Characteristics of populations table. Populations and their ecological characteristics. Age structure of the population

INTRODUCTION………………….……………………………………..………………...3

1. Population - ecological characteristics…………….…………...6

2. Factors in population dynamics……………………....…..9

CONCLUSION…………………………………………………………….……………………14

LIST OF SOURCES………………………………………………………17

APPLICATIONS……………………………………………………………………………….....18

Introduction

Everything is interconnected with everything - says the first environmental law. This means that you cannot take a single step without touching, and sometimes even violating, something environment. Every human step on an ordinary lawn means dozens of destroyed microorganisms, frightened insects, changing their migration routes, and perhaps reducing their natural productivity.

Already in the last century, human concern arose for the fate of the planet, and in the current century it has reached a crisis in the global ecological system due to increasing stress on the natural environment.

Environmental pollution, depletion of natural resources and disruption of ecological connections in ecosystems have become global problems. And if humanity continues to follow the current path of development, then its death, according to the world’s leading ecologists, is inevitable in two or three generations.

Despite the accepted Russian state measures to improve the environment, environmental relations continue to develop in a direction unfavorable for nature and society:

a) the departmental approach still prevails, as a result of which each environmental user exploits natural resources based on their departmental interests;

6) the so-called resource approach to environmental use is applied, as a result of which outside legal protection Many ecological connections and natural objects remain that have no resource value.

The interaction between society and nature crossed the line of the previous equilibrium back in the last century, and at the moment it is no longer possible to do without proper legal intervention in this area. The need to develop a special law on environmental safety in Russia has become urgent.

Unlike legal literature, where natural objects are studied based on their economic value for society, each natural object should be studied in the totality of all its elements that affect the life activity of the entire environment as a whole.

Currently, during a period of impending environmental crisis on the entire planet, all living people need to solve the problem of transition from exploitation and conquest of nature to its conservation and cooperation with it. In these conditions, human ecology becomes especially important, since the normal conditions of its existence directly depend on how well a person fits into nature, is able to understand its laws and creatively use them in his life.

Consuming natural resources more and more intensively with the help of colossally increasing technical means, humanity has progressively improved the conditions for the development of its civilization and its growth as a biological species Homo sapiens. However, by “conquering” nature, it significantly undermined the natural foundations of its own life activity, which created a tense and, in many cases, crisis situation in the interaction between man and nature, fraught with great dangers for the future of civilization. Interdependent changes have created new connections between the global economy and the global ecology. In the past, we have been concerned about the environmental impacts of economic growth. Now we cannot help but be concerned about the consequences of “environmental stress” - deterioration in the quality of soils, water regimes, the state of the atmosphere and forests - for economic development in the future.

It is now increasingly clear that the sources and causes of pollution are much more diverse, complex and interconnected, and that the effects of pollution are more widespread, cumulative and chronic than previously thought. Science has even formulated a definition of anthropogenic environmental pollution. This is a physico-chemical and biological change in the quality of the environment ( atmospheric air, water, soil) as a result of economic or other activities that exceed established standards for harmful effects on the environment and pose a threat to human health, the state of flora and fauna, and material values.

Ecology, like any science, has two aspects. One is the desire for knowledge for the sake of knowledge itself, and in this regard, the first place is given to the search for patterns of development of nature, as well as their explanation; the other is the application of collected knowledge to solve environmental problems. The rapid increase in the importance of ecology is explained by the fact that not a single issue of enormous practical importance can currently be solved without taking into account the connections between the living and non-living components of nature.

The practical solution of ecology can be seen primarily in solving environmental management issues; it is precisely this that must create the scientific basis for the exploitation of natural resources. We can state that neglect of the laws underlying natural processes has led to a serious conflict between man and nature.

Population-ecological characteristics

In ecology, a population is a group of individuals of the same species that interact with each other and jointly inhabit a common territory.

A population is a collection of individuals of the same species that exist for a long time in a certain territory, interbreed freely and are relatively isolated from other individuals of the same species.

The word “population” comes from the Latin “populus” - people, population. An ecological population can thus be defined as a population of one species in a certain area.

The population has only it inherent features: number, density, spatial distribution of individuals. There are age, sex, and size structure of the population. The ratio of groups of different age and gender in a population determines its main functions. The ratio of different age groups depends on two reasons: on the characteristics of the life cycle of the species and on external conditions.

Compound. Conventionally, three ecological age groups can be distinguished in the population: pre-reproductive; reproductive; post-reproductive. The duration of these ages in relation to the total lifespan varies greatly among different organisms.

There are species with a simple age structure, when the population is represented by organisms of the same age, and species with a complex age structure, when all age groups are represented in the population or several generations live simultaneously.

Number and density express the quantitative characteristics of the population as a whole. The size of a population is expressed by the number of individuals of a given species living per unit area occupied by it. The dynamics of population numbers over time is determined by the ratio of fertility, mortality, and survival rates, which in turn are determined by living conditions.

Population density is the size of a population per unit of space: the number of individuals, or biomass, of a population per unit area or volume. Density depends on the trophic level at which the population is located. The lower the trophic level, the higher the density.

In many species, under certain conditions, predominantly males or females are born, and sometimes individuals incapable of reproduction. In aphids, for example, in the summer generations consisting of only females replace each other. Under unfavorable conditions, males appear. Some gastropods, polychaete worms, fish, crustaceans, the sex of an individual changes with age.

There are several options for defining a population. A population is a collection of individuals of the same species inhabiting a certain territory or water area for a long time, connected by varying degrees of free interbreeding and sufficiently isolated from other similar populations. As follows from the above definition of a population, it includes the following features inherent to it:

1 Existence throughout large number generations, which distinguishes a population from short-term unstable associations of individuals.

2 The presence of a certain degree of free crossing of individuals. It is this feature of the population that ensures its unity as an evolutionary structure.

3 The degree of free crossing within a population is higher than between different (even neighboring) populations.

4 A certain degree of isolation of populations from each other.

The reasons that force individuals of a population to group within limited areas are extremely numerous and varied, but the main one is the uneven distribution of environmental conditions in geographic space and the similarity of requirements for these conditions among organisms of the same species.

Depending on the size of the occupied territory, three types of populations are distinguished: elementary, ecological and geographical (see Appendix 1)

Ecological characteristics of the population.

1) number – the total number of individuals in the allocated territory;

2) population density - the average number of individuals per unit area or volume of space occupied by the population;

3) birth rate - the number of new individuals appearing per unit of time as a result of reproduction;

4) mortality - an indicator reflecting the number of individuals who died in a population over a certain period of time;

5) population growth - the difference between birth and death rates; the increase can be both positive and negative;

6) growth rate – average increase per unit of time.

Related information.

In nature everyone existing look is a complex complex or even a system of intraspecific groups that include individuals with specific structural features, physiology and behavior. This intraspecific association of individuals is population.

The word “population” comes from the Latin “populus” - people, population. Hence, population- a collection of individuals of the same species living in a certain territory, i.e. those that only interbreed with each other. The term “population” is currently used in the narrow sense of the word, when talking about a specific intraspecific group inhabiting a certain biogeocenosis, and in a broad, general sense - to designate isolated groups of a species, regardless of what territory it occupies and what genetic information it carries.

Members of the same population have no less influence on each other than physical factors environments or other species of organisms living together. In populations, all forms of connections characteristic of interspecific relationships are manifested to one degree or another, but most clearly expressed mutualistic(mutually beneficial) and competitive. Populations can be monolithic or consist of subpopulation-level groups - families, clans, herds, packs and so on. The combination of organisms of the same species into a population creates qualitatively new properties. Compared to the lifespan of an individual organism, a population can exist for a very long time.

