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 <> 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.
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