Most living organisms eat organic food, this is the specificity of their life on our planet. Among this food are plants, and the meat of other animals, their products of activity and dead matter, ready for decomposition. The very process of nutrition in different species of plants and animals occurs in different ways, but the so-called They always form, they transform matter and energy, and nutrients can thus pass from one creature to another, carrying out the circulation of substances in nature.

In the woods

Forests of various kinds cover quite a lot of land surface. It is the lungs and the instrument of cleansing our planet. It is not for nothing that many progressive modern scientists and activists oppose mass deforestation today. The food chain in the forest can be quite diverse, but, as a rule, includes no more than 3-5 links. In order to understand the essence of the issue, let us turn to the possible components of this chain.

Producers and consumers

1. The first are autotrophic organisms that feed on inorganic food. They take energy and matter to create their own bodies, using gases and salts from their environment. An example is green plants that get their nutrition from sunlight through photosynthesis. Or numerous types of microorganisms that live everywhere: in the air, in the soil, in the water. It is the producers that for the most part make up the first link in almost any food chain in the forest (examples will be given below).
2. The second are heterotrophic organisms that feed on organic matter. Among them are those of the first order that directly carry out nutrition at the expense of plants and bacteria, producers. The second order - those who eat animal food (predators or carnivores).

Plants

As a rule, the food chain in the forest begins with them. They are the first link in this cycle. Trees and shrubs, grasses and mosses obtain food from inorganic substances using sunlight, gases and minerals. A food chain in a forest, for example, may begin with a birch tree, the bark of which is eaten by a hare, who, in turn, is killed and eaten by a wolf.

herbivorous animals

In a variety of forests, animals that feed on plant foods are found in abundance. Of course, for example, it is very different in its content from the lands of the middle zone. Various species of animals live in the jungle, many of which are herbivores, which means they make up the second link in the food chain, eating plant foods. From elephants and rhinos to barely visible insects, from amphibians and birds to mammals. So, in Brazil, for example, there are more than 700 species of butterflies, almost all of them are herbivores.

Poorer, of course, is the fauna in the forest belt of central Russia. Accordingly, there are much fewer options for the supply chain. Squirrels and hares, other rodents, deer and elk, hares - this is the basis for such chains.

Predators or carnivores

They are called so because they eat flesh, eating the meat of other animals. They occupy a dominant position in the food chain, often being the final link. In our forests, these are foxes and wolves, owls and eagles, sometimes bears (but in general they belong to which they can eat both plant and animal food). In the food chain, both one and several predators can take part, eating each other. The final link, as a rule, is the largest and most powerful carnivore. In the forest of the middle lane, this role can be played, for example, by a wolf. There are not too many such predators, and their population is limited by the food base and energy reserves. Since, according to the law of conservation of energy, when nutrients pass from one link to the next, up to 90% of the resource can be lost. This is probably why the number of links in most food chains cannot exceed five.

Scavengers

They feed on the remains of other organisms. Oddly enough, there are also quite a lot of them in the nature of the forest: from microorganisms and insects to birds and mammals. Many beetles, for example, use the corpses of other insects and even vertebrates as food. And bacteria are able to decompose the dead bodies of mammals in a fairly short time. Scavenging organisms play a huge role in nature. They destroy matter, transforming it into inorganic substances, release energy, using it for their life activity. If it were not for scavengers, then, probably, the entire earthly space would be covered with the bodies of animals and plants that have died for all time.

In the woods

To make a food chain in the forest, you need to know about those inhabitants who live there. And also about what these animals can eat.

1. Birch bark - insect larvae - small birds - birds of prey.
2. Fallen leaves - bacteria.
3. Butterfly caterpillar - mouse - snake - hedgehog - fox.
4. Acorn - mouse - fox.
5. Cereals - mouse - eagle owl.

There are also more authentic ones: fallen leaves - bacteria - earthworms - mice - mole - hedgehog - fox - wolf. But, as a rule, the number of links is not more than five. The food chain in a spruce forest is slightly different from that in a deciduous forest.

1. Cereal seeds - sparrow - wild cat.
2. Flowers (nectar) - butterfly - frog - already.
3. Fir cone - woodpecker - eagle.

Food chains can sometimes intertwine with each other, forming more complex, multi-level structures that combine into a single forest ecosystem. For example, the fox does not disdain to eat both insects and their larvae and mammals, so several food chains intersect.

