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Ch. 19 - Communities and Ecosystems How do organisms interact in a community? Properties of a community: • Diversity - variety of different kinds of organisms - richness and relative abundance of organisms (see left) • Form of Vegetation -types and features of plants determine kinds of animals in a community • Stability - community’s ability to resist change and return to its original species composition after being disturbed. • Trophic structure - feeding relationships among the speciespassing nutrients from plants to animals Interactions in Communities: • Interspecific competition - various kinds of interactions between species. Competition for resources (such as food), with competing species, or with ones own population. Ex: Competitive exclusion principle : in Paramecium populations (see above). - 2 species that are so similar that they compete for same limiting resources cannot coexist in the same place. The inferior competitor will be eliminated. • Ecological niche - the total of a species’ use of biotic and abiotic resources - how it fits into an ecosystem; its “job.” • Resource partitioning differentiation of niches that enables similar species to coexist in a community. One species may evolve enough to use a different set of resources. Ex: lizards (see left) • Predation: Predator = consumer Prey = food species (including plants) • Predator Adaptations: acute senses, claws, teeth, stingers, poisons • Plant Defenses: chemical toxins in plants, thorns • Animal Defenses - hiding, fleeing, cryptic coloration (camouflage), warning coloration. • • • • • Batesian mimicry - a palatable or harmless species mimics an unpalatable or harmful model. Ex. Viceroy butterfly mimics Monarch butterfly (tastes bad) Mullerian mimicry - 2 or more unpalatable species resemble each other. Ex: cuckoo bee and yellow jacket (see left) Keystone predator - a species that reduces the density of the strongest competitors in a community. Helps maintain species diversity. Ex: sea stars eating abundant mussels Q: What would happen if humans removed the sea stars? A: More mussels, mussels would eat much of the kelp, sea otters would disappear.