The geographical criterion of the species considers. Lesson View

View- a set of individuals with a hereditary similarity of morphological, physiological and biological features, freely interbreeding and producing offspring, to certain living conditions and occupying a certain area in nature.

Species are stable genetic systems, as in nature they are separated from each other by a number of barriers.

A species is one of the main forms of organization of living things. However, it is sometimes difficult to determine whether these individuals belong to the same species or not. Therefore, in order to resolve the issue of belonging of individuals to this species A number of criteria are used:

Morphological criterion- the main criterion based on external differences between animal or plant species. This criterion serves to distinguish organisms that are clearly distinguished by external or internal morphological characters. But it should be noted that very often there are very subtle differences between species, which can be revealed only with a long study of these organisms.

Geographic criterion- based on the fact that each species lives within a certain space (). The area is the geographical boundaries of the distribution of the species, the size, shape and location of which is different from the areas of other species. However, this criterion is also not universal enough for three reasons. Firstly, the ranges of many species coincide geographically, and secondly, there are cosmopolitan species for which the range is almost the entire planet (killer whale). Thirdly, in some rapidly spreading species (house sparrow, house fly, etc.), the range changes its boundaries so quickly that it cannot be determined.

Environmental criterion- assumes that each species is characterized by a certain type of food, habitat, timing, i.e. occupies a certain niche.
Ethological criterion - lies in the fact that the behavior of animals of some species differs from the behavior of others.

Genetic criterion- contains the main property of the species - its isolation from others. Animals and plants of different species almost never interbreed. Of course, a species cannot be completely isolated from the flow of genes from closely related species, but at the same time it maintains a constant genetic composition over a long time. The clearest boundaries between species are precisely from a genetic point of view.

Physiological and biochemical criterion- this criterion cannot serve as a reliable way to distinguish between species, since the main biochemical processes proceed in similar groups of organisms in the same way. And within each species there are a large number of adaptations to specific living conditions by changing the course of physiological and biochemical processes.
According to one of the criteria, it is impossible to accurately distinguish species from each other. It is possible to determine whether an individual belongs to a particular species only on the basis of a combination of all or most of the criteria. Individuals occupying a certain territory and freely interbreeding with each other are called a population.

population- a set of individuals of the same species occupying a certain territory and exchanging genetic material. The totality of the genes of all individuals in a population is called the gene pool of the population. In each generation, individual individuals contribute more or less to the total gene pool, depending on their adaptive value. The heterogeneity of the organisms included in the population creates the conditions for the action, therefore, the population is considered the smallest evolutionary unit, from which the transformation of the species begins -. The population, therefore, is a supra-organismal formula for the organization of life. The population is not a completely isolated group. Sometimes interbreeding occurs between individuals of different populations. If a population turns out to be completely geographically or ecologically isolated from others, then it can give rise to a new subspecies, and subsequently a species.

Each population of animals or plants consists of individuals of different sexes and different ages. The ratio of the number of these individuals may be different depending on the time of year, natural conditions. The size of a population is determined by the ratio of births and deaths of its constituent organisms. If for a sufficiently long time these indicators are equal, then the population size does not change. Environmental factors, interaction with other populations can change the size of the population.

View (lat. species) - taxonomic, systematic unit, a group of individuals with common morphophysiological, biochemical and behavioral characteristics, capable of interbreeding, giving fertile offspring in a number of generations, regularly distributed within a certain range and similarly changing under the influence of factors external environment. A species is a really existing genetically indivisible unit of the living world, the main structural unit in the system of organisms, a qualitative stage in the evolution of life.

For a long time it was believed that any species is a closed genetic system, that is, there is no exchange of genes between the gene pools of two species. This statement is true for most species, but there are exceptions to it. So, for example, lions and tigers can have common offspring (ligers and tigers), the females of which are fertile - they can give birth both from tigers and lions. Many other species are also interbred in captivity, which do not naturally interbreed due to geographic or reproductive isolation. Crossing (hybridization) between different species can also occur in natural conditions, especially in the case of anthropogenic disturbances of the habitat that violate the ecological mechanisms of isolation. Especially often plants hybridize in nature. A noticeable percentage of species of higher plants is of hybrid origin - they were formed during hybridization as a result of partial or complete merging of parental species.

Basic view criteria

1. Morphological criterion of the species. It is based on the existence of morphological features characteristic of one species, but absent in other species.

For example: in an ordinary viper, the nostril is located in the center of the nasal shield, and in all other vipers (nosed, Asia Minor, steppe, Caucasian, viper) the nostril is shifted to the edge of the nasal shield.
At the same time, there are significant individual morphological differences within species. For example, the common viper is represented by a variety of color forms (black, gray, bluish, greenish, reddish and other shades). These features cannot be used to distinguish species.

2. geographical criterion. It is based on the fact that each species occupies a certain territory (or water area) - a geographical area. For example, in Europe, some species of the malarial mosquito (genus Anopheles) inhabit the Mediterranean, others - the mountains of Europe, Northern Europe, Southern Europe.

However, the geographical criterion is not always applicable. The ranges of different species may overlap, and then one species smoothly passes into another. In this case, a chain of vicarious species (superspecies, or series) is formed, the boundaries between which can often be established only through special studies (for example, the herring gull, the black-backed gull, the western gull, the California gull).

3. ecological criterion. Based on the fact that two species cannot occupy the same ecological niche. Therefore, each species is characterized by its own relationship with the environment.

However, within the same species, different individuals can occupy different ecological niches. Groups of such individuals are called ecotypes. For example, one ecotype of Scotch pine inhabits swamps (marsh pine), another - sand dunes, the third - leveled areas of forest terraces.

A set of ecotypes that form a single genetic system (for example, capable of interbreeding with each other to form full-fledged offspring) is often called an ecospecies.

4. Molecular genetic criterion. Based on the degree of similarity and difference in nucleotide sequences in nucleic acids Oh. As a rule, "non-coding" DNA sequences (molecular genetic markers) are used to assess the degree of similarity or difference. However, DNA polymorphism exists within the same species, and different species can be characterized by similar sequences.

