Interactions in Communities 1. Predator/Prey: one organism kills another for food Predator populations are affected by the size of the prey population, and vice versa. Why do animals compete? 2. 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. 3. Symbiosis • 2 species living closely connected to one another 1. Mutualism 2. Commensalism 3. Parasitism 7 Mutualism Both species benefit. Ex: CLOWNFISH AND SEA ANEMONE 8 Commensalism One member benefits and the other is not helped or harmed. • Ex: Whale and Barnacle 9 30 Parasitism one organism benefits and the other is harmed Types of Symbiosis Interaction Species A Species B Mutualism Benefit (+) Benefit (+) Commensalism Benefit (+) No Effect (0) Parasitism Harm (-) Benefit (+) More about Parasitism – One organism feeds on another organism called the host – Host is almost always larger than the parasite – Parasites often live on or in host – Host usually harmed but not killed Riverblindness: Parasitic worm transmitted by blackfly Isopod parasitizing a fish tongue Herbivores don’t often kills plants Plant defenses thorns/spines chemical compounds that taste bad, kill, or make herbivores sick 5. Coevolution: back and forth evolutionary adjustment between two species that interact What is the difference between a habitat and a niche? • A habitat is the area in which an organism lives. (where) • A niche includes the role that the organism plays in the environment. (how) Are the following part of the habitat or niche? a) Lions eat zebras b) Lions hunt in groups c) Lions live in the savanna d) Lions live near a watering hole e) Lions are most active just after dusk f) Lions reproduce starting at age 4 Fundamental niche : entire range of conditions where an organism could survive. Realized niche: the actual niche that a species occupies. Competition between two species of barnacles. The realized niche of each barnacle growth rate Balanus realized niche low Balanus and Chthamalus Chthamalus realized niche middle high Location in intertidal zone The fundamental niche of each barnacle. 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 occurs when one species eliminates another through competition.. Two species of Paramecia predict the outcome of interspecific competition P. aurelia P. caudatum Gause (1934) 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.