Population-species level. Population-species level of life organization

Population-species level of living systems is a collection of individuals of the same species, united by a common territory and gene pool.

View - the main structural unit in the system of living organisms. Under view is understood as a set of individuals that have a hereditary similarity of morphological, physiological and biochemical properties, freely interbreed and give fertile offspring, adapted to certain living conditions and occupying a certain area in nature. Individuals of the same species have a common origin and a single gene pool. The species is characterized by almost complete non-crossing with other species under natural conditions.

Species differ from each other in many ways - criteria, among which there are morphological, genetic, physiological, geographical and ecological.

Morphological criterion is based on the similarity of the external and internal structure of individuals of the same species.

Genetic criterion- this is a set of chromosomes characteristic of each species, their strictly defined number, size and shape; genetic criterion - the main species trait.

Physiological criterion- this is the similarity of all life processes, and above all the similarity of reproduction. Individuals of the same species are able to interbreed in natural conditions and produce viable offspring.

Geographic criterion- this is a certain area (territory, water area) occupied by a species in nature. It can be large or small, intermittent or continuous. There are species that are ubiquitous, and often - in connection with human activities (insect pests - flies, cockroaches, etc., species of weeds).

In the process of evolution, each species has developed adaptations to a specific environment. This determines the division of species into populations.

Environmental criterion- a set of environmental factors in which the species exists.

Only the combination of these criteria characterizes the belonging of individuals to one species.

The integrity of the species is due to the relationships between its individuals.

Currently, about 2 million species of organisms (approximately 1.5 million animal species and 0.5 million plant species) have been recorded. There are reasons to believe that due to the large number of unidentified lower forms of organisms, the actual number of species can be 2-3 times higher.

Each species consists of separate individuals (individuals) with their own distinctive features.

population- the form of existence of the species; a collection of individuals of the same species that exists for a long time and occupies a certain part of the range, relatively isolated from other populations of the same species. The population is the structural unit of the species and the elementary unit of the evolutionary process. Examples of populations: in humans - nationalities, races; in animals - breeds.

Population - a dynamic group of organisms, adapted to changing environmental conditions by changing the number of age groups and genetic composition.

A population as a biological unit has a certain structure and functions. It is characterized by growth, development, the ability to maintain existence in constantly changing conditions. Hereditary changes constantly occur in a population: a struggle for existence takes place in it, as well as natural selection, due to which only individuals with properties that are useful under given conditions survive and give offspring. The population has many features that characterize the group as a whole. The main characteristics of the population are density, abundance, birth rate, mortality, age composition, and the nature of distribution in the territory.

Density population is determined by the number of individuals per unit area or volume. Each species has a certain optimal population density, deviations from which in one direction or another adversely affect the rate of reproduction and life of individuals.

population population is different for different species, but it cannot be below certain limits (critical abundance). A drop in numbers below the critical level can lead to the extinction of the population. Population size can change dramatically with seasons and years.

Age composition population is of great importance for its existence and prosperity. Under favorable conditions, all age groups are present in the population and a more or less stable age composition is maintained. The age composition of the population depends on the life span of individuals, the period they reach sexual maturity, and the number of generations.

The nature of the distribution individuals of a population in space can be uniform, random and crowded.

At the level of populations, ecology deals with issues related to the number of individual species, changes and fluctuations in the number of individual populations.

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The cell is the basic unit of life.

A cell is an isolated structure, the smallest in size, which has the whole set of properties of life and which, under suitable environmental conditions, can maintain these properties in itself, and also transmit them in a number of generations.

The cell is the basis of the structure, life and development of all living forms - unicellular, multicellular and even non-cellular.

In nature, there is a significant variety of cells that differ in size, shape, and chemical characteristics. The number of main types of cellular organization is limited to two. Prokaryotic and eukaryotic types are distinguished, with the second being subdivided into a subtype characteristic of the simplest organisms, and a subtype characteristic of multicellular organisms.

Cells of the prokaryotic type are characterized by small sizes (no more than 0.5-3 microns in diameter and length), the absence of a separate nucleus. The cell lacks a developed system of membranes. The genetic apparatus is represented by the DNA of a single ring chromosome, which is devoid of the main proteins - histones.

