Main ecological characteristics of the population table. Basic characteristics of populations. Age structure of the population

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THEORETICAL PART The concept of population and its main.

group characteristics Population

- a set of organisms of the same species that jointly inhabit a common territory, interact with each other and interbreed freely. Population is the elementary form of existence of a species in nature. One species of organism may include several, sometimes many, populations, more or less isolated from each other. In populations, all forms of connections characteristic of interspecific relationships are manifested to varying degrees, but mutualism and competition are most pronounced. There are also specific intraspecific relationships: a) between individuals of different sexes; b) between the parent and daughter generations. The most important property of a population is its ability to reproduce.

1) A population as a group association of individuals has the following main characteristics: number

2) - the total number of individuals in the allocated territory; the number is not constant, because depends on many factors (rate of reproduction, death of individuals as a result of old age, disease, destruction by predators, migration); if for some reason it is impossible to determine the population size, then its density is determined; population density -

3) the average number (biomass) of individuals per unit area or volume of space occupied by the population; birth rate - the number of new individuals (eggs, seeds) that appeared in a population per unit of time, per a certain number of its members (for example, the number of offspring produced by one female per year; in humans, the birth rate is usually expressed as the number of births per 1000 people per year); differentiate absolute And specific birth rate; the first is characterized by the total number of individuals born (for example, if in a population reindeer

4) , numbering 16 thousand heads per year. 2 thousand fawns were born in a year, then this number expresses the absolute birth rate); specific birth rate is calculated as the average change in the number per individual over a certain time interval (in this example it will be, i.e. one newborn per eight members of the population per year); an indicator reflecting the number of individuals who died in a population over a certain period of time, expressed either as a percentage of the total number of individuals, or as the average number of deaths per 1000 individuals per year; differentiate accordingly the number of new individuals (eggs, seeds) that appeared in a population per unit of time, per a certain number of its members (for example, the number of offspring produced by one female per year; in humans, the birth rate is usually expressed as the number of births per 1000 people per year); differentiate And specific mortality; the value of the specific birth rate or specific mortality rate is used to compare the birth rate or mortality rate in different populations;

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

6) growth rate- average population growth per unit of time.

Population research has important practical applications: for example, pest control, wildlife restoration, rational use biological resources(fish catching, etc.), conservation of rare species.

Population structure.

A population is characterized by a certain organization (structure). It is formed on the basis of general biological properties species, under the influence of populations of other species and abiotic environmental factors.

The population structure is adaptive in nature. Different populations of the same species have distinctive features that characterize the specific environmental conditions in their habitats.

The population structure can be spatial, age, sex, genetic and environmental.

Spatial structure determined by the distribution of individuals in the population territory. All individuals in a population have individual and group space. There are certain radii of trophic (feeding) and reproductive activity. There are two opposing processes going on in a population - isolation and aggregation. Isolation factors are competition between individuals for food when it is scarce and direct antagonism. This leads to uniform or random distribution of individuals. Aggregation - the union of individuals into groups - although it increases competition between them, it contributes to the survival of the group as a whole due to mutual assistance. Aggregation leads to crowded distribution of individuals in the population. For example, organisms of many species prefer to live in flocks (birds) or herds (mammals).

Age structure A population is determined by the number and ratio of individuals of different ages, reflects the intensity of reproduction, the mortality rate, and the rate of generational change. In a stable population mixed age groups are in approximately the same ratio, the birth rate is equal to the death rate and the population size remains almost unchanged. The growing population is represented mainly by young individuals, where the birth rate exceeds the death rate. If senile individuals predominate in a population, then its number decreases.

Sexual structure- the number and ratio of males and females of the population. Genetic two-factor chromosomal sex determination ensures equal numbers of sexes. But in some cases, the sex ratio is determined by hormonal factors acting after fertilization, as well as environmental ones. As a result, the sex ratio in the population fluctuates over the years, deviating from 1:1.

Genetic structure is determined by the variability and diversity of genotypes, the frequencies of variations of individual genes, as well as the division of the population into groups of genetically similar individuals, between which constant exchange occurs. The diversity of genotypes depends on the size of the population and external factors influencing its structure. In small isolated and stable populations, the frequency of inbreeding naturally increases, which reduces genetic diversity and increases the threat of extinction.

