What are morphological criteria in biology. Define a species

1. Biological species and its criteria.

All life on the planet is represented by separate species.

A species is a historically established set of individuals that have a hereditary similarity in morphological, physiological and biochemical features; able to freely interbreed with each other and produce fertile offspring; adapted to certain environmental conditions and occupying a certain area.

Each type of organism can be described by a set of characteristic features and properties, which are called features of the species. Features of a species that distinguish one species from another are called type criteria.

The most commonly used general view criteria are: morphological, physiological, genetic, biochemical, geographical and ecological.

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

The morphological criterion is the most convenient and is therefore widely used in species taxonomy.

However, the morphological criterion is insufficient to determine the difference sibling species with significant morphological similarity.

Twin species practically do not differ in appearance, however, individuals of such species do not interbreed.

Species-twins are quite common in nature. About 5% of all species of insects, birds, fish, etc. have twin species:

- black rats have two twin species;

- the malarial mosquito has six twin species.

The use of a morphological criterion is also difficult in cases where individuals of the same species differ sharply from each other in terms of appearance, so called polymorphic species.

The simplest example of polymorphism is sexual dimorphism, when there are morphological differences between males and females of the same species.

It is difficult to use the morphological criterion in the diagnosis of domestic animal species. Breeds bred by humans can differ significantly from each other, remaining within the same species (breeds of cats, dogs, pigeons).

Thus, the morphological criterion is insufficient to determine the species belonging of individuals.

The physiological criterion characterizes the similarity of life processes in individuals of the same species, primarily the similarity of reproduction.

Between individuals different types there is a physiological isolation, which is manifested in the fact that individuals of different species almost never interbreed with each other. This is due to differences in the structure of the reproductive apparatus, the timing and places of reproduction, in the rituals of behavior during mating, etc.

If interspecific crossing does occur, then the result is interspecific hybrids that are characterized by reduced viability or are infertile and do not produce offspring:

For example, a hybrid of a horse and a donkey is known - a mule, which is quite viable, but barren.

However, in nature there are such species that can interbreed with each other and produce fertile offspring. (for example, some species of canaries, finches, poplars, willows, etc.).

Consequently, the physiological criterion is insufficient to characterize the species.

A genetic criterion is a set of chromosomes characteristic of each species, a strictly defined number, size and shape.

Individuals of different species cannot interbreed, as they have different sets of chromosomes, differ in number, size and shape:

- for example, two closely related species of black rats differ in the number of chromosomes (one species has 38 chromosomes, and the other 48) and therefore do not interbreed.

However, this criterion is not universal:

- first, in many different species, the number of chromosomes can be the same (for example, many species of the legume family have 22 chromosomes each);

- secondly, within the same species, individuals with a different number of chromosomes can be found, which is the result of mutations (for example, in silver carp there are populations with a set of chromosomes 100, 150, 200, while their normal number is 50).

Thus, on the basis of a genetic criterion, it is also impossible to reliably determine the belonging of individuals to a particular species.

The biochemical criterion makes it possible to distinguish species according to biochemical parameters (the composition and structure of certain proteins, nucleic acids, and other substances).

It is known that the synthesis of certain macromolecular substances is characteristic only of certain species ( for example, many plant species differ in their ability to form and accumulate certain alkaloids).

However, there is significant intraspecific variability in almost all biochemical parameters, up to the sequence of amino acids in protein molecules and nucleic acids.

Therefore, the biochemical criterion is also not universal. In addition, it is not widely used, as it is very laborious.

The geographical criterion is based on the fact that each species occupies a certain territory or water area.

In other words, each species is characterized by a specific geographical range.

Many species occupy different ranges, but most species have overlapping ranges.

There are species that do not have a specific geographical range, i.e. living on vast expanses of land or ocean, the so-called cosmopolitan species :

- some inhabitants of inland waters - rivers and freshwater lakes (many species of fish, reeds);

- Cosmopolitans also include medicinal dandelion, shepherd's purse, etc.;

- cosmopolitans are found among synanthropic animals - species that live near a person or his dwelling (lice, bedbugs, cockroaches, flies, rats, mice, etc.);

- Cosmopolitans also include indoor and cultivated plants, weeds, pets that are under human care.

