Variant – 3

1. Rate of a growth population

Rate of a growth community is a change of the community number in unit of time. Rate of a growth community can be positive, zero and negative. It depends on parameters of birth rate, death rate and migration (immigrations and emigrations). The rise (profit) of number occurs in the result of the birth rate and immigration of species, and reduction (loss) of number is in the result of the death rate and emigration of species.

There are absolute and specific growth rates of community.

Absolute (general) growth rate is expressed by the relation:

dN/dt,

where dN is a change of the community number for a time interval dt.

Specific growth rate is a relation of growth rate to initial number (N):

dN/(Ndt).

In the absence of limiting factors of environment specific growth rate is equal to size r which characterizing properties of the community and it is called specific (congenital) growth rate of the community or biotic potential of a kind:

r == dN/(Ndt) или dN/dt = rN.

The value of biotic potential is differed for different species. For example, roe is capable to make for a life of 10-15 kids, female of melliferous bee - 50 thousand eggs, a fish-moon - to 3 billion of calves.

However in the nature, due to action of limiting factors, the biotic potential of community is never realized completely. Usually its size is defined as a difference between birth rate and death rate in the population:

R = b - d.

Where b is a number of born species, d is a number of lost species in the community for the same period of time.

When b = d, r = 0 and the community is in stationary conditions. When b> d, r> 0, number of the community increases. When b <d, r <0, number of the community is decreased. The formula d = b - r makes it possible to define death rate which it is difficult to measure directly, and it is possible to simply define r by direct supervision.

Growth rate can be expressed in the form of a curve of population growth. There are two basic models of the community growth: J-shaped and S-shaped.

2. Commensalism and Amensalism

Types of communications and mutual relations between organisms

Alive organisms are definitely connected to each other.

Types of relations between organisms. Influence of one species on another can be positive, negative and neutral. Thus different combinations of types of influence are possible. There are neutralism, mutualism, commensalism, predatoriness, parasitism, a competition, amensalism.

Commensalism

A symbiotic relationship in which one organism derives benefit while causing little or no harm to the other.

Amensalism

Definition of Amensalism : between two species involves one impeding or restricting the success of the other without being affected positively or negatively by the presence of the other. It is a type of symbiosis. Usually this occurs when one organism exudes a chemical compound as part of its normal metabolism that is detrimental to another organism.<br><br> The bread mold Penicillium is a common example of this; penicillium secrete penicillin, a chemical that kills bacteria. A second example is the black walnut tree, which secrete juglone, a chemical that harms or kills some species of neighboring plants, from its roots.

A symbiotic relationship in which one organism is harmed or inhibited and the other is unaffected.

3. Static parameters of community

Static parameters of community.

Quantity indicators (characteristics) of community can be divided into static and dynamic. Static parameters characterize a condition of community at present time, including number, density and also parameters of structure.

Number is a number of species in community. Number of community can be changed considerably in time. It depends on biotic potential of kind and external conditions.

Density is a number of species or biomass of community on unit of the area or volume.

Community is characterized by the certain structural organization - a relationship of species groups on sex, age, the size, a genotype, distribution of species on territory, etc. Thus, there are various structures of community: sexual, age, dimensional, genetic, spatially etc. On the one hand structure of community is formed on the basis of the general biological properties of species, on the other hand - under influence of environment factors, i.e. it has adaptive character.

According to the form of animal coexistence there are single ways of life, family, colonies, flights, herds. The single way of life is shown that species in communities are independent and isolated from each other (hedgehogs, pikes etc.). However it is characteristic only for the certain stages of life cycle. Completely single existence of organisms in the nature does not meet, as thus breeding would be impossible. The family way of life is observed in populations with strengthening communications between parents and posterity (lions, bears etc.). Colonies are group settlements of settled animals. Flocks are temporary associations of animals facilitating performance of any function: protection against enemies, migration (wolves, a herring, etc.). Herds are longer, than flocks, or constant associations of animals in which, as a rule, all vital functions of species are carried out, including protection against enemies, migrations, breeding, education of young growth, etc. (deers, zebras, etc.).

Genetic structure is a relationship of various genotypes and equilocal genes in the community. Totality of genes of all community species is called genofund. The genofund is characterized with frequencies of equilocal genes and genotypes. Frequency of equilocal genes is its share in all totality of equilocal genes of the given gene. The sum of frequencies of all equilocal genes is equal to unit.