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Ch. 53 Community Ecology

Ch. 53 Community Ecology A community's interactions include competition, predation, herbivory, symbiosis and disease Dominant and keystone species exert strong controls on community structure Disturbance influences species diversity and composition

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Ch. 53 Community Ecology

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  1. Ch. 53 Community Ecology A community's interactions include competition, predation, herbivory, symbiosis and disease Dominant and keystone species exert strong controls on community structure Disturbance influences species diversity and composition Biogeographic factors affect community biodiversity Contrasting views of community structure are the subject of continuing debate

  2. Interspecific competition - species compete for a particular resource that is in short supply Ex: grasshopper and bison in Great Plains (-, -) Competitive exclusion - strong competition can lead to the local elimination of one of the two competing species

  3. Ecological niche - sum total of a species' use of the biotic and abiotic resources in its environment If an organism's habitat is its "address," the niche is the organism's "profession" Resource partitioning - differentiation of niches that enables similar species to coexist in a community

  4. Character displacement - the tendency for characteristics to be more divergent in sympatric (geographically overlapping) populations of two species than in allopatric (geographically separate) populations of the same two species

  5. Predation - (+, -) one species, the predator, kills and eats the other, the prey Seed predators - chew up or digest plant seeds Cryptic coloration - camouflage Aposematic coloration - animals with effective chemical defenses often exhibit bright warning coloration

  6. Mimicry Batesian mimicry - a palatable or harmless species mimics an unpalatable or harmful model Ex: hawkmoth larva puffs up and weaves head like a poisonous snake Mullerian mimicry - two or more unpalatable species resemble each other Ex: cuckoo bee and yellow jacket

  7. Herbivory - (+, -) when an herbivore eats a plant or alga Herbivores have adaptations to detect palatable plants and digest them Plants have chemical defenses

  8. Parasitism - (+, -) one organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process Endoparasitism - parasites that live inside the host Ectoparasitism - parasites that feed on the external surface of hosts Parasitoidism - insects lay eggs on or in living hosts, then the larvae then feed on the body of the host, eventually killing it

  9. Disease - when pathogens invade a host (+, -) Pathogen - disease causing agent, microscopic Ex: virus, bacteria, protist, fungi, prions

  10. Mutualism - benefits both species (+,+)

  11. Commensalism - one species benefits, the other is not affected (+, 0)

  12. Coevolution - reciprocal evolutionary adaptations of two interacting species

  13. Species Diversity - the variety of different kinds of organisms that make up the community 1. Species richness - total number of different species in the community 2. Relative abundance - the proportion each species represents of the total individuals in the community

  14. Limits to Food Chain Length Energetic hypothesis - suggests that the length of a food chain is limited by the inefficiency of energy transfer along the chain Food chains should be relatively longer in habitats of higher photosynthetic productivity since the starting amount of energy is greater Dynamic stability hypothesis - long food chains are less stable than short food chains Food chains should be shorter in unpredictable environments

  15. Dominant species - those species in a communit that are the most abundant or that collectively have the highest biomass (total mass of all individuals in a population) Ex: American chestnut in NYC

  16. Keystone species - not always the most abundant, but exerts a strong control on community by its niche Ex: sea stars A noticeable change in the food chain/web if it is absent

  17. Foundation Species - Ecosystem Engineers

  18. Bottom-up Model N V H P *Add fertilizer to soil Top-Down Model N V H P *Remove a top predator

  19. Biomanipulation - improving water quality top-down

  20. Stability - tendency of a community to reach and maintain a relatively constant composition of species in the face of disturbances Disturbance - an event that changes a community, removes organisms from it, and alters resource availability Beneficial disturbances?? Forest fires?? Human disturbance is often severe and reduces species diversity in a community

  21. Ecological succession - when a disturbed area is colonized by a variety of species, which are gradually replaced by other species, which are in turn replaced by still other species Primary succession - when process begins in a virtually lifeless area where soil has not yet been formed; after a volanic eruption or a glacier retreated Secondary succession - when process beings after a disturbance that leaves soil intact; after a forest fire Pioneer organisms - first to live in an area

  22. Two key factors correlated with a community's species diversity are its geographic location and size Tropical habitats support many more species than do temperate and polar regions Biological time (growing seasons) runs 5 times faster in tropical regions and there are less disturbances in tropical regions

  23. Two climatic factors correlated with biodiversity are solar energy input and water availability Evapotranspiration - evaporation of water from soil plus the transpiration of water from plants

  24. Species-area curve - quantifies the idea that the larger the geographic area of a community, the greater the number of species

  25. Species richness on islands depends on: island size distance from the mainland immigration extinction

  26. The equilibrium model of island biogeography maintains that species richness on an ecological island levels off at some dynamic equilibrium point

  27. Integrated hypothesis - describes a community as an assemblage of closely linked species, locked into association by mandatory biotic interactions Individualistic hypothesis - proposes that communities are loosely organized associations of independently distributed species with the same abiotic requirements A mix of both?

  28. Rivet model: Suggests that all species in a community are linked together in a tight web of interactions States that the loss of even a single species has strong repercussions for the community Redundancy model: Proposes that if a species is lost from a community, other species will fill the gap

  29. It is important to keep in mind that community hypotheses and models represent extremes, and that most communities probably lie somewhere in the middle

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