In addition, there are species that do not have clear distribution boundaries or have a broken geographical range.

Due to these circumstances, the geographical criterion, like others, is not absolute.

The ecological criterion is based on the fact that each species can exist only under certain conditions, fulfilling its functional role in a particular biogeocenosis.

In other words:

Each species occupies a certain ecological niche in a complex system of ecological relationships with other organisms and factors of inanimate nature.

An ecological niche is a set of all environmental factors and conditions within which a species can exist in nature.

It includes the whole complex of abiotic and biotic environmental factors necessary for the organism to live, and is determined by its morphological fitness, physiological reactions and behavior.

The classic definition of an ecological niche was given by the American ecologist J. Hutchinson (1957).

According to the concept formulated by him, an ecological niche is a part of an imaginary multidimensional space (hypervolume), individual dimensions of which correspond to the factors necessary for the normal existence of a species (Fig. 1).

two-dimensional niche three-dimensional niche

Rice. 1. Ecological niche model according to Hutchinson

(F 1, F 2, F 3 - the intensity of various factors).

For example:

- for the existence of a terrestrial plant, a certain combination of temperature and importance is sufficient (two-dimensional niche);

- for a marine animal, temperature, salinity, oxygen concentration (three-dimensional niche) are necessary.

It is important to emphasize that the ecological niche is not just the physical space occupied by a species, but also its place in the community, determined by its ecological functions and its position relative to the abiotic conditions of existence.

According to the figurative expression of Y. Odum, an “ecological niche” is the “profession” of a species, its way of life, and “habitat” is its “address”. ”

For example, a mixed forest is a habitat for hundreds of species of plants and animals, but each of them has its own and only one "profession" - an ecological niche. Elk and squirrel have the same habitat, but their ecological niches are completely different.

Consequently, the ecological niche is not a spatial, but a functional category.

At the same time, it is important to realize that the ecological niche is not something that can be seen. An ecological niche is an abstract abstract concept.

An ecological niche defined only by the physiological characteristics of organisms is called fundamental and the one within which the species actually occurs in nature - implemented.

However, the ecological criterion is also insufficient to characterize the species.

Some different species in different habitats may occupy the same ecological niches:

- antelopes in the savannas of Africa, bison in the prairies of America, kangaroos in the savannas of Australia, marten in the European and sable in the Asian taiga lead the same way of life, have a similar type of nutrition, i.e. in different biogeocenoses they perform the same functions and occupy similar ecological niches.

It often happens the other way around - the same species in different habitats is characterized by different ecological niches. Most often this is due to the availability of food and the presence of competitors:

In addition, the same species in different periods of its development can occupy different ecological niches:

- so, the tadpole eats plant food, and the adult frog is a typical carnivore, so they are characterized by different ecological niches;

- migratory birds in connection with migrations are also characterized by different ecological niches in winter and summer;

- among algae there are species that function either as autotrophs or as heterotrophs. As a result, at certain periods of their lives, they occupy certain ecological niches.

Thus, none of these criteria can be used to determine whether an individual belongs to a particular species. It is possible to characterize a species only by the totality of all or most of the criteria.

In biology, a species refers to a certain set of individuals that have a hereditary similarity of physiological, biological and morphological features are able to interbreed freely and produce viable offspring. Species are stable genetic systems, because in nature they are separated by some series of barriers from each other. Scientists distinguish between them according to a number of basic features. Usually, the following species criteria are distinguished: morphological, geographical, ecological, genetic, physico-biochemical.

Morphological criterion

Such signs are the main ones in this system. Morphological criteria of a species are based on external differences between individual groups of animals or plants. This condition subdivides into species organisms that clearly differ from each other in internal or external morphological features.

