Публикация на аглийском языке на тему "ECOLOGICAL SUCCESSION" для студентов колледжа

ECOLOGICAL SUCCESSION

          Progressive changes in communities take place from one geological

epoch to another and also within much chorter periods of time.Here we chall

concern ourselves primarily with the replacement of one community by

another in particular areas and within the same general climatic condition.

          Observation has revealed the fact that in given biotopes certain communities

end to succeed one another.The occurrence of a relatively definite sequence of

communities in an area is known ecological succession.The change in the communities

may be due in part to independent physiographic changes such as alteration of drainage,

erosion,or deposition,but more especially it is caused by modification produced by the

action of each community on its own environment.The two types of causes are frequently

operating together,as is seen,for exampel,in the replacemnt of a pond community by a

marsh community.The filling of the pond is brought about by the deposition not only of

a certain amount of inorganic silt,but also of a large amountof the organic remains of successive

communities,and the accumulation of both types of deposit is enhanced by the presence of  the

roots and stems of the living community members.

          The extent to which ecological succession is self-induced varies greatly in different

situations.Similarly,the predictability of the course and speed of succession is variable.

In many instances the presumed course of succession is based on inference derived from

studies of surrounding areas so that <<space is substituted for time>> but in other instances

the nature of the succession is substantiated by actual records.Self-induced ecological

succession is  another outstanding example of the organism and the environment acting

as a reciprocating system.

          Living things modify their own habitat so as to cause one community to give way to

another in a variety of ways.All species of animals and plants end to increase in a number

and/or size.The  conditions of the community consequently change because of the growth

of the inhabitants even without any change in species composition.Consider a forest, for

example.As the trees increase in size,they provide more chade, higher humidiry,and differents

condition of food and cover.New types of animals fing suitable conditions here; old forms may

be eliminated.Wildlife managers have come to realize that the carrying capacity of a forest

area for game changes with time because the availability of food and shelter in a stand of

saplings is entirely different from that in a stand of mature trees.