Population-specific level of organization of life. Description and examples

In modern biology, living matter is usually regarded as a hierarchical structure. Each level is a system of interrelated elements. At the same time, a separate structural unit is also a collection of "details" of a lower order. Population-species level of organization of life is one of such stages in the hierarchical ladder of organisms. It is on him that all evolutionary changes begin to manifest themselves fully.

Hierarchical model

Living systems are usually divided into four groups:

• Molecular-genetic level. It contains such components of living organisms as lipids, carbohydrates, proteins and nucleic acids. This level can not yet be called alive, but the macromolecules, its constituents, create the basis for the next stage of development.

• Ontogenetic level. Here are placed cells, organs, tissues and multicellular organisms, from hydra to man. It is at this level that life first appears.

• Population-species level. This article is devoted to the description of its features.

• Biogeocenotic level. Includes communities of organisms, biocenoses and the biosphere. This is the level at which the organization of living matter achieves the greatest complexity.

Some features

The structures located on each of the levels are systemic. They tend to consist of a number of elements, constantly interact with the environment, manage internal processes through self-regulation. They have a boundary that determines where the system ends and the outside world begins. The population-species level is a structure with similar properties. The boundary that separates it from the environment is not a certain physical structure, but complex relationships between individuals and genetic factors.

Population-species level of organization of life is the most important for understanding evolutionary processes. It is at this stage that all the basic selection mechanisms are clearly visible. The main elements of the level are species and population.

Selection Criteria

There are many kinds of living creatures on our planet. The differences between them are determined by a whole set of characteristics. All of them represent different variants of similarity of individuals of one species:

1. Morphological sign. In other words, this similarity of the external structure.

2. Uniformity of physiological and biochemical processes. In individuals of one species, the metabolism proceeds in a similar way, the molecular composition of tissues and organs is the same.

3. Geographical feature. All individuals of this species are located within the same range.

4. Ecological feature. Organisms belonging to the same species respond in a similar way to changes in habitat conditions. For normal operation, they require a certain level of temperature, humidity, lighting and other parameters.

5. Genetic trait. For individuals of one species, the same nucleotide sequence of DNA is characteristic. They have the same number of chromosomes.

Absence of the main

Any of these features, taken separately and found in a group of individuals, does not guarantee that we have before us the described element that constitutes the population-species standard of living. Only all the parameters taken together allow us to state that the group of organisms under consideration is a single whole. According to the morphological sign, so-called twin species may be similar. An example of them are ascarids, on the whole identical in structure, but differing in their habitat. It also happens that individuals of one species differ externally. A common example is the discrepancy in the color and size of females and males of some birds or insects. Unified habitat in isolation from other indicators can also lead to erroneous reference of individuals to one species. The area is often scattered due to some characteristics of the landscape. Conversely, in one territory, individuals of completely different species often live together.

Definition

Similar examples can be found for any of the listed parameters. Elements that make up the population-species level of organization of life can be distinguished only by using the entire set of characteristics. The most important significance is the free crossing of individuals and fertile offspring. On the basis of these characteristics, one can derive a definition of the concept. A species is a collection of individuals that are similar in internal and external structure, as well as the processes of vital activity occupying one area and capable of interbreeding freely with each other, leaving fertile offspring.

Divisions

The population-species level, examples of which are found in any territory, is the level of the hierarchy of life where all the mechanisms of natural selection are fully developed. It is here that the so-called unit of evolution is located. This is a population that is both a structural element of the species. The latter is, rather, a systematic unit. In nature, one can not find a species that is not divided into populations.

This element, entering the population-species level, has several characteristics:

• All individuals belong to the same species;
• They inhabit a relatively isolated area on the territory of this species;
• Individuals cross freely and leave fertile offspring.

Indicators

Division of the species into populations is most often the result of geographical or biological isolation of one group of individuals from others. In the first case, they are divided by mountains, lakes, rivers or other natural obstacles. In the second, as a result of somewhat different needs in environmental conditions, differences in behavior or the presence of mutations, the possibility of crossing individuals of different groups disappears.

Populations have a set of indicators such as numbers, fertility, mortality and growth. The first is the totality of all individuals. The population is distinguished by its ability to self-regulate its numbers. Restraining factor is the resistance of the environment: as a result of the increase in the number of individuals, the forage base in this territory decreases, other conditions worsen. The answer to this will be a decrease in the number - its recovery to a certain average level.

Important indicators of this element, which is part of the population-specific level of organization of the living, are fertility and mortality. They represent the number of individuals that have appeared and died within a certain period, respectively. The difference between them is called increment. It is negative and positive. In the first case, the population decreases, and in the second case it increases.

Structure

The individuals of the element under consideration, which is part of the population-species level of organization of life, differ in their sex and age. These indicators formed the basis for the allocation of the relevant structures. The ratio of male and female individuals, as a rule, is one to one, but due to the influence of external factors, disharmony can arise on this parameter. The simultaneous presence in the population of individuals of different ages contributes to greater adaptability. At the same time, an increase in the number of "youngsters" makes it possible to predict a rise in the population in the future.

There is also a behavioral structure, characteristic exclusively for animals. Individuals in the population may be single individuals or form flocks, families and herds. The first, sooner or later, are looking for a society of their own, because otherwise reproduction is impossible. The flock is characterized by a large number of imitative reactions, a clear internal order developed by the alarm system. During the breeding season, as a rule, it breaks up into pairs. The relationship between offspring and parents is stronger in the family. A good example of this type of behavioral structure is the lion pride, consisting of one male, several females and their young. The herd is the most constant association of animals. It is characterized by a strict hierarchy led by the leader.

Unit of Evolution

As already noted, the population-specific level of organization is the level in the hierarchy of living systems, on which the evolutionary process can be fully traced. Changes begin with the population. Individuals, its components, have a gene pool, that is, a collection of hereditary material of all organisms. It is characterized by the ability to directional change. A population is called a unit of evolution, because a single organism can not change during life due to the fixed set of its genes.

Evolutionary material

The gene pool changes as a result of the appearance and accumulation of mutations. They appear quite rarely and can affect any sign. There are dominant and recessive mutations. The first, appearing, immediately appear. Individuals with a new trait are then subjected to natural selection. If the mutation is useful, then it is fixed. Gradually, the number of individuals with this sign increases in the population.

Recessive mutations that occur in nature are much more often dominant, initially inactive. They accumulate in the gene pool for often quite a long period. When a certain level of concentration of such mutations is reached, they can appear as a new feature, and the process will proceed similarly to that described above.

Also, the appearance of different characteristics of individuals is possible on the basis of mixing (combination) of the material in the gene pool as a result of free crossing. In this case, the number of possible variations will be the greater, the more impressive the population size.

Directional change

In relatively calm, that is, constant, conditions, individuals with a different set of characters coexist in the population. At the same time, a certain average composition of genes is maintained. In the case when individuals are subject to the constant influence of aggressive environmental factors, only the fittest organisms will survive. This is how natural selection works , vigilantly "controlling" the population-species level. Examples of its impact are the entire evolution of the animal kingdom. Such changes in the gene pool are a necessary prerequisite for all larger transformations.

The most important and necessary structures can not be distinguished in the natural hierarchy. Each higher level of development is impossible without the "development" of the previous ones. However, the new stage is always qualitatively different from the simple sum of the features of the underlying ones. Thus, the population-specific level of organization of living matter becomes a "field of activity" of natural selection, the main evolutionary process.