5. Physiological and biochemical criterion. It is based on the fact that different species can differ in the amino acid composition of proteins. At the same time, protein polymorphism exists within a species (for example, intraspecific variability of many enzymes), and different species can have similar proteins.

6. Cytogenetic (karyotypic) criterion. It is based on the fact that each species is characterized by a certain karyotype - the number and shape of metaphase chromosomes. For example, all hard wheats have 28 chromosomes in the diploid set, and all soft wheats have 42 chromosomes. However, different species can have very similar karyotypes: for example, most species of the cat family have 2n=38. At the same time, chromosomal polymorphism can be observed within the same species. For example, in elks of Eurasian subspecies 2n=68, and in elks of North American species 2n=70 (in the karyotype of North American elks there are 2 less metacentrics and 4 more acrocentrics). Some species have chromosome races, for example, in a black rat - 42 chromosome (Asia, Mauritius), 40 chromosome (Ceylon) and 38 chromosome (Oceania).

7. reproductive criterion. It is based on the fact that individuals of the same species can interbreed with each other with the formation of fertile offspring similar to their parents, and individuals of different species living together do not interbreed with each other, or their offspring are sterile.

However, it is known that interspecific hybridization is often common in nature: in many plants (for example, willows), a number of fish species, amphibians, birds and mammals (for example, a wolf and a dog). At the same time, within the same species, there may be groupings that are reproductively isolated from each other.

8. ethological criterion. Associated with interspecies differences in behavior in animals. In birds, song analysis is widely used for species recognition. By the nature of the sounds produced, different types of insects differ. Different types of North American fireflies differ in the frequency and color of light flashes.

9. Historical (evolutionary) criterion. Based on the study of the history of a group of closely related species. This criterion is complex in nature, since it includes a comparative analysis of modern species ranges (geographical criterion), a comparative analysis of genomes (molecular genetic criterion), a comparative analysis of cytogenomes (cytogenetic criterion), and others.

None of the considered species criteria is the main or the most important one. For a clear separation of species, they must be carefully studied according to all criteria.

Due to unequal environmental conditions, individuals of the same species within the range break up into smaller units - populations. In reality, a species exists precisely in the form of populations.

Species are monotypic - with a weakly differentiated internal structure, they are characteristic of endemics. Polytypic species are characterized by a complex intraspecific structure.

Within species, subspecies can be distinguished - geographically or ecologically isolated parts of a species, individuals of which, under the influence of environmental factors, in the process of evolution have acquired stable morphophysiological features that distinguish them from other parts of this species. In nature, individuals of different subspecies of the same species can freely interbreed and produce fertile offspring.

species name

The scientific name of a species is binomial, that is, it consists of two words: the name of the genus to which the given species belongs, and the second word, called the species epithet in botany, and the species name in zoology. The first word is a noun singular; second - either adjective in nominative case, agreed in gender (masculine, feminine or neuter) with a generic name, or a noun in genitive case. The first word is capitalized, the second is lowercase.

• Petasites fragrans- the scientific name of a species of flowering plants from the genus Butterbur ( Petasites) (Russian name species - fragrant Butterbur). The adjective is used as a specific epithet Fragrans("fragrant").
• Petasites fominii- the scientific name of another species from the same genus (Russian name - Fomin Butterbur). The Latinized surname (in the genitive case) of the botanist Alexander Vasilyevich Fomin (1869-1935), a researcher of the flora of the Caucasus, was used as a specific epithet.

Sometimes entries are also used to designate indeterminate taxa at species rank:

• Petasites sp.- the entry indicates that the taxon at the rank of species, belonging to the genus, is meant Petasites.
• Petasites spp.- entry means that all taxa in the rank of species included in the genus are meant Petasites(or all other taxa in the rank of species included in the genus Petasites, but not included in any given list of such taxa).

Species (lat. species) - a taxonomic, systematic unit, a group of individuals with common morphophysiological, biochemical and behavioral characteristics, capable of interbreeding, producing fertile offspring in a number of generations, regularly distributed within a certain range and similarly changing under the influence of environmental factors. A species is a really existing genetically indivisible unit of the living world, the main structural unit in the system of organisms, a qualitative stage in the evolution of life.

For a long time it was believed that any species is a closed genetic system, that is, there is no exchange of genes between the gene pools of two species. This statement is true for most species, but there are exceptions to it. So, for example, lions and tigers can have common offspring (ligers and tigers), the females of which are fertile - they can give birth both from tigers and lions. Many other species are also interbred in captivity, which do not naturally interbreed due to geographic or reproductive isolation. Crossing (hybridization) between different species can also occur in natural conditions, especially in the case of anthropogenic disturbances of the habitat that violate the ecological mechanisms of isolation. Especially often plants hybridize in nature. A noticeable percentage of species of higher plants is of hybrid origin - they were formed during hybridization as a result of partial or complete merging of parental species.

Basic view criteria

1. Morphological criterion of the species. It is based on the existence of morphological features characteristic of one species, but absent in other species.

For example: in an ordinary viper, the nostril is located in the center of the nasal shield, and in all other vipers (nosed, Asia Minor, steppe, Caucasian, viper) the nostril is shifted to the edge of the nasal shield.
At the same time, there are significant individual morphological differences within species. For example, the common viper is represented by a variety of color forms (black, gray, bluish, greenish, reddish and other shades). These features cannot be used to distinguish species.

2. geographical criterion. It is based on the fact that each species occupies a certain territory (or water area) - a geographical range. For example, in Europe, some species of the malarial mosquito (genus Anopheles) inhabit the Mediterranean, others - the mountains of Europe, Northern Europe, Southern Europe.

However, the geographical criterion is not always applicable. The ranges of different species may overlap, and then one species smoothly passes into another. In this case, a chain of vicarious species (superspecies, or series) is formed, the boundaries between which can often be established only through special studies (for example, the herring gull, the black-backed gull, the western gull, the California gull).

