I. Learn the vocabulary.

Vocabulary before text 3

interbreed скрещиваться

individual особь, индивидуум

species биологический вид, виды

density плотность

age structure возрастная структура

birth-rate рождаемость

gene pool генетический фонд

assemblage собрание, группа

competition конкуренция

maintain поддерживать, сохранять

livestock домашний скот

interconnect (взаимно)связывать

habitat место обитания

behaviour поведение

overlap перекрываться, частично совпадать

coincide совпадать

niche (экологическая) ниша

organic whole единое целое

bind связывать

disruption распад, разрушение

property свойство

severe резкий, сильный

irreparable непоправимый, невосстановимый

slight незначительный, слабый

carbon dioxide углекислый газ, двуокись углерода minute [mai'nju:t] мельчайший

ancestor предок, прародитель

progeny потомство, потомок

generation поколение

II. Translate text 3 into Russian. Text 3

POPULATIONS. COMMUNITIES. ECOSYSTEMS

A population is a group of interbreeding individuals of the same species occupying a given area. Populations are characterized by density, age structure, birth and death rate. Each individual carries a certain combination of genes (sum total of an individual's genes is called genotype). The sum of all genetic information stored in genes of individuals of a given species is called a gene pool of the species. The population is also an evolutionary unit. Evolution suggests changes in the gene information.

Lifetime of any species is very long and can reach a million years. It exceeds the lifetime of an individual (a member of a population) by many orders. Thus, the stability of a population as a system is achieved through continuous renewal of its elements. In the reproduction process there may appear individuals whose properties differ from normal. As a rule, such weaker (non-competitive) individuals will be forced out of reproduction by the competition process. These two processes – reproduction and competition – are vitally important for maintaining stable existence of any species in nature. Normally, the genotype of any species corresponds to the maximum competitiveness, which is a set of properties that provides species capability to fulfil its most important function – to sustain the ecosystem stability and, eventually, to keep matter cycles in the biosphere closed. Notice that stability of natural ecosystems does not concern any domestic species such as agricultural plants, livestock, etc. as well as pigeons, sparrows, rats, and other "companions" of men.

A group of interconnected populations of all species that occupy a habitat composes a community. Each habitat has a characteristic range of physical and chemical conditions, such as amount of light, typical temperature, pH of water, and so on. And each species is adapted to those conditions in terms of its morphology, physiology, and behaviour. A full range of abiotic and biotic conditions under which a particular species can live and reproduce is called its ecological niche. Each niche may overlap with many others, which belong to neighbouring species, but it coincides with none. Organisms have arrived at their niches through long periods of evolution.

As a rule, the more complex the system is, the more successfully it can resist the outer stress. An ecosystem is a natural organic whole of a biologic community and its nonliving environment. Constant interactions between living organisms, say, plants, bacteria, and animals and their physical environment in any ecosystem are the pathways by which matter and energy are distributed. Most important is that these interactions bind the living and nonliving components together into a stable system. Many opposing forces operate within the ecosystem which may be stabilized due to its self-compensating properties. The state of balance in any ecosystem is self-sustainable so that even slight imbalances are corrected before they become severe, irreparable, and fatal.

Any stable natural ecosystem consists of a great number of various species, from minute living things like viruses or bacteria to giants like whales or sequoias, each playing a unique role in relation to the whole system. Biologist Edward 0. Wilson, who coined the term "biodiversity" in the book "The Diversity of Life", writes that biological diversity is the key to the maintenance of the world as we know it and it holds the world steady.