Nutrition what is the criterion of the species. What are the criteria for the type? Morphological criterion of the species

A species is one of the main forms of organization of life on Earth (along with a cell, an organism and an ecosystem) and the basic unit of classification of biological diversity. 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: the types of ducks (mallard, pintail, teal) did not have any fundamental differences from the 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 unchangeable, created once and for all by God.

Species were identified at that time on the basis of differences between individuals in a limited number of external characteristics. This method is called the typological approach. The assignment of an individual to a particular species was carried out on the basis of comparison of its characteristics with descriptions of already known species. If its characteristics could not be correlated with any of the existing species diagnoses, then a new species was described from this specimen (it was called the type specimen). 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 of evolutionary theories - Jean-Baptiste Lamarck and Charles Darwin denied the reality of species. Charles Darwin, the author of “The Origin of Species by Means of Natural Selection...”, considered them “artificial concepts invented for the sake of convenience.”

By the end of the 19th century, 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 reliably differ from each other. In accordance with established rules, they had to be given the status of independent species. The number of new species grew like an avalanche. Along with this, doubt grew stronger: should different populations of closely related animals be assigned 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 viewed as a group of populations with a common unique gene pool, possessing its own “protection system” for the integrity of its gene pool. Thus, the typological approach to the identification of species was replaced by an evolutionary one: species are determined not by difference, but by isolation. Populations of a species that are morphologically distinct from each other, but are capable of freely interbreeding 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 merits 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.

The view and its reality. Charles 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 a species as stable and at the same time changing over time, leading first to the appearance of varieties, which he called “emergent species.”

View– a set of geographically and ecologically close populations, capable of interbreeding with each other under natural conditions, possessing common morphophysiological characteristics, biologically isolated from populations of other species.

Type criteria– a set of certain characteristics characteristic of only one species (T.A. Kozlova, V.S. Kuchmenko. Biology in tables. M., 2000)

Type criteria	Indicators of each criterion
Morphological	The similarity of the external and internal structure of individuals of the same species; characteristics of the structural features of representatives of one species
Physiological	The similarity of all life processes, and above all reproduction. Representatives of different species, as a rule, do not interbreed or their offspring are infertile
Biochemical	Species specificity of proteins and nucleic acids
Genetic	Each species is characterized by a certain, unique set of chromosomes, their structure and differentiated coloring
Ecological-geographical	Habitat and immediate habitat - ecological niche. Each species has its own habitat niche and distribution area

It is also important that a species is a universal discrete (fragmentable) 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 a 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 crossing between individuals, which results in a constant flow of genes in the intraspecific community. Therefore, each species exists steadily in one area or another for many generations, and this is where its reality is manifested. 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 turns out to be heterogeneous. It breaks down into populations, races, subspecies.

The genetic isolation of species is achieved by geographic (related groups are separated by the sea, desert, mountain range) and ecological isolation (discrepancy in the timing and places of reproduction, the habitat of animals in different tiers of the biocenosis). In cases where interspecific crossing does occur, the 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 unchangeable, does not exist in nature. But at the same time we must recognize that species, at the moment we observe, have a real existence.”

Population. Within the range of any species, its individuals are distributed unevenly, since in nature there are no identical conditions for existence and reproduction. For example, mole colonies are found only in separate meadows, nettle thickets are found in ravines and ditches, frogs of one lake are separated from another neighboring lake, etc. The population of a species is divided into natural groups - populations. However, these distinctions do not eliminate the possibility of interbreeding between individuals occupying border areas. The population density of the 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, existing for a long time in a certain part of the range within the species and relatively isolated from other populations. Individuals of one population have the greatest similarity in all characteristics inherent to the species, due to the fact that the possibility of crossing within the 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 characters and properties of descendants in relation to the original forms) can only occur through the divergence of populations. This position was first substantiated in 1926 by S.S. Chetverikov, showing that behind the apparent external homogeneity, any species has a huge hidden reserve of genetic variability in the form of many different recessive genes. This genetic reserve is not the same in different populations. That is why a population is an elementary unit of a species and an elementary evolutionary unit.

Types of species

Species are identified on the basis of two principles (criteria). This is a morphological criterion (revealing differences between species) and a criterion of reproductive isolation (assessing 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 species criteria to each other, and with the gradual and incomplete process of speciation. Depending on what kind of difficulties arose when identifying species and how they were resolved, so-called “types of species” are distinguished.

Monotypic species. Often no difficulties arise when describing new species. Such species usually have a large, unbroken range over which geographic variability is weak.

Polytypic species. Often, using morphological criteria, a whole group of closely related forms is distinguished, usually living in highly dissected areas (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 it is possible to apply the criterion of reproductive isolation: if hybrids do not arise 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 quite 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 becomes enclosed in a ring that spans a mountain range or the globe. In this case, it may turn out that “good” (co-living and non-hybridizing) species are connected to each other by a chain of subspecies.

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

Adaptive polymorphism of the praying mantis

Hybridogenic polymorphism of the Spanish wheatear

The mantis has green and brown morphs. The first is poorly visible on the green parts of plants, the second - on tree branches and dry grass. In experiments on transplanting mantises onto a background that does not match their color, it was possible to show that polymorphism in this case could arise and is maintained due to natural selection: the green and brown coloration of mantises is protection from predators and allows these insects to compete less with each other.

Male Spanish wheatears have white-necked and black-throated morphs. The nature of the relationship between these morphs in different parts of the range suggests that the black-necked morph was formed as a result of hybridization with a closely related species, the bald wheatear.

Twin species- species that live together and do not interbreed with each other, but differ very little morphologically. The difficulty of distinguishing such species is associated with the difficulty of isolating or the inconvenience of using their diagnostic characters - 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 tree(Loxia pytyopsittacus). These two species of crossbills are one of the few examples of sibling species among birds. Living together over a large area covering Northern Europe and the Scandinavian Peninsula, these species do not interbreed with each other. The morphological differences between them, insignificant and very unreliable, are expressed in the size of the beak: in the pine tree it is somewhat thicker than in the spruce tree.

"Half-species". Speciation is a long process, and therefore one may encounter forms whose status cannot be assessed objectively. They are not yet independent species, since they hybridize in nature, but they are no longer subspecies, since the morphological differences between them are very significant. Such forms are called "borderline cases", "problem species" or "semi-species". Formally, they are assigned binary Latin names, like “normal” species, and are placed next to each other in taxonomic lists. “Half-species” are not so rare, and we ourselves often do not suspect 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 independent species would not be in doubt if there had not been a second contact zone in Europe. Italy is inhabited by a special form of sparrows, which arose as a result of the hybridization of the brownie and the Spanish. Moreover, in Spain, where house sparrows and Spanish sparrows also live together, hybrids are rare.