At the same time, a population is similar to an organism as a biosystem, since it has a certain structure, integrity, a genetic program for self-reproduction, and the ability to reproduce and adapt. The interaction of people with species of organisms found in the environment, in the natural environment or under human economic control, is usually mediated through populations. It is important that many patterns of population ecology also apply to human populations.

Population is the genetic unit of a species, changes in which are carried out by the evolution of the species. As a group of cohabiting individuals of the same species, a population acts as the first supraorganismal biological macrosystem. A population's adaptive capabilities are significantly higher than those of its constituent individuals. A population as a biological unit has certain structure and functions.

Population structure characterized by its constituent individuals and their distribution in space.

Population functions similar to the functions of other biological systems. They are characterized by growth, development, and the ability to maintain existence in constantly changing conditions, i.e. populations have specific genetic and environmental characteristics.

Populations have laws that allow limited environmental resources to be used in this way to ensure the preservation of offspring. Populations of many species have properties that allow them to regulate their numbers. Maintaining optimal numbers under given conditions is called population homeostasis.

Thus, populations, as group associations, have a number of specific properties that are not inherent in each individual individual. Main characteristics of populations: number, density, birth rate, death rate, growth rate.

A population is characterized by a certain organization. The distribution of individuals across the territory, the ratio of groups by sex, age, morphological, physiological, behavioral and genetic characteristics reflect population structure. It is formed, on the one hand, on the basis of the general biological properties of the species, and on the other, under the influence of abiotic environmental factors and populations of other species. The structure of populations therefore has an adaptive character.

The adaptive capabilities of a species as a whole as a system of populations are much broader than the adaptive characteristics of each individual individual.

Population structure of the species

The space or habitat occupied by a population may vary between species and within the same species. The size of a population's range is determined to a large extent by the mobility of individuals or the radius of individual activity. If the radius of individual activity is small, the size of the population range is usually also small. Depending on the size of the occupied territory, we can distinguish three types of populations: elementary, environmental and geographical (Fig. 1).

Rice. 1. Spatial division of populations: 1 - species range; 2-4 - geographical, ecological and elementary populations, respectively

There are gender, age, genetic, spatial and ecological structure populations.

Sex structure of the population represents the ratio of individuals of different sexes in it.

Age structure of the population- the ratio in the population of individuals of different ages, representing one or different offspring of one or several generations.

Genetic structure of the population is determined by the variability and diversity of genotypes, the frequencies of variations of individual genes - alleles, as well as the division of the population into groups of genetically similar individuals, between which, when crossed, there is a constant exchange of alleles.

Spatial structure of the population - the nature of the placement and distribution of individual members of the population and their groups in the area. The spatial structure of populations differs markedly between sedentary and nomadic or migrating animals.

Ecological population structure represents the division of any population into groups of individuals that interact differently with environmental factors.

Each species, occupying a specific territory ( range), represented on it by a system of populations. The more complex the territory occupied by a species is, the greater the opportunities for the isolation of individual populations. However, to a lesser extent, the population structure of a species is determined by its biological characteristics, such as the mobility of its constituent individuals, the degree of their attachment to the territory, and the ability to overcome natural barriers.

Isolation of populations

If the members of a species are constantly intermingled and intermingled over large areas, the species is characterized by a small number of large populations. With poorly developed ability to move, many small populations are formed within the species, reflecting the mosaic nature of the landscape. In plants and sedentary animals, the number of populations is directly dependent on the degree of heterogeneity of the environment.

The degree of isolation of neighboring populations of the species varies. In some cases, they are sharply separated by territory unsuitable for habitation and are clearly localized in space, for example, populations of perch and tench in lakes isolated from each other.

The opposite option is the complete settlement of vast territories by the species. Within the same species there can be populations with both clearly distinguishable and blurred boundaries, and within the species, populations can be represented by groups of different sizes.

Connections between populations support the species as a whole. Too long and complete isolation of populations can lead to the formation of new species.

Differences between individual populations are expressed to varying degrees. They can affect not only their group characteristics, but also the qualitative features of the physiology, morphology and behavior of individual individuals. These differences are created mainly under the influence natural selection, adapting each population to the specific conditions of its existence.

Classification and structure of populations

A mandatory feature of a population is its ability to exist independently in a given territory for an indefinitely long time due to reproduction, and not the influx of individuals from the outside. Temporary settlements of different scales do not belong to the category of populations, but are considered intra-population units. From these positions, the species is represented not by hierarchical subordination, but by a spatial system of neighboring populations of different scales and with varying degrees of connections and isolation between them.

Populations can be classified according to their spatial and age structure, density, kinetics, constancy or change of habitats and other environmental criteria.

The territorial boundaries of populations of different species do not coincide. The diversity of natural populations is also expressed in the variety of types of their internal structure.

The main indicators of population structure are the number, distribution of organisms in space and the ratio of individuals of different qualities.

The individual traits of each organism depend on the characteristics of its hereditary program (genotype) and how this program is implemented during ontogenesis. Each individual has a certain size, sex, distinctive morphological features, behavioral characteristics, its own limits of endurance and adaptability to environmental changes. The distribution of these characteristics in a population also characterizes its structure.

The population structure is not stable. The growth and development of organisms, the birth of new ones, death from various causes, changes in environmental conditions, an increase or decrease in the number of enemies - all this leads to changes in various relationships within the population. The direction of its further changes largely depends on the structure of the population in a given period of time.

Sexual structure of populations

The genetic mechanism for sex determination ensures that the offspring are separated by sex in a 1:1 ratio, the so-called sex ratio. But it does not follow from this that the same ratio is characteristic of the population as a whole. Sex-linked traits often determine significant differences in the physiology, ecology and behavior of females and males. Due to the different viability of male and female organisms, this primary ratio often differs from the secondary and especially from the tertiary - characteristic of adult individuals. Thus, in humans, the secondary sex ratio is 100 girls to 106 boys; by the age of 16-18 this ratio levels out due to increased male mortality and by the age of 50 it is 85 men per 100 women, and by the age of 80 it is 50 men per 100 women.

The sex ratio in a population is established not only according to genetic laws, but also to a certain extent under the influence of the environment.

Age structure of populations

Fertility and mortality, population dynamics are directly related to the age structure of the population. The population consists of individuals of different ages and sexes. Each species, and sometimes each population within a species, has its own age group ratios. In relation to the population it is usually distinguished three ecological ages: pre-reproductive, reproductive and post-reproductive.

With age, an individual's requirements for the environment and resistance to its individual factors naturally and very significantly change. At different stages of ontogenesis, changes in habitats, changes in the type of food, the nature of movement, and the general activity of organisms can occur.

Age differences in a population significantly increase its ecological heterogeneity and, consequently, its resistance to the environment. The likelihood increases that in the event of strong deviations of conditions from the norm, at least some viable individuals will remain in the population, and it will be able to continue its existence.

The age structure of populations is adaptive in nature. It is formed on the basis of the biological properties of the species, but always also reflects the strength of the influence of environmental factors.

Age structure of plant populations

In plants, the age structure of the cenopopulation, i.e. population of a particular phytocenosis is determined by the ratio of age groups. The absolute, or calendar, age of a plant and its age state are not identical concepts. Plants of the same age can be in different age states. The age-related, or ontogenetic state of an individual is the stage of its ontogenesis, at which it is characterized by certain relationships with the environment.

