Community Ecology

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It has led to evolution of plant defenses against herbivores: secondary compounds = are chemical defenses; and mechanical defenses which are often osmoregulated.

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Symbiosis: + + + 0 + -

Symbiosis is a dependency relationship where two or more species live in direct and intimate contact with one another. The relationship is generally based one or some combination of the following benefits:

Nutrition (food, water)

Protection

Reproduction

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Parasitism + -

In parasitism (+/– interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process.

Endoparasites = parasites that live within the body of their host.

Ectoparasites = parasites that live on the external surface of a host.

Many parasites have a complex life cycle involving a number of hosts.

Some parasites change the behavior of the host to increase their own fitness (reproduce more offspring).

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Mutualism + +

Mutualistic symbiosis, or mutualism (+/+ interaction), is an interspecific interaction that benefits both species.

A mutualism can be:

Obligate = MUST where one species cannot survive without the other.

Facultative = OPTIONAL where both species can survive alone.

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Commensalism + 0

In commensalism (+/0 interaction), one species benefits and the other is apparently unaffected.

Commensal interactions are hard to document in nature because any close association likely affects both species.

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A possible example of commensalism between cattle egrets (birds) and water buffalo: The Birds eat insects disturbed by the Buffalo as they move.

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Dominant and keystone species exert strong controls on community structure

A few species in a community often exert strong control on that community’s structure.

Two fundamental features of community structure = species diversity and feeding relationships.

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Species Diversity

Species diversity of a community is the variety of organisms that make up the community.

It has two components: species richness and relative abundance.

Species richness is the total number of different species in the community.

Relative abundance is the proportion each species represents of the total individuals in the community.