Structure and properties of populations. The concept of population and population structure - test

entropy protein synthesis population

Population (populus - from the Latin people. population) is one of the central concepts in biology and means a collection of individuals of the same species, which has a common gene pool and has 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.

Ecological population is 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, north Khabarovsk Territory); forest stands in sedge (dry) and forb (wet) oak forests (Primorsky Territory, Amur Region); squirrel populations in pine, spruce-fir and deciduous forests one district.

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.

Any population has a strictly defined structure: genetic, age-sex, spatial, etc., but it cannot consist of fewer individuals than necessary for stable development and resistance of the population to factors external environment. 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.

Knowledge of the population structure allows the researcher to draw conclusions about its well-being or disadvantage. For example, if there are no generative (that is, capable of producing offspring) individuals in the population and there are many old-age (senile) individuals, then an unfavorable prognosis can be made. Such a population may have no future. It is advisable to study the population structure in dynamics: knowing its changes over several years, one can speak much more confidently about certain trends.

Age structure of the population. This type of structure is associated with the ratio of individuals of different ages in the population. Individuals of the same age are usually grouped into cohorts, that is, age groups.

The age structure of plant populations is described in great detail. It distinguishes (according to T.A. Robotnov) the following ages (age groups of organisms):

· latent period - the state of the seed;

· pregenerative period (includes the states of a seedling, a juvenile plant, an immature plant and a virginal plant);

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

· post-generative period (includes the states of a subsenile plant, a senile plant and the death phase).

Of course, this raises the problem of the relationship between calendar and biological age. Belonging to a certain age state is determined by the degree of expression of certain morphological (for example, the degree of dissection of a complex leaf) and physiological (for example, the ability to give birth) characteristics. In this way, first of all, the biological age of the individual is recorded. Biological age has for an ecologist higher value, since it is he who determines the role of the individual in population processes. At the same time, as a rule, there is a relationship between biological and calendar age.

Animal populations can also be divided into different age stages. For example, insects that develop with complete metamorphosis go through the stages of egg, larva, pupa, and imago (adult insect). In other animals (which develop without metamorphosis), various age-related states can also be distinguished, although the boundaries between them may not be so clear.

The nature of the age structure (or as they say, age spectrum) of a population depends on the type of so-called survival curve characteristic of a given population. The survival curve shows the mortality rate in different age groups. Thus, if the mortality rate does not depend on the age of individuals, then the survival curve is a decreasing line. That is, the death of individuals occurs evenly in this type, the mortality rate remains constant throughout life. Such a survival curve is characteristic of species whose development occurs without metamorphosis with sufficient stability of the born offspring. This type is usually called the hydra type - it is characterized by a survival curve approaching a straight line.

In species for which the role of external factors in mortality is small, the survival curve is characterized by a slight decrease until a certain age, after which there is a sharp drop as a result of natural (physiological) mortality. The nature of the survival curve close to this type is characteristic of humans (although the human survival curve is somewhat flatter and, thus, is something between types I and II). This type is called the Drosophila type: it is what fruit flies exhibit in laboratory conditions (not eaten by predators).

Many species are characterized by high mortality in the early stages of ontogenesis. In such species, the survival curve is characterized by a sharp drop in the region younger ages. Individuals that survive the “critical” age exhibit low mortality and live to older ages. The type is called the oyster type.

The study of survival curves is of great interest to the ecologist. It allows us to judge at what age a particular species is most vulnerable. If the effects of causes that can change fertility or mortality occur at the most vulnerable stage, then their influence on the subsequent development of the population will be greatest. This pattern must be taken into account when organizing hunting or pest control.

Sexual structure of the population. We can talk about the sex structure of a population, of course, only if we're talking about about the dioecious (bisexual) species. Bisexuality plays a huge role in maintaining the genetic diversity of individuals in a population. The importance of genetics for population sustainability will be discussed in detail in the next lesson. Now we note that the sexual structure, that is, the sex ratio, is directly related to the reproduction of the population and its stability.

It is customary to distinguish primary, secondary and tertiary sex ratios in a population. The primary sex ratio is determined by genetic mechanisms - the uniformity of divergence of sex chromosomes. For example, in humans, XY chromosomes determine the development of the male sex, and XX chromosomes determine the development of the female sex. In this case, the primary sex ratio is 1:1, that is, equally probable.

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

Tertiary sex ratio is the sex ratio of adult animals.

Spatial structure of the population. The spatial structure of a population reflects the nature of the distribution of individuals in space.

There are three main types of distribution of individuals in space:

· uniform (individuals are distributed evenly in space, at equal distances from each other), the type is also called uniform distribution;

· congregational, or mosaic (that is, “spotted”, individuals are located in isolated clusters);

· random, or diffuse (individuals are randomly distributed in space).

Uniform distribution is rare in nature and is most often caused by intense intraspecific competition (as, for example, in predatory fish).

Random distribution can only be observed in a homogeneous environment and only in species that do not show any tendency to form groups. As a textbook example of uniform distribution, the distribution of the Tribolium beetle in flour is usually cited.

Distribution in groups is much more common. It is associated with the characteristics of the microenvironment or with the behavioral characteristics of animals.

