The Open Door Web Site
Part XXII: The Interdependence of Living Things : The Ecosystem : An Interacting Community Index
Earthworms in compost heap, Sheffield, UK
THE ECOSYSTEM: AN INTER-ACTING COMMUNITY
The missing link
Although the sun is a constant energy source the soil does not provide an infinite supply of minerals. The minerals which are absorbed into the plant roots need to be replaced. All organisms produce waste; trees lose their leaves which fall to the ground and animals produce solid waste. This waste becomes food for the decomposer organisms, such as fungi and bacteria. These organisms break down the waste of other organisms and return minerals to the soil as well as returning carbon dioxide and nitrogen into the air.
The earthworm is also a decomposer. It feeds on dead leaves which it breaks down to smaller pieces in its body. As it burrows through the soil, the earthworm excretes its own waste which is rich in minerals and other compounds which make the soil more fertile.
Dead plants and animals are also decomposed. When a pride of lions leaves the remains of a large herbivore, the vultures move in. Vultures are scavengers. A scavenger is a carnivore which does not hunt and kill a prey. It eats the left-overs of other carnivores. The hyena can also be a scavenger. It will even eat the bones of a dead herbivore killed by a lion. After the scavengers have finished with the carcass, the decomposers feed on the remains.
Vulture, Vincennes Zoo, Paris
The scavengers and the decomposer organisms are essential members of the ecosystem community. They liberate chemicals which are then re-cycled to be used again and again throughout the food web.
The control of nature
In an ecosystem the number of animals present will depend on the amount of food available. If there is a good summer and the plants grow well, producing lots of fruits and seeds, the herbivores will flourish. This will eventually benefit all of the animals in the ecosystem through the food web.
The reverse is also true. If a flood, fire or disease destroys some of the vegetation, less food will be available throughout the ecosystem. Many animals, particularly the young ones, may starve. Severe winters or drought conditions will reduce the numbers of both plants and animals in an ecosystem.
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