The age structure of the coenopopulation is largely determined by the biological characteristics of the species: the frequency of fruiting, the number of produced seeds and vegetative rudiments, the ability of vegetative rudiments to rejuvenate, the rate of transition of individuals from one age state to another, the ability to form clones, etc. The manifestation of all these biological characteristics, in turn turn depends on environmental conditions. The course of ontogenesis also changes, which can occur in one species in many ways.

Different plant sizes reflect different vitality individuals within each age group. The vitality of an individual is manifested in the power of its vegetative and generative organs, which corresponds to the amount of accumulated energy, and in resistance to adverse influences, which is determined by the ability to regenerate. The vitality of each individual changes in ontogenesis along a single-peak curve, increasing on the ascending branch of ontogenesis and decreasing on the descending branch.

Many meadow, forest, steppe species, when grown in nurseries or crops, i.e. on the best agrotechnical background, they shorten their ontogeny.

The ability to change the path of ontogenesis ensures adaptation to changing environmental conditions and expands the ecological niche of the species.

Age structure of populations in animals

Depending on the characteristics of reproduction, members of a population may belong to the same generation or to different ones. In the first case, all individuals are close in age and approximately simultaneously go through the next stages of the life cycle. The timing of reproduction and the passage of individual age stages is usually confined to a certain season of the year. The size of such populations is, as a rule, unstable: strong deviations of conditions from the optimum at any stage of the life cycle immediately affect the entire population, causing significant mortality.

In species with single reproduction and short life cycles, several generations occur throughout the year.

When humans exploit natural animal populations, taking into account their age structure is of utmost importance. In species with large annual recruitment, larger portions of the population can be removed without the threat of depleting its numbers. For example, in pink salmon that mature in the second year of life, it is possible to catch up to 50-60% of spawning individuals without the threat of a further decline in population size. For chum salmon, which mature later and have a more complex age structure, removal rates from a mature stock should be lower.

Analysis of the age structure helps to predict the population size over the life of a number of next generations.

The space occupied by a population provides it with the means to live. Each territory can support only a certain number of individuals. Naturally, the complete use of available resources depends not only on the total population size, but also on the distribution of individuals in space. This is clearly manifested in plants, the feeding area of ​​which cannot be less than a certain limiting value.

In nature, an almost uniform, ordered distribution of individuals within an occupied territory is rarely encountered. However, most often the members of a population are distributed unevenly in space.

In each specific case, the type of distribution in the occupied space turns out to be adaptive, i.e. allows optimal use of available resources. Plants in a cenopopulation are most often distributed extremely unevenly. Often the denser center of the aggregation is surrounded by individuals located less densely.

The spatial heterogeneity of the cenopopulation is associated with the nature of the development of clusters over time.

In animals, due to their mobility, the ways of regulating territorial relations are more diverse compared to plants.

In higher animals, intrapopulation distribution is regulated by a system of instincts. They are characterized by special territorial behavior - a reaction to the location of other members of the population. However, a sedentary lifestyle poses the risk of rapid depletion of resources if population densities become too high. The total area occupied by the population is divided into separate individual or group areas, thereby achieving the orderly use of food supplies, natural shelters, breeding sites, etc.

Despite the territorial isolation of members of the population, communication is maintained between them using a system of various signals and direct contacts at the borders of their possessions.

“Securing an area” is achieved in different ways: 1) protecting the boundaries of the occupied space and direct aggression towards a stranger; 2) special ritual behavior demonstrating a threat; 3) system special signals and marks indicating the occupancy of the territory.

The usual reaction to territorial marks—avoidance—is inherited in animals. The biological benefit of this type of behavior is obvious. If the mastery of a territory were decided only by the outcome of a physical struggle, the appearance of each stronger alien would threaten the owner with the loss of the site and exclusion from reproduction.

Partial overlapping of individual territories serves as a way to maintain contacts between members of the population. Neighboring individuals often maintain a stable, mutually beneficial system of connections: mutual warning of danger, joint protection from enemies. Normal animal behavior includes active search contacts with representatives of their own species, which often intensifies during periods of population decline.

Some species form widely wandering groups that are not tied to a specific territory. This is the behavior of many fish species during feeding migrations.

There are no absolute distinctions between different ways of using the territory. The spatial structure of the population is very dynamic. It is subject to seasonal and other adaptive changes in accordance with place and time.

The patterns of animal behavior constitute the subject of a special science - ethology. The system of relationships between members of one population is therefore called the ethological, or behavioral structure of the population.

The behavior of animals in relation to other members of the population depends, first of all, on whether a solitary or group lifestyle is characteristic of the species.

A solitary lifestyle, in which individuals of a population are independent and isolated from each other, is characteristic of many species, but only at certain stages of the life cycle. Completely solitary existence of organisms does not occur in nature, since in this case it would be impossible to carry out their main vital function - reproduction.

With a family lifestyle, the bonds between parents and their offspring also strengthen. The simplest type of such connection is the care of one of the parents for laid eggs: protection of the clutch, incubation, additional aeration, etc. In a family lifestyle, the territorial behavior of animals is most pronounced: various signals, markings, ritual forms of threat and direct aggression ensure ownership of an area sufficient for feeding offspring.

Larger animal associations - flocks, herds And colonies. Their formation is based on the further complication of behavioral connections in populations.

Life in a group, through the nervous and hormonal systems, affects the course of many physiological processes in the animal’s body. In isolated individuals, the level of metabolism changes noticeably, reserve substances are consumed faster, a number of instincts do not manifest themselves, and overall vitality deteriorates.

Positive group effect manifests itself only up to a certain optimal level of population density. If there are too many animals, this threatens everyone with a lack of environmental resources. Then other mechanisms come into play, leading to a decrease in the number of individuals in the group through its division, dispersal, or a drop in the birth rate.

Area- part of the surface of land or water area within which individuals of a given species (genus, family or a certain type of community) are distributed and undergo the full cycle of their development.

Endemic- a species occupying a small territory.
■ Examples of endemics: relict plants ginkgo and metasequoia, platypus, echidna, lobe-finned fish coelacanth.

❖ Causes of endemism:
■ geographic isolation (on oceanic islands, mountainous areas or isolated bodies of water);
■ climatic and soil conditions;
■ biotic factors (competition, predation, symbiosis).

Cosmopolitan- a species found in most of the inhabited regions of the Earth, distributed everywhere.
■ Examples of cosmopolitans: weeds (great plantain, shepherd's purse, etc.), aquatic and marsh plants (duckweed, cattail), as well as houseflies, city sparrows, gray rats and other animals that settle after humans.

❖ Factors influencing the formation and characteristics of the habitat:
■ ecological plasticity of the species;
■ its ability to reproduce and disperse;
■ historical age;
■ rate of speciation.

Continuous range- this is the range within which individuals of a species are found in all habitats suitable for their life.

Discontinuous range- this is an area that breaks up into several isolated territories, so distant from each other that the exchange of pollen or spores between plants or the migration of animals living in these territories is impossible.

Ecological niche of the species- this is a complex of living conditions of a species, i.e. the totality of all environmental factors (including microclimate) within which a species can exist in nature.

■ Two species cannot occupy the same ecological niche, so one of the species either creates a new ecological niche or disappears.

Populations and their main characteristics

Population- this is a collection of individuals of the same species, inhabiting a certain part of the range for a long time, relatively isolated from other groups of individuals of the same species and interacting with each other (competing, helping each other, freely interbreeding, etc.).