The spatial structure has important ecological significance. First of all, certain type use of territory allows the population to effectively use environmental resources and reduce intraspecific competition. Efficient use of the environment and reduced competition between members of a population allow it to strengthen its position in relation to other species inhabiting a given ecosystem.

Another important significance of the spatial structure of a population is that it facilitates the interaction of individuals within a population. Without a certain level of intrapopulation contacts, the population will not be able to perform both its species functions (reproduction, settlement) and functions associated with participation in the ecosystem (participation in substance cycles, creation of biological products, and so on) such as the ability to produce work. The properties of energy are described by the laws of thermodynamics.

The first law (beginning) of thermodynamics or the law of conservation of energy

states that energy can change from one form to another, but it does not disappear or be created anew.

The second law (law) of thermodynamics or the law of entropy states that in a closed system entropy can only increase. In relation to energy in ecosystems, the following formulation is convenient: processes associated with energy transformations can occur spontaneously only under the condition that the energy passes from a concentrated form to a dispersed one, that is, it degrades. The measure of the amount of energy that becomes unavailable for use, or otherwise the measure of the change in order that occurs during energy degradation, is entropy. The higher the order of the system, the lower its entropy.

Thus, any living system, including an ecosystem, maintains its vital activity thanks to, firstly, the presence in the environment of an excess of free energy (the energy of the Sun); secondly, the ability, due to the design of its constituent components, to capture and concentrate this energy, and when used, to dissipate it into the environment.

Thus, first capturing and then concentrating energy with the transition from one trophic level to another ensures an increase in the orderliness and organization of a living system, that is, a decrease in its entropy. According to modern concepts, life is the process of the existence of complex biological systems consisting of large organic molecules and capable of self-reproduction and maintaining their existence as a result of the exchange of energy and substances with the environment. Each organism is a collection of ordering interacting structures that form a single whole, that is, it is a system. Living organisms have characteristics that are absent in most nonliving systems.

Population structure is usually understood as its spatial, age, sex and genetic composition.

Sometimes they talk about the ecological structure of a population, including in this concept the distribution of individuals in the population by sex and age, often expressed in the form of so-called “life tables”. IN lately the generalized concept of biochorological is often used population structure(from Greek choros - space).

The spatial structure of the population, i.e. the distribution of individuals within the population, is characterized by unevenness. This unevenness is determined by the heterogeneity of biogeocenotic conditions and determines the existence within the population of smaller spatial groupings of individuals - settlements occupying one or another part of its range; between such settlements there remain unoccupied or sparsely populated spaces.

An example of differences in the spatial structure of populations of different species is the distribution of individuals of the main background species of plants and animals on a small island (with an area of ​​100 ha). Skolme off the southwest coast of England. Certain plant species (agrostis bentgrass, Pteridium bracken, Armeria) and typical communities (swamp vegetation, hummock grass) form patches of unequal size on the island. Groupings of individual species of birds and mammals stand out even more clearly: 35,000 pairs of adult birds, the little petrel Puffinus puffinus, are united in 8 colonies, 900 pairs of black bird Larus fuscus - 10 nesting groups of different sizes. Nesting grounds of the herring gull L. argentatus and puffins Fratercula arctica - about 500 and 5000 pairs, respectively, border the island along the coasts with a broken ribbon of complex configuration.

In terms of the number of rabbits Oryctolagus cuniculus (in autumn up to 100 individuals per 1 ha) Scocolm is the most densely populated area of ​​England, and yet the distribution of its settlements (dense and sparse) is uneven and forms a complex mosaic of patches. House mice living here in the wild are characterized by a combination of “lace” and “spotted” types of distribution in one territory. Tagging made it possible to find out that, despite the apparent isolation of some groups of individuals, a number of individuals are characterized by movements that cover the entire studied territory.

Not all of the species considered form true populations on the island. There is no doubt that black whales and herring gulls inhabiting the island. Skokolm are only parts of some populations of these large birds. The issue of population independence is not entirely clear for colonies of puffins and petrels - their settlements on the island can be real populations, or only part of the population. The same can be said about the population of plant species if their pollen is effectively distributed over tens or hundreds of kilometers. But the population of rabbits and house mice on the island can rightfully be called populations.

The decision of whether to consider the group of individuals under study as a population or to consider it only a spatially isolated part of the population depends on how large the exchange of individuals is between neighboring groups. When studying a population snapping lizard Lacerta agilis in Western Altai, groups ranging from several individuals to hundreds of thousands of individuals were found.

A population here can rightfully be called a group of individuals of level IV with an exchange of about 0.01% of individuals of each generation and with a duration of existence of hundreds of generations. Before this - the population level - in the species population of the sand lizard, groups of individuals of two lower levels of integration (I and II) are clearly distinguished. They exist for a relatively short time (several generations) and widely exchange individuals, due to which their genetic composition changes sharply and quickly, it is unstable. In addition, the very fragility of such associations determines their ephemeral nature. The third level of integration in a number of cases can probably be recognized as a real population one. This depends in no small part on how strong the local selection pressure will be: with strong selection directed against newcomers, they will not be able to significantly change the genetic structure of the group; with a weak one, after just a few generations the genetic structure of groups exchanging individuals on such a wide scale (about 3-4% in each generation) is leveled out, and they form a single genetic totality.

