Ecological Succession
Uploaded by ihatesuchin on Jul 05, 2004
Ecological Succession
Ecosystems undergo changes in their structure and function as time passes. Some of these changes are minor and only affect a small area, others are the cause of major changes in the species present and affect the ecosystem as a whole.
Major changes can be caused by changes in climate, external factors such as fire, trampling or pollution and development due to the system itself.
Succession is a result of these changes and is defined as a series of progressive changes in an area with one community replacing the other until a climax community is created. A climax community consists of plants and animals, the animals present are dictated by the plants available. There will normally be a dominant species of plant and animal or a number of co-dominant species, these species are normally the most numerous and have the greatest biomass. The climax community is normally seen as the ultimate development of the ecosystem.
There are 2 types of succession; primary and secondary. Primary succession is the colonisation of an area which has not supported an ecosystem before, eg sand dunes, volcanoes and new ponds. Secondary succession is ecological succession in an area which has supported an ecosystem whose development to a steady state has been prevented by inhibitory factors such as grazing or fire. When the inhibitory factor is removed secondary succession takes the ecosystem to maturity.
The sequence of communities during succession is known as a sere, the type of sere is determined by the environment being colonised, eg a hydrosere is a series of successions in an aquatic environment and a xerosere is a succession beginning in a dry area. The individual communities of each succession are the seral stages, the seral stages are not normally distinct but tend to merge into one another as the succession progresses.
During succession energy flow in an ecosystem is fundamentally changed, the changes are demonstrated in the quantity of standing crop in the ecosystem.
During early seral stages the energy inputs to the system are larger than the energy outputs, this results in little change in the standing crop. The energy flow is at a maximum during the climax stage. When the ecosystem is disturbed by external factors, eg fire the energy loss is greater than energy inputs. This results in a decrease in the amount of standing crop.
The accumulation of energy as biomass is most marked...