■ Population is an elementary form of existence and evolution of a species.

The role of populations in evolution: Due to the spatial separation of populations, a species exists in a variety of environmental conditions and is subject to the action of natural selection of varying intensity and in different directions, which leads to the formation of new varieties, subspecies and species of organisms.

Main characteristics of populations: area, numbers, density, fertility, mortality, spatial, ecological, sex and age structures, genetic heterogeneity.

The size of a stable population is limited by maximum and minimum values.

■ The maximum population size is determined by environmental resources (amount of food, water, etc.).

■ The minimum population size is at least several hundred individuals. With a smaller population, any random cause (fire, flood, drought, severe frost, etc.) can lead to extinction of the population.

Population homeostasis- the property of a population to maintain its size at a certain optimal average level.

Population density- the average number of individuals per unit area or volume of space occupied by a population.

As the number of individuals increases, the population density tends to increase. It can remain unchanged only if the range expands due to the dispersal of individuals.

Regulation of population density is achieved:

■ in plants - due to intraspecific competition, leading to self-rarefaction (in this case, not only the density, but also the vegetative power of individual individuals changes);

■ in animals through complex behavioral and physiological mechanisms and manifests itself only in cases of limited environmental resources and the impossibility of searching for them in other territories (in small reservoirs where there are no other fish species, adult perches feed on their own young).

Fertility (absolute)— the number of new individuals in a population that appeared per unit of time as a result of reproduction.

Specific fertility- the average number of individuals born in a population per unit of time per 1, 100 or 1000 individuals of the population. This indicator allows you to compare birth rates in populations of different sizes.

The birth rate of each species was determined historically as an adaptation to compensate for population decline and depends on:
■ sex ratio in the population (its sexual structure);
■ the ratio of age groups (its age structure);
■ frequency of reproductive cycles (breeding cycles);
■ fertility of individuals (which, in turn, depends on the degree of development of care for offspring and provision of eggs with nutrients).

Typically, the birth rate in each population is balanced by its characteristic mortality.

Biotic Potential characterizes the theoretically possible number of descendants from one pair (or one individual) over a certain period of time (for example, over the entire life cycle or per year).

■ Examples: the number of many insects and crustaceans (aphids, daphnia) per year can increase 10 10 -10 30 times; number large mammals even under the most favorable conditions, it can only increase by 1.05-1.1 times per year.

Specific mortality— the number of individuals that died in a population per unit of time per individual.

Survival curve- a graph showing the percentage of individuals surviving to a particular age.

Types of survival of organisms(determined by the mortality of individuals).
■ increased mortality of individuals in the early period of life (in fish);
■ uniform death of individuals at all periods of life (in hydras, some worms, etc.);
■ survival of individuals to the age limit and mass death in the later periods of life (most insects); less common; leads to outbreaks of reproduction.

Population structure

Spatial structure population characterizes the characteristics of the distribution of individuals in the occupied territory. It depends on the size of the population and its age and sex structure, can change throughout the year and is determined by the properties of the habitat and the biological characteristics of the species.

❖ Types of spatial structure of populations:
■ random distribution across the territory;
■ uniform distribution across the territory;
■ group distribution, when individuals live in groups: families, herds, colonies, harems. This distribution is most common because it helps to better protect against predators, search for and obtain food.

Ecological structure characterizes the attitude of different groups of organisms of the same population to environmental conditions (for example, individuals of one population of plants differ in size, number of leaves and flowers, do not bloom at the same time, their fruits do not ripen at the same time, etc.).

■ This difference in individuals allows the population to survive as a whole during the onset of various unfavorable conditions, although one or another part of the individuals may die.

Sexual structure expresses the ratio of the numbers of male and female individuals in a population. It usually differs from the 1:1 ratio determined by the genetic mechanism, which is mainly explained by the different viability of male and female individuals.

■ The predominance of the proportion of females over males ensures more intensive growth of the population.

■ Since males and females of many species differ in their feeding patterns, behavior, etc., a change in the sexual structure of a population to one degree or another changes its role in the ecosystem.

■ In human populations, the sex ratio at birth is 100 girls to 106 boys, by the age of 18 it becomes 1:1, by the age of 50 there are 85 men per 100 women, by the age of 80 the sex ratio becomes 2:1 (100 women for 50 men).

Age structure of the population reflects the ratio of different age groups in the population. It depends on the life expectancy of individuals, the time of their onset of sexual maturity, the number of offspring in the litter, the number of offspring per season, etc.

■ Presence in the population large quantity individuals of younger age groups indicates its well-being. The predominance of old individuals in the population indicates that this population is ending its existence.

■ The age structure reflects the adaptive nature of individuals, since resistance to the environment in individuals different ages is not the same (adult cockchafers live for several weeks, and their larvae in the soil for three years).

❖ Types of ecological age:
■ pre-reproductive;
■ reproductive;
■ post-reproductive.

Population dynamics

Population growth is the difference between fertility and... mortality. It can be positive (the population size increases) and negative (the population size decreases).

Growth rate— average population growth per unit of time. In most species it depends on population density. The highest growth rate is observed at a certain optimal population density or when the population enters a new, unoccupied ecological niche.

Growth in numbers. Any population, if it is not limited by environmental factors (limited resources, diseases, predators, etc.), is theoretically capable of unlimited population growth. In this case, the rate (speed) of population growth depends only on the size biotic potential , and the population growth itself occurs in geometric progression(exponential) and is called exponential.

Conditions for exponential growth. In reality, exponential population growth can only occur over a limited period of time in the following cases:

■ the population is in conditions of abundant environmental resources (food, breeding sites) and is not exposed to adverse factors;

■ the population finds itself in new conditions, where it has no enemies or competitors (example: rabbits in Australia);

■ the population exists in artificially created laboratory conditions (bacteria, yeast, etc.).

An increase in population size leads to an increase in its density. But as the population density increases, limited environmental resources begin to affect them, and conditions for the reproduction and growth of individuals become less favorable, which leads to a slowdown in population growth.

Logistic type of population growth- a type of growth under limited resources, characterized by a decrease in growth rate as population density increases.

Medium capacity— optimal population density under specific environmental conditions.

■ If the population density matches the carrying capacity of the environment, then the population size will fluctuate around the average level.

■ If the population density exceeds the carrying capacity of the environment, then the population size and its density decrease.

Regulation of population size.Two groups of factors influencing population size:

■ modifying, independent of population density (this is, as a rule, abiotic environmental factors; for example, a harsh winter leads to the death of animals and birds feeding on the ground, etc.);

■ regulating, depending on population density (as a rule, these are different biotic factors: fertility, mortality, migration, behavioral factors, depletion of environmental resources, etc.).

Migrations- these are regular daily or seasonal movements of animals between significantly different, spatially separated habitats. They are caused by changes in living conditions in habitats or changes in the requirements of animals to these conditions at different stages of development.

The role of migrations:

■ allow organisms to use optimal environmental conditions for a certain time in places where permanent residence of organisms of this species is impossible;

■ lead to the development of new biotopes and expansion general range type;

■ lead to the exchange of individuals between populations, which can change their structure and basic properties, prevent the death of a population on the verge of extinction, or, conversely, lead it to a sharp decline;

■ increase the unity and overall stability of the species;

■ contribute to success in the struggle for existence.

In the absence of migration, the change in population size depends on the ratio of birth rates and deaths.