The eukaryotic type of cellular organization is represented by two subtypes. A feature of protozoan organisms is that they correspond structurally to the level of one cell, and physiologically to a full-fledged individual. One of the features of protozoan cells is the presence in the cytoplasm of miniature formations that perform the functions of vital organs of a multicellular organism at the cellular level.

For the first time the name "cell" in the middle of the XVII century. applied by R. Hooke. Examining a thin section of cork with a microscope, Hooke saw that the cork consists of cells - cells.

Modern cellular theory includes the following provisions:

The cell is the basic unit of the structure and development of all living organisms, the smallest unit of the living;

The cells of all unicellular and multicellular organisms are similar (homologous) in their structure, chemical composition, basic manifestations of vital activity and metabolism;

Reproduction of cells occurs by their division, and each new cell is formed as a result of the division of the original (mother) cell;

In complex multicellular organisms, cells are specialized in their function and form tissues; tissues consist of organs that are closely interconnected and are subject to nervous and humoral systems of regulation.

Individuals in nature are not absolutely isolated from each other, but are united by a higher rank of biological organization. This is the population-species level. It arises where and when individuals unite in a population, and populations into species.

The basic, elementary and really existing unit of the organic world, or otherwise - the universal form of the existence of life, is view(from lat. species- look, image).

View - a historically established set of populations, individuals of which have a hereditary similarity of morphological, physiological and biochemical features, can freely interbreed and produce fertile offspring, are adapted to certain living conditions and occupy a certain area - area.

concept "view" was first introduced at the end of the 17th century. English botanist John Ray

So, for example, a bear and a wolf clearly differ from each other in appearance, while a wolf, a jackal, a hyena, a fox are outwardly more similar, since they belong to the same family - the wolf.

The features by which one species can be distinguished from another are called species criteria:

1. morphological criterion - the similarity of the external and internal structure between individuals of the same species

2. physiological criterion the similarity of all life processes in individuals of the same species, primarily the similarity of reproduction. Individuals of different species, as a rule, do not interbreed, or their offspring are sterile. For example, in many species of Drosophila fly, the sperm of a foreign species triggers an immune response, which leads to the death of spermatozoa in the female genital tract. At the same time, there are species in nature whose individuals interbreed and produce fertile offspring (some species of canaries, finches, poplars, willows).

3. Geographic criterion is based on the fact that each species occupies a certain territory or water area, called the range. It can be large or small, intermittent or continuous. However, a huge number of species have overlapping or overlapping ranges. In addition, there are species that do not have clear distribution boundaries, as well as cosmopolitan species that live on vast expanses of land on all continents or the ocean. For example, plants - shepherd's purse, medicinal dandelion, species of pondweed, duckweed, reed, synanthropic animals - bed bug, red cockroach, house fly). Therefore, the geographical criterion, like the others, is not absolute.

4. Environmental criterion is based on the fact that each species can exist only under certain conditions, performing its own functions in a certain biogeocenosis. So, for example, the caustic buttercup grows in floodplain meadows, the creeping buttercup grows along the banks of rivers and ditches, the burning buttercup grows in wetlands. There are, however, species that do not have a strict ecological confinement. These include many weeds, as well as species under human care: indoor and cultivated plants, pets.

5. Genetic (cytomorphological) criterion is based on the difference between species by karyotypes, i.e. number, shape and size of chromosomes. The vast majority of species are characterized by a strictly defined karyotype. However, this criterion is not universal. First, in many species the number of chromosomes is the same and their shape is similar. For example, some species of the legume family have 22 chromosomes (2n = 22). Secondly, within the same species, individuals with different numbers of chromosomes can occur, which is the result of genomic mutations (poly- or aneu-ploidy). For example, goat willow can have a diploid (38) or tetraploid (76) chromosome number.

6. Biochemical criterion allows you to distinguish between species according to the composition and structure of certain proteins, nucleic acids, etc. Individuals of one species have a similar DNA structure, which leads to the synthesis of identical proteins that differ from proteins of another species. At the same time, in some bacteria, fungi, and higher plants, the DNA composition turned out to be very similar. Consequently, there are twin species in terms of biochemical characteristics.

Thus, only taking into account all or most of the criteria makes it possible to distinguish individuals of one species from another.

The part of the earth's surface (or water area) within which a given species occurs is called habitat.