3. ecological criterion. Based on the fact that two species cannot occupy the same ecological niche. Therefore, each species is characterized by its own relationship with the environment.

However, within the same species, different individuals can occupy different ecological niches. Groups of such individuals are called ecotypes. For example, one ecotype of Scotch pine inhabits swamps (marsh pine), another - sand dunes, the third - leveled areas of forest terraces.

A set of ecotypes that form a single genetic system (for example, capable of interbreeding with each other to form full-fledged offspring) is often called an ecospecies.

4. Molecular genetic criterion. Based on the degree of similarity and difference in nucleotide sequences in nucleic acids. As a rule, "non-coding" DNA sequences (molecular genetic markers) are used to assess the degree of similarity or difference. However, DNA polymorphism exists within the same species, and different species can be characterized by similar sequences.

5. Physiological and biochemical criterion. It is based on the fact that different species can differ in the amino acid composition of proteins. At the same time, protein polymorphism exists within a species (for example, intraspecific variability of many enzymes), and different species can have similar proteins.

6. Cytogenetic (karyotypic) criterion. It is based on the fact that each species is characterized by a certain karyotype - the number and shape of metaphase chromosomes. For example, all hard wheats have 28 chromosomes in the diploid set, and all soft wheats have 42 chromosomes. However, different species can have very similar karyotypes: for example, most species of the cat family have 2n=38. At the same time, chromosomal polymorphism can be observed within the same species. For example, in elks of Eurasian subspecies 2n=68, and in elks of North American species 2n=70 (in the karyotype of North American elks there are 2 less metacentrics and 4 more acrocentrics). Some species have chromosome races, for example, in a black rat - 42 chromosome (Asia, Mauritius), 40 chromosome (Ceylon) and 38 chromosome (Oceania).

7. reproductive criterion. It is based on the fact that individuals of the same species can interbreed with each other with the formation of fertile offspring similar to their parents, and individuals of different species living together do not interbreed with each other, or their offspring are sterile.

However, it is known that interspecific hybridization is often common in nature: in many plants (for example, willows), a number of fish species, amphibians, birds and mammals (for example, a wolf and a dog). At the same time, within the same species, there may be groupings that are reproductively isolated from each other.

8. ethological criterion. Associated with interspecies differences in behavior in animals. In birds, song analysis is widely used for species recognition. By the nature of the sounds produced, different types of insects differ. Different types of North American fireflies differ in the frequency and color of light flashes.

9. Historical (evolutionary) criterion. Based on the study of the history of a group of closely related species.

THE GEOGRAPHICAL CRITERIA OF THE SPECIES IS THAT

This criterion is complex in nature, since it includes a comparative analysis of modern species ranges (geographical criterion), a comparative analysis of genomes (molecular genetic criterion), a comparative analysis of cytogenomes (cytogenetic criterion), and others.

None of the considered species criteria is the main or the most important one. For a clear separation of species, they must be carefully studied according to all criteria.

Due to unequal environmental conditions, individuals of the same species within the range break up into smaller units - populations. In reality, a species exists precisely in the form of populations.

Species are monotypic - with a weakly differentiated internal structure, they are characteristic of endemics. Polytypic species are characterized by a complex intraspecific structure.

Within species, subspecies can be distinguished - geographically or ecologically isolated parts of a species, individuals of which, under the influence of environmental factors, in the process of evolution have acquired stable morphophysiological features that distinguish them from other parts of this species. In nature, individuals of different subspecies of the same species can freely interbreed and produce fertile offspring.

species name

The scientific name of a species is binomial, that is, it consists of two words: the name of the genus to which the given species belongs, and the second word, called the species epithet in botany, and the species name in zoology.

The first word is a singular noun; the second is either an adjective in the nominative case, agreed in gender (masculine, feminine or neuter) with a generic name, or a noun in the genitive case. The first word is capitalized, the second is lowercase.

• Petasites fragrans is the scientific name of a species of flowering plants from the genus Butterbur (Petasites) (the Russian name for the species is Fragrant Butterbur). The adjective fragrans ("fragrant") is used as a specific epithet.
• Petasites fominii is the scientific name of another species from the same genus (Russian name is Fomin Butterbur). The Latinized surname (in the genitive case) of the botanist Alexander Vasilyevich Fomin (1869-1935), a researcher of the flora of the Caucasus, was used as a specific epithet.

Sometimes entries are also used to designate indeterminate taxa at species rank:

• Petasites sp. - the entry indicates that it means a taxon at the rank of species belonging to the genus Petasites.
• Petasites spp. - entry means that all taxa at the species rank included in the genus Petasites are meant (or all other taxa at the species rank included in the genus Petasites, but not included in a given list of such taxa).

The concept of a species. Species as a taxonomic category

In order to study the diversity of life, man needed to develop a classification system for organisms to divide them into groups. As you already know, the smallest structural unit in the taxonomy of living organisms is the species.

A species is a historically established set of individuals that are similar in morphological, physiological and biochemical characteristics, freely interbreed and produce fertile offspring, are adapted to certain environmental conditions and occupy a common territory in nature - an area.

In order to attribute individuals to the same or to different species, they are compared with each other according to a number of specific characteristic features - criteria.

View criteria

The set of characteristic features of the same type, in which individuals of the same species are similar, and individuals of different species differ from each other, is called the species criterion. AT modern biology distinguish the following main criteria of the species: morphological, physiological, biochemical, genetic, ecological, geographical.

Morphological criterion reflects a set of characteristic features external structure. For example, clover species differ in the color of the inflorescences, the shape and color of the leaves. This criterion is relative. Within a species, individuals can differ markedly in structure. These differences depend on sex (sexual dimorphism), stage of development, stage in the breeding cycle, environmental conditions, belonging to varieties or breeds.

For example, in the mallard, the male is brightly colored, and the female is dark brown; in the red deer, the males have antlers, while the females do not. In the cabbage white butterfly, the caterpillar differs from the adult in external signs. In the male thyroid fern, the sporophyte has leaves and roots, and the gametophyte is represented by a green plate with rhizoids. At the same time, some species are so similar in morphological features that they are called twin species. For example, some species of malarial mosquitoes, fruit flies, North American crickets do not differ in appearance, but do not interbreed.