Food or trophic chain called the relationship between different groups of organisms (plants, fungi, animals and microbes), in which energy is transported as a result of eating some individuals by others. Energy transfer is the basis for the normal functioning of an ecosystem. Surely these concepts are familiar to you from the 9th grade of the school from the general biology course.

Individuals of the next link eat the organisms of the previous link, and this is how matter and energy are transported along the chain. This sequence of processes underlies the living cycle of substances in nature. It is worth saying that a huge part of the potential energy (about 85%) is lost during the transfer from one link to another, it dissipates, that is, it is dissipated in the form of heat. This factor is limiting in relation to the length of food chains, which in nature usually have 4-5 links.

Types of food relationships

Within ecosystems, organic matter is produced by autotrophs (producers). Plants, in turn, are eaten by herbivorous animals (first-order consumers), which are then eaten by carnivores (second-order consumers). This 3-link food chain is an example of a proper food chain.

Distinguish:

pasture chains

Trophic chains begin with auto- or chemotrophs (producers) and include heterotrophs in the form of consumers of various orders. Such food chains are widely distributed in terrestrial and marine ecosystems. They can be drawn and compiled in the form of a diagram:

Producers —> Consumers of the 1st order —> Consumers of the 1st order —> Consumers of the 3rd order.

A typical example is the meadow food chain (this can be both a forest zone and a desert, in which case only the biological species of various participants in the food chain and the branching of the network of food interactions will differ).

So, with the help of the energy of the Sun, a flower produces nutrients for itself, that is, it is a producer and the first link in the chain. A butterfly that feeds on the nectar of this flower is a consumer of the first order and the second link. The frog, which also lives in the meadow and is an insectivorous animal, eats a butterfly - the third link in the chain, a consumer of the second order. A frog is swallowed already - the fourth link and consumer of the III order, a hawk is eaten by a hawk - a consumer of the IV order and the fifth, as a rule, the last link in the food chain. A person can also be present in this chain as a consumer.

In the waters of the World Ocean, autotrophs, represented by unicellular algae, can exist only as long as sunlight is able to penetrate through the water column. This is a depth of 150-200 meters. Heterotrophs can also live in deeper layers, rising to the surface at night to feed on algae, and in the morning again leaving to the usual depth, while making vertical migrations up to 1 km per day. In turn, heterotrophs, which are consumers of subsequent orders, living even deeper, in the morning rise to the level of habitation of consumers of the first order in order to feed on them.

Thus, we see that in deep water bodies, as a rule, seas and oceans, there is such a thing as a “food ladder”. Its meaning lies in the fact that organic substances that are created by algae in the surface layers of the earth are transferred along the food chain to the very bottom. Given this fact, the opinion of some ecologists that the entire reservoir can be considered a single biogeocenosis can be considered reasonable.

Detrital trophic relationships

To understand what a detrital food chain is, you need to start with the very concept of “detritus”. Detritus is a collection of the remains of dead plants, corpses and end products of animal metabolism.

Detritus chains are typical for communities of inland waters, the bottom of lakes with great depth, and oceans, many of whose representatives feed on detritus formed by the remains of dead organisms from the upper layers or accidentally falling into a reservoir from ecological systems located on land, in the form, for example , leaf litter.

The bottom ecological systems of the oceans and seas, where there are no producers due to the lack of sunlight, can only exist at the expense of detritus, the total mass of which in the World Ocean for a calendar year can reach hundreds of millions of tons.

Also, detrital chains are common in forests, where a considerable part of the annual increase in the biomass of producers cannot be eaten directly by the first link of consumers. Therefore, it dies off, forming litter, which, in turn, is decomposed by saprotrophs, and then mineralized by decomposers. Fungi play an important role in the formation of detritus in forest communities.

Heterotrophs that feed directly on detritus are detritivores. In terrestrial ecological systems, detritivores include some types of arthropods, in particular insects, as well as annelids. Large detritus feeders among birds (vultures, crows) and mammals (hyenas) are usually called scavengers.

In the ecological systems of waters, the bulk of detritus feeders are aquatic insects and their larvae, as well as some representatives of crustaceans. Detritophages can serve as food for larger heterotrophs, which, in turn, can later become food for higher-order consumers.

