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Community Ecology Community = group of populations of different species living close enough to interact Interspecific interactions – can be positive (+), negative (-), or neutral (0)-Includes…--Competition (-/-): two or more species compete for a resource that is in short supply. --Predation (+/-): one species, the predator, kills and eats the other, the prey. Predation has lead to diverse adaptations, including mimicry. ---Defensive adaptations to predation:-cryptic coloration – camouflaged by coloring-aposematic/warning color – bright color of poisonous animals-Batesian mimicry – harmless sp mimic color of harmful sp-Mullerian mimicry – 2 bad-tasting sp resemble each other, both to be avoided --Herbivory (+/-): An herbivore eats part of a plant or alga. Plants have various chemical and mechanical defenses against herbivory (toxins, spines/thorns), and herbivores have special adaptations for feeding. --Symbiosis: individuals of 2 or more species live in close contact with one another. Symbiosis includes parasitism, mutualism and commensalism.---parasitism (+/-): the parasite derives its nourishment from a second organism, the host, which is harmed.---mutualism (+/+): both species benefit from the interaction---commensalism (+/0): one species benefits from the interaction while the other is unaffected by it. --Facilitation (+/+ or 0/+): species have positive effects on the survival and reproduction of other species without the intimate contact of a symbiosis. Interspecific competition: resources are in short supply. Species interaction is -/--Competitive exclusion principle: two species cannot coexist in a community if their niches are identical – the one with the slight advantage will eliminate the other.-Resource partitioning: differences in niches that enable similar species to coexist. Ecological niche = the sum total of an organism’s use of abiotic/biotic resources in the environment.-fundamental niche: the niche potentially occupied by the species-realized niche: portion of fundamental niche the species ACTUALLY occupies Community Structure-Species diversity = species richness (# of different species) + relative abundance of each species.-Shannon Diversity Index: calculate diversity based on species richness and relative abundance.-Highly diverse communities are more resistant to invasive species-Invasive species = organisms that become established outside native range ex: kudzu – vine from japan, noxious weed that kills trees and shrubsex: dutch elm disease – fungus carried by beetles, arrived in US on logs imported from Netherlands, killed many elm trees across US, Canada, Europe.ex: potato blight – fungus-like disease caused Irish potato famine in 1840s, arrived in Ireland from US ships, only 1 species of potato planted in Ireland (all susceptible to the disease), 1 million people died, problem with monoculture and lack of genetic diversity of crops Trophic Structures:-the trophic structure of a community is determined by the feeding relationships between organisms.-trophic levels = links in the trophic structure-the transfer of food energy from plants à herbivores à carnivores à decomposers is the food chain-inefficiency of energy transfer between trophic levels limits the length of the food chain (10% rule)-long food chains are less stable that short ones-two or more food chains linked together are called food webs-a given species may weave into a web at more than one trophic level Dominant species: has the highest biomass or is the most abundant in the community Keystone species: exert control on community structure by their important ecological niches. -ex: sea otter (loss à increase sea urchins à destruction of kelp forests) -ex: grizzly bear (transfer nutrients from sea to land by salmon diet) -ex: prairie dogs (burrows, soil aeration, trim vegetation) Disturbances influence species diversity and composition-a disturbance changes a community by removing organisms or changing resource availability (fire, drought, flood, storm, human activity) Ecological Succession: transitions in species composition in a certain area over ecological time.-Primary Succession: plants and animals invade where soil has not yet formed. Ex: colonization of volcanic island or glacier.-Secondary Succession: occurs when existing community is cleared by a disturbance that leaves soil intact. Ex: abandoned farm, forest fire. Biogeographic Factors:Important factors:1. Latitude: species more diverse in tropics than poles2. Area: larger areas are more diverse Biogeographic islands = natural labs for studying species diversity-influenced by size and distance -larger islands à greater immigration, lower extinction -far from mainland à immigration falls, extinction rates increase
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