The struggle for existence

Organisms produce more offspring than - given the limited amounts of resources - can ever survive, and organisms therefore compete for survival. Only the successful competitors will reproduce themselves. It was Charles Darwin (opposite) who first discussed this competition and described it as the "struggle for existence".

The struggle for existence takes place within a web of ecological relations. Above an organism in the ecological food chain, there will be predators and parasites, seeking to feed off it; and below it are the food resources it must in turn consume in order to stay alive. At the same level in the chain are competitors, which may be competing for the same limited resources of food, or space.

An organism competes most closely with other members of its own species, because they have the most similar ecological needs to its own; other species, in decreasing order of ecological similarity, also compete and exert a negative influence on the organism's chance of survival.