Ecological structure- this is the subdivision of a population into groups of individuals that interact differently with environmental factors. Groups are identified by nutrition (individuals of different sexes and ages have different food preferences), by indicative behavior, by motor activity. A distribution of functions is often observed when hunting prey and caring for offspring. All populations are also characterized by phenological differentiation (different start and end times of seasonal cycles of development and behavior: hibernation, sexual activity, molting, flowering, fruiting, leaf fall, etc.).

Population dynamics.

A population cannot exist without constant changes, due to which it adapts to changing environmental conditions. Changes in the number of organisms over time are called dynamics populations. Ideas about population growth are necessary to understand their ability to restore numbers, as well as to understand some of the properties of dynamics.

Any population is theoretically capable of unlimited growth in numbers if it is not limited by factors external environment. In this case, the population growth rate will depend only on the size biotic potential (b.p.), characteristic of the species. B.P. reflects the theoretical maximum of descendants from one pair or individual per unit of time. B.P. is expressed by coefficient r and calculated using the following formula:

where ΔN is population growth;

Δt is the period of time during which an increase in ΔN is observed;

N 0 - initial population size.

In nature, the B.P. of a population is never fully realized. Usually its value is the difference between the birth rate and death rate in populations:

where: in - number of births,

d is the number of dead individuals in the population over the same period of time.

Population growth and growth curves. If the birth rate in a population exceeds the death rate, then the population will grow (if changes due to migration are insignificant). To understand the patterns of population growth, it is useful to first consider a model that describes the growth of a bacterial population after inoculation on fresh culture medium. In this new and favorable environment, conditions for population growth are optimal and exponential growth (J-shaped) is observed. This growth curve is called exponential, or logarithmic (Fig. 1).

Fig.2. Logistic population growth curve (S-shaped)

Eventually, a point is reached where, for several reasons, including dwindling food resources and the accumulation of toxic metabolic waste, exponential growth becomes impossible. It begins to slow down so that the growth curve takes on a sigmoid (S-shaped) shape and is called logistics(Fig. 2).

The sigmoid and J-curve are two patterns of population growth. It is assumed that all organisms are very similar to each other, have an equal ability to reproduce and an equal probability of dying, so that the rate of population growth in the exponential phase depends only on its size and is not limited by environmental conditions, which remain constant.

In nature, after the exponential phase, further development of the population follows a logistic model, with the population growth rate linearly decreasing as the population grows, down to zero at a certain value of K. The value of K is called biological capacity of the environment(the degree of ability of the natural or natural-anthropogenic environment to provide normal life activity to a certain number of organisms without noticeable disruption of the environment itself).

A survival curve can be obtained by starting with a population of newborns and then plotting the number of survivors as a function of time. The vertical axis usually plots either the absolute number of surviving individuals or their percentage of the original population:

Each species has a characteristic survival curve, the shape of which depends in part on the mortality of immature individuals. Typical examples are shown in Figure 3.

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Fig.3. Three Types of Survival Curves

Most animals and plants are subject to senescence, which is manifested by a decrease in vitality with age after a period of maturity. Once aging begins, the likelihood of death within a certain period of time increases. The immediate causes of death may be different, but they are based on a decrease in the body’s resistance to adverse factors (for example, diseases). Curve A in Fig. 2 is very close to the ideal survival curve for a population in which aging is the main factor influencing mortality. An example would be a human population in a modern developed country with a high level of medical care and rational nutrition, where most people live to old age. A curve similar to curve A is also characteristic of annual cultivated plants when they age simultaneously in a given field.

A type B curve is characteristic of populations of organisms with high mortality rates early in life, such as mountain sheep or a human population in a country where famine and disease are widespread. A smooth type B curve can be obtained if mortality is constant throughout the life of the organisms (50% for a certain unit of time). This may occur when chance becomes the main factor determining mortality, and individuals die before noticeable aging begins. A similar curve is typical for populations of some animals (for example, hydra), which are not particularly endangered at an early age. Most invertebrates and plants also exhibit this type of curve, but high mortality among young individuals causes the initial part of the curve to descend even more steeply.

There are small intraspecific differences in survival curves. They may be due for various reasons and are often related to gender. In humans, for example, women live slightly longer than men, although the exact reasons for this are unknown.

By plotting survival curves for different species, mortality rates for individuals can be determined. of different ages and thus find out at what age a given species is most vulnerable. Having established the causes of death at this age, one can understand how the population size is regulated.

