Community Ecology Interactions between populations Density dependent factors Operate as negative feedback mechanisms The population maintains a steady level Disease transmission Vulnerability to predators Food supply Over crowding What Controls Population Size and Growth Rate • Density-dependent factors: • Intra-specific competition • Food • Space • Contagious disease • Waste production • Inter specific competition • Other species interactions • Density-independent factors: • disturbance, environmental conditions • Hurricanes • Floods • Colder than normal winter Types of Interactions Competition Predator-Prey Mutualism Commensalism Parasitism Competition Natural Selection minimizes competition! Competition: Iftwo species are competing, the growth of one population should reduce the size of the other Predator-prey Predator-Prey Relationships • Prey defenses: avoid conflict! • Coevolution • as predator evolves, prey evolves to evade it • Warning coloration and mimicry • Camouflage Predator-Prey Relationships •Predatorscan promote diversity by keeping competition in check Idealized Predator-Prey Population Graph Predatory-Prey If it is a predator-prey relationship, then the two populations have opposite effects on one another Mutualism Both species benefit Mutualism If it is a mutually beneficial relationship, then the two populations increase each other’s size Commensalism One species benefits, the other is unaffected Is this mutualism or commensalism? Commensalism If the relationship is commensalistic, one species benefits (the commensal) and the other is unaffected Parasitism Test you knowledge! What type of relationship–? A coati eats tree fruit. Your dog has a flea You use a fast bicyclist to “draft” off of Carrying Capacity The number of individuals that a habitat can support. If the population is a herbivore, K may depend on the population of plants Community Dynamics Community: a group of populations (both plants and animals) that live together in a defined region. Trophic Levels predator/ Eagles 4th trophic level tertiary consumer predator/ Foxes 3rd trophic level secondary consumer herbivore/ Mice 2nd trophic level primary consumer autotroph/ Plants 1st trophic level primary producer Trophic Levels Eagles 4th trophic level if eagles go extinct, what Foxes 3rd trophic level could happen to… foxes? Mice 2nd trophic level mice? plants? Plants 1st trophic level Trophic Levels Eagles 4th trophic level If a new predator on mice is introduced, what Foxes 3rd trophic level could happen to… mice? Mice 2nd trophic level plants? foxes? Plants 1st trophic level eagles? Trophic Levels Eagles 4th trophic level If drought caused a dip in plant production, what Foxes 3rd trophic level would happen to… mice? Mice 2nd trophic level foxes? eagles? Plants 1st trophic level Simplified Temperate Forest Food Web What happens to when it’s a WEB instead of a CHAIN? Wolf Eagle Fox Shrews Deer Rabbit Caterpillars Oak seedling Grasses Herbs In long term, balance is restored That is the end!
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