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Interactions in Ecosystems Why do animals compete? What is the difference between a habitat and a niche? • A habitat is all biotic and abiotic aspects of the area in which an organism lives. • An ecological niche includes all of the factors that a species needs to survive, stay healthy, and reproduce. Are the following part of the habitat or niche? a) b) c) d) e) Zebra as food Hunting behavior Savanna Grass Temperature it can tolerate f) Watering hole g) Time of day it is active h) Sand i) Number of young produced • Competition occurs when two organisms fight for the same limited resource. – Intraspecific competition – Interspecific competition Interspecific or intraspecific? • Two red squirrels race up a tree to find a hidden pile of nuts. • A hyena chases off a vulture to feast on an antelope carcass. • Shrubs and grasses on the forest floor compete for sunlight. • Brown bears hunting for fish on a river’s edge fight over space. • Male big horn sheep butt heads violently in competition for mates. Fundamental niche : entire range of conditions an organism is potentially able to occupy. Realized niche the part of the fundamental niche that a species occupies. Competition between two species of barnacles. Is this the realized niche or fundamental niche? How can we determine the realized niche of each barnacle? Observe where they grow when allowed to compete. growth rate Balanus realized niche low Balanus and Chthamalus Chthamalus realized niche middle high Location in intertidal zone How can we determine the fundamental niche of each barnacle? Removal experiments – remove each species and see where the other grows Balanus alone Balanus fundamental niche growth rate Chthamalus alone Chthamalus fundamental niche low middle high Location in intertidal zone Streams with only Planaria species A Streams with only Planaria species B Streams with both Planaria species What are the fundamental and realized niches for each species? Competitive exclusion keeps two species from occupying the same niche. Two species of Paramecia predict the outcome of interspecific competition P. aurelia P. caudatum Gause (1934) Types of Interactions Interaction Species A Species B Mutualism Benefit (+) Benefit (+) Commensalism Benefit (+) No Effect (0) Parasitism Benefit (+) Harm (-) Predation Benefit (+) Harm (-) Competition Harm (-) Harm (-) Amensalism Harm (-) No Effect (0) • What is symbiosis? • How are predators different from parasites? • How are they similar? • How are predators of animals different from predators of plants? • What is the difference between ectoparasite and an endoparasite? A black rhinoceros grazes on the African plains. As it forages, the rhino disturbs multitudes of insects in the grass, crushing some and inadvertently eating others. Birds known as egrets forage on the ground near the rhino, eating insects flushed out by the hooves. Other birds known as oxpeckers eat ticks from the skin of the rhino.