Geographic criteria of the species

They are based on the fact that representatives of each stable genetic system live within limited spaces. Such areas are called areas. However, the geographical criterion has some shortcomings. It is not universal enough for the following reasons. First, there are some cosmopolitan species that are distributed all over the planet (for example, the orca whale). Secondly, in many biological aggregates, the ranges coincide geographically. Thirdly, in the case of some too rapidly dispersing populations, the ranges are very variable (for example, a sparrow or a house fly).

Ecological criterion of the species

It is assumed that each species is characterized by certain characteristics, such as the type of food, timing of reproduction, habitat, and everything that determines the ecological niche it occupies. This criterion is based on the assumption that the behavior of some animals differs from the behavior of others.

Genetic criterion of the species

This takes into account the main property of any species - its genetic isolation from others. Plants and animals of different stable genetic systems almost never interbreed. Of course, a species cannot be completely isolated from the influx of genes from related species. However, at the same time, he generally retains the constancy of his genetic composition for a really long period of time. It is in the genetic component that the clearest differences between representatives of different biological populations lie.

Physico-biochemical criteria of the species

Such criteria also cannot serve as an absolutely reliable way to distinguish between species, since fundamental biochemical processes
occur in similar groups in the same way. And in the environment of each individual species there is a certain number of adaptations to certain living conditions, which affects the change in biochemical processes.

conclusions

Thus, according to some single criterion, it is very difficult to distinguish between species. The belonging of an individual to any particular species should be determined only through a comprehensive comparison according to a number of criteria - all or at least the majority. Individuals that occupy a certain territory and are able to freely interbreed with each other are a species population.

The set of properties and common features inherent in one species is called the species criterion. Typically, six to ten species definition criteria are used.

Systematization

Species - a systematic or taxonomic unit that has general characteristics and uniting on its basis a group of living organisms. To isolate a biological group into one species, one should take into account a number of features associated not only with distinctive external features, but also with living conditions, behavior, distribution, etc.

The concept of "species" was used to group outwardly similar animals into groups. By the end of the 17th century, a lot of information about species diversity had accumulated, and the classification system required revision.

Carl Linnaeus in the 18th century united species into genera, and genera into orders and classes. He proposed a binary nomenclature of designations, which helped to significantly shorten the names of species. According to Linnaeus, the names began to consist of two words - the names of the genus and the species.

Rice. 1. Carl Linnaeus.

Linnaeus was able to systematize species diversity, but he himself erroneously distributed animals by species, relying mainly on external data. For example, he attributed the male and female ducks to different species. Nevertheless, Linnaeus made a huge contribution to the study of species diversity:

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• classified plants by gender (dioecious, monoecious, polyecious);
• identified six classes in the animal kingdom;
• attributed man to the class of primates;
• described about 6000 animals;
• He was the first to conduct experiments on plant hybridization.

Later, the biological concept of the species appeared, confirming that the classification by species is natural, genetically determined, and not artificial, created by people for the convenience of systematization. In fact, the species is an indivisible unit of the biosphere.

Despite the possibilities modern science many species have not yet been described. As of 2011, about 1.7 million species have been described. At the same time, there are 8.7 million species of plants and animals in the world.

Criteria

According to the criteria, it is possible to determine whether individuals belong to the same or to different species. First of all, the morphological criterion of the species is distinguished, i.e. representatives of different species should differ in external and internal structure.

However, often this criterion is not enough to distinguish a group of living organisms into a separate species. Individuals may differ in behavior, lifestyle, genetics, so it is important to take into account a set of criteria and not draw conclusions based on one trait.

Rice. 2. Morphological similarity of barbel species.

The table “Criteria of species” describes the most important criteria by which a species can be recognized.