From the foregoing it is clear that the essential point in determining the independence of a particular group of individuals is its sufficient number and isolation from neighboring similar populations. The measure of isolation can theoretically be the level of transfer of alleles from one gene pool to another, or practically the level of exchange of individuals. In turn, this level depends on the radius of individual activity, i.e., the distance that the average individual actually covers during its life through passive or active movement. In plants, for example, it can be determined by the distance of pollen distribution, the distance from the parents of their vegetative descendants (cuttings, buds, shoots, tumbleweed forms, etc.), seed dispersal (by wind, water, when carried by animals, etc.) .p.). It has been established that the population size of rodents, reptiles and amphibians is relatively small, while that of birds and widely migratory mammals is significant. The main reason for this is considered to be differences in the mobility of individuals of the mentioned groups of animals.

The size of the radius of individual activity is closely related to the nature of the use of the territory. To the species that lead sedentary image life is characterized by an intensive type of space use (I. A. Shilov, 1977), in which individual individuals or their groups (in higher vertebrates, mainly family ones) use the resources of a relatively limited territory for a long time. The radii of individual activity and the territories of intrapopulation groups in such species are usually small, although they vary depending on the level of abundance. Species characterized by a nomadic lifestyle or other types of migration are characterized by an extensive type of space use, in which the food resources of the area are developed during the regular movements of groups of individuals. The radius of individual activity and the size of the territory of intrapopulation groups in such species are significant. There is no sharp boundary between intensive and extensive methods of using space, since during the nesting period populations often lead a sedentary lifestyle with intensive use of space, and then switch to a migratory lifestyle with an extensive type of use of the territory.

As a result, the spatial structure of populations will differ between species. Prides of lions, harems of eared seals, packs of wolves and jackals, pods of killer whales - these are just a few of a number of spatial-genetic groupings known in mammals.

Several terms have been proposed to designate such small, relatively independent, but short-lived groups of individuals, consisting of intensively interbreeding individuals and their descendants. IN recent years in zoological literature, the term dem (from the Greek demos people) is used to designate such groups. For plants and fungi, the question of the spatial structure of the population has not been developed in as much detail as for vertebrates, which is due to the specifics of their structure and way of life. We can assume that each population has its own spatial structure, which is maintained in a form adaptive for a given place and time. At the same time, the placement of individuals in space represents the “morphological” aspect of the spatial structure of the population, and the system of relationships between them is its functional aspect, which is discussed in more detail below.

One of the common mistakes in population research is obtaining not population characteristics, but characteristics of individual demes or other short-term populations of individuals, i.e. obtaining a non-representative sample. For example, when studying the sand lizard Lacerta agilis on the Kalbinsky ridge, we first encountered a group of individuals of 7 individuals, two of which (29%) were melanistic. However, it would be wrong to consider such a high frequency of melanists as a population characteristic: among the dozens of other individuals subsequently caught, there were no melanists.

The age structure of a population, i.e. the ratio of groups of individuals of different ages, is one of the most important characteristics of a population.

The age of any organism can be expressed in units of astronomical time - minutes, hours, months, years. Age can also be judged by the degree of development of the organism or its physiological maturity, i.e., determine physiological age. Unfortunately, the possibilities of determining the astronomical (calendar) age of individuals in natural populations are quite limited. They come down to the study of recording structures (M.V. Mina, G.A. Klevezal, 1976): layering of tree trunks, bones and teeth in vertebrates, rings or branches on the horns of some ungulates, age-related changes in color, structure of feathers or fur. etc.

Determination of physiological age is carried out by changes in body size and shape, color, state of the generative system, maturation of the skeletal system, involution of glands (for example, the thymus), abrasion of the chewing surface of the teeth and other signs.

In the process of postnatal development of an individual, its morphophysiological and other characteristics and properties change; accordingly, age groups and populations differ in the specificity of the same characteristics.

The age structure of populations can be expressed primarily by the ratio of the average durations of the pre-reproductive, reproductive and post-reproductive stages individual development, characteristic of a given population. In more detail, the age structure of the population can be presented in the form of age pyramids, which take into account the relative numbers of each age group.

The age structure of a population reflects such important processes as the intensity of reproduction, the mortality rate, and the rate of population renewal. It is closely related to the genetic characteristics of the generations that form a population and to the characteristics of the specific conditions of development of individual generations.

To accurately describe the age structure of the population, we will give definitions of some terms.

A generation (generation) includes all the offspring of individuals of the previous generation (children - parents). This concept is genetic. The transmission of hereditary material occurs through generations. Taking into account the number and ratio of generations is one of the important conditions for studying the structure of populations. The duration of a generation corresponds to the average reproductive age in a given population of individuals of a certain species and can serve as the basis for establishing the duration of existence of the population and its rank (recall that a population exists for many - hundreds and thousands - generations).

Offspring- simultaneously born individuals from a certain set of parents (which can belong to one or several generations). It ensures an increase in population size within a certain time frame. This is an ecological concept associated with the study of the demographic characteristics of a population: density, size, birth rate.

