1. What is a species?

Answer. 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.

2. What types of plants and animals do you know?

Answer. Types of plants: European swimsuit, Altai anemone, bifolia lyubka, needle-leaved carnation, Lady's slipper, etc.

Types of animals: Brown bear, Siberian roe deer, common lynx, pine marten, black ferret, European mink. striped chipmunk, flying squirrel, gray partridge, black grouse and others.

Questions after § 53

1. Define a biological species.

Answer. Biological species- this is a set of individuals that have the ability to interbreed with the formation of fertile offspring; inhabiting a certain area; possessing a number of common morphological and physiological characteristics and similarities in relationships with the biotic and abiotic environment.

A biological species is not only a systematic category. This is a holistic element of living nature, isolated from other species. The integrity of the species is manifested in the fact that its individuals can live and reproduce only by interacting with each other thanks to the mutual adaptations of organisms developed in the process of evolution: the peculiarities of the coordination of the structure of the maternal organism and the embryo, signaling and perception systems in animals, common territory, similarity of life habits and reactions to seasonal climate changes, etc. Species adaptations ensure the preservation of the species, although sometimes they can harm individual individuals. River perch, for example, feeds on its own young, due to which the species survives when there is a lack of food, even despite the loss of part of the offspring. Each species exists in nature as a historically emerged integral formation.

2. What species criteria do you know?

Answer. Characteristic signs and the properties by which some species differ from others are called species criteria.

The morphological criterion is the similarity of external and internal structure organisms. Carl Linnaeus, for example, defined species as integral groups of organisms that differ from other life forms based on structural characteristics. In other words, the presence of structural features that make a certain group of organisms similar friend on each other and at the same time different from all other groups, and there is a criterion for classifying them as a given species.

Individuals within a species are sometimes so variable that it is not always possible to determine the species based on morphological criteria alone. There are species that are morphologically similar. These are twin species that are discovered in all systematic groups. For example, two twin species are known in black rats - with 38 and 49 chromosomes; the malaria mosquito has 6 twin species, the small spined lance fish, widespread in fresh water bodies, – 3 such types. Twin species are found among the most various organisms: fish, insects, mammals, plants, but individuals of such twin species do not interbreed.

The genetic criterion is a set of chromosomes characteristic of each species; their strictly defined number, sizes and shapes, DNA composition. The chromosome set is the main species characteristic. Individuals of different species have different sets of chromosomes, so they cannot interbreed and are reproductively limited from each other in natural conditions.

The physiological criterion is the similarity of the body’s reactions to external influences, the rhythms of development and reproduction. This criterion is based on 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. However, there are exceptions. For example, dogs can produce offspring by mating with wolves. Hybrids of some species of birds (canaries, finches), as well as plants (poplars, willows) can be fertile. Consequently, the physiological criterion is also insufficient to determine the species identity of individuals.

An ecological criterion is a characteristic position of a species in natural communities, its connections with other species, sets of environmental factors necessary for existence.

Geographic criterion - area of distribution, a certain area occupied by a species in nature.

The historical criterion is the community of ancestors, a single history of the emergence and development of the species.

3. What is the integrity of the species, how is it manifested?

Answer. View is a complete system. The view is a single integral system. The integrity of the species is ensured by its isolation from other species due to a specific chromosome set (reproductive isolation).

The integrity of a species is also determined by the connections that its individuals form in populations and subspecies. Relationships between males and females, parents and their offspring, individuals different ages in a flock, herd and colony they allow one to successfully reproduce, take care of offspring, provide protection from enemies, etc. The entire set of connections ensures the existence of the species as an integral system.

4. Why is it important to preserve species in nature?

Answer. Biological diversity on the planet is presence on it large quantity species of all kingdoms: animals, plants, fungi. The task of preserving them is one of the main ones in ecology. Planet Earth is truly rich, therefore, a person is obliged to protect this wealth, at least so that it goes to the next generations of people. So that grandchildren and great-grandchildren can see wonderful animals, beautiful corners of nature, and can use medicinal plants. Any plant or animal (even the smallest one) is part of the biogeocenosis, and in general, is included in the entire ecosystem of the Earth. The body participates in the cycle of substances, being a link in the food chain. Producer plants synthesize nutrients using solar energy. Consumers consume energy accumulated by plants and other animals, deritophages “recycle” dead animals, and decomposers finally decompose nutrient residues. Thus, each organism occupies a certain place in nature and performs a certain role. The disappearance of one link can cause the disappearance of several more, changing the entire chain. There will be not only a depletion of the food chain, but also an imbalance of species in the ecosystem. Some species may increase disproportionately in numbers and cause environmental disaster. For example, an unprecedented proliferation of locusts can deprive entire regions of crops. By preserving the wealth of species on the planet, we thus maintain the stability of ecosystems and ensure the safety of life of all species, including human life. In addition, scientists want to preserve the genetic information of each species, counting on future technologies that will make it possible to recreate animal world of the past, for example, in isolated recreation areas (parks), to recreate extinct and currently endangered species of animals and plants.