Goals: form the concepts of “type” and “type criteria”; showmechanisms of reproductive isolation in nature; continue to develop the skills to give a morphological description of plants, work with texts, draw up tables, analyze, and formulate conclusions.

Equipment: paintings on zoology: “Hare-hare", "Brown hare", "Brown bear", "White bear"; distributionexact material “White Hare and Brown Hare”, “Raven and Crow”.

During the classes

I.Organizing time

The teacher announces the topic and objectives of the lesson.

11. Updating knowledge

1. Completing tasks (orally).

Task No. 1

Name the species of plants and animals that you know and live near your home or school.

Task No. 2

The teacher shows the painting “Brown Bear” and asks questions:

The name of this type of animal is Brown Bear. Which of thesetwo words refer to the generic name, which one refers to the specific name?

Name another species of animal from the same genus. (This is a bear white).

The teacher hangs a picture of a polar bear next to the picture “Brown Bear.”

Compare two species of the same genus. Show similarities and differences.

Task No. 3,

In the given list of animals, count the number of individuals, species and genera.

1. Common hedgehog.

2. Common fox.

3. Himalayan or white-breasted bear.

4. Djungarian hamster.

5. White hare.

6. Brown bear.

7. Syrian or golden hamster.

8. Brown hare.

9. Eared hedgehog.

10. Common fox.

(Answer:number of individuals - 10; species - 9; births - 5 (Hedgehog, Fox-tsa, Bear, Hamster, Hare).)

When completing the last task, a number of students have a problem: to classify the white hare and the brown hare as the same species or totwo different types. Is it true or false that the hareIs a white hare a brown hare in winter?

Report “The Brown Hare and the White Hare.”

- What conclusion can be drawn based on the results of completing all tasks to update knowledge?

Conclusion:

1. To indicate the type, double (binary) butnomenclature, according to which the genus to which they belong is first indicatedrefers to the species (noun) and then the species name (adj. adjective).

2. Individuals of different species differ from each other in their habitats.tania, external signs, etc.

3. Similar species are combined into one genus.

4. Species is the main category of biological classification.

III . Learning new material

1. Teacher's story.

- What is a species and what are its criteria?

IN Questioning about species and species criteria occupies a central place in the theory of evolution and is the subject of numerous studies.knowledge in the field of taxonomy, zoology, botany and othersSci. And this is understandable: a clear understanding of the essencespecies is necessary to clarify the mechanisms of evolutionary process.

A strict generally accepted definition of species has not yet been developed.nerdy. In the biological encyclopedic dictionary we are onWe use the following definition of the form:

“A species is a set of populations of individuals capable of interbreedingniyu with the formation of fertile offspring inhabiting the definitionnative habitat, having a number of common morphophysiological characteristics and individuals that are distant from other similar groups of individuals are practicallypurely by the complete absence of hybrid forms.”

Compare this definition with the one given in your textbook(textbook by A.A. Kamensky, § 4.1, p. 134).

Let us explain the concepts that occur. in the definition of the form:

Area- area of ​​distribution of a given species or population in nature.

Population(from Latin “por uius” " - people, population) - totalitythe number of individuals of the same species having a common gene pool and historysweeping a certain territory - habitat.

Gene pool- a set of genes that individuals haveof this population.

Let us consider the history of the development of views on species in biology.

The concept of species was first introduced into science by an English botanist John Ray inXVII century. The seminal work on the species problemwas written by a Swedish naturalist and naturalistCarl Linnaeus in XVIII century, in which he proposed the firstscientific definition of the species, clarified its criteria.

Teacher's comments. K. Linnaeus believed that the species is a unisebaceous, actually existing unit of living matter, morphologically homogeneous and unchanging . All individuals of the species, according to the scientist, have a typical morphological appearance, and variations represent random deviations , the result of an imperfect embodiment of the idea of ​​the form (a kind of deformity). Scientistbelieved that species are unchangeable, nature is unchangeable. The idea is unchangednew nature was based on the concept of creationism, according toby which all things were created by God. Applied to biologyLinnaeus expressed this concept in his famousmule “There are as many species as the number of different forms that the Infinite first produced. creature".

Another concept belongs to Tom Baptiste Lamarck- ledto a French naturalist. According to his concept, the views are real Not exist, is a purely speculative concept invented forin order to make it easier to consider collectively a larger numberindividuals, since, according to Lamarck, “in nature there is noanything other than individuals.” Individual variability is continuous, therefore, the boundary between species can be drawn both here and there - where is more convenient.

The third concept was prepared in the first quarter XIX century. It was justified Charles Darwin and subsequent biologistsmi. According to this concept, species have an independent reality. Viewheterogeneous, is a system of subordinate units. WITHAmong them, the basic elementary unit is the population. Types, by Darwin, change, they are relatively constant and are resthe result of evolutionary development .

Thus, the concept of “species” has a long history of development in biological science.

Sometimes the most experienced biologists are stumped when determiningwhether these individuals belong to the same species or not . Why is that happens, are there precise and strict criteria thatCould you resolve all doubts?

Species criteria are the characteristics by which one species is distinguishedcomes from someone else. They are also isolating mechanisms.preventing interbreeding, independence, independent sti species.

We know that one of the main features of biological matter on our planet is discreteness. This is in is expressed in the fact that it is represented by separate species, notinterbreeding with each other, isolated from each other gogo.

The existence of a species is ensured by its genetic unity(individuals of a species are capable of interbreeding and producing viable fertile offspring) and its genetic independence (impossiblepossibility of crossing with individuals of another species, not viablepresence or sterility of hybrids).

The genetic independence of a species is determined by a combination ofthe completeness of its characteristic features: morphological, physiological, biochemical, genetic, lifestyle features, behavior, geographical distribution, etc. This is crit eriispida.

Let's get to know them.

2. Work in groups

Each group receives a text illustrating one of the criteria for the type. After 5 minutes, you need to talk about the essence of this criterion and what the disadvantage of this criterion is. As the groups perform, the class fills out the “View Criteria” table.

Table No. 1

Type criteria.