Age group- a group of individuals of the same age. The classification of age groups is often arbitrary (for example, “young”, “adults”, “old”), but it allows us to identify comparable groups of individuals in the studied samples from different populations. The age structure depends on the different combination of individuals of different generations, offspring and age groups in the population. In species that reproduce once in a lifetime (salmon and some other fish, many insects, annual plants), the age structure of populations is very simple, since a generation is both an offspring and an age group. The population then contains a maximum of two generations, two offspring and two age groups (if the parent generation does not die off before the generation of children is formed).

One generation may include more than one offspring and one age group. The simplest example of such a combination can be observed in the population of the shrew Sorex araneus. The parent generation of shrews gives one or two offspring during the spring-summer period and completely dies out by autumn. The daughter generation, which includes two offspring, in the fall consists of still immature individuals that reach maturity in the spring.

More often, a generation consists of individuals from several offspring and age groups (repeatedly reproducing animals and perennial plants). The age structure of the population in this case is very complex, especially since then the formation of one offspring occurs from individuals belonging to different generations. This phenomenon is observed, for example, in many voles that give two or three litters per season: if young individuals from the first litter quickly become involved in reproduction, then the pre-autumn litters can consist of individuals of two generations.

The age structure of long-lived animal species and especially plants is even more complex. It is difficult to imagine a combination of generations and offspring in forest plantations, where representatives of a number of successive generations bear fruit for tens (sometimes hundreds) of years, together producing one offspring each season. In addition, individual seeds can be stored without germinating for tens or hundreds of generations and, once in favorable conditions, can easily be integrated into the gene pool of descendant populations. The following real-life situation turns out to be similar to this: an acorn fallen from a 1000-year-old oak tree can germinate in 20-30 years; pollen from this young oak tree can pollinate the flowers of the parent oak tree, which is 50 generations older than its crossing partner. In these and other similar cases, one age group may include more than one offspring and generation.

Methods for studying the age structure of populations are determined by the purpose of the study. Ecologists study the morphophysiological characteristics of different age groups, age structure as indicators current state populations, identify trends in population changes, etc. When evolutionary approach The main attention of the researcher is drawn to identifying the characteristics of generations, through which the transformation of the genotypic and phenotypic structures of the population is carried out.

In close unity with the age structure, the sexual structure of the population should be considered, which also determines the intensity of reproduction, population dynamics and features of the geno- and phenotypic composition of the population.

Sex structure of the population, i.e. numerical ratio sexes, varies extremely among different species of animals and plants, in different populations of the same species, in different times and in different age groups in the same population.

The genetic mechanism ensures a certain primary sex ratio during the formation of zygotes, usually in a 1:1 ratio. Other relationships are also possible. For example, the wood lemming Myopus schisticolor is consistently female dominated due to the presence of XXY females.

Due to the different viability of male and female organisms, the primary sex ratio differs markedly from the secondary sex ratio characteristic of newborns (regardless of the “mode of birth”), and even more from the tertiary sex ratio (at the onset of puberty). In humans, for example, the secondary sex ratio (on average for many populations) is 100 girls per 106 boys; by the age of 16-18 it levels out as a result of increased male mortality, and by the age of 50 it is 85 men per 100 women.

The secondary and tertiary sex ratio varies significantly both among different species of animals and plants, and within species, but there is little accurate data. In recent years, the attention of researchers has been drawn to the variability of the tertiary sex ratio within the species' range and the change in this indicator within one population over time.

Genetic structure of the population, i.e. frequencies of alleles and genotypes, - most important characteristic populations.

To understand the basic genetic processes occurring in a population, it is necessary to remember that it is not traits as such that are transmitted through generations, but certain hereditary structures. Moreover, each genotype determines a certain range of possibilities for the development of a trait depending on environmental conditions. In other words, each genotype is characterized by a certain reaction norm. The implementation of any trait in the ontogenesis of an individual is determined, as a rule, by many genes; on the other hand, a gene usually affects not one, but many traits. The limits of the reaction norm of each genotype are expressed by the set of phenotypes that can develop from this genotype under all environmental conditions that do not lead to death.

This results in an ambiguous correspondence between genotype and phenotype and, therefore, the impossibility of unambiguously judging the genetic structure of a population based on phenotypes.

S.S. Chetverikov and his students showed the enormous genetic heterogeneity of natural populations; It is rare to find genetically identical individuals in a population.

Genetic heterogeneity of populations maintained both by newly arising mutations different types, and due to the processes of recombination of the genetic diversity already existing in the population under the influence of evolutionary factors - natural selection, migration, random processes, a certain system of crossings.

Genetic heterogeneity allows the population and the species as a whole to use, to adapt to constantly changing conditions of existence, not only newly emerging hereditary changes, but also those that arose a long time ago and exist in the population for a long time. hidden form(“mobilization reserve” of variability).

The manifestation of genetic heterogeneity and one of important features genetic structure of natural populations is intrapopulation polymorphism, i.e. long-term coexistence in a population of two or more genetically various forms(in such ratios that the frequency of even the rarest form cannot be explained only by repeated mutations).

There are heterozygous and adaptation polymorphisms. The first is established as a result of the greater fitness of heterozygotes, the second - as a result of selection in different environmental conditions of genetically different forms within the population. A classic example of the latter is seasonal changes in the frequency ratios of the red and black forms ladybug Adalia bipunctata the former tolerate cold better in winter, the latter reproduce more intensively in summer.