Examples of physiological and behavioral factors regulating population size and density:

■ with a high population density in some animal species (rodents), the concentration of the hormone adrenaline increases in the blood, causing aggression (fighting) and various hormonal disorders (embryo resorption may occur in females), which ultimately leads to a reduction in population size;

■ chemical reaction individuals (for example, tadpoles release substances into the water that retard the growth of other tadpoles);

■ tagging(secretion of scent glands, scratches on trees, singing of male birds, etc.), security individual plot of territory and prevention the reproduction of “alien” individuals on it allows the most rational use of the space occupied by the population. The excess part of the population does not reproduce or is forced to move out of the occupied space.

The multiplicity of mechanisms for regulating numbers leads to the fact that catastrophic growth in numbers, undermining of resources (lack of food, shelter, space) and death of the population very rarely occur in nature.

Populations: structure and dynamics Lecture 7.

Moskaluk T.A.

Bibliography

Stepanovskikh A.S. General ecology: Textbook for universities. M.: UNITY, 2001. 510 p.

Radkevich V.A. Ecology. Minsk: Higher School, 1998. 159 p.

Bigon M., Harper J., Townsend K. Ecology. Individuals, populations and communities / Transl. from English M.: Mir, 1989. Vol. 2..

Shilov I.A. Ecology. M.: graduate School, 2003. 512 p. (LIGHT, cycles)

1. The concept of population. Population types

2. Main characteristics of populations

3. Structure and dynamics of populations

4. The dual nature of population systems

a) evolutionary and functional essence of the population

b) biological inconsistency of population functions (Lotka-Volterra model; law of emergence)

5. Fluctuations in numbers

6. Ecological strategies of populations

1. The concept of population. Population types

Population(populus - from Latin people. population) is one of the central concepts in biology and denotes a collection of individuals of the same species that has a common gene pool and a common territory. It is the first supraorganismal biological system. From an ecological perspective, a clear definition of a population has not yet been developed. The interpretation of S.S. has received the greatest recognition. Schwartz, a population is a grouping of individuals, which is a form of existence of a species and is capable of independently developing indefinitely.

The main property of populations, like other biological systems, is that they are in continuous movement and constantly changing. This is reflected in all parameters: productivity, stability, structure, distribution in space. Populations are characterized by specific genetic and environmental characteristics that reflect the ability of systems to maintain existence in constantly changing conditions: growth, development, stability. The science that combines genetic, ecological, and evolutionary approaches to the study of populations is known as population biology.

EXAMPLES. One of several schools of fish of the same species in the lake; microgroups of Keiske lily of the valley in white birch forests, growing at the bases of trees and in open areas; clumps of trees of the same species (Mongolian oak, larch, etc.), separated by meadows, clumps of other trees or shrubs, or swamps.

Ecological population – a set of elementary populations, intraspecific groups, confined to specific biocenoses. Plants of the same species in a cenosis are called a cenopopulation. The exchange of genetic information between them occurs quite often.

EXAMPLES. Fish of the same species in all schools of a common reservoir; tree stands in monodominant forests representing one group of forest types: grass, lichen or sphagnum larch (Magadan region, northern Khabarovsk Territory); forest stands in sedge (dry) and forb (wet) oak forests (Primorsky Territory, Amur Region); squirrel populations in pine, spruce-fir, and broadleaf forests in one area.

Geographic population– set ecological populations who populated geographically similar areas. Geographic populations exist autonomously, their habitats are relatively isolated, gene exchange occurs rarely - in animals and birds - during migration, in plants - during the spread of pollen, seeds and fruits. At this level, the formation of geographical races and varieties occurs, and subspecies are distinguished.

EXAMPLES. The geographical races of Dahurian larch (Larix dahurica) are known: western (west of the Lena (L. dahurica ssp. dahurica) and eastern (east of the Lena, distinguished in L. dahurica ssp. cajanderi), northern and southern races of the Kuril larch. Similarly identification by M.A. Shemberg (1986) of stone birch of two subspecies: Erman's birch (Betula ermanii) and woolly birch (B. lanata).In the lower reaches of the Yama River there is a center of Norway spruce (Picea obovata), separated from the continuous massif of spruce forests to the east 1000 km, to the north - 500 km. Zoologists distinguish tundra and steppe populations of the narrow-skulled vole (Microtis gregalis). The species "common squirrel" has about 20 geographical populations, or subspecies.

2. Main characteristics of populations

Number and density are the main parameters of a population. Number– the total number of individuals in a given territory or in a given volume. Density– the number of individuals or their biomass per unit area or volume. In nature, there are constant fluctuations in numbers and density.

Population dynamics and density is determined mainly by fertility, mortality and migration processes. These are indicators that characterize population changes during a certain period: month, season, year, etc. The study of these processes and the causes that determine them is very important for forecasting the state of populations.

Fertility is distinguished between absolute and specific. Absolute fertility is the number of new individuals appearing per unit of time, and specific- the same quantity, but assigned to a certain number of individuals. For example, an indicator of a person's fertility is the number of children born per 1000 people during the year. Fertility is determined by many factors: environmental conditions, the availability of food, the biology of the species (the rate of sexual maturation, the number of generations during the season, the ratio of males and females in the population).

According to the rule of maximum fertility (reproduction), under ideal conditions, the maximum possible number of new individuals appears in populations; birth rate is limited physiological characteristics kind.

EXAMPLE. In 10 years, a dandelion can fill the entire Earth, provided that all its seeds germinate. Willows, poplars, birches, aspens, and most weeds produce exceptionally abundant seeds. Bacteria divide every 20 minutes and within 36 hours can cover the entire planet in a continuous layer. Fertility is very high in most insect species and low in predators and large mammals.

Mortality, like birth rate, it can be absolute (the number of individuals that died during certain time), and specific. It characterizes the rate of population decline from death due to disease, old age, predators, lack of food, and plays a major role in population dynamics.

There are three types of mortality:

Same at all stages of development; rare, under optimal conditions;

Increased mortality at an early age; characteristic of most species of plants and animals (in trees, less than 1% of seedlings survive to maturity, in fish - 1-2% of fry, in insects - less than 0.5% of larvae);

High death in old age; usually observed in animals whose larval stages take place in favorable, little-changing conditions: soil, wood, living organisms.

Stable, growing and declining populations. The population adapts to changing environmental conditions by updating and replacing individuals, i.e. processes of birth (renewal) and decline (death), supplemented by migration processes. In a stable population, the birth and death rates are close and balanced. They may be variable, but the population density differs slightly from some average value. The range of the species neither increases nor decreases.

In a growing population, the birth rate exceeds the death rate. Growing populations are characterized by outbreaks of mass reproduction, especially in small animals (locusts, 28-spotted potato beetle, Colorado potato beetle, rodents, crows, sparrows; among plants - ragweed, Sosnovsky's hogweed in the northern Komi Republic, dandelion, Himalayan stick, partly oak Mongolian). Populations of large animals often grow under conditions of conservation (elk in the Magadan Nature Reserve, Alaska, sika deer in the Ussuri Nature Reserve, elephants in the Kenya National Park) or introduction (elk in the Leningrad region, muskrat in Eastern Europe, domestic cats in separate families). When overdensification occurs in plants (usually coincides with the beginning of the closure of the canopy), differentiation of individuals begins in size and life state, self-thinning of populations, and in animals (usually coincides with the achievement of sexual maturity of young animals) migration to adjacent free areas begins.