Thus, based on one morphological criterion it is impossible to judge the belonging of an individual to one species or another.

Physiological criterion- aggregate characteristic features life processes (reproduction, digestion, excretion, etc.). One of the important features is the ability of individuals to interbreed. Individuals of different species cannot interbreed due to the incompatibility of germ cells, the mismatch of the genital organs. This criterion is relative, since individuals of the same species sometimes cannot interbreed. In Drosophila flies, the impossibility of mating may be due to differences in the structure of the reproductive apparatus. This leads to disruption of the reproduction processes. Conversely, there are known species whose representatives can interbreed with each other. For example, a horse and a donkey, representatives of some species of willows, poplars, hares, canaries. From this it follows that in order to determine the species affiliation of individuals, it is not enough to compare them only according to a physiological criterion.

Biochemical criterion reflects the characteristic chemical composition body and metabolism. This is the most unreliable criterion. There are no substances or biochemical reactions that are specific to a particular species. Individuals of the same species can vary significantly in these indicators. Whereas in individuals of different species, the synthesis of proteins and nucleic acids occurs in the same way. A number of biologically active substances play a similar role in the metabolism of different species. For example, chlorophyll in all green plants is involved in photosynthesis. This means that the determination of the species affiliation of individuals on the basis of one biochemical criterion is also impossible.

Genetic criterion characterized by a certain set of chromosomes, similar in size, shape and composition. This is the most reliable criterion, as it is the reproductive isolation factor that maintains the genetic integrity of the species. However, this criterion is not absolute. In individuals of the same species, the number, size, shape, and composition of chromosomes may differ as a result of genomic, chromosomal, and gene mutations. At the same time, when crossing some species, viable fertile interspecific hybrids sometimes appear. For example, a dog and a wolf, a poplar and a willow, a canary and a finch, when crossed, produce fertile offspring. Thus, the similarity according to this criterion is also not enough to classify individuals as one species.

Environmental criterion is a set of characteristic environmental factors necessary for the existence of a species. Each species can live in an environment where climatic conditions, soil features, topography and food sources correspond to its tolerance limits. But under the same environmental conditions, organisms of other species can also live. Human breeding of new breeds of animals and plant varieties has shown that individuals of the same species (wild and cultivated) can live in very different environmental conditions.

THE GEOGRAPHICAL CRITERION OF THE SPECIES IS…

It proves relative nature ecological criterion. Therefore, there is a need to use other criteria when determining whether individuals belong to a particular species.

Geographic criterion characterizes the ability of individuals of one species to inhabit in nature a certain part of the earth's surface (range).

For example, Siberian larch is common in Siberia (Trans-Urals), and Dahurian larch - in Primorsky Krai (Far East), cloudberries - in the tundra, and blueberries - in the temperate zone.

This criterion indicates the confinement of the species to a particular habitat. But there are species that do not have clear boundaries of settlement, but live almost everywhere (lichens, bacteria). In some species, the range coincides with the range of humans. Such species are called synanthropic (housefly, bed bug, house mouse, gray rat). Different species may have overlapping habitats. Hence, this criterion is also relative. It cannot be used as the only one for determining the species of individuals.

Thus, none of the described criteria is absolute and universal. Therefore, when determining whether an individual belongs to a particular species, all its criteria should be taken into account.

The area of ​​the species. The concept of endemics and cosmopolitans

According to the geographical criterion, each species in nature occupies a certain territory - an area.

area(from lat. area - area, space) - part of the earth's surface, within which individuals of this species are distributed and go through a full cycle of their development.

The range can be continuous or discontinuous, extensive or limited. Species that have a vast range within different continents are called cosmopolitan species(some types of protists, bacteria, fungi, lichens). When the distribution area is very narrow and is located within a small region, then the species inhabiting it is called endemic(from Greek endemos - local).

For example, kangaroo, echidna and platypus live only in Australia. Ginkgo's vivo grows only in China, spiky rhododendron and Daurian lily - only in the Far East.

A species is a collection of individuals that are similar in morphological, physiological and biochemical characteristics, freely interbreed and produce fertile offspring, are adapted to certain environmental conditions and occupy a common territory in nature - an area. Each species is characterized by the following criteria: morphological, physiological, biochemical, genetic, ecological, geographical. All of them are relative in nature, therefore, when determining the species affiliation of individuals, all possible criteria are used.

According to the simplified morphological concept of species, natural populations that are morphologically distinct from each other are recognized types.

It is more accurate and more correct to define species as natural populations within which the variability of morphological (usually quantitative) characters is continuous, separated from other populations by a gap. If the differences are small, but the continuity of distribution is broken, then such forms should be taken for different species. In aphoristic form, this is expressed as follows: the criterion of the species is the discreteness of the boundaries of the distribution of features.

When determining species, difficulties often arise due to two circumstances. Firstly, the cause of difficulties may be a strong intraspecific variability, and secondly, the presence of so-called twin species. Let's consider these cases.

Intraspecific variability can reach a large scale. First of all, these are differences between males and females of the same species. Such differences are clearly manifested in many birds, diurnal butterflies, German wasps, some fish and other organisms. Similar facts were used by Darwin in his work on sexual selection. In a number of animals, sharp differences are observed between adults and immature individuals. Similar facts are widely known to zoologists. Therefore, samples from populations of species at different stages of their development are very useful. life cycle. Theoretical basis intraspecific variability (individual or group) is outlined in a number of guidelines. Here we will consider only the characters that are most often used in establishing the species status of individuals from the sample.

Morphological features is the general external morphology and, if necessary, the structure of the genital apparatus. The most important morphological features are found in animals with an external skeleton, such as arthropods or mollusks, but they can be found in many other animals without shells or shells. These are all kinds of differences in the coat of animals, the plumage of birds, the pattern of butterfly wings, etc.

