Chapter53CommunityEcology[1]

Chapter53CommunityEcology[1] - BLY 122 Community Ecology I...

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Chapter 53 Community Ecology 1 BLY 122 C. S. Major Community Ecology I. Species Interactions A. Commensalism 1. Definition: Commensalism is a +/0 interaction. 2. Example: Some birds follow moving army ants on the forest floor. As the ants march along the forest floor, hunting insects and small vertebrates, the birds follow and pick off individuals that fly or jump out of the way of the ants. B. Competition 1. Definition: Competition is a –/– interaction that occurs when individuals use the same resources and when those resources are limited. 2. Example: G. Evelyn Hutchinson proposed that a species’ niche could be envisioned by plotting habitat requirements along a series of axes. 3. The consequences of competition—theory a. The principle of competitive exclusion states that it is not possible for species within the same niche to coexist. But, if the niches do not overlap completely, then the weaker species should be able to retreat into an area of non-overlap, a mechanism called niche differentiation. b. The fundamental niche is the combination of conditions that the species will occupy in the absence of competitors; its realized niche is that portion of resources used when competition occurs. c. Mechanisms of competitive exclusion are explained. 4. The consequences of competition—experimental studies a. Example: Joseph Connell noticed two species of barnacles with interesting distributions on an intertidal rocky shore of Scotland. b. This is one of the first experimental examples of how competition can modify a distribution of a species. In this case, the poorer competitor ( Chthamalus ) is restricted to the upper intertidal zone, which is a more severe habitat. C. Consumption 1. Definition: Consumption occurs when one organism eats another. a. Herbivory—when herbivores consume plant tissues. b. Parasitism—when parasite consumes small amounts of tissues from another organism, or host. c. Predation—when a predator kills and consumes most or all of another individual 2. How do prey defend themselves? a. Some species run or hide in response to predators; others sequester or spray toxins or employ weaponry for defense. b. Mimicry occurs when one species closely resemble another species. c. Müllerian mimicry occurs when harmful species resemble each other. For example, brightly colored wasps resemble each other and by this, predators tend to avoid these colors. d. Batesian mimicry occurs when a harmless species resembles a harmful one. e. Researchers hypothesized that if blue mussels possess inducible defenses against crabs, they should occur in the low-flow area where predation pressure is higher. They found that mussels in the high-predation area had thicker shells. 3. Are animal predators efficient enough to reduce prey populations?
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