chain (from Latin worn out), which starts from the decay products of dead organic matter. In the formation of this chain, a decisive role is played by various microorganisms that feed on dead organic matter and mineralize it, again turning it into the simplest inorganic compounds. Food chains are not isolated from one another, but closely intertwined with each other. Often, an animal consuming living organic matter also eats microbes that consume nonliving organic matter. Thus, the pathways of food consumption branch out, forming the so-called food webs. [...]

The food web is a complex entanglement in the food chain community. [...]

Food webs are formed because almost any member of any food chain is simultaneously a link in another food chain: it is consumed and consumed by several types of other organisms. So, in the food of the meadow wolf - coyote, there are up to 14 thousand species of animals and plants. Probably, the same order of the number of species participating in the eating, decomposition and destruction of substances from the corpse of a coyote. [...]

Food chains and trophic levels. By tracing the food relationships between members of the biocenosis ("who eats whom and how much"), it is possible to build food chains of food for various organisms. An example of a long food chain is the sequence of inhabitants of the Arctic sea: “microalgae (phytoplankton) -\u003e small herbivorous crustaceans (zooplankton) - carnivorous plankton-feeders (worms, crustaceans, molluscs, echinoderms) -\u003e fish (2-3 links of the sequence of predatory fish are possible) - \u003e seals -\u003e polar bear ". Terrestrial ecosystem chains are usually shorter. The food chain, as a rule, is artificially separated from the real food web - the intertwining of many food chains. [...]

The food web is a complex web of food relationships. [...]

Food chains imply a linear flow of resources from one trophic level to the next (Fig. 22.1, a). In this design, interactions between species are simple. However, no system of resource flows in BE follows this simple structure; they are much more like a network structure (Figure 22.1, b). Here, species at one trophic level feed on several species at the next, lower level, and omnivorousness is widespread (Fig. 22.1, c). Finally, a fully defined food web can exhibit various characteristics: multiple trophic levels, predation, and omnivorousness (Figure 22.1, [...]

Many food chains, intertwining in biocenoses and ecosystems, form food webs. If the general food chain is depicted in the form of building blocks, conditionally representing the quantitative ratio of the energy absorbed at each stage, and stacked on top of each other, you get a pyramid. It is called the ecological pyramid of energies (Fig. 5). [...]

Food chain and food web diagrams. Dots represent views, lines represent interactions. Higher species are predators relative to lower ones, so resources flow from the bottom up. [...]

In the first type of food web, the flow of energy goes from plants to herbivorous animals, and then to consumers of a higher order. This is a grazing net, or a grazing net. Regardless of the size of the biocenosis and habitat, herbivorous animals (terrestrial, aquatic, soil) graze, eat up green plants and transfer energy to the following levels (Fig. 96). [...]

In communities, food chains are intricately intertwined and form food webs. The composition of the food of each type usually includes not one, but several types, each of which, in turn, can serve as food for several species. On the one hand, each trophic level is represented by many populations of different species; on the other hand, many populations belong to several trophic levels at once. As a result, due to the complexity of food links, the loss of one species often does not upset the balance in the ecosystem. [...]

[ ...]

This diagram not only illustrates the intertwining of food links and shows three trophic levels, but also reveals the fact that some organisms occupy an intermediate position in the system of three main trophic levels. Thus, caddis larvae building a trapping net feed on plants and animals, occupying an intermediate position between the primary and secondary consumers. [...]

The primary source of human food resources were those ecosystems in which he could exist. The methods of obtaining food were gathering and hunting, and as the manufacture and use of more and more sophisticated tools developed, the share of hunting prey increased, which means the share of meat, that is, complete proteins, in the diet. The ability to organize large stable groups, the development of speech, which allows organizing the complex coordinated behavior of many people, made a person a "superpredator" who took the top position in the food webs of those ecosystems that he mastered as he settled on the Earth. So, the only enemy of the mammoth was a man who, together with the retreat of the glacier and climate change, became one of the reasons for the death of these northern elephants as a species. [...]

[ ...]

Based on a study of 14 food webs in communities, Cohen found a surprising constancy of the ratio of the number of "types" of prey to the number of "types" of predators, which was about 3: 4. Further evidence confirming this ratio is provided by Bryand and Cohen, who studied 62 similar networks. The graph of such proportionality has a slope of less than 1 in both fluctuating and constant media. The use of "types" of organisms, rather than genuine species, usually gives not entirely objective results, however, although the resulting prey / predator ratio may be underestimated, its consistency is remarkable. [...]

In BE, many (but certainly not all) food webs have a large number of primary producers, fewer consumers, and very few top predators, giving the web the shape shown in Figure 1. 22.1, b. Omnivores in these systems may be rare, while decomposers are abundant. Food web models have provided a potential basis for fruitful analysis of resource flows in both BE and PE. Difficulties arise, however, when one tries to quantify resource flows and subject network structure and stability properties to mathematical analysis. It turns out that many of the required data are difficult to identify with certainty, especially with regard to organisms that function at more than one trophic level. This property does not create the main difficulty in studying resource flows, but it seriously complicates the analysis of stability. The assertion that more complex systems are more stable - since the destruction of one kind or paths of flows simply transfers energy and resources to other paths, rather than blocking the path for the entire flow of energy or resources - is hotly debated. [...]