If the mortality rate exceeds the birth rate, then such a population is considered to be declining. In the natural environment, it decreases to a certain limit, and then the birth rate (fertility) increases again and the population goes from declining to growing. Most often, populations of undesirable species are growing uncontrollably, while populations of rare, relict, and valuable species are declining, both economically and aesthetically.

3. Structure and dynamics of populations

The dynamics, condition and reproduction of populations are consistent with their age and sex structure. The age structure reflects the rate of population renewal and the interaction of age groups with the external environment. It depends on the characteristics of the life cycle, which differ significantly among different species (for example, birds and mammalian predators), and external conditions.

IN life cycle individuals are usually divided into three age periods: pre-reproductive, reproductive and post-reproductive. Plants are also characterized by a period of primary dormancy, which they go through in the stage of feeding seeds. Each period can be represented by one (simple structure) or several (complex structure) age stages. Annual plants and many insects have a simple age structure. A complex structure is typical for tree populations of different ages and for highly organized animals. The more complex the structure, the higher the adaptive capabilities of the population.

One of the most famous classifications of animals by age is G.A. Novikova:

Newborns - until the moment of sight;

Young – growing individuals, “teenagers”;

Sub-adults – close to sexually mature individuals;

Adults are sexually mature animals;

Old are individuals that have stopped reproducing.

In geobotany, N.M.’s classification of plants by age has gained recognition. Chernova, A.M. Bylovoy:

Dormant seeds;

Seedlings (shoots) are plants of the first year of life, many of them live off the nutrients in the cotyledons;

Juveniles - begin to feed independently, but are still different in size and morphologically from adult plants;

Immature - have transitional characteristics from juvenile to adult plants, they are still very small, they have a change in the type of growth, branching of shoots begins;

Virginiles - “adult teenagers”, can reach the size of adults, but there are no regenerative organs;

Young generative - characterized by the presence of generative organs, the formation of the appearance typical of an adult plant is completed;

Middle-aged generative - characterized by maximum annual growth and maximum reproduction;

Old generative - plants continue to bear fruit, but their shoot growth and root formation completely stop;

Subsenile - bear fruit very weakly, vegetative organs die off, new shoots are formed due to dormant buds;

Senile - very old, decrepit individuals, features of juvenile plants appear: large single leaves, shoots.

A cenopopulation in which all of the listed stages are represented is called normal, complete.

In forestry and taxation, the classification of tree stands and plantings by age classes is accepted. For conifers:

Seedlings and self-seeding – 1-10 years, height up to 25 cm;

Young growth stage – 10-40 years, height from 25 to 5 m; under the forest canopy corresponds to small (up to 0.7 m), medium (0.7-1.5 m) and large-sized (>1.5 m) undergrowth;

Perch stage – middle-aged plantings 50-60 years old; trunk diameters from 5 to 10 cm, height – up to 6-8 m; under the forest canopy there is a young generation of the tree stand, or a thin tree with similar dimensions;

Maturing plantings – 80-100 years; they may be slightly smaller in size than the mother tree; they bear fruit abundantly in open areas and in open forests; in the forest they may still be in the second tier, but do not bear fruit; under no circumstances are they assigned to the wheelhouse;

Mature forest stands - 120 years and older, trees of the first tier and stunted trees of the second tier; bear fruit abundantly, at the beginning of this stage they reach technical ripeness, at the end - biological;

Overmature - over 180 years old, continue to bear fruit abundantly, but gradually become decrepit and dry out or fall out while still alive.

For deciduous species, the gradations and holdings are similar in size, but due to their faster growth and aging, their age class is not 20, but 10 years.

Ratio of age groups in the population structure characterize its ability to reproduce and survive, and is consistent with fertility and mortality rates. In growing populations with a high birth rate, young (Fig. 2), not yet reproductive individuals predominate; in stable ones, these are usually multi-age, full-fledged populations in which a certain number of individuals regularly move from younger to older age groups; the birth rate is equal to the population decline. In declining populations, the basis is made up of old individuals; renewal in them is absent or very insignificant.

Sexual structure according to genetic laws, it should be represented by an equal ratio of male and female individuals, i.e. 1:1. But due to the specific physiology and ecology characteristic of different sexes, due to their different viability, the influence of environmental, social, and anthropogenic factors, there may be significant differences in this ratio. And these differences are not the same both in different populations and in different age groups of the same population. This is clearly shown in Fig. 3, representing sections of the age and sex structure for the population former USSR and the African Republic of Kenya. Taking a cross-section of the USSR, against the background of the natural distribution of age groups in the life cycle, a decrease in the birth rate during the war years and an increase in the post-war years are obvious. The disproportion between the female and male sexes is also undoubtedly associated with the war. In Kenya, there is a natural connection between sex distribution and apparent population decline in pre-reproductive age with low level life, dependence on natural conditions.

The study of the sexual structure of populations is very important, since both ecological and behavioral differences are strongly expressed between individuals of different sexes.

EXAMPLE. Males and females of mosquitoes (family Culicidae) differ greatly from each other: in growth rates, timing of puberty, and resistance to temperature changes. Males in the imago stage do not feed at all or feed on nectar, and females need to drink blood to fully fertilize the eggs. In some species of flies, populations consist only of females.

There are species in which sex is initially determined not by genetic, but by environmental factors, as, for example, in Arizema japonica, when a mass of tubers is formed, female inflorescences are formed on plants with large fleshy tubers, and male inflorescences are formed on plants with small ones. The role of environmental factors in the formation of the sexual structure in species with alternating sexual and parthenogenetic generations is clearly visible. At optimal temperature in daphnia (Daphnia magna), the population is formed by parthenogenetic females, and when deviating from it, males also appear.

The spatial distribution of individuals in populations is random, group and uniform.

Random (diffuse) distribution – uneven, observed in a homogeneous environment; relationships between individuals are weakly expressed. Random distribution is characteristic of populations in the initial period of settlement; plant populations experiencing severe oppression by community edifiers; populations of animals in which social communication is weakly expressed.

EXAMPLES. At the initial stages of settlement and establishment - insect pests on the field; seedlings of expansive (pioneer) species: willow, choicenia, larch, lespedeza, etc., in disturbed areas (mountain ranges, quarries);

Group distribution is the most common; reflects the heterogeneity of living conditions or different ontogenetic (age) patterns of the population. It ensures the greatest stability of the population.

EXAMPLES. No matter how uniform the structure of the forest may seem, it does not have such uniform distribution of vegetation cover as in a field or lawn. The more pronounced the microrelief that determines the microclimate in the forest community, the more pronounced the diversity of ages of the forest stand, the more clearly expressed is the parcel structure of the stand. Herbivorous animals unite in herds in order to more successfully resist predatory enemies. Group character is typical for sedentary and small animals.

Uniform distribution is rare in nature. It is characterized by secondary even-aged stands after crown closure and intensive self-thinning, sparse stands growing in a homogeneous environment, unpretentious plants lower tiers. Most predator animals leading an active lifestyle are also characterized by uniform distribution after they settle and occupy the entire territory suitable for life.

How to determine the nature of plant placement?

This can be done using simple mathematical processing of accounting data. A plot or trial area is divided into counting plots of the same size - at least 25, or plant counts are carried out on counting plots of the same size located at approximately the same distance. The set of sites represents a sample. By denoting the average number of individuals of a species on sites in a sample by the letter m, the number of sites (counts) in a sample by n, the actual number of individuals of a species on each site by x, we can determine the dispersion, or measure of dispersion s2 (deviation of the value of x from m):

s2 = S(m-x)2 /(n-1)

With a random distribution s2=m (provided there is a sufficient sample size). With a uniform distribution, s2=0, and the number of individuals on each site should be equal to the average. With a group distribution, s2>m is always, and the greater the difference between the deviation and the average number, the more pronounced the group distribution of individuals.