The size of the ranges of different species can vary greatly. In terrestrial sedentary species, the distribution of which is limited by some insurmountable barriers, the range may cover an area of ​​only a few square kilometers or even less. These include island or cave species, inhabitants of mountain valleys or upper zones of mountain ranges. For example, the viviparous golomyanka fish inhabits only Lake Baikal, the beetles of the ground beetle-bryzguny live in the Caucasus within one or two ridges. Species with a narrow distribution area are called endemic or endemic.

Other species have extensive ranges, often located on several continents. For example, on all continents there are dung beetles, peregrine falcons. Mobile marine animals have a huge range - sperm whale, gray dolphin, blue whale, killer whale. The same wide distribution is characteristic of many plants and animals that accompany humans - synanthropic species (lice, fleas, cockroaches, rats). Species whose ranges are located within all continents are called all-world, or cosmopolitans.

The main factors that influence the formation and features of the range structure are the ecological plasticity of the species, its ability to disperse, and its historical age.

A population is a structural unit of a species. Areas completely inhabited by one or another species do not exist in nature. Within the range, individuals of this species develop only habitats suitable for their life. The degree of filling of the occupied space in different species is different. But there are always “voids” and accumulations in it. In other words, the range consists of more or less numerous areas where a certain species is found.

The number of individuals in such groups can significantly increase under favorable conditions and decrease under unfavorable ones, however, they have a chance of long-term existence in the given territory. Such groupings (aggregations) of individuals of the same species, inhabiting a certain part of the range for a long time, freely interbreeding with each other and producing fertile offspring, relatively isolated from other aggregates of the same species, are called population(from lat. populus - people, population).

Each population of any species as a biological system has a certain structure. Under structure population refers to a certain quantitative ratio of individuals that differ in morphological and physiological characteristics, age, sex, the nature of distribution in space and other properties.

The main parameters of a population are, first of all, its abundance and density.

population is the total number of individuals in the population. It is not constant, as the conditions of the habitat of the population are changeable. The population size depends on the ratio of the intensity of reproduction (fertility) and mortality. In the process of reproduction, the population grows, while mortality leads to a decrease in its number. For each population there are upper and lower limits of abundance, which can be measured by studying its seasonal and interannual changes.

Density populations is the number of individuals or their biomass per unit area or volume (for example, 150 pine plants per 1 ha; 0.5 cyclops per 1 m 3 of water). Population density is also variable and depends on abundance. With an increase in numbers, the density does not increase only if it is possible to resettle the population and expand its range.

An increase in density above the optimal one adversely affects the state of the population, since in this case the food supply dries up, living space is reduced, etc.

A drop in density below the optimum leads to a weakening of the protective reactions of the population, reduces its fecundity, which can ultimately lead to the extinction of the population.

Age structure reflects the ratio of different age groups in the population, as well as the seasonal and interannual dynamics of this ratio. Three ecological ages are usually distinguished in a population: prereproductive (before reproduction), reproductive (during the breeding season), and postreproductive (after reproduction).

Any population is a continuous stream of generations due to the exchange of genes that occurs as a result of crossing individuals with each other. The traits that appeared during the independent combination of genes determine the formation of the phenotype of organisms and determine the variability in the population. In the course of natural selection, adaptive phenotypes persist, while maladaptive ones disappear. This is how it is formed genetic response the entire population, which determines the survival of a given species. Only those individuals of a population that survive and leave offspring contribute to the future of their species.

The population includes a huge number of diverse genes that form it gene pool. Each gene can exist in several forms called alleles. The number of individuals in a particular population that carry a particular allele determines the frequency of this allele.

The number of populations does not remain constant, as the conditions for their existence change. The resulting changes in population size over time are called population dynamics

Living organisms are found on Earth not in any random combinations, as independent individuals, but form regular complexes (communities). For the first time, the German biologist Karl August Möbius (1825-1908) drew attention to the possibility of distinguishing such communities. In 1877, he proposed the term biocenosis(from Greek. bios- life and koinos- general, to do something in general).

Biocenosis- it is a historically established grouping of plants, animals, fungi and microorganisms inhabiting a relatively homogeneous living space (a piece of land or a reservoir).

So, each biocenosis consists of a certain set of living organisms belonging to different species. But we know that individuals of the same species are united in natural systems, which are called populations. Therefore, a biocenosis can also be defined as a set of populations of all types of living organisms that inhabit common habitats.