Analysis of a large number of industrial food webs can thus reveal characteristics not shown in other approaches. In the ecosystem project in Fig. 22.5, for example, network analysis may reflect a missing sector or type of industrial activity that can increase connectivity. These topics provide a rich area for detailed research [...]

Within each ecosystem, food webs have a well-defined structure, which is characterized by the nature and the number of organisms present at each level of the various food chains. To study the relationships between organisms in an ecosystem and for their graphic image usually they use not schemes of food webs, but ecological pyramids. Ecological pyramids express the trophic structure of an ecosystem in geometric form. [...]

The length of food chains is of some interest. It is clear that the decrease in available energy in the transition to each successive link limits the length of food chains. However, the availability of energy is probably not the only factor, as long food chains are often found in infertile systems, such as oligotrophic lakes, and short ones in highly productive, or eutrophic, systems. Rapid production of nutritious plant material can stimulate rapid grazing, as a result of which the energy flow is concentrated at the first two to three trophic levels. The eutrophication of lakes also changes the composition of the planktonic food web “phytoplankton-large zooplankton-predatory fish”, turning it into a microbial-detrital microzooplankton system, which is not so conducive to the maintenance of sport fishing. [...]

With a constant energy flow in the food web, or chain, smaller terrestrial organisms with a high specific metabolism create relatively less biomass than large ones1. A significant part of the energy is spent on maintaining metabolism. This rule of "metabolism and size of individuals", or the rule of Y. Odum, is usually not implemented in aquatic biocenoses when taking into account the real living conditions in them (under ideal conditions, it has universal significance). This is due to the fact that small aquatic organisms largely support their metabolism due to external energy from the immediate environment. [...]

The soil microflora has a well-developed food web and a powerful compensatory mechanism based on the functional interchangeability of some species with others. In addition, thanks to the labile enzymatic apparatus, many species can easily switch from one nutrient substrate to another, thereby ensuring the stability of the ecosystem. This significantly complicates the assessment of the impact of various anthropogenic factors on it and requires the use of integral indicators. [...]

[ ...]

First of all, randomized food webs often contain biologically meaningless elements (for example, loops of this type: A eats B, B eats C, C eats A). Analysis of “meaningfully” constructed networks (Lawlor, 1978; Pimm, 1979a) shows that (a) they are more stable than those considered and (b) there is no such abrupt transition to instability (compared to the above inequality), although the stability still decreases with increasing complexity. [...]

21.2

Of course, yes, if not in the composition of biogeocenoses - the lowest levels of the hierarchy of ecosystems - then at least within the framework of the biosphere. People get food from these networks (agrocenoses are modified ecosystems with a natural base). Only from the "wild" nature do people extract fuel - energy, main fish resources, other "gifts of nature". V.I.Vernadsky's dream of the complete autotrophy of humanity remains an irrational dream1 - evolution is irreversible (L. Dolo's rule), as well as historical process... Without genuine autotrophs, mainly plants, a person cannot exist as a heterotrophic organism. Finally, if he was not physically included in the food webs of nature, then his body after death would not be subject to destruction by organisms-decomposers, and the Earth would be littered with non-decaying corpses. The thesis of the separateness of man and natural food chains is based on a misunderstanding and is clearly erroneous. [...]

In ch. 17 analyzes the ways of combining various groups of consumers and their food into a network of interacting elements, through which the transfer of matter and energy occurs. In ch. 21 we will return to this topic and consider the influence of the structure of the food web on the dynamics of communities as a whole, paying particular attention to the features of their structure that contribute to stability. [...]

Four examples will suffice to illustrate the basic features of food webs, food webs and trophic levels. The first example is the region of the Far North, called the tundra, where relatively few species of organisms live that have successfully adapted to low temperatures. Therefore, the food chains and food webs are relatively simple here. One of the founders of modern ecology, British ecologist Charles Elton, realizing this, already in the 1920s and 1930s, began to study the Arctic lands. He was one of the first to clearly outline the principles and concepts associated with the food chain (Elton, 1927). Plants of the tundra - lichen ("deer moss") C1a donia, grasses, sedges and dwarf willows constitute the food of caribou deer in the North American tundra and its ecological counterpart in the tundra of the Old World - reindeer. These animals, in turn, serve as food for wolves and humans. Tundra plants are also eaten by lemmings - fluffy short-tailed rodents that resemble a miniature bear and tundra partridges. Throughout the long winter and all the short summer, Arctic foxes and snowy owls feed mainly on lemmings. Any significant change in the number of lemmings is reflected in other trophic levels, since there are few other food sources. This is why the abundance of some groups of Arctic organisms varies greatly from super abundance to almost complete extinction. This often happened in human society if it depended on one or more of a few food sources (remember the "potato famine" in Ireland1). [...]