Criterion name	Characteristics of individuals according to criterion	Exception
1. Morphological	The similarity of the external and internal structure of organisms.	Twin species, sexual dimorphism, polymorphism.
2. Physiological	The similarity of all life processes and the possibility of obtaining fertile offspring through crossing.	Different species have similarities in their life processes. Presence of interspecific hybrids.
3. Ecological	Similarity in feeding methods, habitats, and sets of environmental factors necessary for existence.	The ecological niches of different species overlap.
4. Geographical	They occupy a specific area.	Cosmopolitans. Coincidence of ranges of different species.
5. Biochemical	Similarity in biochemical parameters - composition and structure of proteins, nucleic acids.	There are species that are very similar in biochemical composition.
6. Ethological	Similarities in behavior. Especially during the mating season (courtship rituals, mating songs, etc.).	There are species with similar behavior.
7. Cyto-genetic a) Cytological	Individuals of the same species interbreed and produce fertile offspring (based on the similarity of the number of chromosomes, their shape and structure).	Chromosomal polymorphism within a species; Many different species have the same number of chromosomes.
b) Genetic	Genetic isolation of species. Presence of post-population isolation mechanisms. The most important of them are the death of male gametes (genetic incompatibility), the death of zygotes, the non-viability of hybrids, their sterility, and finally, the inability to find a sexual partner and produce viable fertile offspring	A dog and a wolf, a poplar and a willow, a canary and a finch give fertile offspring. (Presence of interspecific hybrids)
8. Historical	Community of ancestors, a common history of the origin and development of the species.

So, the species criteria by which we distinguish one species from another collectively determine the genetic isolation of speciesdov, ensuring the independence of each species and diversityin nature. Essentially, in the development of these isolating species characteristicsThis is what the process of species formation consists of. That is whythe study of species criteria is of decisive importance forunderstanding the mechanisms of the evolutionary process occurring on our planet.

3. Formulation of conclusions.

After filling out the table, conclusions are formulated:

1) Species criteria by which one species differs from anotherth, together they determine the genetic isolation of species, ensuring the independence of each species and their diversity in nature.

2) There is not a single species criterion that could berecognized as absolute and universal.

3) To methods of isolation that prevent the crossing of different species include:

A) differences in habitats => impossibility of meeting;

b) different periods of reproduction;

V) differences in the structure of the genital organs;

G) non-viability or sterility of hybrids;

d) various “courtship” rituals during the breeding season.

4) The species is genetically relatively isolated bathroom system, which proves the reality of the existence of species in nature.

Remember what was said in the text “The White Hare and the Hare”hare". What type criteria are used to describe hares? tsev?

Answer the question:

- What species criteria are used to describe animals?

1). The mute swan often bends neck in the shape of the letter S , and holds its beak and head inclined towards the water. Whenduring the fight it makes a characteristic hissing sound, which is how it gotits name. The mute swan is common in isolated areasin central and southern Europe and Asia from southern Sweden, Denmark andPoland in the West to Mongolia, Primorsky Krai and China in the East.Everywhere in this territory it is rare, often a pair from a pair nests on the groundat some distance, and in many areas it is completely absent.Inhabits estuaries and lakes overgrown with aquatic vegetation, sometimeseven swamps, preferring remote ones, little visited by humans.

The small or tundra swan is distributed throughout the tundraAsia from the Kola Peninsula in the west to the Kolyma delta in the East,entering the forest-tundra region and the western islands of the Arctic. For nestingselects marshy and low grassy areaslakes scattered throughout them, as well as river valleys aboundingoxbows and channels.

Mating games are unique and take place on land. At the same time, the male walks in front of the female, stretches his neck, sometimes raises his wings,making a special clapping sound with them and screaming loudly.

2). Go family martin. Top of the gocatches, back, wings and tailblue-black, rump and entire underbodywhite. Tail with sharp triangularcut out at the end. Occupantmountain and cultural landscapes.Nests on the walls of rocks and buildings. P migratory bird. Keeps in packsin the air or sitting on wires, more often than other swallows sits on theI eat. Breeds in colonies. The nest is made from lumps of clay in the formhemisphere with side entry. Clutch of 4-6 white eggs in May–June. Goal os – voiced “tirrch-tirrch”

Shore swallow. The top of the head, neck, back, wings, tail and stripe across the chest are grayish-brown, the throat, chest and belly are white. Tail with a shallow notch.

Inhabits river valleys, where it nests along steep clay or sandy banks. Common or numerous migratory bird. Keeps in flocks, nests in colonies. It makes nests in burrows along steep river banks. Clutch of 4-6 white eggs in May-July. Voice - quiet "chirr- chirr

Homework

According to the textbook by A.A. Kamensky, § 4.1, questions after the paragraph, terms.

Individually:

1) The message “Is it true that the raven is the crow’s husband?”

2 ) Using literary sources, give specific examplesExamples of geographical, environmental and ethological criteria.

Additional material for group work.

Type criteria

Morphological criterion

This was the first and for a long time the only criterion used to describe species.

The morphological criterion is the most convenient and noticeable, thereforeand is now widely used in the taxonomy of plants and animals.

We can easily distinguish by the size and color of the plumage of the greatspotted woodpecker from green woodpecker, lesser spotted woodpecker and yellow woodpecker(black woodpecker), great tit from tufted, long-tailed, blueand chickadees, meadow clover from creeping and lupine, etc.

Despite its convenience, this criterion does not always work. You can’t use it to differentiate sibling species, practically notdifferent morphologically. There are many such species among malariamosquitoes, fruit flies, whitefish. Even in birds, 5% of species are twins, andThere are 17 of them in one row of North American crickets.

The use of morphological criteria alone canlead to erroneous conclusions. So, C. Linnaeus in particularexternal structure classified the male and female mallard duck as different species. Siberian hunters have identified five variations based on the fur color of foxes: greyhounds, moths, crosses, black-brown and black. In England, 70 species of butterflies, along with individuals with light colors, also haveny morphs, the number of which in populations began to increase inconnection with forest pollution. Polymorphism is widespreadphenomenon. It occurs in all species. It also affects the characteristics by which species differ. In woodcutter beetles, for example, in the longhorned beetle,exact, found in late spring on a swimsuit, in addition to the teeIn the peak form, up to 100 color aberrations occur in populations. In the time of Linnaeus, the morphological criterion was the main one, sinceshowed that there is one typical form for the species.

Now that it has been established that a species can have many forms, likethe logical concept of species is discarded and the morphological criterion is notalways satisfies scientists. However, it should be recognized that this criterionIt is very convenient for systematizing species and in most keys to animals and plants it plays a major role.

Physiological criterion

Physiological characteristics of various plant species and stomachgenetics are often a factor ensuring their genetic selfworthiness. For example, many fruit flies have sperm from individuals of foreign species.Yes, it causes an immunological reaction in the female genital tract, which leads to the death of sperm. Hybridization of various species andsubspecies of goats often leads to disruption of the periodicity of fruitwearing - the offspring appears in winter, which leads to its death. Crossesthe formation of different subspecies of roe deer, for example Siberian and European,sometimes leads to the death of females and offspring due to their large size fetus

Biochemical criterion

Interest in this criterion has appeared in recent decades due todevelopment of biochemical research. It is not widely used, since there are no specific substances characteristiconly for one species and, in addition, it is very labor-intensive and far not universal. However, it can be used in cases wherewhen other criteria “do not work”. For example, for two twin speciesbutterflies from the genus amata (A. r h e g ea and A. g ugazzii ) diagnosticand the signs are two enzymes - phosphoglucomutase and esterase-5, allowing able to even identify hybrids of these two species. Last timecomparative study of the composition of DN has become widespreadK in practical taxonomy of microbes. Studying the composition of DNA made it possible revise the phylogenetic system of various groups microorganisms. The developed methods make it possible to compare the compositionDNA in bacteria conserved in the earth and living todayforms For example, a comparison was made of the DNA composition of agedabout 200 million years in the thickness of the salts of the Paleozoic bacterium pseudosalt-loving monads and living pseudomonads. The composition of their DNA turned out to be identical, and biochemical properties - similar.