In many cases, the criterion for distinguishing closely related species is the structure of the genitalia. This is especially emphasized by proponents of the biological concept of the species, since differences in the shape of the chitinized or sclerotized parts of the genital apparatus prevent interbreeding between males of one species and females of another. In entomology, Dufour's rule is known, according to which, in species with chitinized parts of the male genitalia and the copulatory organs of females, such a ratio is observed as that of a key and a lock. Sometimes it is called that - the "key and lock" rule. However, it should be remembered that the genitalia characters, like other morphological characters, also vary in some species (for example, in leaf beetles of the genus Altica), which has been repeatedly shown. Nevertheless, in those groups where the systematic significance of the structure of the genitalia has been proven, it is a very valuable feature, since with the divergence of species, their structure should be one of the first to change.

Anatomical features, such as details of the skull structure or the shape of teeth, are commonly used in supraspecific taxonomy of vertebrates.

environmental signs. It is known that each animal species is characterized by certain ecological preferences, knowing which, it is often possible, if not quite accurately, to decide which species we are dealing with, then at least greatly facilitate identification. According to competitive exclusion rule(Gause's rule), two species cannot exist in the same place if their ecological requirements are the same.

In the study of gall-forming or mining phytophagous insects (midge flies, gall wasps, mining larvae of butterflies, beetles and other insects), the main features often turn out to be forms of mines, for which a classification has even been developed, or galls. So, on rosehips or on oaks, several types of nutcrackers develop, causing education galls on leaves or shoots of plants. And in all cases, the galls of each species have their own characteristic shape.

The food preferences of animals have reached a large scale - from strict monophagy through oligophagy to polyphagy. It is known that silkworm caterpillars feed exclusively on mulberry leaves, or mulberry. Caterpillars of white butterflies (cabbages, turnips, etc.) gnaw the leaves of cruciferous plants without moving to plants of other families. And a bear or a wild boar, being polyphages, feed on both animal and plant foods.

In groups of animals where a strict choice of food is established, it is possible to establish their species affiliation by the nature of the gnawing of a certain plant species. This is what entomologists do in the field. It is better, of course, to collect for further study the herbivorous insects themselves. An experienced naturalist, who knows the natural conditions of a particular area well, can predict in advance what set of animal species can be encountered when visiting certain biotopes - a forest, a meadow, sand dunes, or a river bank. Therefore, on the labels accompanying collection fees, it is imperative to indicate the conditions under which certain species were collected. This greatly facilitates further processing of the collection and identification of species.

Ethological signs. A number of authors point to the taxonomic value of ethological features. The well-known ethologist Hynd considers behavior to be a taxonomic feature that can be used to clarify the systematic position of species. To this it should be added that the most useful are stereotyped actions. They are as characteristic of each species as any morphological features. This should be kept in mind when studying closely related or twin species. Even if the elements of behavior may be similar, the expression of these elements is specific to each species.

Question: THE GEOGRAPHICAL CRITERION OF THE SPECIES IS THAT

The fact is that behavioral features in animals are important isolating mechanisms that prevent interbreeding between different species. Examples of ethological isolation are cases where potential marriage partners meet but do not mate.

As shown by numerous observations in nature and experiments in the laboratory, the otological features of the species are primarily manifested in the characteristics of mating behavior. These include the characteristic postures of males in the presence of a female, as well as vocal signals. The invention of sound recording devices, especially sonographs, which make it possible to represent sound in a graphic form, finally convinced researchers of the species-specificity of the songs not only of birds, but also of crickets, grasshoppers, leafhoppers, as well as the voices of frogs and toads.

But not only the poses or voices of animals are ethological species features. These include the features of building nests in birds and insects from the Hymenoptera order (bees and wasps), the types and nature of egg-laying in insects, the shape of spider webs in spiders, and much more. Species-specific ootheca of praying mantises and capsules of locusts, light flashes of firefly beetles.

Sometimes the differences are quantitative, but this is enough to recognize the species of the object of study.

Geographic features. Often geographic features are a convenient means of distinguishing between populations, more precisely, deciding whether two populations under study are the same or different species. If a number of forms replace each other geographically, forming a chain or ring of forms, each of which differs from its neighbors, then they are called allopatric forms. Allopatric forms are considered to be a polytypic species, consisting of several subspecies.

The opposite picture is presented by cases where the ranges of forms partially or completely coincide. If there are no transitions between these forms, then they are called sympatric forms. This nature of distribution indicates the complete species independence of these forms due to the fact that sympatric (joint) existence, not accompanied by crossing, is one of the main criteria of the species.

In taxonomy practice, it is often difficult to assign a specific allopatric form to a species or subspecies. If allopatric populations are in contact, but do not interbreed in the zone of contact, then such populations should be considered as species. In contrast, if allopatric populations are in contact and interbreed freely in a narrow zone of contact or are connected by transitions in a wide zone of contact, then they should almost always be considered subspecies.

The situation is more complicated when there is a gap between the ranges of allopatric populations, due to which contact is impossible. In this case, we can deal with either species or subspecies. A classic example of this kind is the geographic dispersal of blue magpie populations. One subspecies (C. c. cooki) inhabits the Iberian Peninsula, and the other (C. c. cyanus) - the south of the Far East (Primorye and adjacent parts of China). It is believed that this is the result of a break in the former continuous range that arose in the Ice Age. Many taxonomists are of the opinion that questionable allopatric populations are more appropriately considered subspecies.

Other signs. In many cases, closely related species are easier to distinguish by chromosome morphology than by other characters, which has been demonstrated in species of the genus Drosophila and in bugs of the family Lygaeidae. The use of physiological characters by which closely related taxa can be distinguished is gaining more and more scope. It has been shown that closely related species of mosquitoes differ significantly in growth rate and duration of the egg stage. The conclusion that the main part of proteins is specific for each species is gaining increasing recognition. The conclusions in the field of serosystematics are based on this phenomenon. It also turned out to be useful to study specific secretions that form a certain pattern on the body or wax structures in the form of caps, like in scale insects or mealybugs from the class of insects. They are also species specific. It is often necessary to use the entire set of characters of a different nature to solve complex taxonomic problems. In modern works on zoological systematics, as acquaintance with the latest publications shows, the authors are not limited to morphological characters alone. Most often there are indications of the chromosomal apparatus.

