Living organisms require energy and nutrients to exist. Autotrophs transform the radiant energy of the Sun in the process of photosynthesis, synthesizing organic substances from carbon dioxide and water.

Heterotrophs use these organic substances in the process of nutrition, ultimately decomposing them again into carbon dioxide and water, and the energy accumulated in them is spent on various processes vital activity of organisms. Thus, the light energy of the Sun turns into chemical energy of organic substances, and then into mechanical and thermal energy.

All living organisms in the ecological system can be divided into three according to the type of nutrition functional groups- producers, consumers, decomposers.

1. Producers- these are green autotrophic plants that produce organic substances from inorganic ones and are capable of accumulating solar energy.

2. Consumers- These are heterotrophic animals that consume ready-made organic substances. First order consumers can use organic matter from plants (herbivores). Heterotrophs that use animal food are divided into consumers of orders II, III, etc. (carnivores). They all use energy chemical bonds, stored in organic matter by producers.

3. Decomposers- These are heterotrophic microorganisms, fungi, that destroy and mineralize organic residues. Thus, decomposers, as it were, complete the cycle of substances, forming inorganic substances to enter a new cycle.

The sun provides a constant supply of energy, and living organisms eventually dissipate it as heat. During the life activity of organisms, a constant cycle of energy and substances occurs, and each species uses only part of the energy contained in organic substances. As a result, there are power circuit - trophic chains, food chains, representing a sequence of species that extract organic matter and energy from the original food substance, with each previous link becoming food for the next (Fig. 98).

Rice. 98. General scheme food chain

In every link most energy is consumed in the form of heat and is lost, which limits the number of links in the chain. But most chains begin with a plant and end with a predator, and the largest one at that. Decomposers break down organic matter at every level and are the final link in the food chain.

Due to the decrease in energy at each level, there is a decrease in biomass. Trophic chain usually has no more than five levels and is an ecological pyramid, with a wide base at the bottom and tapering at the top (Fig. 99).

Rice. 99. Simplified diagram of the ecological pyramid of biomass (1) and pyramid of numbers (2)

Ecological pyramid rule reflects the pattern according to which in any ecosystem the biomass of each next link is 10 times less than the previous one.

There are three types of ecological pyramids:

A pyramid reflecting the number of individuals at each level of the food chain - pyramid of numbers;

Biomass pyramid organic matter, synthesized at each level, - mass pyramid(biomass);

- energy pyramid, showing the amount of energy flow. Typically the power chain consists of 3-4 links:

plant → hare → wolf;

plant → vole → fox → eagle;

plant → caterpillar → tit → hawk;

plant → gopher → viper → eagle.

However, in real conditions In ecosystems, different food chains intersect with each other, forming branched networks. Almost all animals, with the exception of rare ones specialized types, use a variety of food sources. Therefore, if one link in the chain falls out, there is no disruption to the system. The more species diversity and the richer the food webs, the more stable the biocenosis.

In biocenoses, two types of trophic networks are distinguished: pasture and detritus.

1. IN grassland type food web flow energy goes from plants to herbivorous animals, and then to consumers more high order. This gorging network. Regardless of the size of the biocenosis and habitat, herbivorous animals (terrestrial, aquatic, soil) graze, eat up green plants and transfer energy to the next levels (Fig. 100).

Rice. 100. Pasture food network in a terrestrial biocenosis

2. If the flow of energy begins with dead plant and animal remains, excrement and goes to the primary detritivores - decomposers, partially decomposing organic matter, then such a trophic network is called detrital, or network of decomposition(Fig. 101). Primary detritivores include microorganisms (bacteria, fungi), small animals (worms, insect larvae).

Rice. 101. Detrital food chain

In terrestrial biogeocenoses, both types of trophic chain are present. In aquatic communities, the grazing chain predominates. In both cases, the energy is fully used.

Trophic chains form the basis of relationships in living nature, but food connections are not the only type of relationship between organisms. Some species can participate in the distribution, reproduction, settlement of other species, and create appropriate conditions for their existence. All the many and varied connections between living organisms and the environment ensure the existence of species in a stable, self-regulating ecosystem.