Cytological criterion

The development of cytological methods allowed scientists to study the backgroundrmu and the number of chromosomes in many species of animals and plants. A new direction has emerged - karyosystematics, which has introduced someamendments and clarifications to the phylogenetic system constructed on the basis of morphological criteria. In some cases, the number of chromosomes servescharacteristic feature of the species. Karyological analysis allowed, for example, to streamline the taxonomy of wild mountain sheep, whichVarious researchers have identified from 1 to 17 species. The analysis showedthe presence of three karyotypes: 54 chromosome - in mouflons, 56romosomal - in argali and argali and 58-chromosomal - in the inhabitantsmountains of Central Asia - Urials.

However, this criterion is not universal. Firstly, atIn many different species, the number of chromosomes is the same and their shape is similar. Secondly, within the same species there can be individuals with different numbers of chromosomes. These are the so-called chromosomal and genomicpolymorphism. For example, goat willow has diploid - 38 and tetraploid The number of chromosomes is 76. In silver crucian carp there are populations with a setrom chromosomes 100, 150, 200, while the normal number is 50. In rainbow trout, the number of chromosomes varies from 58 to 64, in the White SeaThere are also individuals with 52 and 54 chromosomes. In Tajikistan on the sitewith a length of only 150 km, zoologists discovered a population of mole voles with a set of chromosomes from 31 to 54. Gerbils from different habitats have a different number of chromosomes: 40 - in Algerian gerbils Chinese populations, 52 - among Israeli and 66 - among Egyptian populations. To infusion Currently, intraspecific chromosomal polymorphism has been found in 5% of c.ito-genetically studied mammalian species.

Sometimes this criterion is misinterpreted as genetic. Undoubtedly, the number and shape of chromosomes is an important feature that prevents crossbreedingunderstanding of individuals of different species. However, this is rather cytomorphologicalimportant criterion, since we are talking about intracellular morphology: the numberand the shape of chromosomes, and not about the set and structure of genes.

E tological criterion

For some animal species, a mechanism that preventsbaptism and leveling the differences between them are especiallythe importance of their behavior, especially during the mating season. Partner recognition of one's own species and rejecting courtship attempts by males of another speciesbased on specific stimuli - visual, soundchemical, tactile, mechanical, etc.

In the widespread genus warbler, different species are very similarlive on each other morphologically, in nature they cannot be distinguished either by color or size. But they all differ very well in song and according to habits. The song of the willow warbler is complex, similar to the song of the chaffinch, only without his final knee, and the chiffchaff song is aboutTiny monotonous whistles. Numerous sibling species of ameRican fireflies from the genus P hotinus were first identified only bydifferences in their light signals. Male fireflies in flight flashes of light, the frequency, duration and alternation of whichspecific for each species. Well known but that a number of species of Orthoptera and Homoptera living within,same biotope and reproducing synchronously, differ onlythe nature of their calling signals. Such twin species with acousticreproductive isolation is found, for example, in crickets, pipits, cicadas and other insects. Two closely related species of AmericanToads also interbreed due to differences in male calls.

Differences in display behavior often play a decisive role in reproductive isolation. For example, closely related species of Drosophila flies fromare characterized by the specifics of the courtship ritual (by the nature of vibrationwings, trembling legs, circling, tactile contacts). Two closespecies - the herring gull and the black whale have differences in the degree of pronouncedsty of demonstrative poses, and seven species of lizards of the genus S se1rogs differ in the degree of head raising when courting sexual partners.

Ecological criterion

Features of behavior are sometimes closely related to the ecological specifics of the species, for example, with the features of the nest structure. Three species of our common tits nest in hollows of deciduous trees, mainly birches. The great tit in the Urals usually chooses deep hollow in the lower part of the trunk of a birch or alder, formed in the as a result of rotting of a knot and adjacent wood. This hollow is inaccessible to woodpeckers, crows, and predatory mammals. Tit Muscovy inhabits frost cracks in birch and alder trunks. HaThe chick prefers to build a hollow itself, plucking out cavities in the rottingold or old trunks of birch and alder, and without this labor-intensive procedure it will not lay eggs.

Features of the lifestyle inherent in each species determineits position, its role in the biogeocenosis, that is, its ecologicalniche. Even the closest species, as a rule, occupy different econiches, that is, they differ in at least one or two ecological signs.

Thus, the economic niches of all our species of woodpeckers differ in their feeding patterns. Great spotted woodpecker feeds on larch seeds in winter Tsy and pine trees, crushing cones in their “forges”. black woodpeckerZhelna extracts longhorned beetle larvae and borers from under the bark and from woodfir trees, and the Lesser Spotted Woodpecker chisels the soft wood of the alder or extracts nase from the stems of herbaceous plants.

Each of the 14 species of Darwin's finches (named afterC. Darwin, who first drew attention to them), living in the Galapagos islands, has its own specific econiche, which differs from others primarily in the nature of the food and the ways of obtaining it.

Neither the ecological nor the ethological criticism discussed aboveries are not universal. Very often individuals of the same species, but onceny populations differ in a number of lifestyle featuresand behavior. And on the contrary, different species, even very distant ones, in the systemchemically, may have similar ethological signsor play the same role in the community (for example, the roles of mammal herbivores insects and insects, such as locusts, are quite comparable).

Geographical criterion

This criterion, along with the ecological one, occupies second place (after morphological) in most determinants. When identifying many species of plants, insects, birds, mammals and othersgroups of organisms whose distribution is well studied, knownThe distribution of the range plays a significant role. The subspecies' habitats, as a rule, do not coincide, which ensures their reproductive isolation and, in fact,, their existence as independent subspecies. Many typesoccupy different habitats (such species are called allopatric And). But a huge number of species have matching or overlapspreading ranges (sympatric species). In addition, there are species that are nothaving clear boundaries of distribution, as well as spit speciesmopolitans, living over vast expanses of land or ocean. INDue to these circumstances, the geographical criterion cannot be used universal.