The composition of the biocenosis includes a set of plants in a certain area - phytocenosis(from Greek. phyton- plant), the totality of animals living within the phytocenosis, - zoocenosis(from Greek. zoon- animal) microbiocenosis- the totality of microorganisms that inhabit the soil, and mycocenosis(from Greek. mykes- mushroom) - a collection of mushrooms. Examples of biocenoses are deciduous, spruce, pine or mixed forest, meadow, swamp, etc.

Each biocenosis develops within a homogeneous space, which is characterized by a certain combination of abiotic factors, such as the amount of incoming solar radiation, temperature, humidity, chemical and mechanical composition of the soil, its acidity, terrain, etc. Such a homogeneous space (part of the abiotic environment) occupied biocenosis is called biotope. It can be any piece of land or water, a seashore or a mountainside. A biotope is an inorganic environment, which is a necessary condition for the existence of a biocenosis. There is a close interaction between biocenosis and biotope.

The scale of biocenoses can be different - from communities of lichen pillows on tree trunks, moss tussocks in a swamp or a decaying stump to the population of entire landscapes. So, on land, one can distinguish the biocenosis of the upland (not flooded with water) meadow, the biocenosis of the white moss pine forest, the biocenosis of the feather grass steppe, the biocenosis of the wheat field, etc.

In the aquatic environment, biocenoses are usually distinguished in accordance with the ecological divisions of water bodies - the biocenosis of coastal sandy or

silty soils, biocenosis of the intertidal zone of the sea, biocenosis of large aquatic plants of the coastal zone of the lake, biocenosis of fresh water, etc. (Fig. 2.2).

A specific biocenosis includes not only organisms that constantly live in a certain territory, but also those that have a significant impact on its life, although they live in other biocenoses.

For example, many insects breed in water bodies, where they are an important food source for fish and some other animals. At a young age, they are part of the aquatic biocenosis, and in adulthood they lead a terrestrial lifestyle, i.e. act as elements of land biocenoses. Hares can eat in the meadow, and live in the forest. The same applies to many species of forest birds that seek food not only in the forest, but also in adjacent meadows or swamps.

Each biocenosis can be described based on the totality of its constituent species. The species diversity of different biocenoses is different, due to their different geographical location. It has been established that it decreases in the direction from the tropics towards high latitudes, which is explained by the deterioration of the living conditions of organisms.

If any kind of plant (or animal) quantitatively prevails in the community (has a large biomass, productivity or abundance), then this species is called dominant, or dominant.

Species are distributed in space according to their needs and habitat conditions. Such a distribution in space of the species that make up the biocenosis is called spatial structure of biocenosis. Distinguish vertical and horizontal structure of the biocenosis.

Vertical structure of biocenosis formed by its individual elements, special layers, which are called tiers. Tier- jointly growing groups of plant species, differing in height and position in the biocenosis of assimilating organs (leaves, stems, underground organs - tubers, rhizomes, bulbs, etc.). As a rule, different tiers are formed by different life forms (trees, shrubs, shrubs, herbs, mosses).

Layering is also observed in the biocenoses of the oceans and seas. Different types of plankton stay at different depths, depending on the lighting, and different types of fish, depending on where they find their food.

Living organisms are distributed unevenly in space. They usually form groupings, which is an adaptive factor in their lives. These groupings of organisms horizontal structure of biocenosis.

Individuals of different species do not exist in isolation in biocenoses; they enter into various direct and indirect relations with each other. Direct relations are divided into four types: trophic, topical, phoric, factory.

Trophic relationships arise when one species in the biocenosis feeds on another (either the dead remains of individuals of this species, or the products of their vital activity). A ladybug feeding on aphids, a cow in a meadow eating succulent grass, a wolf hunting a hare are all examples of direct trophic relationships between species.

Topical Relations characterize the change in the living conditions of one species as a result of the life of another. Spruce, shading the soil, displaces light-loving species from under its crown, crustaceans settle on the skin of whales, mosses and lichens are located on the bark of trees. All these organisms are connected to each other by topical bonds.

Foric relations- the participation of one species in the distribution of another. This role is usually played by animals that carry seeds, spores, and plant pollen. Thus, the seeds of burdock or string, which have clinging spikes, can be captured by the hair of large mammals and carried over long distances.

factory relations- a type of relationship in which individuals of one species use excretory products, dead remains, or even living individuals of another species for their structures. For example, birds build nests from dry twigs, grass, mammal hair, etc. Caddisfly larvae use pieces of bark of sand, fragments of shells, or the shells themselves with live mollusks of small species to build their houses.