The links in the food chain are also called trophic levels. By definition, this is a group of organisms that occupies a specific place in the food chain and represents a source of energy for each of the subsequent levels - food.

organisms I trophic level in pasture food chains are primary producers, autotrophs, that is, plants, and chemotrophs - bacteria that use the energy of chemical reactions to synthesize organic substances. In detrital systems, autotrophs are absent, and trophic level I of the detrital trophic chain forms detritus itself.

Last, V trophic level represented by organisms that consume dead organic matter and end products of decay. These organisms are called destructors or decomposers. Decomposers are mainly represented by invertebrates that are necro-, sapro- and coprophages, using remains, waste and dead organic matter as food. This group also includes saprophage plants that decompose leaf litter.

The level of destructors also includes heterotrophic microorganisms capable of converting organic substances into inorganic (mineral) ones, forming the final products - carbon dioxide and water, which return to the ecological system and re-enter the natural cycle of substances.

The Importance of Nutritional Relationships

In nature, any species, population, and even a single 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.

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

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

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

Ecological systems

Functional systems that include communities of living organisms of different species and their habitats. The connections between the components of the ecosystem arise, first of all, on the basis of food relationships and ways 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 be preserved and function for an indefinitely long time. Biotic community (biocenosis) consists of a community of plants ( phytocenosis), animals ( zoocenosis), microorganisms ( microbiocenosis).

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

The existence of an ecosystem is possible due to the constant influx of energy from the outside - such an energy source, as a rule, is the sun, although this is not true for all ecosystems. The stability of an ecosystem is ensured by direct and feedback links 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. Tensley 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, which ensures the potential immortality of biogeocenosis due to the energy produced by plants. ecosystems may not contain phytocenosis.

Phytocenosis

A plant community that has historically developed as a result of a combination of interacting plants in a homogeneous area.

He is characterized:

- a certain species composition,

- life forms

- tiered (aboveground and underground),

- abundance (frequency of occurrence of species),

- accommodation,

- aspect (appearance),

- vitality

- seasonal changes,

- development (change of communities).

Layered (number of floors)

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

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

According to the method of obtaining and using nutrients All organisms are divided into autotrophs and heterotrophs. In nature, there is a continuous circulation of biogenic substances necessary for life. Chemical substances are extracted by autotrophs from the environment and returned to it through heterotrophs. This process takes on very complex forms. Each species uses only a 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. The basis of them are green plants - producers. Herbivorous and carnivorous animals are necessarily present: consumers of organic matter - consumers and destroyers of organic residues - decomposers.

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

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

Any link broken 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 site, other food chains will develop and another biocenosis will form, which will take more than a dozen years.

Food chain (trophic or food )

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

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 is carried out.

Ecosystem components:

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

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

- decomposers - 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 food. The idea 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 second order - predators that feed on herbivorous animals),
4. the fourth - consumers of the III order (secondary predators).

There are the following types food chains:

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

- detritus chains (decomposition chains) begin with detritus - dead biomass. For example: leaf litter -> earthworms -> bacteria. A feature of detrital chains is also that in them plant products 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, the inhabitants of which feed on dead organisms that have descended from the upper layers of the water.

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. Simplified, the food web can be represented as intertwining food chains.

Organisms of different food chains that receive food through an equal number of links in these chains are 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 represented graphically as ecological pyramid.

ecological pyramid

A way to graphically display the ratio of different trophic levels in an ecosystem - there are three types:

The abundance pyramid reflects the abundance 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 in a given amount of time.

Ecological pyramid rule

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

Pyramid of numbers

An ecological pyramid showing 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 - 150000, herbivorous consumers - 20000, carnivorous consumers - 9000 ind./ar. The meadow biocenosis is characterized by the following number of individuals on an area of ​​4000 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 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 herbivores (consumers of the 1st order), and the mass of herbivores is 10 times greater than the mass of carnivores (consumers of the 2nd order), t i.e. each subsequent food level has a mass 10 times less than the previous one. On average, out of 1000 kg of plants, 100 kg of the body of herbivores is formed. Predators eating herbivores can build 10 kg of their biomass, secondary predators - 1 kg.

energy pyramid

expresses a pattern according to which the flow of energy gradually decreases and depreciates in the transition from link to link in the food chain. So, 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 second order, using consumers of the first order for food, create their own biomass containing 5.46 kJ / cm 2. The loss of energy during the transition from consumers of the 1st order to consumers of the 2nd order, if they are warm-blooded animals, increases. This is explained by the fact that in these animals a lot of energy is spent not only on building their biomass, but also on maintaining a constant body temperature. If we compare the cultivation of a calf and a perch, then the same amount of food energy expended will give 7 kg of beef and only 1 kg of fish, since the calf feeds on grass, and the predatory perch feeds on fish.