Despite heterogeneity, any population is united and represents a complex genetic system in dynamic equilibrium. From a genetic-evolutionary point of view, a population is a minimal system that can exist for a theoretically unlimited number of generations. It is sometimes said that a population is the smallest system, having its own evolutionary destiny that smaller groups of individuals do not have. Therefore, a population is an elementary evolutionary unit.

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- the totality of those living on certain territory 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, in a general sense- to designate isolated groups of a species, regardless of what territory it occupies and what genetic information 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 etc. 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 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.

The population is characterized specific 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 biotic factors environment 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 migratory 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 to varying degrees 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. Growth and development of organisms, birth of new ones, death from various reasons, changes in environmental conditions, an increase or decrease in the number of enemies - all this leads to changes in various ratios 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 environmental age : 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 features, in 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. 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 in 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 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 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.

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 appears only up to a certain point optimal level 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.

Any population is characterized by a certain organization. The distribution of individuals across the territory, the ratio of groups of individuals by sex, age, morphological, physiological, behavioral and genetic characteristics reflect the corresponding population structure: spatial, gender, age, etc. The structure 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. Therefore, it is important to emphasize the frankly adaptive nature of population structure.

Age structure of the population, i.e. the ratio of different age groups in it is determined by the characteristics of the species’ life cycle and external conditions.

In any population, three ecological groups can be roughly distinguished: pre-reproductive, reproductive, post-reproductive. To pre-reproductive refers to a group of individuals whose age has not reached the ability to reproduce; reproductive- a group capable of reproducing new individuals; finally, post-reproductive- individuals who, for a number of reasons, have lost the ability to participate in the reproduction of new generations.

There are species with very simple age structure populations that consist of practically the same age. Thus, all annual plants are in seedlings in the spring, then almost simultaneously they bloom, produce seeds and die by autumn. The vulnerability of such populations is extremely high: if, for example, frosts occur during the development period, mass death of individuals occurs. On the contrary, in a favorable situation such a population can produce an explosion in numbers (locusts, rodents).

In a population with complex age structure All age groups are represented, and several generations live simultaneously. So, in herds of elephants, for example, there are newborns, teenagers, young growing animals, males and females capable of reproduction, and old individuals. Such populations are not subject to sharp fluctuations in numbers. Extreme external conditions can change their age composition due to the death of the weakest, but the most stable age groups survive and then restore the population structure.

It is obvious that a person considered as biological species, has a complex population structure.

Genital Groups within populations are formed on the basis of different morphology (body shape and structure) and ecology of different sexes. The difference between males and females affects not only the structure and function of the reproductive system, but also morphology in general (horns of males and the absence of them in females; winged males and wingless females in some insects; bright plumage of males and modest plumage of females, etc.). There is often a difference between males and females in the nature and type of food. Thus, in many mosquitoes, males feed on nectar or plant juice, and females feed on the blood of victims. Different diets of males and females occur in a number of mammals, birds, and fish.

Spatial structure of populations. The space occupied by a population provides it with the conditions necessary for life. However, each specific territory is capable of feeding only a certain number of individuals. It is obvious that the degree of use of available natural resources is influenced not only by the total population size, but also by the distribution of individuals in space.

Occasionally in nature, an almost uniform, ordered distribution of individuals occurs in an occupied territory, for example, in pure thickets of some plants. However, due to the heterogeneity of the occupied space, as well as some features of the biology of the species, most often the members of the population are distributed unevenly in space. There are two extreme options for the uneven distribution of population members: 1) clearly defined mosaic unoccupied space between individual clusters of individuals (for example, nesting sites of rooks in groves or parks); 2) random distribution, diffuse type when members of a population are more or less independent of each other and live in a relatively homogeneous environment for them.

Plants are most often distributed extremely unevenly, forming more or less isolated groups, clusters, which are called subpopulations. They differ in the number of individuals, density, age structure and extent. On the contrary, in animals, due to their mobility, the ways of organizing territorial relations are more diverse compared to plants. At the same time, intrapopulation distribution in higher animals is regulated by a system of instincts. Such instincts, which help maintain the distribution of individuals or groups in populations across the territory, are characteristic of birds, mammals, reptiles, and fish.

By type of space use all mobile animals are divided into sedentary and nomadic .

Sedentary animals are distinguished by their instincts of attachment to their area, the desire to return to well-known territory (if forced relocation has occurred). This “feeling of home” is called « homing" (from the English home - house). A striking example Homing is the occupation of “their” birdhouse by the same pair of starlings for a number of years.

There are significant biological advantages to living a sedentary lifestyle. In particular, in familiar territory, free orientation is facilitated, the animal spends less time searching for food, finds shelter from the enemy faster, and can also, if necessary, create food reserves (squirrel, marmot, field mouse). At the same time, a sedentary lifestyle threatens the rapid depletion of food resources if, for example, population densities become excessively high.

For sedentary animal species, all options for the general spatial structure of populations are usually reduced to four main types: diffuse, mosaic (discussed earlier), pulsating and cyclic.