Genetic criterion

Genetic unity of the species and, accordingly, genetic isolationit from other species - the main criterion of the species, the main speciesa sign caused by a complex of structural and life featuresactivities of organisms of this species. Genetic compatibilitybridge, similarity of morphological, physiological, cytologicaland other signs, identical behavior, living together - all thiso creates the necessary conditions for successful reproduction and restorationproduction of the species. At the same time, all these characteristics provide geneticisolation of a species from other similar species. For example, oncelyricism in the song of thrushes, warblers, warblers, finches and finch, deafand common cuckoos prevent the formation of mixed pairs,despite the similarity of their coloring and ecology (in birds with a specific song, hybrids are almost never found). Even in those cases I, when, despite isolation barriers, crossing occurredtion of individuals of different species, a hybrid population, as a rule, does not arise, since a whole series of post-populationisolation mechanisms. The most important of them is the death of male gametes (genetical incompatibility), death of zygotes, non-viability of hygotesreads, their sterility, and finally, the inability to find sexualpartner and produce viable fertile offspring. We know thatEach species has its own set of specific characteristics. An interspecific hybrid will have characteristics intermediate betweencharacteristics of the two original parental forms. For example, his song will not be understood by either a finch or a finch if it is a hybrid of these species, and he will not find a sexual partner. Such a hybrid hasthe name of gametes, the chromosomes of the finch contained in its cells “do notfinch chromosomes and, not finding a homologous partner, do notconjugate. As a result, gametes with a disrupted set ofchromosomes, which are usually not viable. And as a resultThis hybrid will be sterile.

Raven and crow

I’ll say right away: The raven is not the “husband” of the crow, but an independent species.

Raven is one of the largest representatives of the raven family., weighs from 0.8 to 1.5 kg. The color of its plumage, beak and legs is uniform black color.

The raven is distributed throughout almost the entire northern hemisphere: it is foundalmost throughout Europe, Asia, excluding Southeast, in NorthernAfrica and North America. Everywhere he leads a sedentary lifestyle. Inhabits forests, deserts and mountains. In treeless areas it stays nearrocks, coastal cliffs of river valleys. Mating and mating games onin the south of the country they are celebrated in the first half of February, in the north - inMarch. Pairs are constant. Nests are usually placed on the tops of tall trees. The clutch contains from 3 to 7, usually 4-6, bluish-green eggs ki with dark markings.

Raven is an omnivorous bird. Its main food is carrion, which it oftenfound in landfills and slaughterhouses. Eating carrion, he performslike a sanitary bird. It also feeds on rodents, eggs,and chicks, fish, various invertebrate animals, and placesmi and cereal grains.

The crow resembles a crow in general physique, but significantlysmaller than it: weighs from 460 to 690 g.

The described species is interesting in that the color of the plumage disintegratesinto two groups: gray and black. The gray crow is well knownnew two-color color: head, throat, wings, tail, beak and legs are black, the rest of the plumage is gray. The Carrion Crow is all black, with a metallic blue and purple sheen.

Each of these groups has a local distribution. The hooded crow is widespread in Europe and Western Asia, the black crow is widespread in Central and Western Europe, on the one hand, in Central, East Asia and North America, on the other.

The crow inhabits the edges and outskirts of forests, gardens, groves, thickets of river valleys, and less often rocks and slopes of coastal cliffs. It is partly sedentary and partly migratory.

At the beginning of March in the southern parts of the country and in April-May in the northern and eastern parts, egg laying begins. The clutch usually contains 4-5 eggs of pale green, bluish-green or partially green color with dark spots and specks. The crow is an omnivorous bird. Among animals, it eats various invertebrates - beetles, ants, mollusks, as well as rodents, lizards, frogs and fish. From plants it pecks grains of cultivated cereals, seeds of spruce, field bindweed, bird buckwheat, etc. In winter it feeds mainly on garbage.

White hare and brown hare

The genus of hares proper, which includes the hare and hare, as well as 28 other species , quite numerous. The most famous hares in Russia are the hare and the hare.. White hare can be found on the territory from the coast of the Arctic Ocean to the southern border of the forest zone, in Siberia - to the borders with Kazakhstannom, China and Mongolia, and in the Far East - from Chukotka to and North Korea. The hare is also widespread in the forests of Europe, as well as in the east of Northern America. The hare lives in the territory of European Russia from Kareliafrom the south of the Arkhangelsk region to the southern borders of the country, in Ukraine and in Transnistriacasier. But in Siberia, this hare lives only in the south and west of Lake Baikal.

The hare got its name due to its snow-white winter fur. Only the tips of his ears remain black all year round. The hare in some northern areas also becomes very light in color in winter, but it is never snow-white. And in the south it does not change color at all.

The hare is more adapted to life in open landscapes, since it is larger than the hare and runs better. At short distances this hare can developspeed up to 50 km/h. The hare's paws are wide, with dense pubescence to avoid falling into loose forest snowdrifts. And the hare already has paws, after all, in open places the snow is usually hard, compacted, “trodden down by the wind.”

The body length of the white hare is 45-75 cm, weight is 2.5-5.5 kg. The ears are shorter than those of a hare. The body length of the hare is 50-70 cm, weight up to 5 (sometimes 7) kg.

Reproduce Hares are usually two, and in the south three or even four times a year. U zaiWhite hare cows may have two, three five, seven hare offspring per hatch, while hare- usually just one or two bunnies. Browns begin to try grass two weeks after birth, and whites even faster - after a week.

Species (lat. species) is a taxonomic, systematic unit, a group of individuals with common morphophysiological, biochemical and behavioral characteristics, capable of mutual crossing, producing fertile offspring in a number of generations, naturally distributed within a certain area 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 a 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 to both tigers and lions. Many other species interbreed in captivity that do not interbreed under natural conditions due to geographic or reproductive isolation. Crossing (hybridization) between different species can also occur in natural conditions, especially with anthropogenic disturbances of the habitat that disrupt ecological isolation mechanisms. Plants hybridize especially often in nature. A significant percentage of higher plant species are of hybridogenic origin - they were formed through hybridization as a result of partial or complete fusion of parent species.

Basic criteria of the type

1. Morphological criterion of the species. Based on the existence of morphological characters characteristic of one species, but absent in other species.

For example: in the common 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 many color forms (black, gray, bluish, greenish, reddish and other shades). These characteristics 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 geographic range. For example, in Europe, some species of malaria 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 can overlap, and then one species smoothly passes into another. In this case, a chain of vicariating species is formed (superspecies, or series), the boundaries between which can often be established only through special research (for example, herring gull, black-billed gull, western gull, Californian gull).

3. Ecological criterion. It is based on the fact that two species cannot occupy the same ecological niche. Consequently, each species is characterized by its own relationship with its 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 Scots pine inhabits swamps (swamp pine), another – sand dunes, and a third – leveled areas of pine 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 between nucleotide sequences in nucleic acids. Typically, “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 may have similar sequences.