View (lat. species) - 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 are interbred in captivity, which natural conditions do not interbreed 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. 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 it belongs this type, and the second word, called a species epithet in botany, and a 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 - scientific name species of flowering plants from the genus Butterbur ( Petasites) (Russian name of the species is 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 - Butterbur Fomina). 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 means a taxon at the rank of species, belonging to the genus Petasites.
Petasites spp.- the entry means that all taxa at the rank of species included in the genus are meant Petasites(or all other taxa at the rank of species included in the genus Petasites, but not included in any given list of such taxa).

What are the species criteria? Name and characterize the main criteria of the species.

Species criteria are characteristics and properties characteristic of a species. None of the criteria is absolute, but their complex is evidence of the reality of the species.

The morphological criterion of a species determines the similarity of the external and internal structure. However, the presence of lookalike species (mosquitoes, aphids, etc.) sometimes complicates its use. At the same time, individuals of the same species can differ in appearance. For example, some animals and birds exhibit sexual dimorphism (male and female individuals are different).

The physiological criterion of a species characterizes the similarity of the life processes of individuals of the same species. It is also not accurate enough. Most species do not interbreed under natural conditions or their offspring are sterile, but there are exceptions - a number of species of canaries, poplars, etc.

The biochemical criterion of a species is based on the ability to synthesize specific proteins. This is due to a unique DNA sequence.

Genetic - shows that species differ in the number and structure of chromosomes.

Ecological - each species exists in certain conditions. For example, creeping buttercup in damp places, and caustic buttercup in dry meadows.

Geographic - determines the habitat of the species, its range. Each species has a specific range.

What are the species criteria? Name and characterize the main criteria of the species.

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Species criteria. The characteristics by which one species can be distinguished from another are called species criteria.

The morphological criterion is based on the similarity of external and internal structure between individuals of the same species. This criterion is the most convenient and is therefore widely used in taxonomy.

However, individuals within a species sometimes differ so greatly that it is not always possible to determine which species they belong to by morphological criteria alone. At the same time, there are species that are morphologically similar, but individuals of these species do not interbreed. These are twin species that researchers discover in many systematic groups. Thus, under the name “black rat,” two twin species are distinguished, having 38 and 42 chromosomes in their karyotypes. It has also been established that under the name “malaria mosquito” there are up to 15 externally indistinguishable species that were previously considered one species. About 5% of all species of insects, birds, fish, amphibians, and worms are twin species.

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

The geographical criterion is based on the fact that each species occupies a certain territory or water area, called the range. It can be larger or smaller, intermittent or continuous (Fig. 1.2). However, 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 on all continents or the ocean (for example, plants - shepherd's purse, dandelion, species of pondweed, duckweed, reeds, animals synanthropes - bedweed bedbug, red cockroach, housefly). Therefore, the geographical criterion, like others, is not absolute.

The ecological criterion is based on the fact that each species can exist only in certain conditions, fulfilling its inherent

functions in a certain biogeocenosis. 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. These include many weeds, as well as species under human care: indoor and cultivated plants, pets.

The genetic (cytomorphological) criterion is based on the difference between species according to karyotypes, i.e., 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. Firstly, in many species the number of chromosomes is the same and their shape is similar. For example, some species of the legume family have 22 chromosomes (2n = 22). Secondly, within the same species there may be individuals with different numbers of chromosomes, which is the result of genomic mutations (poly- or aneuploidy). For example, goat willow can have a diploid (38) or tetraploid (76) number of chromosomes.

The biochemical criterion makes it possible to distinguish species by the composition and structure of certain proteins, nucleic acids, etc. Individuals of one species have a similar DNA structure, which determines the synthesis of identical proteins that differ from those of another species. At the same time, in some bacteria, fungi, and higher plants, the DNA composition turned out to be very similar. Consequently, there are twin species based on biochemical characteristics.

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

Biology. General biology. Grade 11. A basic level of Sivoglazov Vladislav Ivanovich

5. View: criteria and structure

Remember!

What levels of organization of living nature do you know?

What is a species?

What other systematic categories do you know?

The basis of Charles Darwin's evolutionary theory is the idea of species. What is a species and how realistic is its existence in nature?

The first idea of a species was created by Aristotle, who defined a species as a collection of similar individuals. The term “species” itself is translated from Latin as “image”. This word precisely defines the basic criterion that researchers used until the 19th century. when determining the species affiliation of any organism. The famous scientist C. Linnaeus, who created the doctrine of species, believed that a species consists of many similar individuals that produce fertile offspring.

In modern biology view called a set of individuals possessing similar morphological and physiological characteristics, capable of interbreeding to form fertile offspring, inhabiting a certain habitat (habitat), having a common origin and similar behavior.

A biological species is not only the basic taxonomic unit in biological systematics. This is an integral structure of living nature, which is reproductively isolated from other similar structures and has its own destiny. The integrity of this system is given, firstly, by the processes of interaction between individual individuals. The relationships between organisms of different generations, between parents and children, males and females, features of territorial behavior - all this determines the internal structure of the species. Species characteristics do not always ensure the survival of an individual, but they are always favorable for the species as a whole. For example, a bee that has lost its sting will die, but at the same time it will protect the rest of the bees.