Populations characterized by sharp fluctuations in numbers are characterized by pulsating type spatial structure. It is known that during a period of sharp decline in numbers, some animals gather in the most favorable areas for life. For example, root voles in the forest-steppe in dry years primarily colonize the swampy shores of lakes.

Cyclic type The spatial structure of populations of sedentary animals is characterized by a natural alternating use of territory throughout the year, for example, in summer and winter. With this type of space use, a balance is maintained between feed consumption and their annual renewal.

Nomadic lifestyle has certain advantages over sedentary people. Nomadic animals do not depend on food supplies in a specific territory. However constant movement single individuals contribute to increased mortality from predators. That is why the nomadic lifestyle, as a rule, is characteristic of herds and flocks. At the same time, the areas of movement of many species can be quite large. Thus, herds of zebras roam an area of ​​400-600 km 2 during the dry season.

A system of relationships between members of the same population is called ethological, or behavioral structure of the population.

The forms of coexistence of individuals in a population are different.

Solitary lifestyle characteristic of many species (for example, hedgehogs, catfish, pike, etc.), but only at certain stages of the life cycle. Therefore, absolutely solitary existence of organisms does not occur in nature, otherwise the corresponding populations would die.

In species with a predominantly solitary lifestyle, temporary aggregations often occur - in wintering areas, as well as in the period before breeding.

Living in a group of one’s own kind affects the course of many physiological processes in the animal’s body. In artificially isolated individuals, the level of metabolism (metabolism) changes noticeably, reserve substances are consumed faster, a number of instincts do not manifest themselves, and overall vitality deteriorates. Under group effect understand the optimization of physiological processes leading to increased viability of individuals when they coexist.

The group effect manifests itself as the reaction of an individual to the presence of other individuals of its species. So, in sheep outside the herd, the pulse and breathing sharply increase, and at the sight of an approaching herd, these processes are normalized, and the sheep calms down. The effect of the group also consists in accelerating the growth rate of animals, increasing fertility, more rapid formation of conditioned reflexes, and increasing the average life expectancy of an individual. The group effect does not appear in solitary species. If such animals are artificially forced to live together, their irritability increases, collisions become more frequent, and energy costs for maintaining their vital functions increase.

The foregoing allows us to understand why increased requirements are imposed when forming groups of cosmonauts, detachments special purpose, crews who must stay in a confined space for a long time or communicate with each other for a long time. With a successful selection in such a team, the “group effect” clearly manifests itself and it successfully copes with the task.

Family lifestyle dramatically strengthens the bonds between parents and their offspring. A known manifestation of this is the care of one of the parents for laid eggs or the feeding of a female by a male. At the same time, care for the chicks continues until they are raised on the wing, and in some large mammals(bears, tigers) cubs are raised in family groups for several years until they reach puberty. Depending on which parent takes care of the offspring, families are distinguished between paternal, maternal and mixed type. Note that in families with stable pair formation, usually both parents take part in protecting and feeding the young.

Colony. Being a group settlement of sedentary animals, it can exist either for a long time or arise only for the breeding season (rooks, gulls, loons, etc.).

Some social insects - bees, ants, termites - organize very complex colonies - family. Here, insects jointly perform many basic functions: protection, reproduction, providing food for themselves and their offspring, construction, etc., for which they carry out a mandatory division of labor and specialization of individual individuals, including different age groups. At the same time, members of the colony constantly exchange information with each other.

Pack. This is a temporary association of animals of the same species (insects, birds, fish, less often mammals, etc.), associated with a common habitat or breeding place. Schooling makes it easier to perform any functions in the life of the species, for example, protection from enemies, obtaining food, and migration.

Based on the method of coordinating actions, schools are divided into two types: 1) without a clear leader (usually in fish); 2) with leaders on whom other individuals are guided (flocks of large birds and mammals, for example, wolves).

Herd- this is a group of wild or domestic animals of the same species living in some territory (for example, a herd of deer) or water area. All the main functions of life are carried out in a herd: obtaining food, protection from predators, migration, reproduction, raising young animals, etc. At the same time, the basis of group behavior of animals in herds is the relationship of dominance (headship) - subordination, which is determined by individual differences between individuals.

A hierarchically organized herd is characterized by a natural order of movement, a certain organization in protection, location in rest areas, etc. So, when a herd of baboons moves in the center, in greatest security, there are females with cubs or pregnant ones, along the edges there are leaders, young males and non-breeding females. Large males are located in front and behind the herd, ready to repel the attack of a predator.

Intraspecific competition. In this case, solidarity is maintained between individuals, so that they are able to reproduce and thus ensure the transmission of characteristics characteristic of the population hereditary properties. It is obvious that intraspecific competition is fundamentally different from interspecific competition.

Intraspecific competition manifests itself, for example, in territorial behavior, when an animal defends its nesting site and known area in his district.

Another manifestation of intraspecific competition is the existence of a social hierarchy, which is characterized by the presence of dominant and subordinate individuals. In plants, competition concerns mainly light and water. In the first case, plants that are too dense shade each other, which leads to the death of a significant number of plants. Trees develop different kind depending on whether they grow in the forest or separately from other trees.