One of the consequences of the stability hypothesis, which in principle can be tested, is that in environments with less predictable behavior, food chains should be shorter, since in them, apparently, only the most elastic food webs are preserved, and in short chains elasticity higher. Briand (1983) divided 40 food webs (according to the data he collected) into those associated with variable (positions 1-28 in Table 21.2) and constant (positions 29-40) environments. There were no significant differences in the average length of the maximum food chains between these groups: the number of trophic levels was 3.66 and 3.60, respectively (Fig. 21.9). These provisions still need critical scrutiny. [...]

In addition, the simulation results become different when it is taken into account that consumer populations are influenced by food resources, and those do not depend on the influence of consumers (¡3, / X), 3 (/ \u003d 0: the so-called "donor-regulated system" ), In a food web of this type, resilience is either independent of complexity or increases with it (DeAngelis, 1975). In practice, the only group of organisms that usually satisfies this condition are detritus feeders. [...]

However, such a strict picture of the transition of energy from level to level is not entirely realistic, since the trophic chains of ecosystems are complexly intertwined, forming food webs. For example, the phenomenon of a “trophic cascade”, when, as a result of predation, there is a change in density, biomass, or productivity of a population, community, or trophic level along more than one line of the food web (Pace et al., 1999). P. Mitchell (2001) gives such an example: sea otters feed on sea urchins that eat brown algae, the destruction of otters by hunters led to the destruction of brown algae due to the growth of the hedgehog population. When otter hunting was banned, algae began to return to their habitats. [...]

Green plants convert the energy of photons of sunlight into the energy of chemical bonds of complex organic compounds, which continue their way along branched food webs natural ecosystems... However, in some places (for example, in swamps, in river estuaries and seas), part of the organic plant matter, having fallen to the bottom, is covered with sand before it becomes food for animals or microorganisms. In the presence of a certain temperature and pressure of soil rocks for thousands and millions of years, coal, oil and other fossil fuels are formed from organic substances or, in the words of V. I. Vernadsky, “living matter goes into geology.” [...]

Examples of food chains: plants - herbivorous animals - predator; grass-field mouse-fox; fodder plants - cow - man. As a rule, each species feeds on more than one and only species. Therefore, food chains intertwine to form a food web. The more strongly organisms are connected with each other by food webs and other interactions, the more resilient the community is against possible disturbances. Natural, undisturbed ecosystems strive for balance. The state of equilibrium is based on the interaction of biotic and abiotic environmental factors. [...]

For example, the destruction of economically significant pests in forests with pesticides, the removal of part of animal populations, and the catch of certain species of commercial fish are partial obstacles, since they affect only certain links of the food chain, without affecting the food webs as a whole. The more complex the food web, the structure of the ecosystem, the less the significance of such interference, and vice versa. At the same time, the release and discharge into the atmosphere or water of chemical xenobiotics, such as oxides of sulfur, nitrogen, hydrocarbons, fluorine compounds, chlorine, heavy metals, radically changes the quality of the environment, interferes at the level of producers as a whole, and therefore leads to complete ecosystem degradation: as the main trophic level dies - producers. [...]

Volatile capacity \u003d (/ gL -) / k V. Energy diagram of a primitive system in Uganda. D. Energy scheme agriculture in India, where light is the main source of energy, but the flow of energy through livestock and grain is controlled by humans. D. Energy network of highly mechanized agriculture. High yields are based on a significant investment of energy through the use of fossil fuels, due to which work previously done by humans and animals is performed; at the same time, the food web of animals and plants falls out, which had to be “fed” in the two previous systems. [...]

A number of attempts have been made to analyze mathematically the relationship between the complexity of a community and its resilience, most of which the authors came to approximately the same conclusions. May (1981) reviewed such publications. As an example, consider his work (May, 1972), which demonstrates both the method itself and its disadvantages. Each species was influenced by its interactions with all other species; quantitatively, the influence of the density of the species / on the growth of the number i was estimated by the indicator p. In the complete absence of influence, it is equal to zero, in two competing species Pc and Pji are negative, in the case of a predator (¿) and prey (/) Ru is positive, and jjji is negative. [...]

Acidic precipitation causes lethal consequences for life in rivers and bodies of water. Many lakes of Scandinavia and the eastern part North America turned out to be so acidified that the fish cannot not only spawn in them, but also simply survive. In the 70s, fish completely disappeared in half of the lakes in these regions. The most dangerous is acidification of oceanic shallow waters, leading to the impossibility of reproduction of many marine invertebrates, which can cause rupture of food webs and deeply disturb the ecological balance in the oceans. [...]

Models of donor-controlled interactions differ in a number of ways from traditional models of predator-prey interactions of Lotka-Vol-terra (Ch. 10). One of the important differences is that it is believed that interacting groups of species, which are characterized by donor-controlled dynamics, are especially stable and, further, that this resistance does not actually depend on the increase in species diversity and complexity of the food web, or even increases. This situation is completely opposite to that in which the Lotka-Volterra model applies. We will discuss these important issues of food web complexity and community resilience in more detail in Chap. 21.