Ecological Communities: Networks of Interacting Species
We wish to learn:
* What is an ecological community and what kinds of interactions take place within it?
* How important are the various categories of species interactions, including mutualisms, commensalisms, competition and predation?
* What kinds of interactions among species become important when many species affect one another?
* What consequences do these interactions have for biodiversity
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Species Interactions, Food Webs, and Ecological Communities
An ecological community is defined as a group of actually or potentially interacting species living in the same place. A community is bound together by the network of influences that species have on one another. Inherent in this view is the notion that whatever affects one species also affects many others -- the "balance of nature". We build an understanding of communities by examining the two-way, and then the multi-way, interactions involving pairs of species or many species.
type of interaction | sign | effects |
mutualism | +/+ | both species benefit from interaction |
commensalism | +/0 | one species benefits, one unaffected |
competition | -/- | each species affected negatively |
predation, parasitism, herbivory | +/- | one species benefits, one is disadvantaged |
Food webs are graphical depictions of the interconnections among species based on energy flow . Energy enters this biological web of life at the bottom of the diagram, through the photosynthetic fixation of carbon by green plants. Many food webs also gain energy inputs through the decomposition of organic matter, such as decomposing leaves on the forest floor, aided by microbes. River food webs in forested headwater streams are good examples of this.
Energy moves from lower to higher trophic (feeding) levels by consumption: herbivores consumes plants, predators consume herbivores, and may in turn be eaten by top...