Related information.

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. 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 fall of a year with favorable feeding conditions, the population 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 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.

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. individuals of the same species, 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 impact on each other than physical environmental factors 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.

group characteristics 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 sex, age, genetic, spatial and ecological structures of 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 of natural selection, which adapts 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, gender, distinctive features morphology, behavioral characteristics, their 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 growing them 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.

During human exploitation of natural animal populations, taking into account their age structure has vital 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. 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.

“Site consolidation” is achieved different ways: 1) protection of the boundaries of the occupied space and direct aggression towards a stranger; 2) special ritual behavior demonstrating a threat; 3) a system of 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 behavior of animals includes an active search for contacts with members 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 form such a connection is the care of one of the parents for the laid eggs: protection of the clutch, incubation, additional aeration, etc. With 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.

More large associations animals - flocks, herds absolute 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.

The biological term “population” was first used in 1903 by a biologist from Denmark. Wilhelm Ludwig Johansen (1857 - 1927) to denote the group growth of one plant species.

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General concept

What is a population? She (the ancient Latins said: populus from modern English population - population) is a collection of representatives a specific species of living organisms, a long period of time living or growing in one territorial space, separately from individuals of other groups similar in similar characteristics.

The term is used in various fields of natural sciences: ecology, medicine, demography.

If we take for example, then in the appropriate terminology, the concept is defined as a community of animals or plants of the same species, having a single gene pool(we will consider this term below) capable of sustainable self-reproduction. In biology, it refers to groups of organisms within a certain species.

The simplest example is the human population on Earth. If we take examples from the animal world: sika and red deer, brown and polar bears, cod and haddock in the seas of the Northern basin Arctic Ocean. From the plant world: different types pine and spruce, aspen and linden, oak and elm.

What parameters characterize each population? The generally accepted criteria are:

• general habitat (area);
• uniform origin of a community of organisms;
• the relative isolation of a given community from other similar groups (so-called interpopulation barriers);
• compliance with the principle of panmixia (free crossing) within the group, in other words, an equal probability of meeting all existing genotypes within the range.

Population types

Types of living organisms in wildlife great multitude. First of all, we need to highlight two global populations- animals and plants. And they already define the subspecies of a particular group of organisms

In biology, geographically determined groups are structurally distinguished, for example, the settlement of squirrels in the forests of the Ulyanovsk region. Grouped animals of the same subspecies (in our case, squirrels), living in a geographically homogeneous space. Such an area is called a habitat.

In turn, geographic populations are divided into smaller ones - ecological (proteins in coniferous and mixed forests one area), and those - into even smaller ones - elementary or local (the same proteins, but in different parts of the same forest).

According to the ability to reproduce, there is a division into:

• Permanent, which do not require an influx of individuals of their species from the outside to maintain numbers at the level necessary for full existence.
• Semi-dependent, in which a certain number of similar individuals come from outside, but even without them the population is able to exist for a long time.
• Temporary, in them the mortality rate of representatives is higher than the species birth rate, and existence is directly dependent on the influx of individuals from the outside. Temporary populations often form in places with unfavorable climate and unstable food supply.

Attention! A population is very similar to a living organism, as a biosystem; it also has an organized structure that has its own integrity, a genetic program for self-reproduction and special characteristic mechanisms of self-regulation and adaptation.

Population structure

The structure of the predominant number of existing species settlements is determined by the representatives that form them, and the placement of the latter in the habitat (remembering the squirrels - total number and the percentage of different-sex animals in the forest). To make it clearer, let's look at the points.

So, the population structure is

Spatial - the distribution of individuals across the occupied area - how many squirrels are running and where. It, in turn, is divided into:

• Random (if the forest is the same for all squirrels, and they jump in the same natural environment). In this case, there are few animals, they do not form “groups” and do not live crowded together in water.
• Uniform. It is found mainly in animals living in conditions of severe competition for food resources and habitats. Some types predatory fish, birds and mammals (bears, for example) carefully guard their hunting grounds and do not favor strangers on them.
• Group. The most common in nature. Here we will look at the example of plants. Some trees have large, heavy fruits (nuts, acorns, plane nuts, etc.), which, falling next to the tree, immediately germinate, forming groups. And even lilies of the valley! But they owe it to this vegetative method reproduction (offshoots from rhizomes). These growth characteristics are caused the fact that the surrounding environmental conditions are heterogeneous, habitats are limited, the species has characteristic biological qualities and reproduction options.