Biogeocenosis- it is a set of plants, animals, fungi and microorganisms, soil and atmosphere on a homogeneous land area, which are united by the metabolism and energy into a single natural complex . An important feature of biogeocenosis is that it is associated with a certain area of ​​the earth's surface. Biogeocenosis is one of the variants of the terrestrial ecosystem.

The combination of individuals in a population, and the latter into species according to the degree of genetic and ecological unity, leads to the emergence of new properties and features in wildlife. A population is a system of individuals of the same species that occupy a certain space for a long time and reproduce themselves over a large number of generations. A species is a system of populations of individuals that have a number of common morpho-physiological features that are capable of interbreeding with the formation of fertile offspring. A population is an elementary structure at the population-species level, and an elementary phenomenon at this level is a change in the genotypic composition of a population; the elemental material at this level is mutations. Relations between individuals within a population and species play a special role. At the same time, populations act as the main evolutionary units, which are genetically open systems (individuals from different populations sometimes interbreed, thus, genetic information is exchanged). Populations and species are capable of long-term existence and independent evolutionary development. The life of an individual in this case depends on population processes. Population-species integrity is associated with the interaction of individuals within populations and is maintained by the exchange of genetic material in the process of sexual reproduction.

6. Biogeocenotic (ecosystem) level. Principles of sustainability of biogeocenosis.

Populations of different species form complex communities - biocenoses. Biocenoses - a set of plants, animals, fungi and prokaryotes that inhabit areas of land or water and are in certain relationships with each other. Together with specific areas of the earth's surface occupied by biocenoses and the adjacent atmosphere, they form an ecosystem (biogeocenosis). An ecosystem is an interdependent complex of living and non-living (inert) components interconnected by the metabolism and energy. The name "biogeocenosis" is used only in relation to natural systems. In general, the life of a biogeocenosis is mainly regulated by forces acting within the system itself, i.e. we can talk about self-regulation of biogeocenosis. Biogeocenosis is an open system that has energy "inputs" and "outputs" that connect neighboring biogeocenoses, the exchange of substances between which can be carried out both in gaseous and in liquid and solid phases, as well as in the form of living matter (for example, animal migration) . The current state of ecosystems is the result of a long evolution and adaptation of organisms to each other and to the conditions of existence. All ecosystem groups are a product of the joint historical development of species that differ and adapt to each other. The primary basis for the functioning of the ecosystem are plants and prokaryotes - autotrophs, synthesizing organic substances necessary for life from inorganic substances (water, carbon dioxide, nitrogen compounds). Autotrophs use the energy of photosynthesis (green plants) or chemosynthesis (bacteria). They are producers that create a living environment for heterotrophs that consume ready-made organic substances and are incapable of synthesizing them from inorganic ones. Heterotrophs are animals and fungi. These consumers, in turn, are divided into consumers - (herbivorous animals and predators) and decomposers (fungi, microorganisms that decompose organic matter.) Populations of different species in ecosystems affect each other according to the principle of direct and feedback. In ecosystems, food (trophic) chains are distinguished - through them, the transformation of matter and energy occurs. During the transition of energy from one link to another, up to 80-90% of it is lost in the form of heat, so the chains usually include no more than 4-5 links, and the production of each subsequent link is less than the previous one. The totality of all organisms united by a single type of nutrition form a trophic level. In the ecosystem, the pyramid rule is implemented: the production of each subsequent trophic level is approximately 10 times less than the previous one. The composition of the food of each species may include other different species, and each species can serve as food for other different species, i.e. Food chains intertwine to form food webs. The ecosystem implements the principles of stability and balance:

sustainability principle: the more trophic levels in an ecosystem and the more diverse they are, the more stable the ecosystem;

balance principle: there is a balance between species in an ecosystem, and a deviation from it in one direction or another can lead to disaster.

Human economic activity has led to dramatic changes in all components of biocenoses. Natural biocenoses are being replaced by artificial ones - agrobiocenoses, urban biocenoses. Agrobiocenosis (and urban biocenosis) is a secondary biogeocenosis that can exist only with constant renewal by man.

