An organisms "place" in an ecosystem is refered to as it's niche. The niche can be defined as the sum of all the interactions, both biological and physical, that and organism experiences in an ecosystem. The fundamental niche refers to all the elements of an ecosystem that an organism could potentially exploit, but the realized niche is inevitably less than that, due to the effects of competition, predation, and disturbance.
Competition -- is the struggle by two organisms to use the same resource when there is not enough to go around. When two species compete fiercely for the same resource, one species usually wins out and the other becomes extinct. This is refered to as competitive exclusion. This rarely occurs in stable ecosystems--instead what you see are sometimes called the
"ghosts of competition past." Important points about competition (subject of considerable debate):
- Competition is not limited to closely related organisms. (E.g. grasshoppers can compete with antelope)
- Competitiors can coexist by specializing on a subset of the limiting resource. This is called resource partitioning. The partitioning is usually not very equal, and this means that most species in a community are rare, with a few species dominating.
- Competing species differ in at least one way in their use of a limiting resource. This may involve character displacement between the competing species, in which some aspect of anatomy, or behavior, or physiology is different and allows for a difference in the use of the limiting resource. In other words, the ecological niche, defined as the total range of biological and physical conditions within which a species can survive and reproduce, must be different in some way.
- This is called the Competitive Exclusion Principle.
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