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

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 given period of time). Therefore, when fast-growing species are among the producers, the biomass pyramid may turn upside down.

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 pyramid of energy always tapers upward and is never inverted.

Ecological plasticity

The degree of endurance of organisms or their communities (biocenoses) to the effects of environmental factors. Ecologically plastic species have a wide range of reaction rate , i.e., widely adapted to different habitats (stickleback and eel fish, 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 energy contained in it. Biomass is usually expressed in units of mass in terms of dry matter per unit area or volume. Biomass can be determined separately for animals, plants or individual species. 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 there are primary and secondary biological productivity :

ü Primary biological productivity of biocenoses- the total total productivity of photosynthesis, which is the result of the activity of autotrophs - green plants, for example, a 20-30-year-old pine forest 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 population dynamics.

Each species on Earth occupies a certain range because it can exist only under certain environmental conditions. However, the habitat 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 habitat conditions), freely interbreeding with each other (having a common gene pool) and isolated from other populations of a given species, possessing all the necessary conditions to maintain their 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 features of the distribution of individuals of a population in space.

Age structure population is related to 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 a seedling, juvenile plant, immature and virginal plants);

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

Post-generative (includes the states of subsenile, senile plants and the dying phase).

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

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

larvae,

pupae,

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 declining line:

1. If the mortality rate does not depend on the age of individuals, the death of individuals occurs evenly in this type, the mortality rate remains constant throughout life ( type I ). Such a survival curve is characteristic of species whose development occurs without metamorphosis with sufficient stability of the born offspring. This type is 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 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 somewhere between types I and II). This type is called Drosophila type: this is what Drosophila demonstrates in laboratory conditions (not eaten by predators).
3. Many species are characterized by high mortality in the early stages of ontogeny. In such species, the survival curve is characterized by a sharp drop in the region of younger ages. Individuals that have survived the “critical” age demonstrate low mortality and survive to older ages. The type is named oyster type (type III ).

Sex structure populations

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

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

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

- Secondary sex ratio - this is the sex ratio at the time of birth (among newborns). It can differ significantly from the primary one for a number of reasons: the selectivity of eggs 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 characteristic of some insects. So, in ants, fertilization is ensured at temperatures above 20 ° C, and unfertilized eggs are laid at lower temperatures. Males hatch from the latter, and mostly females from the fertilized ones.

- Tertiary sex ratio - 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 the behavior of animals;

- random 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 desire to unite in groups (for example, in a beetle in flour).

Population size denoted by the letter N. The ratio of the increase N to the unit time dN / dt expressesinstantaneous speedchanges in population size, i.e. change in population at time t.Population Growthdepends on two factors - fertility and mortality, provided there is no emigration and immigration (such a population is called isolated). The difference between birth rate b and death rate d and 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. One of the most important conditions for sustainability is internal diversity. In relation to a population, these are mechanisms for maintaining a certain population density.

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 species of birds 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 the density of the population.

The third type ( III ) characteristic of populations in which the “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, for the resumption of populations of heterosexual animals, at least a density is needed that provides a sufficient probability of meeting a male and a female.

Thematic tasks

A1. Biogeocenosis is 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. The 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 that occur 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) the stability of the gene pool in populations

A6. Reducers are

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 that became a source of food for this consumer?

A8. Specify the detrital food chain

1) fly - spider - sparrow - bacteria

2) clover - hawk - bumblebee - mouse

3) rye - titmouse - 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) blackbirds

4) wolves

A11. In one ecosystem you can find oak and

1) gopher

3) lark

4) blue cornflower

A12. Power networks are:

1) relationships between parents and offspring

2) family (genetic) ties

3) metabolism in the cells of the body

4) ways of transferring substances and energy in an 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) food chain structure

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) relationships between species belonging to different functional groups. It is on the basis of these bonds that organic substances synthesized by producers from mineral substances with the absorption of solar energy are transferred to consumers and undergo chemical transformations. As a result of the vital activity of predominantly decomposers, the atoms of the main biogenic chemical elements pass from organic substances to inorganic substances (CO 2, NH 3, H 2 S, H 2 O). Then inorganic substances are used by producers to create new organic substances from them. And they are again involved in the cycle with the help of producers. If these substances were not used repeatedly, life on Earth would be impossible. After all, the reserves of substances absorbed by producers are not unlimited in nature. To implement a full-fledged cycle of substances in an ecosystem, all three functional groups of organisms must be available. And between them there must be constant interaction in the form of trophic links with the formation of trophic (food) chains, or food chains.