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§ 71. Ecological systems§ 73. Properties and structure of biocenoses

Introduction

A striking example of a power chain:

Classification of living organisms regarding their role in the cycle of substances

Any food chain involves 3 groups of living organisms:

Connections between organisms in the food chain

The food chain, whatever it may be, creates close ties between different different objects both living and non-living nature. And the rupture of absolutely any link can lead to disastrous results and an imbalance in nature. The most important and integral component of any power chain is solar energy. Without it, there will be no life. When moving along the food chain, this energy is processed, and each organism makes it its own, passing only 10% to the next link.

When dying, the body enters other similar food chains, and thus the cycle of substances continues. All organisms can easily leave one food chain and move into another.

The role of natural areas in the cycle of substances

Naturally, organisms living in the same natural area, create their own special food chains with each other, which cannot be repeated in any other zone. Thus, the food chain of the steppe zone, for example, consists of a wide variety of grasses and animals. The food chain in the steppe practically does not include trees, since there are either very few of them or they are stunted. As for the animal world, artiodactyls, rodents, falcons (hawks and other similar birds) and various kinds of insects predominate here.

Classification of power circuits

The principle of ecological pyramids

If we consider specifically the chains starting with plants, then the entire cycle of substances in them comes from photosynthesis, during which solar energy is absorbed. Plants spend most of this energy on their vital functions, and only 10% goes to the next link. As a result, each subsequent living organism requires more and more more creatures(objects) of the previous link. This is shown well ecological pyramids, which are most often used for these purposes. They are pyramids of mass, quantity and energy.

Cycle of substances in nature and food chains

All living organisms are active participants in the cycle of substances on the planet. Using oxygen carbon dioxide, water, mineral salts and other substances, living organisms eat, breathe, secrete products of activity, and reproduce. After death, their bodies decompose into simple substances and return to the external environment.

Transfer chemical elements from living organisms to the environment and back does not stop for a second. Thus, plants (autotrophic organisms) are taken from external environment carbon dioxide, water and mineral salts. In doing so, they create organic matter and release oxygen. Animals (heterotrophic organisms), on the contrary, inhale the oxygen released by plants, and by eating plants, they assimilate organic substances and release carbon dioxide and food debris. Fungi and bacteria eat the remains of living organisms and convert organic substances into minerals, which accumulate in soil and water. A minerals are again absorbed by plants. This is how nature maintains a constant and endless cycle of substances and maintains the continuity of life.

The cycle of substances and all the transformations associated with it require a constant flow of energy. The source of such energy is the Sun.

On earth, plants absorb carbon from the atmosphere through photosynthesis. Animals eat plants, passing carbon up the food chain, which we'll talk about later. When plants and animals die, they transfer carbon back to the earth.

At the surface of the ocean, carbon dioxide from the atmosphere dissolves into the water. Phytoplankton absorb it for photosynthesis. Animals that eat plankton exhale carbon into the atmosphere and thereby transmit it further along the food chain. After the death of phytoplankton, it can be processed into surface waters or settle to the bottom of the ocean. Over millions of years, this process has transformed the ocean floor into the planet's rich carbon reservoir. Cold currents transport carbon to the surface. When water is heated, it is released as a gas and enters the atmosphere, continuing the cycle.

Water constantly circulates between the seas, the atmosphere and the land. Under the rays of the sun it evaporates and rises into the air. There, droplets of water collect into clouds and clouds. They fall to the ground as rain, snow or hail, which turns back into water. Water is absorbed into the ground and returned to the seas, rivers and lakes. And everything starts all over again. This is how the water cycle occurs in nature.

Most of the water is evaporated by the oceans. The water in it is salty, and the water that evaporates from its surface is fresh. Thus, the ocean is the world's "factory" fresh water, without which life on Earth is impossible.

THREE STATES OF MATTER. There are three states of matter: solid, liquid and gaseous. They depend on temperature and pressure. IN everyday life we can observe water in all three of these states. Moisture evaporates and goes from a liquid state to a gaseous state, that is, water vapor. It condenses and turns into liquid. At sub-zero temperatures, water freezes and turns into solid state- ice.

Gyre complex substances in living nature includes food chains. This is a linear closed sequence in which each living creature feeds on someone or something and itself serves as food for another organism. Within the grassland food chain, organic matter is created by autotrophic organisms such as plants. Plants are eaten by animals, which in turn are eaten by other animals. Decomposer fungi decompose organic remains and serve as the beginning of the detrital trophic chain.

