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Community Ecology II: Species Interactions Ecological communities: Assemblages of two or more species living and interacting in the same area. Species interactions: the ways different organisms affect each other and how they have adapted to each other’s presence. FOUR main kinds of species interactions; all play a role in the formation of community structure... Competition (-,-) Predation, parasitism (+,-) Mutualism (+,+) Commensalism (+,0) Interspecific Competition: Use or defense of a resource by one species that reduces availability of that resource to a different species. exploitative competition interference competition Competition in Paramecium Competition in Paramecium Competitive Exclusion: A result of competition between species for a limiting resource, in which one species completely eliminates the other. Ecological Niche: • a species’ ecological ‘role’ • all the environmental factors that influence the growth, survival, and reproduction of a species • an n-dimensional hypervolume within which a species’ population growth is positive 3-dimensional niche Fundamental Niche vs Realized Niche Fundamental Niche: the niche that a species potentially could occupy, in the absence of competitors. Realized Niche: the niche to which a species is restricted in the presence of competitors. Competition in Barnacles Competitive Release: Expansion of a species’ ecological niche when a competitor is removed (usually in a removal experiment). Q: How do similar species coexist? A1: Resource Partitioning • Species using similar resources can coexist when the habitat is spatially and temporally complex, thus allowing for resource partitioning. Anolis spp. Number of different Anole species on different islands VIDEO CLIP Q: How do similar species coexist? A2: Character Displacement Character Displacement The tendency for physical characteristics to be more different in sympatric populations of two closely related species than in allopatric populations of the same two species. Sympatric Allopatric FOUR main kinds of species interactions; all play a role in the formation of community structure... Competition (-,-) Predation, parasitism (+,-) Mutualism (+,+) Commensalism (+,0) True Predators - prey is killed immediately upon successful attack Great White Shark, Siberian Tiger, Fox Squirrel Partial Predators - prey usually not killed but many prey organisms affected during predators lifetime - grazers, browsers Giraffe, Bison, Monarch Caterpillar Parasitoids - lay eggs on or in prey and then eggs hatch and developing offspring consume the prey Parasitoid wasp attacking moth caterpillar Predators can influence species within communities by selecting for anti-predator adaptations in prey… Behavioral Defenses Morphological Defenses Crypsis - matching background Cryptic coloration Flexible crypsis Morphological & Physiological Defenses Aposematic or Warning Coloration Monarch Butterfly and Caterpillar Blue jay eats monarch, but vomits due to cardiac glycoside from milkweed Mimicry • Batesian mimicry in which a palatable species mimics a harmful “model” species • Müllerian mimicry in which two or more harmful species come to resemble each other Batesian mimicry – several fly species mimicking bees and wasps Batesian mimicry – coral and king snakes Arizona Coral Snake Central American coral snakes and king snake mimic – coral snake on left or in middle Müllerian Mimicry Monarch Viceroy Complex of Batesian and Müllerian Mimics Predators can also influence the numbers and distribution of their prey. e.g. Wolves and Moose on Isle Royale Parasites can affect host populations by reducing their survival, reproduction and density. Parasitic effects on host species can be indirect or direct. • Ticks (ectoparasites) suck blood and cause irritation • Lead to weakened moose, which are more susceptible to predation by wolves and death from starvation. Parasites can also affect the behavior of the hosts, making them more likely to pass the parasite from one host to another. e.g. endoparasites in sticklebacks cause them to approach water surface more often and increase predation risk.