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

In this case, one organism can eat another, eat 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).

Pasture chains (grazing chains)- food chains that start with producers and include consumers of different orders. In general, a pasture chain can be shown by the following diagram:

Producers -> Consumers of the 1st order -> Consumers of the 2nd order -> Consumers of the 3rd order

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

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

Trophic level - a set of organisms that, depending on the way they eat and the type of food, make up a certain link in the food chain.

Trophic levels are usually numbered. The first trophic level is made up of autotrophic organisms - plants (producers), at the second trophic level there are herbivorous animals (consumers of the first order), at the third and subsequent levels - carnivores (consumers of the second, third, etc. orders).

In nature, almost all organisms feed on not one, but 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, linking them together. So, a hawk can eat a lizard, a hare or a snake, which are part of different food chains.

In nature, pasture chains in their pure form are not found. They are interconnected by common food links and form food web, or power network. Its presence in the ecosystem contributes to the survival of organisms with a lack of a certain type of food due to the ability to use other food. And the wider the species diversity of individuals in the ecosystem, the more food chains 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, as food sources from other food chains can be used.

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

For example: a 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 is closed in nature. Dead organic substances in detrital chains are converted into minerals, which enter the environment, and from it are absorbed by plants (producers).

Pasture chains are predominantly located in the above-ground, and decomposition chains - in the underground tiers of ecosystems. The relationship between pasture chains and detrital chains is carried out through detritus that enters the soil. Detrital chains are connected with pasture chains through mineral substances extracted from the soil by producers. Due to the interconnection of pasture and detrital chains, a complex food web is formed in the ecosystem, which ensures the constancy of the processes of transformation of matter and energy.

Ecological pyramids

The process of transformation of matter and energy in pasture chains has certain regularities. At each trophic level of the pasture chain, not all of the eaten biomass is used to form the biomass of consumers of 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 absorbed and enters the environment in the form of waste products. In other words, most of the matter and the energy contained in it is lost when moving from one trophic level to another. The percentage of digestibility varies greatly and depends on the composition of the food and the biological characteristics of the 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% goes to the next level. The American ecologist R. Lindeman in 1942 formulated this pattern as 10% rule. Using this rule, you can calculate the amount of energy at any trophic level of the food chain, if its rate 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 the food chain to determine the number of individuals, or their biomass, or the amount of energy contained in it, then it becomes obvious that these values ​​decrease 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 ecological pyramid rule and offered to express graphically. If any of the above characteristics of trophic levels are depicted as rectangles with the same scale and placed one above the other, then we get ecological pyramid.

Three types of ecological pyramids are known. Pyramid of numbers reflects the number of individuals in each link in the food chain. However, in the ecosystem, the second trophic level ( consumers of the 1st order) can be numerically richer than the first trophic level ( producers). In this case, an inverted pyramid of numbers is obtained. This is due to the participation in such pyramids of individuals that are not equivalent 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. The pyramid of biomass in terrestrial ecosystems is correct. And in the biomass pyramid 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 a high rate of product formation, in the end, their biomass per season will still be greater than the biomass of first-order consumers. And this means that the rule of the ecological pyramid is also observed in aquatic ecosystems. energy pyramid reflects patterns of energy expenditure at different trophic levels.

Thus, the stock 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 the ecosystem, producers, consumers and decomposers are connected by trophic relationships and form food chains: pasture and detrital. In pasture chains, the 10% rule and the ecological pyramid rule apply. Three types of ecological pyramids can be built: numbers, biomass and energy.

There are complex nutritional interactions between autotrophs and heterotrophs in ecosystems. Some organisms eat others, and thus carry out the transfer of substances and energy - the basis of the functioning of the ecosystem.

Within an ecosystem, organic matter is created by autotrophic organisms, such as plants. Plants are eaten by animals, which in turn are eaten by other animals. Such a sequence is called a food chain (Fig. 1), and each link in the food chain is called a trophic level.