Representatives of the same species of animals also have such a rare phenomenon as cannibalism, those. eating their own kind. It is most developed in predatory fish - pike, perch, cod, navaga, etc.

Population dynamics

Population dynamics - these are processes of changes in its basic biological indicators over time. At the same time, special importance in the study of population dynamics is given to changes in the number of individuals, biomass and population structure. Population dynamics are one of the most significant biological and environmental phenomena. Figuratively speaking, the life of a population is manifested in its dynamics.

This dynamics is described by A. Lotka’s equation:

dN / dt = rN ,

Where N - number of individuals, t - time, r - biotic potential.

The meaning of biotic potential varies enormously between species. Thus, a female roe deer is capable of producing 10 - 15 kids in a lifetime, and a sunfish lays up to 3 billion eggs.

In nature, however, the growth of populations of any species is never infinite, since the resources on which species exist have limits in any territory. These limits are called medium capacity for specific populations. For example, spruce forest- a more capacious environment for squirrels than mixed with birch trees, since the main food of these animals is the seeds of cones.

The population adapts to changes in environmental conditions by updating and replacing individuals. The latter appear in the population as a result of birth and immigration (invasion of aliens), and disappear as a result of death and emigration. If the fertility and mortality rates are balanced, then stable population, and its numbers and habitat remain at the same level. However, in nature there is not a single population that remains unchanged over a more or less long period.

In many cases, there is an excess, sometimes significant, of the birth rate over the death rate; then the population grows, sometimes so quickly that an outbreak of mass reproduction may occur. As an example, this growing population can serve as the Colorado potato beetle, which is relatively short period crossed Atlantic Ocean, quickly settled in France, reached Ukraine, Belarus and occupied large territories of Russia.

However, with excessive development of the population, living conditions worsen, which is caused by its overdensification. According to food correlation rule(Winney-Edwards), during evolution, only those populations are preserved whose reproduction rate is correlated with the amount of food resources in their habitat. Deviation from this rule leads to the fact that the population is left without food and dies out or reduces the rate of reproduction, i.e. she becomes shrinking.

It must be emphasized that the population cannot decline indefinitely. When a certain population size is reached, mortality begins to fall and fertility begins to increase. At a certain point in time, the intensity of mortality and fertility levels out, the population enters a stable state, and then becomes growing.

Population homeostasis. Under natural conditions, population numbers experience constant fluctuations, their amplitude and period depend on the characteristics of the species and on environmental conditions. Thus, in many large vertebrates the number usually fluctuates several times, in insect populations - 40-50 times, and especially favorable conditions sharp outbreaks of numbers occur when it increases millions of times (locusts).

In addition to those indicated irregular fluctuations have been identified in a number of organisms periodic fluctuations in numbers with a relatively constant cycle duration, for example, associated with periodic fluctuations in solar activity.

N.V. Timofeev-Resovsky introduced the term in 1928 "population waves" to indicate fluctuations in the number of individuals in a population that arise under the influence of various factors of the biotic and abiotic environment. Being characteristic of all species, population waves (or “waves of life”) have a certain evolutionary significance, since with a sharp reduction in the size of a population, rare genotypes may appear among the surviving individuals. In the future, the restoration of the size of this population will occur at the expense of surviving individuals, which will lead to a change in gene frequencies, and hence the gene pool.

Factors that influence population size are divided into independent And dependent on its density. It has been established that the former include primarily abiotic factors. Prolonged drought harsh winter, hurricane, etc. can contribute to a sharp decline in the numbers of a variety of populations, regardless of their initial density.

To the dependent The vast majority of biotic factors (competition, predators, food supply, infections, etc.) depend on density. Here, in a number of cases, a monotonic dependence takes place: with increasing population density, the indicated factors have a stronger influence. Thus, the higher the plant population density, the more they shade each other. However, the density dependence can be more complex.

The peculiarity of density-dependent factors is that their influence usually smoothes out fluctuations in numbers, contributing to a return to the average level when population density increases. Consequently, these factors act as another mechanism for regulating numbers, which helps maintain them at a certain level.

The ability of a population to maintain a certain number of its individuals is called population homeostasis. This most important, evolutionarily acquired property is based on changes physiological characteristics, growth, behavior of each individual in response to an increase or decrease in the number of members of the population to which this individual belongs.

The population has the most important property - self-regulation. It is carried out by two mutually balancing buffer forces operating in nature: the ability to reproduce and a reaction dependent on population density, on the contrary, limiting reproduction.

Recently, it has been established that an important mechanism of population regulation that operates in an overcrowded population is stress reaction. When a population is exposed to some strong stimulus, it responds to it with a nonspecific reaction called stress. The diversity of living nature also gives rise to many forms of stress: anthropic (occurs under human influence); neuropsychic (occurs when individuals in a group are incompatible or as a result of population overdensification); thermal; noise, etc. Thus, as a result of population overdensification, significant physiological changes occur in individual individuals, leading to a sharp reduction in the birth rate and an increase in mortality. In mammals this phenomenon is called stress syndrome. When stressed, some animals become so aggressive that they almost completely stop reproducing.