Name	Description	Examples
Morphological	The similarity of the external and internal structure and different from other species. Not to be confused with sexual dimorphism	Titmouse titmouse and moskovka
Physiological	The similarity of life processes in cells and organs, the ability to one type of reproduction	The difference in the composition of insulin in a bull, horse, pig
Biochemical	The composition of proteins, nucleotides, biochemical reactions, etc.	Plants synthesized various substances - alkaloids, essential oils, flavonoids
Ecological	Single ecological niche for one species	intermediate host bull tapeworm- only cattle
ethological	Behavior, especially during mating season	Attracting a mate of one's own species by special birdsong
Geographical	Settlement in one area	The ranges of humpback whales and dolphins do not match
Genetic	A certain karyotype is the similarity in the number, shape, size of chromosomes	The human genotype consists of 46 chromosomes
reproductive	Individuals of the same species can only interbreed, reproductive isolation	Drosophila sperm, falling into a female of a different species, is destroyed by immune cells
Historical	A set of genetic, geographical, evolutionary data about one species	The presence of a common ancestor and differences in evolution

None of the criteria is absolute and has exceptions to the rules:

• outwardly dissimilar species have the same set of chromosomes (cabbage and radish - 18 each), while mutations can be observed within the species and populations with a different set of chromosomes can be found;
• black rats (twin species) are morphologically identical, but genetically they are not, and, therefore, cannot produce offspring;
• in some cases, individuals of different species interbreed (lions and tigers);
• ranges often intersect or are broken (the Western European and East Siberian range of the magpie).

Hybridization is one of the levers of evolution. However, for successful crossing and obtaining fertile offspring, many criteria must match - genetics, biochemistry, physiology. Otherwise, the offspring will not be viable.

Rice. 3. Liger - a hybrid of a lion and a tigress.

What have we learned?

From the 11th grade biology lesson, we learned about the concept of a species and the criteria for its definition, considered nine main criteria with examples given. The criteria should be considered together. Only if several criteria are met can similar organisms be combined into a species.

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

Aggregate hallmarks species is called its criterion.

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

Physiological and biochemical criterion

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

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

Genetic criterion

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

Reproductive criterion

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

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

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

Ecological and geographical criterion

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

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

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

Superorganism systems. Evolution organic world

evolutionary doctrine

Basic concepts:

species, species criteria, population, systematics, classification, history of evolutionary ideas, synthetic theory of evolution, driving forces of evolution, forms of natural selection, population waves, genetic drift, artificial selection, types of struggle for existence, results of evolution, microevolution, speciation, isolation, fitness, relative nature of fitness, forms and directions of evolution, biological progress and regression, macroevolution, aromorphosis, idioadaptation, degeneration, evidence for evolution

There are about 2 million species of animals on Earth, more than 500 thousand species of plants, hundreds of thousands of species of fungi, microorganisms. A species is a collection of organisms that actually exists in nature.

View – This is a collection of individuals that are similar in structure, have a common origin, freely interbreed with each other and give fertile offspring. All individuals of the same species have the same karyotype - a set of chromosomes of a somatic cell (2n), similar behavior, occupy a certain territory - area (from Latin area - area, space). Carl Linnaeus (17th century) introduced the concept of "view".

A species is one of the main forms of organization of living things. Each type of living organisms can be described based on the totality characteristic features, properties, which are called features. Species features that distinguish one species from another are called species criteria.

View criteria - a set of characteristic features, properties and features by which one species differs from another. There are six general species criteria most commonly used: morphological, physiological, genetic, biochemical, geographical, and ecological. At the same time, none of the criteria is absolute; to determine the type, the presence of the maximum number of criteria is necessary.

Morphological criterion- description of external (morphological) features and internal (anatomical) structure of individuals that are part of a particular species. In appearance, size and color of plumage, for example, it is easy to distinguish a large spotted woodpecker from a green one, a great tit from a crested one. By the appearance of the shoots and inflorescences, the size and arrangement of the leaves, the types of clover are easily distinguished: meadow and creeping. The morphological criterion is widely used in taxonomy. However, this criterion is not sufficient to distinguish between species that have significant morphological similarities. For example, in nature there are twin species that do not have noticeable morphological differences (black rats have two twin species - with a set of chromosomes 38 and 42, and the malarial mosquito used to be called six similar species, of which only one carries malaria).