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Type, type criteria. Populations.

View- a set of individuals with a hereditary similarity of morphological, physiological and biological features, freely interbreeding and producing fertile offspring, adapted to certain living conditions and occupying a certain area in nature.

Species are stable genetic systems, as in nature they are separated from each other by a number of barriers.

A species is one of the main forms of organization of living things. However, it is sometimes difficult to determine whether these individuals belong to the same species or not. Therefore, to decide whether individuals belong to this species, a number of criteria are used:

Morphological criterion- the main criterion based on external differences between animal or plant species. This criterion serves to distinguish organisms that are clearly distinguished by external or internal morphological characters. But it should be noted that very often there are very subtle differences between species, which can be revealed only with a long study of these organisms.

Geographic criterion- based on the fact that each species lives within a certain space (range). The area is the geographical boundaries of the distribution of the species, the size, shape and location in the biosphere of which is different from the areas of other species. However, this criterion is also not universal enough for three reasons. Firstly, the ranges of many species coincide geographically, and secondly, there are cosmopolitan species for which the range is almost the entire planet (killer whale). Thirdly, in some rapidly spreading species (house sparrow, house fly, etc.), the range changes its boundaries so quickly that it cannot be determined.

Environmental criterion- assumes that each species is characterized by a certain type of food, habitat, breeding season, i.e.

occupies a certain ecological niche.
Ethological criterion - lies in the fact that the behavior of animals of some species differs from the behavior of others.

Genetic criterion- contains the main property of the species - its genetic isolation from others. Animals and plants of different species almost never interbreed. Of course, a species cannot be completely isolated from the flow of genes from closely related species, but at the same time it retains the constancy of its genetic composition over an evolutionary long time. The clearest boundaries between species are precisely from a genetic point of view.

Physiological and biochemical criterion- this criterion cannot serve as a reliable way to distinguish between species, since the main biochemical processes proceed in similar groups of organisms in the same way. And within each species there are a large number of adaptations to specific living conditions by changing the course of physiological and biochemical processes.
According to one of the criteria, it is impossible to accurately distinguish species from each other. It is possible to determine whether an individual belongs to a particular species only on the basis of a combination of all or most of the criteria. Individuals occupying a certain territory and freely interbreeding with each other are called a population.

population- a set of individuals of the same species occupying a certain territory and exchanging genetic material. The totality of the genes of all individuals in a population is called the gene pool of the population. In each generation, individual individuals contribute more or less to the total gene pool, depending on their adaptive value. The heterogeneity of the organisms included in the population creates the conditions for the action of natural selection, therefore the population is considered the smallest evolutionary unit, from which the evolutionary transformation of the species begins - speciation. The population, therefore, is a supra-organismal formula for the organization of life. The population is not a completely isolated group. Sometimes interbreeding occurs between individuals of different populations. If a population turns out to be completely geographically or ecologically isolated from others, then it can give rise to a new subspecies, and subsequently a species.

Each population of animals or plants consists of individuals of different sexes and different ages. The ratio of the number of these individuals may be different depending on the time of year, natural conditions. The size of a population is determined by the ratio of births and deaths of its constituent organisms. If for a sufficiently long time these indicators are equal, then the population size does not change. Environmental factors, interaction with other populations can change the size of the population.

Vertyanov S. Yu.

Distinguishing supraspecific taxa is, as a rule, quite easy, but a clear distinction between the species themselves encounters certain difficulties. Some species occupy geographically separated areas of habitat (ranges) and therefore do not interbreed, but in artificial conditions give fertile offspring. Linnean's brief definition of a species as a group of individuals that interbreed freely and produce fertile offspring does not apply to organisms that reproduce parthenogenetically or asexually (bacteria and unicellular animals, many higher plants), as well as to extinct forms.

Aggregate hallmarks species is called its criterion.

The morphological criterion is based on the similarity of individuals of the same species in terms of a set of features of external and internal structure. Morphological criterion is one of the main ones, but in some cases morphological similarity is not enough. The malarial mosquito was previously referred to as six non-interbreeding similar species, of which only one carries malaria. There are so-called twin species. Two species of black rats, outwardly almost indistinguishable, live separately and do not interbreed. The males of many creatures, such as birds (bullfinches, pheasants), outwardly bear little resemblance to females. Adult male and female threadtail eels are so dissimilar that for half a century scientists placed them in different genera, and sometimes even in different families and suborders.

Physiological and biochemical criterion

It is based on the similarity of the life processes of individuals of the same species. Some species of rodents have the ability to hibernate, while others do not. Many related plant species differ in their ability to synthesize and accumulate certain substances. Biochemical analysis makes it possible to distinguish between types of unicellular organisms that do not reproduce sexually. Anthrax bacilli, for example, produce proteins that are not found in other types of bacteria.

The possibilities of the physiological-biochemical criterion are limited. Some proteins have not only species, but also individual specificity. There are biochemical signs that are the same in representatives of not only different species, but even orders and types. Physiological processes can proceed in a similar way in different species. Thus, the intensity of metabolism in some arctic fish is the same as in other fish species of the southern seas.

Genetic criterion

All individuals of the same species have a similar karyotype. Individuals of different species have different chromosome sets, cannot interbreed and live in natural conditions separately from each other. Two twin species of black rats have a different number of chromosomes - 38 and 42. The karyotypes of chimpanzees, gorillas and orangutans differ in the arrangement of genes in homologous chromosomes. The differences between the karyotypes of bison and bison, which have 60 chromosomes in the diploid set, are similar. Differences in the genetic apparatus of some species can be even more subtle and consist, for example, in different character turning individual genes on and off. The use of only a genetic criterion is sometimes insufficient. One species of weevil combines diploid, triploid and tetraploid forms, the house mouse also has different sets of chromosomes, and the gene of the human nuclear histone H1 protein differs from the homologous pea gene by only one nucleotide. Such variable DNA sequences have been found in the genome of plants, animals and humans that people can distinguish between brothers and sisters by them.