The previously considered biological phenomena and mechanisms related to the molecular genetic, cellular and ontogenetic levels of life organization were spatially limited to a single organism (multicellular or unicellular, prokaryotic or eukaryotic), and temporally - to its ontogeny, or life cycle. The population-species level of organization belongs to the category of superorganisms.

Life is represented by separate species, which are collections of organisms that have properties heredity and variation.

These properties become the basis of the evolutionary process. The mechanisms that determine this result are selective survival and selective reproduction of individuals belonging to the same species. Under natural conditions, reproduction occurs especially intensively in populations that are the minimum self-reproducing groups of individuals within a species.

Each "of the once existing or living species is the result of a certain cycle of evolutionary transformations at the population-species level, originally enshrined in its gene pool. The latter has two important features. Firstly, it contains biological information about how a given species can survive and reproduce under certain environmental conditions, and secondly, it has the ability to partially change the content of biological information contained in it. The latter is the basis of the evolutionary and ecological plasticity of the species, i.e. the ability to adapt to existence in other conditions that change in historical time or from territory to territory. The population structure of a species, which leads to the disintegration of the gene pool of the species into gene pools of populations, contributes to the manifestation in the historical fate of the species, depending on the circumstances, of both noted qualities of the gene pool - conservatism and plasticity.

Thus, the general biological significance of the population-species level consists in the implementation of the elementary mechanisms of the evolutionary process that determine speciation.

The significance of what is happening at the population-species level for public health is determined by the presence of hereditary diseases, diseases with an obvious hereditary predisposition, as well as pronounced features of the gene pools of different human populations. The processes taking place at this level, combined with the ecological features of various territories, form the basis of a promising area of ​​modern medicine - the epidemiology of non-communicable diseases.

CHAPTER 10

BIOLOGICAL VIEW.

POPULATION STRUCTURE OF THE SPECIES

THE CONCEPT OF THE VIEW

view called a set of individuals similar in basic morphological and functional characteristics, karyotype, behavioral reactions, having a common origin, inhabiting a certain territory (range), under natural conditions interbreeding exclusively with each other and at the same time producing fertile offspring.

The species affiliation of an individual is determined by its compliance with the listed criteria: morphological, physiological-biochemical, cytogenetic, ethological, ecological, etc. The most important features of a species are its genetic(reproductive)insulation, consisting in the non-crossing of individuals of a given species with representatives of other species, as well as genetic stability in natural conditions, leading to an independent evolutionary destiny.

Since the time of K. Linnaeus, the species has been the main unit of taxonomy. The special position of the species among other systematic units (taxa) is due to the fact that this is the group in which individual individuals exist really. As part of a species in natural conditions, an individual is born, reaches puberty and performs its main biological function: participating in reproduction, it ensures the continuation of the genus. In contrast to species, taxa of supraspecific rank, such as genus, order, family, class, phylum, are not the arena of the real life of organisms. Their selection in the natural system of the organic world reflects the results of the previous stages of the historical development of living nature. The distribution of organisms by supraspecific taxa indicates the degree of their phylogenetic relationship.

The most important factor in the association of organisms into species is sexual process. Representatives of the same species, interbreeding with each other, exchange hereditary material. This leads to recombination in each generation of genes (alleles) that make up the genotypes of individual individuals. As a result, leveling differences between organisms within a species and long-term preservation of the main morphological, physiological and other features that distinguish one species from another. Thanks to the sexual process, there is also a combination of genes (alleles) distributed over the genotypes of different individuals, into common gene pool(allele pool) 1 species. This gene pool contains the entire amount of hereditary information that a species has at a certain stage of its existence.

The species definition given above cannot be applied to asexually reproducing agamous (certain microorganisms, blue-green algae), self-fertilizing and strictly parthenogenetic organisms. Groupings of such organisms, equivalent to a species, are distinguished by the similarity of phenotypes, the common area, and the proximity of genotypes by origin. The practical use of the concept of "species" even in organisms with sexual reproduction is often difficult. This is due dynamism of the species manifested in intraspecific variability, "blurring" of the boundaries of the range, the formation and disintegration of intraspecific groups of various sizes and compositions (populations, races, subspecies). The dynamism of species is a consequence of the action of elementary evolutionary factors (see Chapter 11).