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. There is a physiological isolation between different species. At the same time, interbreeding is possible between certain types of living organisms; in this case, fertile hybrids can be formed (canaries, hares, poplars, willows, etc.)

Geographic criterion- each species occupies a certain territory - range. Many species occupy different ranges. But many species have coinciding (overlapping) or overlapping ranges, some have a broken range (for example, linden grows in Europe, is found in Kuznetsk Alatau and Krasnoyarsk Territory). In addition, there are species that do not have clear distribution boundaries, as well as cosmopolitan species that live on vast expanses of land or ocean. Cosmopolitans are some inhabitants of inland waters - rivers and freshwater lakes (duckweed, reed). There are cosmopolitans among weeds, synanthropic animals (species that live near a person or his dwelling) - a bed bug, a red cockroach, a house fly, as well as a medicinal dandelion, a field yarutka, a shepherd's purse, etc. Thus, a geographical criterion, like others, is not absolute.

Environmental criterion is based on the fact that each species can exist only under certain conditions: each species occupies a certain ecological niche. For example, the caustic buttercup grows in floodplain meadows, the creeping buttercup grows along the banks of rivers and ditches, the burning buttercup grows in wetlands. However, there are species that do not have a strict ecological criterion; synanthropic species are an example.

Genetic criterion based on the difference between species according to karyotypes, i.e., according to 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. For example, in many different species, the number of chromosomes is the same and their shape is similar. So, many species from the legume family have 22 chromosomes (2n = 22). Also, within the same species, individuals with a different number of chromosomes can be found (the result of genomic mutations): goat willow has a diploid (38) and tetraploid (76) number of chromosomes; in silver carp there are populations with a set of chromosomes 100, 150,200, while their normal number is 50. Thus, on the basis of a genetic criterion, it is not always possible to determine whether individuals belong to a particular species.

Biochemical criterion is the composition and structure of certain proteins, nucleic acids and other substances. For example, the synthesis of certain macromolecular substances is inherent only certain types: alkaloids are formed by plant species of the nightshade and lily families. But this criterion is not widely used - it is laborious and not always universal. There is a significant intraspecific variability in almost all biochemical parameters (sequence of amino acids in protein molecules and nucleotides in individual sections of DNA). At the same time, many biochemical features are conservative: some are found in all representatives of a given type or class.

Thus, none of the criteria separately can serve to determine the species: to determine the species, it is necessary to take into account the totality of all criteria. In addition to these features, scientists identify historical and ethological criteria.

Characteristics of the type criteria

View criteria	Criteria characteristics
Morphological	The similarity of the external (morphological) and internal (anatomical) structure of individuals of the same species.
Physiological	The similarity of all life processes, and, above all, reproduction. Representatives of different species, as a rule, do not interbreed with each other, or give sterile offspring.
Genetic	Characteristic, unique this species set of chromosomes, their structure, shape, size. Individuals of different species with an unequal set of chromosomes do not interbreed.
Biochemical	The ability to form species-specific proteins; resemblance chemical composition and chemical processes.
Ecological	The adaptability of individuals of a given species to certain environmental conditions is a set of environmental factors in which the species exists.
Geographical	A certain area, habitat and distribution in nature.
Historical	Origin and development of the species.
ethological	Certain specific features in the behavior of individuals: differences in mating songs, in mating behavior.

View- a set of individuals characterized by a common origin, having a hereditary similarity of morphological, physiological and biochemical characteristics, freely interbreeding and producing fertile offspring, adapted to existing living conditions and occupying a certain territory - area. All species are made up of populations, that is, a population is structural unit kind.

Populations – These are groups of organisms of the same species, relatively isolated from each other, with the ability to freely interbreed with each other and produce fertile offspring.

View - a set of individuals that have common morphophysiological features and are united by the ability to interbreed with each other, forming a system of populations that form a common area.