Reproductive criterion

(Latin reproducere reproduce) is based on the ability of individuals of the same species to produce fertile offspring. An important role in crossing is played by the behavior of individuals - marriage ritual, species-specific sounds (birdsong, grasshoppers chirping). By the nature of the behavior, individuals recognize the marriage partner of their species. Individuals of similar species may not interbreed due to inconsistencies in mating behavior or inconsistencies in breeding sites. So, females of one species of frogs spawn along the banks of rivers and lakes, and the other - in puddles. Similar species may not interbreed due to differences in mating periods or mating periods when living in different climatic conditions. Different periods of flowering in plants prevent cross-pollination and serve as a criterion for belonging to different species.

Reproductive criterion is closely related to genetic and physiological criteria. The viability of gametes depends on the feasibility of conjugation of chromosomes in meiosis, and hence on the similarity or difference in the karyotypes of crossing individuals. Difference in daily physiological activity (daytime or nocturnal lifestyle) sharply reduces the possibility of crossing.

The use of only the reproductive criterion does not always make it possible to clearly distinguish species. There are species that are clearly distinguishable by morphological criteria, but which, when crossed, give fertile offspring. From birds, these are some species of canaries, finches, from plants - varieties of willows and poplars. A representative of the order of artiodactyl bison lives in the steppes and forest-steppes North America and never in natural conditions is found with the bison living in the forests of Europe. In zoo conditions, these species produce fertile offspring. Thus, the population of European bison, which was practically exterminated during the world wars, was restored. They interbreed and give fertile offspring of yaks and large cattle, white and brown bears, wolves and dogs, sables and martens. In the plant kingdom, interspecific hybrids are even more common, among plants there are even intergeneric hybrids.

Ecological and geographical criterion

Most species occupy a certain territory (range) and an ecological niche. Buttercup caustic grows in meadows and fields, in more damp places another species is common - creeping buttercup, along the banks of rivers and lakes - burning buttercup. Similar species living in the same range may differ in ecological niches - for example, if they eat different foods.

The use of the ecological-geographical criterion is limited by a number of reasons. The range of the species may be discontinuous. The species range of the white hare is the islands of Iceland and Ireland, the north of Great Britain, the Alps and north-west Europe. Some species have the same range, such as two species of black rats. There are organisms that are distributed almost everywhere - many weeds, a number of insect pests and rodents.

The problem of species definition sometimes grows into a complex scientific problem and is solved using a set of criteria. Thus, a species is a set of individuals occupying a certain area and possessing a single gene pool, providing hereditary similarity of morphological, physiological, biochemical and genetic traits, interbreeding under natural conditions and producing fertile offspring.

The species is one of the main forms of organization of life on Earth (along with the cell, organism and ecosystem) and the main unit of classification biodiversity. But at the same time, the term "species" still remains one of the most complex and ambiguous biological concepts.

The problems associated with the concept of biological species are easier to understand when viewed from a historical perspective.

Background

The term "species" has been used to designate the names of biological objects since ancient times. Initially, it was not purely biological: species of ducks (mallard, pintail, teal) did not differ fundamentally from types of kitchen utensils (frying pan, saucepan, etc.).

The biological meaning of the term "species" was given by the Swedish naturalist Carl Linnaeus. He used this concept to designate an important property of biological diversity - its discreteness (discontinuity; from the Latin discretio - to divide). K. Linnaeus considered species as objectively existing groups of living organisms, quite easily distinguishable from each other. He considered them immutable, once and for all created by God.

The identification of species at that time was based on differences between individuals in a limited number external signs. This method is called the typological approach. The assignment of an individual to a particular species was carried out on the basis of a comparison of its features with descriptions already known species. If its features could not be correlated with any of the existing species diagnoses, then according to this specimen (it received the name of the type) the new kind. Sometimes this led to incidental situations: males and females of the same species were described as different species.

With the development of evolutionary ideas in biology, a dilemma arose: either species without evolution, or evolution without species. The authors evolutionary theories Jean-Baptiste Lamarck and Charles Darwin denied the reality of species. C. Darwin, the author of "The Origin of Species by Means of Natural Selection ...", considered them "artificial concepts invented for the sake of convenience."

To late XIX centuries, when the diversity of birds and mammals was quite fully studied over a large area of ​​the Earth, the shortcomings of the typological approach became obvious: it turned out that animals from different places sometimes, although slightly, but quite reliably differ from each other. In accordance with the established rules, they had to be given the status of independent species. The number of new species grew like an avalanche. Along with this, the doubt grew: should different populations of closely related animals be assigned a species status only on the basis that they are slightly different from each other?

In the 20th century, with the development of genetics and synthetic theory, a species began to be considered as a group of populations with a common unique gene pool, which has its own “protection system” for the integrity of its gene pool. Thus, the typological approach to the identification of species has been replaced by an evolutionary approach: species are determined not by difference, but by isolation. Populations of a species that are morphologically distinct from each other, but are able to interbreed freely with each other, are given the status of subspecies. This system of views formed the basis of the biological concept of the species, which received worldwide recognition thanks to the merit of Ernst Mayr. The change in species concepts "reconciled" the ideas of morphological isolation and evolutionary variability of species and made it possible to approach the task of describing biological diversity with greater objectivity.

View and its reality. C. Darwin, in his book "The Origin of Species" and in other works, proceeded from the fact of the variability of species, the transformation of one species into another. Hence his interpretation of the species as stable and simultaneously changing over time, leading first to the appearance of varieties, which he called "nascent species".

View- a set of geographically and ecologically close populations capable of interbreeding under natural conditions, having common morphophysiological features, biologically isolated from populations of other species.