4. The dual nature of population systems

a) evolutionary and functional essence of the population

Attention should be paid to the dual position of the population in the ranks of biological systems belonging to different levels of organization of living matter (Fig. 4). On the one hand, the population is one of the links in the genetic-evolutionary series, reflecting the phylogenetic relationships of taxa at different levels, as a result of the evolution of life forms: organism - population - species - genus - ... - kingdom In this series, the population acts as a form of existence of a species, the main function of which is survival and reproduction. Playing an important role in the microevolutionary process, a population is the elementary genetic unit of a species. Individuals in a population have characteristic structural features, physiology and behavior, i.e. heterogeneity. These features are developed under the influence of living conditions and are the result of microevolution occurring in a particular population. Changes in populations in the process of adaptation to changing environmental factors and the consolidation of these changes in the gene pool ultimately determine the evolution of the species.

On the other hand, under the same specific environmental conditions, the population enters into trophic and other connections with populations of other species, forming simple and complex biogeocenoses with them. In this case, it is a functional subsystem of biogeocenosis and represents one of the links in the functional-energy series:

organism - population - biogeocenosis - biosphere

b) biological inconsistency of population functions

The “duality” of populations is also manifested in the biological inconsistency of their functions. They are composed of individuals of the same species, and, therefore, have the same ecological requirements for environmental conditions, and have the same adaptation mechanisms. But the populations themselves contain:

1) high probability of intense intraspecific competition

2) the possibility of a lack of stable contacts and relationships between individuals.

Intense competition occurs during overpopulation, leading to depletion of life-sustaining resources: food for animals, moisture, fertility and (or) light for plants. If the number of individuals is too small, the population loses the properties of the system and its stability decreases. Resolving this contradiction is the main condition for maintaining the integrity of the system. It lies in the need to maintain optimal numbers and optimal relationships between intrapopulation processes of differentiation and integration.

Lotka–Volterra model. As an example of the natural regulation of the process of intraspecific competition, we can cite the Lotka–Volterra rule, which reflects the relationships in the food chain of consumers and producers, or predator and prey. It is represented by two equations. The first expresses the success of encounters between prey and predator:

Fertility naturally depends on the efficiency (f) with which food is passed on to offspring, and on the rate of food consumption (a × C" × N).

The growth of population size and density is not infinite. Sooner or later, there is a threat of a lack of environmental resources (food, shelter, breeding sites, soil depletion, excessive shading). Each population has its own resource limits, called the environmental capacity. As it decreases, intraspecific competition increases. Various mechanisms of population regulation are activated. In plants, self-thinning and differentiation of plants in size and physiological state begins, in animals the birth rate decreases, aggression increases, they begin to settle into free territories, and epidemics begin within populations. Each species reacts differently to its own overpopulation, but the result is the same for all – inhibition of development and reproduction.

In Fig. Figure 5 shows the graphical Lotka–Volterra model. It allows us to show the main trend in the predator-prey relationship, which is that fluctuations in the population size of the predator are consistent with fluctuations in the population size of the prey. At the same time, the cycles of increase and decrease in the numbers of predators and prey are shifted in relation to each other. When the number of prey (food resource) is large, the number of predators increases, but not indefinitely, but until there is a tension with food. A decrease in food supplies leads to increased intraspecific competition and a decrease in the number of predators, and this, in turn, again leads to an increase in the number of prey.

Law of emergence. As an integral system, a population can be stable only with close contacts and interaction of individuals with each other. Only in a herd can artiodactyls resist predators. Only in a pack do wolves hunt successfully. In forest communities, as a rule, undergrowth of trees grows better in biogroups (group effect); forest restoration in disturbed areas proceeds better with abundant seeding and the uniform emergence of tree seedlings. Animals live in herds, birds and fish live in flocks.

At the same time, the population, as a system, acquires new properties that are not equivalent to a simple sum of similar properties of individuals in the population. For example, when daphnia, the food of perch, gather in a group, the group forms a protective biofield (Fig. 5), thanks to which the fish do not “notice” the food. One daphnia does not have such a biofield, and it quickly becomes prey for fish. The same pattern manifests itself when populations are combined into a biocenosis system - the biocenosis receives properties that none of its blocks have separately. This law, the law of emergence, was formulated by N.F. Reimers.

5. Fluctuations in numbers

Under favorable conditions, populations experience an increase in numbers and can be so rapid that it leads to a population explosion. The totality of all factors contributing to population growth is called biotic potential. It is quite high for different species, but the probability of the population reaching the population limit under natural conditions is low, because this is opposed by limiting (limiting) factors. The set of factors limiting population growth is called environmental resistance. The state of equilibrium between the biotic potential of a species and the resistance of the environment (Fig. 6), which maintains the constancy of the population size, is called homeostasis or dynamic equilibrium. When it is violated, fluctuations in the population size occur, that is, changes in it.

Distinguish periodic and non-periodic fluctuations in population numbers. The first occurs over the course of a season or several years (4 years - a periodic cycle of cedar fruiting, an increase in the number of lemmings, arctic foxes, polar owls; after a year, apple trees bear fruit in garden plots), the second are outbreaks of mass reproduction of certain pests useful plants, in case of disturbances in habitat conditions (droughts, unusually cold or warm winters, too rainy growing seasons), unexpected migrations to new habitats. Periodic and non-periodic fluctuations in population numbers under the influence of biotic and abiotic environmental factors, characteristic of all populations, are called population waves.

Any population has a strictly defined structure: genetic, age-sex, spatial, etc., but it cannot consist of fewer individuals than necessary for the stable development and resistance of the population to environmental factors. This is the principle of minimum population size. Any deviations of population parameters from optimal ones are undesirable, but if excessive high values they do not pose a direct threat to the existence of the species, then a decrease to a minimum level, especially in population size, poses a threat to the species.

EXAMPLES. Very many species in the Far East are characterized by minimal population sizes: Amur tiger, Far Eastern leopard, polar bear, mandarin duck, many butterflies: Maka's tail-bearer and Ksuta's tail-bearer, admiral, zephyrs, beauty Artemis, Apollo, relict longhorned beetle, stag beetle; from plants: all araliaceae, orchids, whole-leaved fir, dense-flowered pine, Manchurian apricot, hard juniper, pointed yew, two-row lilies, calloused lilies, Daurian lilies, etc., Ussuri fritillary, Kamchatka trillium and many other species.

However, along with the principle of minimum population size, there is also the principle, or rule, of population maximum. It lies in the fact that the population cannot increase indefinitely. Only theoretically is it capable of unlimited growth in numbers.

According to the theory of H.G. Andrevarty – L.K. Bircha (1954) – theory of population limits, the number of natural populations is limited by the depletion of food resources and breeding conditions, inaccessibility of these resources, too short period of acceleration of population growth. The theory of “limits” is supplemented by the theory of biocenotic regulation of population size by K. Fredericks (1927): population growth is limited by the influence of a complex of abiotic and biotic environmental factors.

What are these factors or reasons for population fluctuations?

Sufficient food supplies and food shortages;

Competition between several populations for one ecological niche;

External (abiotic) environmental conditions: hydrothermal regime, illumination, acidity, aeration, etc.

