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COMMUNITY ECOLOGY Chapter 54 What is a community? Many species living closely together, so that they interact with each-other. Population Interactions: Intraspecific competition - within a species Interspecific interactions - Individuals of different species compete for a resource that limits their growth and survival Interspecific competition -/- interaction Competition must occur: ◦ interference competition - actual fighting occurs ◦ exploitation competition - consumption or use of similar resource Ex: weeds growing in a garden compete with garden plants, lynx and foxes compete for snowshoe hares Competitive Exclusion Principle Two species cannot coexist in a community if their niches are identical Ecologically similar species can coexist in a community if there are one or more differences in their niches Competitive Exclusion Principle Ecological Niche Sum total of a species’ use of the biotic and abiotic resources in its environment Habitat=address Niche=habitat + occupation Resource partitioning of lizards Fundamental / Realized Niches Character displacement Upon What Do These Animals Prey? Upon What Do These Animals Prey? Animals Upon What Do These Animals Prey? Plants Animals Animal Defenses Running Hiding Physical or Chemical Defenses Chemical Defense and Aposematic coloration are seen here Aposematic coloration Cryptic coloration is seen here Cryptic Coloration Mimicry Batesian mimicry - harmless species resembles harmful or distasteful species Mullerian mimicry - two or more unpalatable species resemble one another. Batesian Mimicry Batesian Mimicry Mullerian Mimicry Plant Defenses Against Predators: What defense is seen here? Other defenses: • Chemicals that cause plant to taste bad • Poisonous chemicals In this relationship, the ant hollows out the thorns of the plant for nests, feed on sweet secretions from the four nectaries at the base of each petiole, and protect these trees from invertebrate herbivores. Heliconius butterflies (Heliconius sp.) lay their eggs on the leaves of the passionflower vine (Passiflora sp.). When the eggs hatch into hungry, leafeating Heliconius caterpillars, the passionflower vines protect themselves with an array of defenses. Fake eggs . . . some passionflower vines grow parts that look like Heliconius caterpillar eggs. This keeps the female Heliconius butterfly from laying eggs on leaves that appear to be occupied by other cannibalistic caterpillars. Dumpers . . . Some Heliconius butterflies like to lay their eggs on upwardcurling tendrils of passionflower vines. Some vines produce fake tendrils that are weak and fall off under the weight of the developing butterfly eggs. Symbiosis Close association between two species Parasitism +/ Commensalism +/0 interaction Mutualism +/+ interaction Predation +/- interaction Predator eats prey ◦ Ex. Lion eats an antelope, animal eats a plant Predators Can reduce relative abundance Can reduce diversity by eliminating competitors - keystone predators ◦ sea star feeds on mussels and other organisms, remove sea star and mussels take over the region and eliminate species diversity. Parasites are also +/Endoparasites-live within the body of their host ◦ Ex. tapeworms Ectoparasites-parasites that feed on the external surface of a host ◦ Ex. Ticks, lice Parasitoid insects-lay eggs on the body of the host, the larva then feed on the body of the host, eventually killing it One parasite example: Mutualism +/+ interaction ◦ Ex. Nitrogen fixation by bacteria in root nodules of legumes ◦ Ex. Termites and microorganisms in their gut Interspecific Interactions: What is co-evolution? Reciprocal evolutionary changes between two or more species. Results in a close association between certain species Commensalism +/0 interaction ◦ Ex. Cowbirds and cattle egrets feed on insects flushed out of the grass Which symbiosis is seen here? Which symbiosis is seen here? parasitic Which symbiosis is seen here? Which symbiosis is seen here? Mutualism Community Structure Feeding relationships Richness - number of different species Relative abundance - number in individuals in each species Diversity - combination of abundance and richness Communities with even distribution of species are more diverse than communities with greater richness but skewed distributions Trophic Structure Feeding relationships-transfer of food energy Plants to herbivores to carnivores to decomposers = food chain Food web - interconnected food chains Control of community structure Dominant species-species in a community that have highest abundance or biomass ◦ Sugar maples Keystone species-not abundant but exert strong control on community structure ◦ Remove the species to determine if it is a keystone species ◦ Sea otters Invasive species-no natural predators so their population is not held in check ◦ Buckthorn, garlic mustard, purple loosestrife Nonequilibrium Most communities are not stable Disturbances such as storms, floods overgrazing etc. can effect stability Humans bring disturbance Succession Example of disturbance leading to change primary succession - soil never formed before secondary succession - existing community was disturbed and returned to original state. Secondary Succession Biogeography Study of past and present distribution of individual species and communities Limitation of species to one region: ◦ species never dispersed ◦ pioneers did not survive ◦ species retracts from once larger range to smaller boundaries Island biogeography Review the following slides and identify which community interaction you are observing Where is the Moth? Can you see it now? What coloration is seen in the next slides? What does this tell you about the way these animals live in their communities? This animal is not a bee, why does it look like one? Species Richness and Island Size Species diversity Which forest is more diverse?