POPULATION CONCEPT

Under natural conditions, organisms of the same species are distributed unevenly. There is an alternation of areas of increased and reduced concentration of individuals (Fig. 10.1). As a result, the species breaks up into groups or populations corresponding to areas of denser population. The "radii of individual activity" of individual individuals are limited. So, a grape snail is able to overcome a distance of several tens of meters, a muskrat - several hundred meters, an arctic fox - several hundred kilometers. Due to this, reproduction (reproductive areas) is mainly confined to areas with a high density of organisms.

Rice. 10.1. Uneven distribution of individuals over the range of the species.

BUT- tape; B- spotted; AT- island types

The probability of random crossings (panmixia), which determine effective recombination of genes from generation to generation, is higher within the "clumps" than in the zones between them and for the species as a whole. Thus, in the reproductive process, the gene pool of a species is represented by the gene pools of populations.

population called the minimum self-reproducing group of individuals of the same species inhabiting a certain territory (range) for a sufficiently long time (for many generations). The population actually experiences a relatively high level of panmixia and is to some extent separated from other populations by some form of isolation1.

The simplest form of existence of a species in nature is a population. In this article, we will figure out what this concept includes, find out what is the role of the population in the evolutionary process.

Population structure

In biology, a population is the integrity of all existing individuals of the same species living in the same territory and having a common gene pool with the ability to interbreed freely. One type of living organisms can include several ecosystems at once, which are most often isolated from each other.

In the case of placing individuals of the same species taken from different ecosystems under the same conditions, one can observe the preservation of their differences. However, to obtain fertile offspring, such crossing gives the best results.

Rice. 1. Examples of populations.

Populations provide the process of microevolution and are divided into:

• sexual;
• age;
• ecological;
• genetic;
• spatial structure.

Rice. 2. Structure of populations.

Sex structure

It implies the percentage of individuals of different sexes. It is determined by the difference in chromosome sets. However, it often happens that some females give birth only to females or only males. In this case, the sex ratio deviates from 1:1.

The reason for this can be not only genetic disorders, but also environmental conditions.

Age structure of the population

Includes the ratio of individuals of different ages, which represent offspring of the same or different generations. A generation may include representatives of one or more offspring. Age affects the intensity of the reproduction process, the speed of generation change, and the mortality rate.

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genetic structure

It is determined by the diversity and variability of genotypes. The property of ecosystems is the presence of a certain level of diversity of traits that depend on ecology and genetic predisposition. In other words, one genotype is capable of producing many variations in phenotypes. Diversity depends on the number of individuals and the ecological situation. Changing the frequency of genes can lead to the extinction of the species.

Spatial structure

It is determined by the density of placement and distribution of ecosystem members in a certain area. All individuals have both individual and group space. In this way, flocks, colonies, herds are formed. Depending on the method of placement in the group, a random, uniform and crowded distribution is distinguished.

Each individual plays a role in the group, thus forming a social hierarchy.
She may be:

• linear (subordination by ranks, when the next one dominates the previous one);
• parallel (males and females have separate leaders).

Such a system of relationships allows you to coordinate behavior that will be beneficial to all members of the group.

Environmental component

The ecological unit is the species. This structure implies the distribution of members into groups depending on the interaction with the surrounding factors of nature.

The ecological niche includes food, breeding and hiding places, and other environmental factors that are necessary for the existence of the species. When characterizing an ecological niche, two indicators are used: the width and the degree of overlap with other niches.

Population dynamics

The dynamics and growth of the number of ecosystems depends on external and internal factors, such as the availability of food, enemies, and climate.

The founder of population genetics is S.S. Chetverikov, who called the growth in numbers “waves of life”.

It is possible to accurately determine the average number of individuals under the condition of artificial complete isolation of the group. In nature, this is possible when studying island ecosystems. The number can be determined by the ratio of births and deaths.

The “waves of life” sometimes help push rare genotypes forward, testing them by natural selection. So, for example, after a cold winter, stronger, cold-resistant organisms remain alive.

Rice. 3. An example of population dynamics.

Meaning

With the help of the functioning of populations, the conditions necessary to sustain life on our planet are created. By their vital activity, living organisms affect the environment of the area. It is on ecosystems that the circulation of substances in nature depends, certain conditions are created, and there is an interchange between animate and inanimate nature. The joint work of populations determines the characteristics of biotic conglomerations and ecological conditions.3.9. Total ratings received: 114.