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I. Community Ecology A. Competition 3. Resource partitioning • • Competitive exclusion can be minimized if competing species modify niches to reduce overlap Usually involves dividing resource Anolis Dominican Republic Fig. 54.2 I. Community Ecology A. Competition 4. Character displacement • • Resource partitioning may lead to directional selection on one or both species Directional selection may lead to divergence in traits Fig. 54.4 I. Community Ecology B. Predation • • Involves consumption of prey by predator Predator usually has adaptations to facilitate capture of prey Natural selection acts on both predator and prey • • 1. Coevolution Strategies a. b. c. Pursuit predation • Predators chase prey to capture them • Predator usually faster, stronger, &/or more agile than prey • Some species hunt in groups Ambush predation • Predators lie in wait for prey • Predators usually camouflaged or concealed • May involve lures Aggressive mimicry • Ex: Bolas spider mimics odor of female moths to attract male moths I. Community Ecology B. Predation 2. Predator avoidance a. Escape • Running/Swimming/Flying away b. Mechanical defenses • Ex: Porcupine quills, armadillo armor c. Social behavior • Ex: Schooling, standing watch d. Chemical defenses • Ex: Poison dart frog, skunk e. Defensive coloration Cryptic coloration - Canyon tree frog Aposematic coloration - Poison dart frog Müllerian mimicry Batesian mimicry Fig. 54.5 Batesian Mimicry Sam Crothers I. Community Ecology C. Herbivory • • Consumption of plants by animals Most herbivores are small • • • Ex: Insects, snails/slugs Herbivores adapted to consume plants Some plants have anti-herbivore defenses • • • Physical – Ex: Thorns, spines Chemical – Ex: Nicotine in tobacco, pyrethrins in chrysanthemums Coevolution has affected herbivore evolution • Ex: Monarch butterfly caterpillars can eat milkweed • Toxic to most herbivores • Nearly exclusive access to food source • Can sequester noxious compounds for defense I. Community Ecology D. Parasitism • Parasite benefits at expense of host • • Fig. 33.12 • • • • Host harmed in process Ex: Tapeworm absorbs nutrients from host digestive system Endoparasites – Live within body of host Ectoparasites – Live outside body of host Parasitoids – Lay eggs on/in host; larvae feed on host, eventually killing host Many parasites have complex life cycles Fig. 33.11 Schistosoma mansoni I. Community Ecology E. Disease • Widespread disease outbreaks may alter community composition and dynamics • • • • Ex: Dutch elm disease Ex: Sudden oak death Ex: Avian flu Ex: West Nile virus I. Community Ecology F. Mutualism • Symbiotic relationship in which both partners benefit • • • • • Ex: Ants & acacia trees Ex: Nitrogen fixing bacteria (Rhizobium) & legumes Ex: Zooxanthellae & reef-building corals Ex: Mycorrhizae & plants Ex: Anemones & clownfish I. Community Ecology G. Commensalism • One organism benefits, other isn’t harmed or helped • • Ex: Cattle egrets and cowbirds & ungulates (expose insects while grazing) Hard to document (both species usually affected to some degree) • Ex: Some commensal birds may remove ticks & other ectoparasites from herbivores