5. Physiological-biochemical criterion. Based on the fact that different species may differ in the amino acid composition of proteins. At the same time, there is protein polymorphism within a species (for example, intraspecific variability of many enzymes), and different species may 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 durum wheat has 28 chromosomes in the diploid set, and all soft wheat has 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 one species. For example, moose of Eurasian subspecies have 2n=68, and moose of North American species have 2n=70 (in the karyotype of North American moose there are 2 less metacentrics and 4 more acrocentrics). Some species have chromosomal races, for example, the black rat has 42 chromosomes (Asia, Mauritius), 40 chromosomes (Ceylon) and 38 chromosomes (Oceania).

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

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

8. Ethological criterion. Associated with interspecific differences in behavior in animals. In birds, song analysis is widely used to recognize species. Depending on the nature of the sounds produced, different types of insects differ. Different species of North American fireflies vary in the frequency and color of their light flashes.

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

THE GEOGRAPHICAL CRITERION OF A SPECIES IS THAT

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

None of the considered species criteria is the main or most important. To clearly separate species, it is necessary to carefully study them 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 poorly differentiated internal structure, they are characteristic of endemics. Polytypic species are distinguished by a complex intraspecific structure.

Within species, subspecies can be distinguished - geographically or ecologically isolated parts of the species, individuals of which, under the influence of environmental factors in the process of evolution, acquired stable morphophysiological characteristics 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 species belongs, and a 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 the generic name, or a noun in the genitive case. The first word is written with a capital letter, the second with a lowercase letter.

• Petasites fragrans is the scientific name of a species of flowering plants from the genus Butterbur (Petasites) (Russian name of the species is Butterbur fragrant). The adjective fragrans (“fragrant”) was used as a specific epithet.
• Petasites fominii is the scientific name of another species from the same genus (Russian name is Butterbur Fomin). 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 unspecified taxa at species rank:

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

The concept of species. Species as a taxonomic category

To study the diversity of life, man needed to develop a system of classifying 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, interbreed freely and produce fertile offspring, are adapted to certain environmental conditions and occupy a common territory in nature - a habitat.

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

Type criteria

The set of characteristic characteristics of the same type, in which individuals of the same species are similar, and individuals of different species differ from each other, is called a species criterion. In modern biology, the following main criteria for a species are distinguished: morphological, physiological, biochemical, genetic, environmental, geographical.

Morphological criterion reflects a set of characteristic features of the external structure. For example, types of clover 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), developmental stage, stage in the reproductive cycle, environmental conditions, and belonging to varieties or breeds.

For example, in a mallard the male is brightly colored, and the female is dark brown; in the red deer, the males have antlers, but the females do not. In the cabbage white butterfly, the caterpillar differs from the adult in external characteristics. In the male shield 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 characteristics that they are called twin species. For example, some species of malaria mosquitoes, fruit flies, and North American crickets do not differ in appearance, but do not interbreed.

Thus, on the basis of one morphological criterion it is impossible to judge whether an individual belongs to a particular species.

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

Biochemical criterion reflects the body's characteristic chemistry and metabolism. This is the most unreliable criterion. There are no substances or biochemical reactions that are unique to a particular species. Individuals of the same species can differ 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 similar roles in metabolism in different species. For example, chlorophyll in all green plants is involved in photosynthesis. This means that determining the species identity of individuals based on 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, since it is a factor in reproductive isolation 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.

Ecological 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 characteristics, topography and food sources correspond to its tolerance limits. But organisms of other species can also live in the same environmental conditions. The development of new animal breeds and plant varieties by humans has shown that individuals of the same species (wild and domesticated) can live in very different environmental conditions.

THE GEOGRAPHICAL CRITERION OF A SPECIES IS...

This proves the relative nature of the environmental criterion. Consequently, there is a need to use other criteria when determining whether individuals belong to a particular species.

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

For example, Siberian larch is common in Siberia (Trans-Urals), and Daurian larch is common in the Primorsky Territory (Far East), cloudberry is in the tundra, and blueberry is in the temperate zone.

This criterion indicates that the species is confined to a specific habitat. But there are species that do not have clear boundaries of distribution, but live almost everywhere (lichens, bacteria). In some species, the range coincides with the range of humans. Such species are called synanthropic (housefly, bedbug, house mouse, gray rat). Different species may have overlapping habitats. This means that this criterion is relative. It cannot be used as the only one to determine the species identity of individuals.

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

Species range. The concept of endemics and cosmopolitans

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

Area(from Latin area - area, space) - part of the earth's surface within which individuals of a given species are distributed and undergo the full cycle of their development.

The habitat can be continuous or discontinuous, extensive or limited. Species that have a wide range across 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, the species inhabiting it is called endemic(from Greek endemos - local).

For example, kangaroos, echidnas and platypus live only in Australia. Ginkgo grows naturally only in China, rhododendron acuminate and Daurian lily - only in the Far East.

Species - a set of individuals that are similar in morphological, physiological and biochemical characteristics, freely interbreed and produce fertile offspring, adapted to certain environmental conditions and occupy a common territory in nature - habitat. Each species is characterized by the following criteria: morphological, physiological, biochemical, genetic, environmental, 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 species concept, natural populations that are morphologically distinct from each other are recognized species.

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 as different species. In aphoristic form this is expressed as follows: the criterion of the type is the discreteness of the boundaries of the distribution of characteristics.

When identifying species, difficulties often arise due to two circumstances. Firstly, the cause of difficulties may be 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, day butterflies, wasps, some fish and other organisms. Similar facts were used by Darwin in his works on sexual selection. In a number of animals, sharp differences are observed between adult and immature individuals. Similar facts are widely known to zoologists. Therefore, sampling populations of species at different stages of their life cycle is very useful. The theoretical basis of intraspecific variation (individual or group) is outlined in a number of manuals. Here we will consider only the characteristics that are most often used in establishing the species status of individuals from the sample.

Morphological characteristics- this is the general external morphology and, if necessary, the structure of the genital apparatus. The most important morphological characters are found in animals with an exoskeleton, such as arthropods or molluscs, but they can be found in many other animals without shells or shells. These are all kinds of differences in the fur 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 species concept, 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 genitalia of males and the copulatory organs of females, a ratio similar to that of a key and a lock is observed. Sometimes it is called the “key and lock” rule. It should, however, be remembered that the characteristics of the genitalia, 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 genitals has been proven, it serves as a very valuable feature, since when species diverge, their structure should be one of the first to change.

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

Ecological signs. It is known that each species of animal is characterized by certain ecological preferences, knowing which, it is often possible, if not entirely accurately, to decide which species we are dealing with, then at least to significantly 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.

