PDS APES 8th Period 2009-10

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An organism’s niche in its community is more that just its “job,” it is its role in relation to where it works, what it eats, where energy flows, how matter cycles, and how it interacts with other organisms. This interactions with the ecosystem, more specifically the biotic portion, is what shapes an organism’s niche. Niches typically evolve through coevolution, rather than in isolation, due to the necessity of organisms interacting in an environment. Coevolution can be categorized into two relationships: Specialization and Competition. But the types of interactions breakdown even further into subcategories. These different types of interations between species in a community are often labels using positive and negatives to distinguish the type or relationship and which parties are benefiting. Here are the types: 1)Competition (-,-) *interspecific vs intraspecific. While Competition may appear to have a clear winner and loser ecologist classify it as a lose, lose because both organisms expend energy (a negative). 2)Predation (+,-) *carnivory or herbivory. This is clearly a win lose as the loser is almost always killed and eaten by the predator. 3) Parasitism (+,-). This differs from predation in that the loser typically does not die. 4) Commensalism (+,0). Commensalism basically means that there is no established relationship. For example a prairie dog may get stepped on by an elephant and die, but there is no regular relationship between the two. And finally 5) Mutualism (+,+). Here, both organisms benefit from interacting with one another. It is also important to know the Competitive Exclusion Principle: If two species, with the same niche, coexist in the same ecosystem, then one will be excluded from the community due to intense competition. Here both species suffer (-,-). Usually the loser will migrate or die. This Principle leads to resource partitioning and realized niches.