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University of Guelph
BIOL 4150
Scott Brandon

Interactions of organism with one another: o Predation or parasitism: interactions in which one participant is harmed, but the other benefits (+/- interactions). o Competition: interactions in which two organisms use the same resources and those resources are insufficient to supply their combined needs (-/- interactions). o Mutualism: interactions in which both participants benefit (+/+ interactions). o Commensalism: interactions in which one participant benefits but the other is unaffected (+/0 interactions). o Amensalism: interactions in which one participant is harmed but the other in unaffected (0/- interactions). • These influence the population densities of species. • May also restrict the range of environmental conditions under which species can persist. • If there were no predators or pathogens, most species would be able to persist under a broader array of abiotic conditions that they do in the presence of other species. • Presence of mutualists may increase the range of physical conditions under which a species can persist. Predation and parasitism are universal • Predation and parasitism are universal processes. • Predators are typically larger than and live outside the bodies of their prey. • PREDATOR AND PREY POPULATIONS OFTEN OSCILLATEL growth of a predator population nearly always lags behind growth in its prey population. • PREDATORS MANY RESTRICT SPECIES’ RANGES: predators may also restrict the habitat and geographic distribution of their prey. • MIMICRY EVOLVES IN RESPONSE TO PREDATION: o Predators do not capture prey individuals randomly. Prey individuals vary in ways that make them more or less susceptible to being captured. o A palatable species may mimic an unpalatable or noxious one— Batesian mimcry.  Works because a predator that captures an individual of an unpalatable or noxious species learns to avoid other prey individuals of similar appearance.  If a predator captures a palatable mimic; learns to associate palatability with the appearance of that prey.  Directional selection causes unpalatable species to evolve away from their mimics and can be maintained only if the mimic evolves toward an unpalatable species faster tha
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