6. Ecological strategies of populations

Whatever the adaptations of individuals to living together in a population, whatever the adaptations of the population to certain factors, all of them are ultimately aimed at long-term survival and continuation of oneself in any conditions of existence. Among all the adaptations and features, one can distinguish a set of basic features called an ecological strategy. This is a general characteristic of the growth and reproduction of a given species, including the growth rate of individuals, the period when they reach sexual maturity, the frequency of reproduction, the maximum age, etc.

Ecological strategies are very diverse and although there are many transitions between them, two extreme types can be distinguished: r-strategy and K-strategy.

r-strategy– it is possessed by rapidly reproducing species (r-species); it is characterized by selection for increased population growth rates during periods of low density. It is typical for populations in environments with sudden and unpredictable changes in conditions or in ephemeral, i.e. existing for a short time (drying puddles, water meadows, temporary watercourses)

The main characteristics of r-species: high fertility, short regeneration time, high numbers, usually small sizes of individuals (plants have small seeds), small life expectancy, large expenditures of energy on reproduction, short-lived habitats, low competitiveness. R-species quickly and in large numbers populate unoccupied territories, but, as a rule, soon - within the life of one or two generations - they are replaced by K-species.

r-species include bacteria, all annual plants (weeds) and insect pests (aphids, leaf beetles, stem pests, gregarious locusts). Among perennials - pioneer species: fireweed, many grasses, wormwood, ephemeral plants, among tree species - willow, white and stone birch, aspen, choicenia, among conifers - larch; They appear first on disturbed lands: burnt areas, mountain ranges, construction quarries, and along roadsides.

K-strategy – this strategy is possessed by species with a low reproduction rate and high survival rate (K-species); it determines selection for increased survival at high population densities approaching the limit.

The main characteristics of K-species: low fertility, significant life expectancy, large sizes individuals and seeds, powerful root systems, high competitiveness, stability in the occupied territory, high specialization of lifestyle. The reproduction rate of K-species decreases as the maximum population density approaches and increases rapidly at low densities; parents take care of their offspring. K-species often become dominant in biogeocenoses.

K-species include all predators, humans, relict insects (large tropical butterflies, including Far Eastern ones, relict longhorned beetle, stag beetle, ground beetles, etc.), a single phase of locusts, almost all trees and shrubs. The most striking representatives of plants are all conifers, Mongolian oak, Manchurian walnut, hazels, maples, forbs, and sedges.

Different populations use the same habitat differently, so species of both types can exist in it at the same time using a strategy.

EXAMPLES. In the forests on the ecological profile "Mountain Taiga" in the spring, before the leaves bloom on the trees, ephemeroids rush to bloom, bear fruit and finish the growing season: corydalis, Adonis Amur, anemone, oriental violet (yellow). Under the forest canopy, peonies, lilies, and crowberry begin to bloom. On open areas sheep fescue and roseate grass grow in the dry oak trees on the southern slope. Oak, fescue and other species are K-strategists, marianberry is r-strategist. 40 years ago, after a fire, parcels of aspen (r-species) formed in the fir-broadleaved forest type. Currently, aspen is leaving the forest stand, being replaced by K-species: linden, oak, hornbeam, walnut, etc.

Any population of plants, animals and microorganisms is a perfect living system, capable of self-regulation and restoration of its dynamic balance. But it does not exist in isolation, but together with populations of other species, forming biocenoses. Therefore, interpopulation mechanisms that regulate relationships between populations of different species are also widespread in nature. The regulator of these relationships is a biogeocenosis consisting of many populations of different species. In each of these populations, interactions occur between individuals, and each population has an impact on other populations and on the biogeocenosis as a whole, just as the biogeocenosis with its constituent populations has a direct impact on each specific population.

As I.I. writes Schmalhausen: “...In all biological systems there is always an interaction between different regulatory cycles, leading to the self-development of the system in accordance with the given conditions of existence...”

When optimal ratios are achieved, a more or less long-term stationary state (dynamic equilibrium) of the given system occurs under the given conditions of existence. "...For a population this means the establishment of a certain genetic structure, including different forms balanced polymorphism. For a species, this means the establishment and maintenance of its more or less complex structure. ... For a biogeocenosis, this means establishing and maintaining its heterogeneous composition and the established relationships between components. When the conditions of existence change, the stationary state is, of course, disrupted. There is a re-evaluation of the norm and options, and, consequently, a new transformation, i.e. further self-development of these systems...” At the same time, the relationships between links in the biogeocenosis change, and in populations there is a restructuring of the genetic structure.

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Ecologically, a population is characterized by a size assessed by the territory it occupies (area), the number of individuals, age and sex composition. Range size depend on the radii of individual activity of organisms of a given species and the characteristics of natural conditions in the corresponding territory. Number of individuals varies in populations of organisms of different species. So, the number of dragonflies Leucorrhinia albifrons in the population on one of the lakes near Moscow reached 30,000, while the number of earth snails Cepaea nemoralis was estimated at 1000 copies. There are minimum numbers at which a population is able to maintain itself over time. A reduction in numbers below this minimum leads to population extinction.

The population size constantly fluctuates, depending on changes in the environmental situation. Thus, in the autumn of a year with favorable feeding conditions, the population of wild rabbits on one of the islands off the southwest coast of England consisted of 10,000 individuals. After a cold winter with little food, the number of individuals decreased to 100.

Age structure populations of organisms of different species varies depending on life expectancy, reproduction intensity, and age at sexual maturity. Depending on the type of organism, it can be more or less complex. Thus, in gregarious mammals, such as beluga dolphins, Delphinapterus leucas, the population simultaneously contains cubs of the current the year of birth, grown young animals of the previous year of birth, sexually mature, but, as a rule, non-breeding animals aged 2-3 years, adult breeding individuals aged 4-20 years. On the other hand, in shrews Sorex In the spring, 1-2 offspring are born, after which the adults die out, so that in the fall the entire population consists of young immature animals.

Sex composition populations is determined by evolutionarily fixed mechanisms for the formation of primary (at the time of conception), secondary (at the time of birth) and tertiary (in adulthood) sex ratio. As an example, consider the change in the sex composition of the human population. At the time of birth it is 106 boys per 100 girls, at the age of 16-18 it levels off, at the age of 50 it is 85 men per 100 women, and at the age of 80 it is 50 men per 100 women.

Genetic characteristics of the population

Genetically, a population is characterized by its gene pool (allele pool). It is represented by a set of alleles that form the genotypes of organisms in a given population. Gene pools of natural populations are distinguished by hereditary diversity (genetic heterogeneity, or polymorphism), genetic unity, and dynamic balance of the proportion of individuals with different genotypes.

Hereditary diversity consists in the presence in the gene pool of different alleles of individual genes at the same time. It is primarily created by a mutation process. Mutations, being usually recessive and not affecting the phenotypes of heterozygous organisms, are preserved in the gene pools of populations in a state hidden from natural selection. As they accumulate, they form reserve of hereditary variability. Thanks to combinative variability, this reserve is used to create new combinations of alleles in each generation. The volume of such a reserve is enormous. Thus, when crossing organisms that differ in 1000 loci, each of which is represented by ten alleles, the number of genotype variants reaches 10 1000, which exceeds the number of electrons in the Universe.

Genetic unity population is determined by a sufficient level of panmixia. In conditions of random selection of crossing individuals, the source of alleles for the genotypes of organisms of successive generations is the entire gene pool of the population. Genetic unity is also manifested in the general genotypic variability of the population when living conditions change, which determines both the survival of the species and the formation of new species.