Community
A community is made up of all of the populations of different species living in a specific environment. A community is only the living components of the environment. For example, all of the algae, plants, frogs, fish, and other organisms living in and around a pond make up a pond community. The most abundant organism in the community is known as the dominant member of that community.
The species living within a community interact together in numerous different ways. These interactions play an important role in shaping the size and structure of the community. Specifically, the interactions help determine what species are present in the community, and the size of each species' population. These interactions often result in evolution of the species involved and changes in the community. The interactions fall into three general categories: competition, predation and symbiosis.
When individuals of the same or different species share a limited resource, competition will result. Competition can have important effects on community structure. If the resource is severely limited, competition may result in death of some organisms, reducing population size. If competition is between individuals of different species, one species might eventually outcompete the other. The outcompeted species either would have to shift to another resource or would be excluded from that community. As a result of competition, each species has a niche, a specific job or role in a community, and in general, the niche of one species does not overlap with that of another species.
Predation occurs when one organism eats another live organism. As a result of predatory interactions, both the populations of the predator, the organism doing the eating, and the prey, the one being eaten, may evolve. The predator population would evolve better mechanisms to capture the prey. At the same time, the prey population might evolve better ways of escaping the predator. The numbers of both predators and prey will influence community structure. If there are many predators in a particular community, the numbers of prey will likely decrease, because so many are eaten. This could decrease the competition between prey species, resulting in increased species diversity within the community. Similarly, if there are only a few prey available, the numbers of predators will likely fall.
Symbiosis is a close association and interaction between organisms of two or more species within the same community. The interactions can be beneficial, cause harm or have no effect at all. Some symbiotic relationships have resulted in evolutionary changes in the organisms involved, and thus changes in the community.
Since there are so many members within a community, there are countless interactions. These interactions are very complex. As a result, it is often very difficult for scientists to figure out all of the interactions within a community and determine the exact causes of a particular community's structure.
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