Populations are characterized by certain properties:

1) abundance - the total number of organisms in the population;

2) birth rate - the rate of population growth;

3) mortality - the rate of reduction in numbers as a result of the death of individuals;

4) age composition - the ratio of the number of individuals of different ages (the ratio of age groups);

5) sex ratio - based on the genetic definition of sex, the sex ratio in the population should be 1:1, the violation of this ratio leads to a decrease in the population size;

6) population dynamics - under the influence of various factors, periodic and non-periodic fluctuations in the number and size of the range are possible, which can affect the nature of crossings;

7) population density - the number of individuals per unit of space occupied by the population.

Populations do not exist in isolation: they interact with populations of other species, forming biotic communities.

Studying nature, scientists discovered and described previously unknown organisms, giving them names. At the same time, it often turned out that different scientists called the same organism differently. The more materials accumulated, the more difficulties appeared in using the accumulated knowledge. There was a need to bring all the diversity of living organisms into a single system. The branch of biology that deals with the description and classification of organisms is called taxonomy .

The first systems were artificial, as they were built on several arbitrarily taken signs. One of the classification systems for plants and animals was proposed by Carl Linnaeus (1707-1778). The merit of the scientist is not only in creating the system, but also in the fact that he introduced double species names: the first word is the name of the genus, the second - the species, for example, Aurelia aurita - eared jellyfish, Aurelia cyanea - polar jellyfish. This system of names still exists today. Subsequently, the system of the organic world, proposed by K. Linnaeus, was significantly changed. At the core modern classification, which is natural, the principle of kinship of species with both living and extinct lies.

Thus, the goal of natural classification- Creation unified system living organisms, which would cover all the diversity of living organisms, would reflect the origin and history of their development. In the modern system, organisms are divided into groups based on the relationships between them by origin. Systematic categories, or taxa, are the names of groups of living organisms that are united by similar characteristics. For example, the class Birds are highly organized vertebrates, the body of which is covered with feathers, and the forelimbs are turned into wings. The largest systematic categories of organisms are empires (precellular and cellular organisms). Empires are divided into kingdoms.

organic world

Kingdom Viruses

Kingdom of Prokaryotes Kingdom of Eukaryotes

(non-nuclear) (nuclear)

Kingdom Bacteria

Kingdom Plants Kingdom Animals Kingdom Fungi Kingdoms in animals unite types, and in plants departments. Examples of systematic categories:

Systems in which the higher categories consistently include lower and lower categories are called hierarchical (from the Greek hieros - sacred, arche - power), that is, systems whose levels obey certain rules.

An important stage in the development of biology was the period of formation of systematization, which is associated with the name Carl Linnaeus(1707-1778). K. Linnaeus believed that Live nature created by the Creator, the species are immutable. The scientist based the classification on signs of similarity, and not relationship between species. Despite the mistakes made by K. Linnaeus, his contribution to the development of science is enormous: he streamlined ideas about the diversity of flora and fauna.

At the end of the 18th century, changes took place in views on the origin of life: ideas appeared about the origin of modern organisms from distant ancestors.

The idea of ​​the evolution of the organic world is expressed by Jean Baptiste Lamarck(1744-1829). The main merits of Lamarck include the following:

Introduced the term "biology";

Improved the classification already existing at that time;

He tried to determine the causes of the evolutionary process (according to Lamarck, the cause of evolution is the desire for self-improvement - an exercise and not an exercise of organs);

He believed that the process of historical change occurs from simple to complex; species change under conditions external environment;

He expressed the idea of ​​the origin of man from ape-like ancestors.

Lamarck's fallacies include:

The idea of ​​internal striving for self-improvement;

The assumption of the inheritance of changes that have arisen under the influence of the external environment.

The merit of Lamarck is the creation of the first evolutionary doctrine.

In the 19th century, science, industry, Agriculture. Advances in science and practical activities humans laid the foundation upon which evolutionary theory developed.