When studying gall-forming or leaf-mining phytophagous insects (gall midge flies, gall wasps, leaf-mining larvae of butterflies, beetles and other insects), the main features are often the forms of mines, for which a classification has even been developed, or galls. Thus, several types of gallworms develop on rosehips and oaks, causing the formation of galls on the 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 wide range - from strict monophagy through oligophagy to polyphagy. It is known that silkworm caterpillars feed exclusively on mulberry or mulberry leaves. Caterpillars of white butterflies (cabbage butterflies, reptiles, etc.) gnaw the leaves of cruciferous plants without moving on to plants of other families. And a bear or wild boar, being polyphagous, feeds on both animal and plant foods.

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

Ethological signs. A number of authors point out the taxonomic value of ethological characters. The famous ethologist Hind considers behavior a taxonomic character that can be used to clarify the systematic position of species. It should be added that stereotypical actions are the most useful. They are as characteristic of each species as any morphological characters. This should be kept in mind when studying closely related or sibling 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 A SPECIES IS THAT

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

As numerous observations in nature and experiments in laboratory conditions show, the otological characteristics of a 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 graphic form, finally convinced researchers of the species-specificity of songs not only of birds, but also of crickets, grasshoppers, leafhoppers, as well as the voices of frogs and toads.

But not only the postures or voices of animals are ethological species characteristics. These include the peculiarities of nest construction in birds and insects from the order Hymenoptera (bees and wasps), the types and nature of oviposition in insects, the shape of cobwebs in spiders, and much more. Oothecae of praying mantises and egg capsules of locusts, and light flashes of fireflies are species-specific.

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

Geographical features. Geographical features are often a useful means of distinguishing populations, or more precisely, of 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 is different from its neighbors, then they are called allopatric forms. Allopatric forms are believed to be a polytypic species consisting of several subspecies.

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

In taxonomy practice, difficulties often arise in assigning a specific allopatric form to a species or subspecies. If allopatric populations come into contact but do not interbreed in the contact zone, then such populations should be considered species. In contrast, if allopatric populations come into contact and interbreed freely in a narrow contact zone or are connected by transitions in a wide contact zone, 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 geographical dispersion of blue magpie populations. One subspecies (C. c. cooki) inhabits the Iberian Peninsula, and the other (C. c. cyanus) inhabits the south of the Far East (Primorye and adjacent parts of China). It is believed that this is the result of the rupture of the former continuous habitat that arose during the Ice Age. Many taxonomists are of the opinion that it is more appropriate to consider questionable allopatric populations as subspecies.

Other signs. In many cases, closely related species are easier to distinguish by chromosome morphology than by other characteristics, as has been demonstrated in species of the genus Drosophila and in bugs of the family Lygaeidae. The use of physiological characteristics by which one can distinguish between closely related taxa is becoming increasingly widespread. Closely related mosquito species have been shown to vary significantly in growth rate and duration of the egg stage. There is increasing recognition that the bulk of proteins are species specific. 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 or waxy structures in the form of caps on the body, 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 a review of the latest publications shows, the authors do not limit themselves 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 hereditary similarity of morphological, physiological and biological characteristics, freely interbreeding and producing fertile offspring, adapted to certain living conditions and occupying a certain area in nature.

Species are stable genetic systems, since 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, determining whether given individuals belong to the same species or not can sometimes be difficult. Therefore, to decide whether individuals belong to a given species, a number of criteria are used:

Morphological criterion- the main criterion based on external differences between species of animals or plants. This criterion serves to separate organisms that clearly differ in external or internal morphological characteristics. But it should be noted that very often there are very subtle differences between species that can only be revealed through long-term study of these organisms.

Geographical criterion– is based on the fact that each species lives within a certain space (area). The habitat is the geographical boundaries of the distribution of a species, the size, shape and location in the biosphere of which is different from the habitats 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 (orca whale). Thirdly, for some rapidly spreading species (house sparrow, house fly, etc.), the range changes its boundaries so quickly that it cannot be determined.

Ecological criterion– assumes that each species is characterized by a certain type of nutrition, habitat, and timing of reproduction, i.e.

occupies a certain ecological niche.
The ethological criterion is 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 maintains the constancy of its genetic composition over an evolutionarily long time. The clearest boundaries between species are from a genetic point of view.

Physiological-biochemical criterion– this criterion cannot serve as a reliable way to distinguish species, since the main biochemical processes occur in the same way in similar groups of organisms. 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 between species. It is possible to determine whether an individual belongs to a specific 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 collection of individuals of the same species occupying a certain territory and exchanging genetic material. The set of 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 overall gene pool, depending on their adaptive value. The heterogeneity of organisms included in a population creates conditions for the action of natural selection, therefore a population is considered the smallest evolutionary unit from which evolutionary transformations of a species—speciation—begin. The population, therefore, represents a supraorganismal formula for the organization of life. A population is not a completely isolated group. Sometimes interbreeding occurs between individuals from different populations. If some 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 vary depending on the time of year and natural conditions. The size of a population is determined by the ratio of birth and death rates of its constituent organisms. If these indicators are equal for a sufficiently long time, then the population size does not change. Environmental factors and interaction with other populations can change the population size.

The qualitative stage of the evolutionary process is species. Bud- is a collection individuals|individuals that are similar in morphophysiological characteristics are capable of interbreeding, producing fertile offspring, and forming a system of populations that form a common habitat.

Each type of living organisms can be described based on a set of characteristic|characteristic features|traits, properties, which are called signs. Characteristics of a species by which one species is distinguished from another are called criteria kind. The most commonly used are six general species criteria: morphological, physiological, geographical, environmental, genetic and biochemical.

Morphological criterion involves a description of the external (morphological) characteristics of individuals that are part of a certain species. By appearance, size and color of plumage, you can, for example, easily distinguish a great spotted woodpecker from a green one, a lesser spotted woodpecker from a yellow woodpecker, a great tit from a tufted tit, a long-tailed tit, a blue tit, and from a chickadee. Based on the appearance of the shoots and inflorescences, the size and arrangement of the leaves, the types of clover are easily distinguished: meadow, creeping, lupine, mountain.

The morphological criterion is the most convenient and is therefore widely used in taxonomy. However, this criterion is not sufficient to distinguish between species that have significant morphological similarities. To date, facts have accumulated indicating the existence of twin species that do not have noticeable morphological differences, but do not interbreed in nature due to the presence of different chromosome sets. Thus, under the name “black rat,” two twin species are distinguished: rats with 38 chromosomes in their karyotype and living throughout Europe, Africa, America, Australia, New Zealand, Asia to the west of India, and rats with 42 chromosomes, the distribution of which is associated with the Mongoloid sedentary civilizations inhabiting Asia east of Burma. It has also been established that under the name “malaria mosquito” there are 15 outwardly indistinguishable species.