Each link in the food chain is called a trophic level (from the Greek word “trophos” - “nutrition”).
1. Producers, or producers, produce organic substances from inorganic ones. Producers include plants and some bacteria.
2. Consumers, or consumers, consume ready-made organic substances. First-order consumers feed on producers. 2nd order consumers feed on 1st order consumers. Consumers of the 3rd order feed on consumers of the 2nd order, etc.
3. Reducers, or destroyers, destroy, that is, mineralize organic substances to inorganic ones. Decomposers include bacteria and fungi.

DETRITAL FOOD CHAINS. There are two main types of food chains - grazing (grazing chains) and detrital (decomposition chains). The basis of the pasture food chain is made up of autotrophic organisms that are eaten by animals. And in detrital trophic chains, most of the plants are not consumed by herbivores, but die and then decompose by saprotrophic organisms (for example, earthworms) and are mineralized. Thus, detrital trophic chains start from detritus, and then go to detritivores and their consumers - predators. On land, these are the chains that predominate.

WHAT IS AN ECOLOGICAL PYRAMID? The ecological pyramid is graphic image relationships between different trophic levels of the food chain. The food chain cannot contain more than 5-6 links, because when moving to each next link, 90% of the energy is lost. The basic rule of the ecological pyramid is based on 10%. So, for example, to form 1 kg of mass, a dolphin needs to eat about 10 kg of fish, and they, in turn, need 100 kg of food - aquatic vertebrates, which need to eat 1000 kg of algae and bacteria to form such mass. If these quantities are depicted on an appropriate scale in the order of their dependence, then a kind of pyramid is actually formed.

FOOD NETWORKS. Often the interactions between living organisms in nature are more complex and visually resemble a network. Organisms, especially carnivores, can feed on a wide variety of creatures from different food chains. Thus, food chains intertwine to form food webs.

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

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

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

Biogenocenosis- a self-regulating ecological system formed by people living together and interacting with each other and with inanimate nature, populations different types under relatively homogeneous environmental conditions.

Ecological systems

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

Ecosystem

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

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

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

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

Phytocenosis

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

He is characterized:

- a certain species composition,

- life forms,

- tiering (aboveground and underground),

- abundance (frequency of occurrence of species),

- accommodation,

- aspect (appearance),

- vitality,

- seasonal changes,

- development (change of communities).

Tiering (number of floors)

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

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

Underground tiering - mirror image aboveground: the roots of trees go deepest; the underground parts of mosses are located near the surface of the soil.

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

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

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

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

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

Food chain (trophic or food )

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

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

Ecosystem components:

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

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

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

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

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

The following types are distinguished: food chains:

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

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

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

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

Ecological pyramid

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

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

The biomass pyramid reflects the biomass of each trophic level;

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

Ecological pyramid rule

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

Number pyramid

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

Biomass pyramid

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

Pyramid of Energy

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

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

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

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

Ecological plasticity

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

Generally ecosystem (biogeocenosis) characterized by the following indicators:

Species diversity

Density of species populations,

Biomass.

Biomass

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

In biogeocenoses there are primary and secondary biological productivity :

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

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

Populations. Structure and dynamics of numbers.

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

Population

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

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

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

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

IN age structure of plant populations allocate following periods:

Latent - state of the seed;

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

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

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

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

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

Larvae,

dolls,

Imago (adult insect).

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

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

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

Sexual structure populations

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

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

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

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

- Tertiary sex ratio - sex ratio among adult animals.

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

Highlight three main types of distribution of individuals in space:

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

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

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

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

Population stability

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

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

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

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

Thematic assignments

A1. Biogeocenosis formed

1) plants and animals

2) animals and bacteria

3) plants, animals, bacteria

4) territory and organisms

A2. Consumers of organic matter in forest biogeocenosis are

1) spruce and birch

2) mushrooms and worms

3) hares and squirrels

4) bacteria and viruses

A3. Producers in the lake are

2) tadpoles

A4. The process of self-regulation in biogeocenosis affects

1) sex ratio in populations of different species

2) the number of mutations occurring in populations

3) predator-prey ratio

4) intraspecific competition

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

1) her ability to change

2) variety of species

3) fluctuations in the number of species

4) stability of the gene pool in populations

A6. Decomposers include

2) lichens

4) ferns

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

A8. Indicate the detrital food chain

1) fly – spider – sparrow – bacteria

2) clover – hawk – bumblebee – mouse

3) rye – tit – cat – bacteria

4) mosquito - sparrow - hawk - worms

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

1) organic compounds

2) inorganic compounds

4) chemosynthesis

1) hares

2) bees

3) fieldfare thrushes

4) wolves

A11. In one ecosystem you can find oak and

1) gopher

3) lark

4) blue cornflower

A12. Power networks are:

1) connections between parents and offspring

2) family (genetic) connections

3) metabolism in body cells

4) ways of transferring substances and energy in the ecosystem

A13. The ecological pyramid of numbers reflects:

1) the ratio of biomass at each trophic level

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

3) structure of the food chain

4) diversity of species at different trophic levels

Question 28. Food chain. Types of food chains.

FOOD CHAIN(trophic chain, food chain), the interconnection of organisms through food-consumer relationships (some serve as food for others). In this case, a transformation of matter and energy occurs from producers(primary producers) through consumers(consumers) to decomposers(converters of dead organic matter into inorganic substances assimilated by producers). There are 2 types of food chains - pasture and detritus. Pasture chain starts with green plants, goes to grazing herbivorous animals (consumers of the 1st order) and then to the predators that prey on these animals (depending on the place in the chain - consumers of the 2nd and subsequent orders). The detrital chain begins with detritus (a product of the breakdown of organic matter), goes to microorganisms that feed on it, and then to detritivores (animals and microorganisms involved in the process of decomposition of dying organic matter).

An example of a pasture chain is its multi-channel model in the African savanna. Primary producers are grass and trees, 1st order consumers are herbivorous insects and herbivores (ungulates, elephants, rhinoceroses, etc.), 2nd order are predatory insects, 3rd order are carnivorous reptiles (snakes, etc.), 4th – predatory mammals and birds of prey. In turn, detritivores (scarab beetles, hyenas, jackals, vultures, etc.) at each stage of the grazing chain destroy the carcasses of dead animals and the food remains of predators. The number of individuals included in the food chain in each of its links consistently decreases (the rule of the ecological pyramid), i.e., the number of victims each time significantly exceeds the number of their consumers. Food chains are not isolated from one another, but are intertwined with each other to form food webs.

Question 29. What are ecological pyramids used for? Name them.

Ecological pyramid- graphic images of the relationship between producers and consumers of all levels (herbivores, predators, species that feed on other predators) in the ecosystem.

The American zoologist Charles Elton suggested schematically depicting these relationships in 1927.

In a schematic representation, each level is shown as a rectangle, the length or area of ​​which corresponds to the numerical values ​​of a link in the food chain (Elton’s pyramid), their mass or energy. Rectangles arranged in a certain sequence create pyramids of various shapes.

The base of the pyramid is the first trophic level - the level of producers; subsequent floors of the pyramid are formed by the next levels of the food chain - consumers of various orders. The height of all blocks in the pyramid is the same, and the length is proportional to the number, biomass or energy at the corresponding level.

Ecological pyramids are distinguished depending on the indicators on the basis of which the pyramid is built. At the same time, the basic rule has been established for all pyramids, according to which in any ecosystem there are more plants than animals, herbivores than carnivores, insects than birds.

Based on the rule of the ecological pyramid, it is possible to determine or calculate the quantitative ratios of different species of plants and animals in natural and artificially created ecological systems. For example, 1 kg of mass of a sea animal (seal, dolphin) requires 10 kg of eaten fish, and these 10 kg already need 100 kg of their food - aquatic invertebrates, which, in turn, need to eat 1000 kg of algae and bacteria to form such a mass. IN in this case the ecological pyramid will be sustainable.

However, as you know, there are exceptions to every rule, which will be considered in each type of ecological pyramid.

The first ecological schemes in the form of pyramids were built in the twenties of the 20th century. Charles Elton. They were based on field observations of a number of animals of different size classes. Elton did not include primary producers and did not make any distinction between detritivores and decomposers. However, he noted that predators are usually larger than their prey, and realized that this ratio is extremely specific only to certain size classes of animals. In the forties American ecologist Raymond Lindeman applied Elton's idea to trophic levels, abstracting from the specific organisms that constitute them. However, while it is easy to distribute animals into size classes, it is much more difficult to determine which trophic level they belong to. In any case, this can only be done in a very simplified and generalized manner. Nutritional relationships and the efficiency of energy transfer in the biotic component of an ecosystem are traditionally depicted in the form of stepped pyramids. This provides a clear basis for comparison: 1) different ecosystems; 2) seasonal states of the same ecosystem; 3) different phases of ecosystem change. There are three types of pyramids: 1) pyramids of numbers, based on counting organisms at each trophic level; 2) biomass pyramids, which use the total mass (usually dry) of organisms at each trophic level; 3) energy pyramids, taking into account the energy intensity of organisms at each trophic level.