Sexuality - the ratio of specimens of different sexes (how many male and female squirrels are in the forest).

Age is the most understandable. How many individuals of different ages. In any species, and sometimes in each population within a species, there are different ratios of age groups. As a rule, the following ecological ages are distinguished:

• pre-reproductive (organisms that have not reached sexual maturity);
• reproductive (sexually mature);
• post-reproductive (representatives who have lost the ability to reproduce).

For animals and plants, this structure has significant differences, but this is a separate topic for consideration.

Genetic structure of the population due to variability and diversity of genotypes(roughly speaking, the difference in squirrel color and size, and their variations during mating with subsequent offspring).

Ecological structure consists of dividing a species into groups of individual representatives that interact in their own way with environmental conditions. This is where local populations often show up. The whole point is that the difference between type and separate group representatives existing in special conditions general range residence, very conditional.

In principle, the system functions like almost any biological system. Accordingly, it is characterized by: growth, development, survival in changing environmental conditions. This determines the presence of certain parameters.

Squirrel population

Options

Most existing populations are characterized by: number, density, birth rate and death rate. All these characteristics are also closely interconnected and interdependent.

Population size- the total number of representatives of the species living in the territory. Density, respectively, is the number of individuals of a given species per unit area of ​​the area.

In many large groups, the average size does not change much each year due to the fact that:

• approximately the same number of representatives die from natural causes;
• the intensity of reproduction of organisms increases with a low population density, and with an increase, it correspondingly decreases;
• constantly changing natural conditions and climatic factors create obstacles to the high realization of reproductive potential.

But, even with a certain stability, the population size is characterized by fluctuations. The main reasons for these fluctuations associated with changes in living conditions. Namely:

These periodic fluctuations lead to changes in the total population, which consist of the following phenomena:

• fertility;
• mortality;
• immigration (movement - influx of individuals from outside);
• emigration (eviction of representatives of the species).

These factors are associated with so-called population waves.

Important! Population waves are sudden, significant numerical changes.

Example: a reduction in the number of foxes as a result of shooting (an abiotic factor) leads to a population increase in field mice (voles).

Populations are characterized by numbers, densities, birth rates, and deaths.

Gene pool

But of particular importance is the effective number - the number of sexually mature representatives of the species capable of producing offspring. It is they who form the gene pool. And now let's look at this concept specifically.

What is the gene pool of a population(gene pool). This is the totality of all the characteristics (genes) of a species and their variations that are inherited. It is thanks to genes that squirrels from Siberia differ from squirrels from Canada. Gene variations (alleles) determine the ability of organisms to adapt to constantly changing environmental features. How more variety genes, the more capable the body is of adapting to life.

In biology there is such a thing as an ideal population. But, it is purely theoretical and is used to model processes. Ideal population can be defined as a hypothetical panmictic (i.e., individuals of which have the same chance of interbreeding), with an infinitely growing population that persists through generations and is independent of natural selection, external factors and mutations.

What is the main role of the concept for the existence of living organisms on the planet? In ecology it is defined as an elementary unit of the process microevolution(intraspecific small gene changes over several generations, leading to certain changes in the individual, both external and internal), responding to changing environmental factors by restructuring the gene pool.

Population functioning and population dynamics in nature

Population as a form of existence of species in nature

Conclusion

Based on the above , Let's summarize. A population is a collection of representatives of the same species living in a common territory, interbreeding freely, possessing a single gene pool, having its own structure, characteristics and parameters similar to existing biosystems, and is an elementary microevolutionary unit.

The concept of population. Population types

group characteristics(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 a white birch forest, growing at the bases of trees and on open places; 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. Exchange genetic information happens between them 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, north 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– a set of ecological populations inhabiting 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 M.A. Shemberg (1986) identified two subspecies of stone birch: Erman birch (Betula ermanii) and woolly birch (B. lanata). 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.

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; Fertility is limited by the physiological characteristics of the species.

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, Just like birth rate, it can be absolute (the number of individuals who died in a certain time) or specific. It characterizes the rate of population decline from death due to disease, old age, predators, lack of food, and plays main 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.