Security questions for self-test

1. Define a population and name the properties of a population.

2. Why elementary particle evolution is a population?

3. Characterize the static and dynamic indicators of the state of the population.

4. What is the species' range?

5. What equation describes population dynamics?

6. Name the forms of coexistence of individuals in a population.

7. What is population homeostasis?

8. Formulate the Winney-Edwards food correlation rule.

Literature

11. Korobkin V.I., Peredelsky L.V. Ecology. - Rostov n/d: Phoenix Publishing House, 2000.

12. Nikolaikin N. I., Nikolaikina N. E., Melekhova O. P. Ecology: textbook. for universities. – M.: Bustard, 2006.

13. General ecology. In 2 parts / Ed. N. I. Nikolaikina. - M.: MSTU GA, 2000-2001.

15. Ecology / Ed. V. V. Denisova. – M.: ICC “MarT”, Rostov n/a: Publishing center “MarT”, 2006.

Topic 4. synecology

Target setting: To study the patterns of the interconnected existence of populations of living organisms, their relationships with the environment.

After studying this topic, students will be able to:

Define biocenosis, biotope, biogeocenosis;

Name the principles of the relationship between biocenosis and biotope;

Talk about trophic, topical, phoric and industrial interspecific connections, about the species, spatial and ecological structure of the biocenosis;

Determine the basis for the sustainability of biocenoses;

Knowledge of the characteristics of the sexual structure of a population makes it possible to determine the state and prospects for its existence in specific environmental conditions, to identify the optimal ratios of sexual groups for the progressive development of the population.

Basic concepts and terms: sexual structure, unisexual, bisexual populations, parthenogenesis, primary sex ratio, secondary sex ratio, sexual dimorphism, sexual selection, partner choice.

Sexual structure determines the ratio of articles of individuals included in the population and is aimed at its growth.

Same-sex populations consist of females and reproduce parthenogenetically. Parthenesis called the development of an egg without fertilization. It is characteristic of bees, aphids, many spore plants and some seed plants.

In nature, the most common bisexual populations are male and female. Such populations predominate in the animal world and are less common in plants. Dioecious dioecious plants are poplars, willows, hops, hemp, sea buckthorn and others.

Some invertebrate animals and higher plants are characterized by hermaphroditism, that is, the presence of male and female genital organs (gonads) in one individual.

In many animals, the ratio of males and females is separate, according to the laws of genetics, 1:1, i.e. the number of males and females is almost the same. The sex of the future individual is determined at the moment of fertilization as a consequence of the combination of sex chromosomes. Darwin considered such an even ratio of articles to be beneficial for the population, since it minimizes competition for a sexual partner. According to other researchers, a ratio in which females predominate is more promising for population growth, since this helps to increase the number of offspring. Thus, in most mammals, including domestic and agricultural ones, one male is capable of fertilizing several females.

Hence, in populations of individual organisms, the sex ratio is defined as the ratio of the number of males to the number of females, or as the proportion of males in the population (that is, the ratio of the number of males to total number males and females).

However, primary ratio of articles, which is determined at the moment of fertilization, is not preserved due to the higher probability of death of representatives of one or the other sex. Differences in the mortality of individuals of different sexes appear even in the embryonic period. Thus, among muskrats in many areas of their distribution, among newborns there are one and a half times more females than males. Some bats number of females in the population after hibernation often decreases to 20%.

Pheasants, ducks, great tits, and many species of rodents are characterized by higher mortality rates for males.

Thus secondary ratio sexes in a population are established not according to genetic laws, but under the influence of environmental conditions and characteristics of reproduction.

As studies have shown, the ratio of the number of males and females in a population changes over time (Fig. 5.10), which is due to the specific mortality of different age groups and the survival of offspring.

Rice. 5.10. Changes in the ratio of the number of males and females in penguins over 10 years of life.

Various factors, in particular temperature, have a significant influence on the development of sex and the formation of the sexual structure (Fig. 5.11, 5.12).

Rice. 5.11. Dependence of sex development in red ants on the temperature at which eggs are laid.

Rice. 5.12. The influence of environmental conditions on the sexual structure of the population in Daphnia.

In recent years, data have been obtained that indicate the possibility of natural regulation secondary ( in newborns) and tertiary(in individuals reproducing) the ratio of articles as a result of exposure to unfavorable living conditions. This confirms that natural populations have hidden reserves for regulating structure, the value of which could become the basis for planning measures to protect the population.

In many cases, anthropogenic pressure is directed at one of the species' species. Thus, in birds, ungulates, and cetaceans, the number of males decreases the most as a result of fishing. This significantly disrupts the sexual structure of the population.

When characterizing the sexual structure of populations, it is necessary to pay attention to sexual selection, the system of mating relations, and sexual dimorphism. They influence the development of the population and its composition, since they select stronger and more stable individuals.

An important role in sex ratio is played by sexual dimorphism, that is physiological, morphological and behavioral differences between the sexes. It plays an important role in choosing a partner. Those members of the population who find best partners for mating, resulting in better offspring.

Sexual dimorphism sometimes performs another ecological function - it reduces the competition between representatives of different articles for a food source. One of the advantages given to an individual by sexual reproduction is that he can increase (or decrease) the overall fitness of his offspring by combining his genes with other genes (of his partner) that affect survival. This feature has direct practical significance and is the basis of breeding work.