Types of ecological pyramids

pyramids of numbers- at each level the number of individual organisms is plotted

The pyramid of numbers displays a clear pattern discovered by Elton: the number of individuals making up a sequential series of links from producers to consumers is steadily decreasing (Fig. 3).

For example, to feed one wolf, he needs at least several hares for him to hunt; To feed these hares, you need a fairly large variety of plants. In this case, the pyramid will look like a triangle with a wide base tapering upward.

However, this form of a pyramid of numbers is not typical for all ecosystems. Sometimes they can be reversed, or upside down. This applies to forest food chains, where trees serve as producers and insects serve as primary consumers. In this case, the level of primary consumers is numerically richer than the level of producers (a large number of insects feed on one tree), therefore the pyramids of numbers are the least informative and least indicative, i.e. the number of organisms of the same trophic level largely depends on their size.

biomass pyramids- characterizes the total dry or wet mass of organisms at a given trophic level, for example, in units of mass per unit area - g/m2, kg/ha, t/km2 or per volume - g/m3 (Fig. 4)

Usually in terrestrial biocenoses the total mass of producers is greater than each subsequent link. In turn, the total mass of first-order consumers is greater than that of second-order consumers, etc.

In this case (if the organisms do not differ too much in size) the pyramid will also have the appearance of a triangle with a wide base tapering upward. However, there are significant exceptions to this rule. For example, in the seas, the biomass of herbivorous zooplankton is significantly (sometimes 2-3 times) greater than the biomass of phytoplankton, represented mainly by unicellular algae. This is explained by the fact that algae are very quickly eaten by zooplankton, but they are protected from complete consumption by the very high rate of division of their cells.

In general, terrestrial biogeocenoses, where producers are large and live relatively long, are characterized by relatively stable pyramids with a wide base. In aquatic ecosystems, where producers are small in size and have short life cycles, the pyramid of biomass can be inverted or inverted (with the tip pointing down). Thus, in lakes and seas, the mass of plants exceeds the mass of consumers only during the flowering period (spring), and during the rest of the year the opposite situation can occur.

Pyramids of numbers and biomass reflect the statics of the system, that is, they characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of an ecosystem, although they allow solving a number of practical problems, especially related to maintaining the sustainability of ecosystems.

The pyramid of numbers allows, for example, to calculate the permissible amount of fish catch or shooting of animals during the hunting season without consequences for their normal reproduction.

energy pyramids- shows the amount of energy flow or productivity at successive levels (Fig. 5).

In contrast to the pyramids of numbers and biomass, which reflect the statics of the system (the number of organisms at a given moment), the pyramid of energy, reflecting the picture of the speed of passage of food mass (amount of energy) through each trophic level of the food chain, gives the most complete picture of the functional organization of communities.

The shape of this pyramid is not affected by changes in the size and metabolic rate of individuals, and if all energy sources are taken into account, the pyramid will always have a typical appearance with a wide base and a tapering apex. When constructing a pyramid of energy, a rectangle is often added to its base to show the influx of solar energy.

In 1942, the American ecologist R. Lindeman formulated the law of the energy pyramid (the law of 10 percent), according to which, on average, about 10% of the energy received at the previous level of the ecological pyramid passes from one trophic level through food chains to another trophic level. The rest of the energy is lost in the form of thermal radiation, movement, etc. As a result of metabolic processes, organisms lose about 90% of all energy in each link of the food chain, which is spent on maintaining their vital functions.

If a hare ate 10 kg of plant matter, then it dead weight may increase by 1 kg. A fox or wolf, eating 1 kg of hare meat, increases its mass by only 100 g. In woody plants, this proportion is much lower due to the fact that wood is poorly absorbed by organisms. For grasses and seaweeds, this value is much greater, since they do not have difficult-to-digest tissues. However general pattern the process of energy transfer remains: much less of it passes through the upper trophic levels than through the lower ones.