Concept of a community.

Lecture 3. Ecology of populations - demecology. Population. Classification of population.

Outline

1. Concept of a community.

2. Static parameters of community.

3. Dynamic parameters of population: birth rate, death rate, growth rate of population.

4. Life expectancy and survival rate.

5. Ecological strategy of survival.

6. Regulation of population number.

Concept of a community.

Totality of the individuals possessing hereditary similarity of morphological, physiological and biochemical features, capable to interbreeding with formation of the prolific posterity, adapted for the certain life conditions and occupying in the nature the certain area is called a species. Species often occupy the big area within the limits of which species are distributed non-uniformly, with groups - populations. Integrity of the species is supported by communications between communities.

The community is a totality of individuals of one species capable to self-reproduction which long exists in the certain part of area rather separately from other totality of the same species. Contacts between individuals of one community more often, than between individuals of different communities. The community is structural unit of species and unit of evolution.

Area. A space on which the community or species as a whole meets during all ability to live is called an area of distribution. The area can be continuous or broken off (disjunctive), that is, if between its parts there are various barriers (water, orographical, etc.), the spaces are not populated by representatives of the given species. There are various centers of areas: the geometrical center; the center of species occurrence within the limits of an area; the center of abundance is a part of area to which the greatest quantity of individuals is concentrated.

Depending on size of area and character of distribution there are cosmopolitans, ubikvists and endemics. Cosmopolitans are species of plants and animals which representatives meet on a greater part of inhabitant areas of the Earth (for example, the room fly, grey rat). Ubikvists a re species of plants and animals with wide ecological valency, they are capable to exist in various conditions of environment, have extensive areas (for example, a reed ordinary, the wolf). Endemics are species of plants and animals which have the small limited areas (often they are met on islands of an oceanic origin, in mountain areas and the isolated basin).

For animals there are trophic and reproductive areas between which there is a communication in the form of ways of flight for birds or ways of migration for some mammals and fishes.

Classification of community. Community is differed in sizes and a degree of «genetic independence», duration of existence, a way of breeding of species, etc.

Depending on sizes of occupied community of territory and communication degree between species there are elementary (local), ecological and geographical communities. The elementary (local) community is an elementary grouping of the species, described practically full panmixia. Ecological community is a totality of spatially adjacent elementary communities. A geographical community is a totality of groups of spatially adjacent ecological communities.

According to ability to self-reproduction and independent evolution there are permanent (constants) and (time) communities. Permanent (constants) communities are ones which are rather steadily in space and in time and which are capable to unlimitedly long self-reproduction, are elementary units of evolution. T ime communities are ones which are unstable in space and in time and unable to long self-reproduction. Eventually or they will be transformed in permanent, or they will disappear.

Depending on breeding, communities are divided into panmictic, clonal and clonal-panmictic. Panmictic communities consist of the species, breeding by sexual way for which cross impregnation is characteristic. Clonal communities consist of species for which only sexual breeding is characteristic. Clonal-panmictic communities are formed by species with alternation sexual and sexual breeding.

communities, being group associations, possess a number of specific properties which are not inherent in each separate individual: number, density, birth rate, death rate, growth rate, etc. In addition to this, community has certain organization: sexual, age, genetic, spatially and other structures.

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