The second reason for preserving the unity and integrity of the species is reproductive isolation, i.e. the impossibility of crossing with individuals of another species. This is how protection is carried out gene pool of the species(the entire set of genes of the species) from the influx of foreign genetic information. There are various factors that prevent interspecific crossing. For example, in California there are two closely related species of pine. One of them releases pollen in early February, and the other in April, so there is seasonal isolation between these species. In higher animals, mating behavior has characteristic species-specific characteristics, so females of one species do not respond to the courtship of males of another closely related species - this is an example of behavioral isolation (Fig. 12).

The presence of reproductive isolation in natural conditions is a decisive factor in defining a species as a genetically closed biological system.

The characteristic features and properties that distinguish some species from others are called species criteria.

Type criteria. There are several basic criteria for the type.

Morphological criterion lies in the similarity of the external and internal structure of organisms. For a long time, this criterion was the main, and sometimes the only one. With its help, individuals of distant species can be easily identified. Even a cat and a mouse can be distinguished Small child, a mouse and a rat - any adult, but only a specialist can distinguish between a house mouse and a small mouse. There are special qualifiers that are based on the morphological characteristics of the organization. However, within a species there is always structural variability between different individuals, so it can sometimes be quite difficult to determine the species of a particular individual.

Genetic criterion. Sometimes, among very similar individuals, groups are found that do not interbreed. These are the so-called twin species, which are found in almost all large systematic groups and differ from each other in the number of chromosomes. For example, among insects there are two widespread species of ichneumonids, which until recently were considered as a single species (Fig. 13).

Rice. 12. Different types mating behavior of two closely related gull species

Rice. 13. Twin species. Insects (A, B), having different karyotypes (B): 2n = 10 and 2n = 14

Each species has a specific set of chromosomes - a karyotype, which differs in the number of chromosomes, their shape, size, and structure. The different number of chromosomes in the karyotype of different species and species-specific differences in genomes provide genetic isolation during interspecific crossing, because they cause the death of gametes, zygotes, embryos or lead to the birth of infertile offspring (hinnie is a hybrid of a horse and a donkey). It is the use of genetic criteria that makes it possible to reliably distinguish sibling species.

Physiological criterion reflects the similarity of all life processes in individuals of the same species: the same methods of feeding, reproduction, similar reactions to external stimuli, the same biological rhythms (periods of hibernation or migration). For example, in two closely related species of the Drosophila fruit fly, sexual activity is observed at different times of the day: in one species - in the morning, in the other - in the evening.

Biochemical criterion determined by the similarity or difference in the structure of proteins, chemical composition cells and tissues. For example, individual species of lower fungi differ from each other in their ability to synthesize different biologically active substances.

Ecological criterion characterized by certain forms of relationships between organisms of a given species and representatives of other species and factors inanimate nature, i.e., the conditions in which this species is found in nature. In Texas, closely related species of oak grow in different soils: one species is found only on limestone soil, another on sandy soil, and a third grows on igneous rock outcrops.

Geographical criterion determines the area of distribution, i.e. habitat, kind. The size of their ranges varies greatly among species. Species that occupy large areas and are found everywhere are called cosmopolitans, and those living in small areas and not found in other places - endemic.

Thus, to determine the species identity of an organism, it is necessary to use all criteria together, because individual criteria may coincide in different species.

View structure. In reality, in nature, individuals of any species within the range are distributed unevenly: somewhere they form clusters, and somewhere they may be completely absent. Such partially or completely isolated groups of individuals of the same species are called populations (from the Latin populus - people, population), i.e., under natural conditions, any species consists of a collection of populations.

Population is a collection of individuals of the same species over a fairly long period of time ( large number generations) inhabiting a certain territory within the range of a species, freely interbreeding and partially or completely isolated from individuals of other similar populations.

It is the population that is elementary unit of evolution.

Review questions and assignments

1. Define the concept of “species”.

2. Explain what biological mechanisms prevent the exchange of genes between species.

3. What is the reason for the infertility of interspecific hybrids? Explain this phenomenon using your knowledge of the mechanism of meiosis.

4. What criteria do scientists use to characterize a species? What criteria do you consider most important when determining a species?

5. What is the species' range?

6. Characterize the species Domestic cat according to the main criteria.

7. Define the concept “population”.

Think! Do it!

1. Why can one species be distinguished from another only by a combination of various criteria? Which criteria do you think are most important?

2. Do you know of examples where the formulation “species as genetically closed system“turned out to be wrong? (Remember the material on selection from the 10th grade course.)

3. Do your research. Find out which species in your area are endemic and which are cosmopolitan. Prepare a report on the work done in the form of a stand.

4. Do you think the words “population” and “popular” can be considered the same root? Explain your point of view.

5. Provide evidence indicating that species objectively exist in nature.

Work with computer

Refer to the electronic application. Study the material and complete the assignments.

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