Distinguish

pasture food chains(eating chains) - food chains that begin with autotrophic photosynthetic or chemosynthetic organisms (Fig. 2.). Pasture food chains are predominantly found in terrestrial and marine ecosystems.

An example is the grassland food chain. Such a chain begins with the capture of solar energy by a plant. A butterfly feeding on the nectar of a flower is the second link in this chain. Dragonfly - a predatory flying insect - attacks a butterfly. A frog hiding among the green grass catches a dragonfly, but itself serves as prey for such a predator as snake. He could have digested a frog all day, but before the sun had set, he himself became the prey of another predator.

The food chain, going from the plant through the butterfly, dragonfly, frog, grass snake to the hawk, indicates the direction of the movement of organic substances, as well as the energy contained in them.

In the oceans and seas, autotrophic organisms (unicellular algae) exist only up to the depth of light penetration (up to a maximum of 150-200 m). Heterotrophic organisms living in deeper layers of water rise to the surface at night to feed on algae, and in the morning again go to the depth, making daily vertical migrations up to 500-1000 m long. In turn, with the onset of morning, heterotrophic organisms from even deeper layers rise to the top to feed on the descending from the surface layers of other organisms.

Thus, in the deep seas and oceans there is a kind of "food ladder", thanks to which the organic matter created by autotrophic organisms in the surface layers of water is transferred along the chain of living organisms to the very bottom. In this regard, some marine ecologists consider the entire water column to be a single biogeocenosis. Others believe that the environmental conditions in the surface and bottom layers of water are so different that they cannot be considered as a single biogeocenosis.

Detrital food webs(decomposition chains) - food chains that begin with detritus - dead plant remains, corpses and animal excrement (Fig. 2).

Detrital chains are most typical for communities of continental water bodies, the bottom of deep lakes, and oceans, where many organisms feed on detritus formed by dead organisms of the upper illuminated layers of a water body or that have entered the water body from terrestrial ecosystems, for example, in the form of leaf litter.

The ecosystems of the bottom of the seas and oceans, where sunlight does not penetrate, exist only due to the constant settling of dead organisms that live in the surface layers of water. The total mass of this substance in the World Ocean per year reaches at least several hundred million tons.

Detrital chains are also widespread in forests, where most of the annual increase in the live weight of plants is not consumed directly by herbivorous animals, but dies off, forming litter, and then decomposes by saprotrophic organisms, followed by mineralization by decomposers. Mushrooms are of great importance in the decomposition of dead plant residues, especially wood.

Heterotrophic organisms that feed directly on detritus are called detritophages. In terrestrial ecosystems, they are many species of insects, worms, etc. Large detritivores, which include some species of birds (vultures, crows, etc.) and mammals (hyenas, etc.) are called scavengers.

In aquatic ecosystems, the most common detritophages are arthropods - aquatic insects and their larvae, and crustaceans. Detritophages can feed on other, larger heterotrophic organisms, which themselves can serve as food for predators.

Trophic levels

Typically, different trophic levels in ecosystems are not spatially separated. However, in some cases they are quite clearly differentiated. For example, in geothermal springs, autotrophic organisms - blue-green algae and autotrophic bacteria that form specific algal-bacterial communities ("mats") are common at temperatures above 40-45 ° C. At lower temperatures, they do not survive.

On the other hand, heterotrophic organisms (molluscs, larvae of aquatic insects, etc.) do not occur in geothermal springs at temperatures above 33–36°C, so they feed on mat fragments carried by the current to zones with lower temperatures.

Thus, in such geothermal springs, an autotrophic zone is clearly distinguished, where only autotrophic organisms are distributed, and a heterotrophic zone, where autotrophic organisms are absent and only heterotrophic organisms are found.

food webs

In ecological systems, despite the existence of a number of parallel food chains, for example,

herbaceous vegetation -> rodents -> small carnivores
herbaceous vegetation -> ungulates -> large carnivores,

which unite the inhabitants of the soil, herbaceous cover, tree layer, there are other relationships. In most cases, the same organism can serve as a food source for many organisms and thus be part of different food chains and prey to different predators. For example, daphnia can be eaten not only by small fish, but also by the predatory crustacean cyclops, and roach can be eaten not only by pike, but also by otters.

The trophic structure of the community reflects the ratio between producers, consumers (separately of the first, second, etc. orders) and decomposers, expressed either by the number of individuals of living organisms, or by their biomass, or by the energy contained in them, calculated per unit area per unit time.