Physiological criterion lies in the similarity of life processes, primarily in the possibility of crossing between individuals of the same species with the formation of fertile offspring. Physiological isolation exists between different species. For example, in many species of Drosophila, sperm from individuals of a foreign species causes an immunological reaction in the female genital tract, which leads to the death of sperm. At the same time, crossing is possible between some species of living organisms; in this case, fertile hybrids can be formed (finches, canaries, crows|ravens, hares, poplars|poplars, willows, etc.)

Geographic criterion (geographical certainty of the species) based on the fact that each species occupies a certain territory or water area. In other words, each species is characterized by a certain geographical area. Many species occupy different habitats. But a huge number of species have overlapping or overlapping ranges. In addition, there are species that do not have clear boundaries of distribution, as well as cosmopolitan species that live on vast expanses of land or ocean. Some inhabitants of inland bodies of water - rivers and freshwater lakes (species of pondweed, duckweed, reed) are cosmopolitans. An extensive set of cosmopolitans is found among weeds and garbage plants, synanthropic animals (species that live near humans or his dwelling) - bedbug, red cockroach, housefly, as well as dandelion, field grass, shepherd's purse, etc.

There are also species that have a discontinuous range. For example, linden grows in Europe and is found in the Kuznetsk Alatau and Krasnoyarsk Territory. The blue magpie|magpie has two parts of its range - Western European and Eastern Siberian. Due to these circumstances, the geographical criterion, like others, is not absolute.

Ecological criterion is based on the fact that each species can exist only in certain conditions, performing a corresponding function in a certain biogeocenosis. In other words, each species occupies a specific ecological niche. For example, acrid buttercup grows in floodplain meadows, creeping buttercup grows along the banks of rivers and ditches, and burning buttercup grows in wetlands. There are, however, species that do not have a strict ecological association. Firstly, these are synanthropic species. Secondly, these are species that are under human care: indoor and cultivated plants, pets.

Genetic (cytomorphological) criterion based on the difference between species by karyotypes, i.e., by the 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, many different species have the same number of chromosomes and their shape is similar. Thus, many species from the legume family have 22 chromosomes (2n = 22). Secondly, within the same species there may be individuals with different numbers of chromosomes, which is the result of genomic mutations. For example, goat willow has a diploid (38) and tetraploid (76) number of chromosomes. In silver crucian carp, there are populations with a set of chromosomes of 100, 150,200, while the normal number is 50. Thus, in the case of the occurrence of polyploid or aneushyoid (the absence of one chromosome or the appearance of an extra one in the genome) forms, based on a genetic criterion, it is impossible to reliably determine the identity of individuals | individuals to a specific species.

Biochemical criterion allows you to distinguish species by biochemical parameters (composition and structure of certain proteins, nucleic acids and other substances). It is known that the synthesis of certain high-molecular substances is characteristic only of certain groups of species. For example, plant species differ in their ability to form and accumulate alkaloids within the families Solanaceae, Asteraceae, Liliaceae, and Orchids. Or, for example, for two species of butterflies from the genus Amata, a diagnostic sign is the presence of two enzymes - phosphoglucomutase and esterase-5. However, this criterion is not widely used - it is labor-intensive and far from universal. There is significant intraspecific variability in almost all biochemical parameters, down to the sequence of amino acids in protein molecules and nucleotides in individual sections of DNA.

Thus, none of the criteria alone can serve to determine the species. A species can only be characterized by their totality.

Species Definition

At all times, different researchers had their own views on the species as such. Jean-Baptiste Lamarck recognized only groups of individuals living in certain conditions, that is, populations. Carl Leinaeus, while recognizing the reality of species, denied the fact of evolution.

According to Charles Darwin and his followers, species actually exist as a collection of individuals. Each species is more or less clearly separated from others and has certain properties and habitat. As a result of evolution, species change. Each species is preceded by a whole chain of ancestral forms, forming a phylogenetic series.

The modern biological concept gives the following definition of species:

Definition 1

A species is a collection of populations of individuals similar to each other in structure, functions, place in the biogeocenosis (ecological niche), which inhabit a certain part of the biosphere (area), interbreed freely, produce fertile offspring and do not hybridize with other species.

But recently, the thesis about the impossibility of hybridization with other species has been revised. Scientists have stopped viewing species as genetically closed systems. Some species can interbreed and produce fertile hybrid offspring. But this is only an exception from the general pattern.

Type criteria

In order to clearly distinguish one species from another, taxonomists (classifiers) developed a clear list of rules and characteristics. These characteristics are called species criteria. Let's take a closer look at them.

• The morphological criterion is based on an analysis of the presence or absence of similarity in external or internal characteristics of individuals of the same species (from the structure of chromosomes to the structural features of individual organs and their parts). Morphological characteristics unique to a particular species are called diagnostic.
• The genetic criterion is the number of chromosomes characteristic of each species, their size, and shape. This criterion makes it possible to judge the main, key characteristics of the species.
• The physiological criterion is based on an analysis of the similarities and differences in the life processes of organisms. These include the ability to fallow and give birth to fertile offspring.
• The biochemical criterion is the features of the structure and composition of macromolecules (primarily proteins) and the course of chemical reactions characteristic of individuals of a given species.
• The geographical criterion is that individuals of one species occupy a certain part of the biosphere, which differs from the ranges of closely related species. But this criterion cannot be decisive, since there are species. Distributed everywhere (often with human assistance) - for example, some rodents or insect pests.
• The ecological criterion implies a set of environmental factors in which the species lives. The living conditions in each individual place are unique and inimitable. They influence the organisms living there and cause adaptive reactions in them. Each species occupies its own ecological niche in the biogeocenosis.

Note 1

To clearly and reliably determine the species identity of an individual, it is not enough to use any one criterion. Only their combination and mutual confirmation can give a true description of the species.

Integrity of the species

As we already know, species exist in the form of populations. Each of these populations, under the influence of the driving forces of evolution, adapted to life in certain conditions (adapted). Thanks to this circumstance, the species consists of numerous populations. It occupies a wide range, despite the diversity of natural conditions within its boundaries.

Note 2

But, despite this, any species, whether consisting of one population or composed of a large number of them, constitutes a single whole. This integrity is achieved by the isolation of one species from the rest.

The integrity of a species is also determined by the connections between its individual individuals (in a flock, herd, family). This entire system of various connections ensures the existence of the species as an integral system.

In the process of evolution, individuals of each species can develop mutual adaptations (caring for offspring, a communication system, protection from enemies). Sometimes species adaptations can lead to the death of individual individuals, but they turn out to be beneficial to the species as a whole.