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#3 Ch. 5: Ecosystems and Living Organisms Objectives: Describe the factors that contribute to an organism’s ecological niche. Define competition, and relate the concepts of competitive exclusion and resource partitioning. Define symbiosis, and distinguish among mutualism, commensalism, and parasitism. Define predation, and describe the effects of natural selection on predatorprey relationships. Define keystone species, and discuss the sea otter as a keystone species. Community Ecology Community: an association of different populations of organisms that live and interact in the same place at the same time o the organisms in a community play a variety of roles and interdependent on one another in many ways Ecological niche: an organism’s role within the structure and function of an ecosystem o takes into account all aspects of the organism’s existence the jobs and relationships it has, all the things it needs to survive, its habitat, etc. if there was no competition, an organism’s niche could be very large (fundamental niche), but because competition does exist, organisms are limited in the lifestyles they can actually live and the resources they can actually use (realized niche) example: mangrove trees versus other tree species o a species’ adaptations help determine its niche determine the species’ tolerance for different environmental conditions (organisms cannot just live any old place!) limiting resource: any resource at a suboptimal level relative to an organism’s need for it or at a level in excess of an organism’s tolerance for it #3 3 main types of interactions that occur among species in a community: Competition can be either intra- or inter-specific competitive exclusion: no two species can indefinitely occupy the same niche in the same community one species will eventually outcompete the other and exclude the losing species from a portion of the niche competition is always negative for all species involved (takes E to compete) natural selection favors individuals of each species that avoid or attempt to reduce competition resource partitioning o may include timing of feeding, location of feeding, nest sites, etc. Symbiosis – when individuals of one species usually live in or on the individuals of another species – at least one of the species will use the other’s resources and benefit – the result of coevolution (the evolution of one species directly affects the evolution of another, and vice versa) • e.g. flowers + animal pollinators – flowers attract animals with scents, colors, foods – animals have body parts and behaviors that are perfect for carrying pollen #3 Mutualism +, + o e.g. flowers + animal pollinators! o e.g. mycorrhizae o mutualistic associations between fungi and about 80% of all plants o fungus absorbs nutrients and provides them to the plant o the plant provides food for the fungus o plants grow more vigorously and are better able to tolerate stressors Commensalism +, o o e.g. trees + epiphytes o small plants that live attached to the bark of tree branches o the epiphyte has better access to water and light Parasitism +, o the parasite lives on (exo-) or in (endo-) the host, and weakens it, but rarely kills it o e.g. dogs + ticks o e.g. humans + tapeworms Predation includes animals eating animals AND animals eating plants coevolution of predator and prey strategies Predator Strategies pursuit requires traits that increase hunting efficiency (speed, intelligence) o e.g. orcas ambush make use of camouflage and lures o e.g. goldenrod spider o e.g. anglerfish Prey Strategies plant defenses since plants can’t move, they have to have adaptations that protect them #3 hard to eat = spines, thorns, tough leaves, wax unpalatable or toxic = protective chemicals (e.g. marijuana, opium poppy, tobacco, peyote) example of coevolution milkweed and monarch butterflies animal defenses the #1 defense used is RUNNING mechanical defenses = barbed quills, shells social behavior = dilution effect chemical defenses o e.g. South American poison arrow frog warning coloration camouflage o e.g. caterpillar “twigs,” pipefish “eelgrass,” pygmy seahorse “coral” Keystone Species species vital in determining the nature and structure of the entire ecosystem usually not the most abundant, but if you take them out of the ecosystem … e.g. gray wolf, sea otter