View criteria- a set of certain features that are characteristic of only one kind of species (T.A. Kozlova, V.S. Kuchmenko. Biology in tables. M., 2000)

It is also significant that the species is a universal discrete (crushable) unit of life organization. A species is a qualitative stage of living nature, it exists as a result of intraspecific relationships that ensure its life, reproduction and evolution.

The main feature of the species is the relative stability of its gene pool, supported by the reproductive isolation of individuals from other similar species. The unity of the species is maintained by free interbreeding between individuals, which results in a constant flow of genes in the intraspecific community. Therefore, each species has stably existed for many generations in one area or another, and its reality is manifested in this. At the same time, the genetic structure of the species is constantly being rebuilt under the influence of evolutionary factors (mutations, recombinations, selection), and therefore the species is heterogeneous. It breaks down into populations, races, subspecies.

The genetic isolation of species is achieved by geographical (related groups are separated by the sea, desert, mountain range) and ecological isolation (mismatch in terms and places of reproduction, animals living in different tiers of the biocenosis). In cases where interspecific crossing nevertheless, hybrids are either weakened or sterile (for example, a hybrid of a donkey and a horse - a mule), which indicates the qualitative isolation of the species and its reality. According to the definition of K. A. Timiryazev, “a species as a strictly defined category, always equal and unchanged, does not exist in nature. But at the same time, we must recognize that the species, at the moment we observe, have a real existence.

population. Within the range of any species, its individuals are unevenly distributed, since in nature there are no identical conditions for existence and reproduction. For example, mole colonies are found only in separate meadows, nettle thickets - along ravines and ditches, frogs of one lake are separated from another neighboring lake, etc. The population of a species breaks up into natural groupings - populations. However, these distinctions do not eliminate the possibility of interbreeding between individuals occupying border areas. The population density of a population is subject to significant fluctuations in different years and different seasons of the year. A population is a form of existence of a species in specific environmental conditions and a unit of its evolution.

A population is a collection of freely interbreeding individuals of the same species that exist for a long time in a certain part of the range within the species and are relatively isolated from other populations. Individuals of one population have the greatest similarity in all characteristics inherent in the species, due to the fact that the possibility of interbreeding within a population is higher than between individuals of neighboring populations and they experience the same selection pressure. Despite this, populations are genetically heterogeneous due to continuously emerging hereditary variability.

Darwinian divergence (divergence of characteristics and properties of descendants in relation to the original forms) can occur only through the divergence of populations. For the first time this position was substantiated in 1926 by S. S. Chetverikov, who showed that behind the apparent external uniformity, any species has a huge hidden reserve of genetic variability in the form of a variety of recessive genes. This genetic reserve is not the same in different populations. That is why the population is the elementary unit of the species and the elementary evolutionary unit.

View types

The selection of species occurs on the basis of two principles (criteria). This is a morphological criterion (revealing differences between species) and a reproductive isolation criterion (estimating the degree of their genetic isolation). The procedure for describing new species is often associated with certain difficulties, associated both with the ambiguous correspondence of the species criteria to each other, and with the gradual and incomplete process of speciation. Depending on what kind of difficulties arose in the selection of species and how they were resolved, the so-called "types of species" are distinguished.

monotypic appearance. Often there are no difficulties in describing new species. Such species usually have a vast, unbroken range over which geographical variability is weakly expressed.

polytypic look. Often, with the help of a morphological criterion, a whole group of closely related forms is singled out, living, as a rule, in a highly dissected area (in the mountains or on islands). Each of these forms has its own, usually rather limited range. If there is geographic contact between the compared forms, then the criterion of reproductive isolation can be applied: if hybrids do not occur, or are relatively rare, these forms are given the status of independent species; otherwise, they describe different subspecies of the same species. A species that includes several subspecies is called polytypic. When the analyzed forms are geographically isolated, the assessment of their status is rather subjective and occurs only on the basis of a morphological criterion: if the differences between them are “significant”, then we have different species, if not, subspecies. It is not always possible to unambiguously determine the status of each form in a group of closely related forms. Sometimes a group of populations closes in a ring, covering a mountain range or the globe. In this case, it may turn out that the "good" (living together and not hybridizing) species are related to each other by a chain of subspecies.

polymorphic look. Sometimes within a single population of a species there are two or more morphs - groups of individuals that are sharply different in color, but able to freely interbreed with each other. Usually, genetic basis polymorphism is simple: differences between morphs are determined by the action of different alleles of the same gene. The ways in which this phenomenon occurs can be very different.

Species-twins- species that live together and do not interbreed with each other, but differ very slightly morphologically. The difficulty of distinguishing such species is associated with the difficulty of isolating or inconveniencing the use of their diagnostic features - after all, the twin species themselves are well versed in their own "taxonomy". More often, twin species are found among groups of animals that use smell to find a sexual partner (insects, rodents) and less often among those that use visual and acoustic signaling (birds).

Spruce crossbills(Loxia curvirostra) and pine(Loxia pytyopsittacus). These two species of crossbills are one of the few examples of sibling species among birds. Living together in a large area covering Northern Europe and the Scandinavian Peninsula, these species do not interbreed with each other. Morphological differences between them, insignificant and very unreliable, are expressed in the size of the beak: in the pine it is somewhat thicker than in the spruce.

"Half-kinds". Speciation is a long process, and therefore one may encounter forms whose status cannot be objectively assessed. They are not yet independent species, since they hybridize in nature, but these are no longer subspecies, since the morphological differences between them are very significant. Such forms are called "borderline cases", "problem types", or "semi-types". Formally, binary Latin names are assigned to them, as in "normal" species, and they are placed next to each other in taxonomic lists. "Semi-species" are not uncommon, and we ourselves are often unaware that the species around us are typical examples of "borderline cases." In Central Asia, the house sparrow lives together with another closely related species - the black-breasted sparrow, from which it differs well in color. There is no hybridization between them in this area. Their systematic status as distinct species would not be in doubt if there were no second zone of contact in Europe. Italy inhabits special form sparrows, resulting from the hybridization of brownie and Spanish. At the same time, in Spain, where house and Spanish sparrows also live together, hybrids are rare.