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ANTHROPOGENIC ENVIRONMENTS - ANTHROPOGENIC ENVIRONMENTS...

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1/15/12 ANTHROPOGENIC ENVIRONMENTS 1/4 courses.Zashington.edu/anth457/anthropogenic.htm ANTHROPOGENIC ENVIRONMENTS & NON-EQUILIBRIUM ECOLOGY Topics for this lecture: 1) Basic concepts of ecological dynamics & succession 2) Equilibrium vs. non-equilibrium paradigms 3) Anthropogenic environmental change: Ecological d\namics: basic concepts Ecological community: set of species (flora & fauna) inhabiting a given place Succession: change in community composition over time (e.g., following a disturbance) Ecological disturbance: major perturbation (in species composition, ecosystem function, etc.) ± Disturbance agents = fire, wind, volcanism, etc. (see below for more) ± Disturbances vary in magnitude and frequency ± Intermediate-level disturbance regime continually "resets" the succession cycle in small areas ("patches") ± This results in a shifting ³patch mosaic´ at the landscape scale Patch mosaic = set of habitat patches differing in species composition, age since disturbance, etc. ± Mosaics classified by patch size & degree of heterogeneity (³coarse-grained, fine-grained´) Ecological succession Ecological succession refers to a fairly regular sequence of changes in plant (and to a lesser extent animal) species composition following a disturbance Initially, pioneering plant species ("weeds," generalists with a high reproductive rate) colonize disturbed habitats (e.g., Mt. St. Helens after eruption) These are gradually replaced (out-competed) by more specialized species (lower reproductive rate, more shade-tolerant, etc.) Classic view is that late-succession habitats (³climax´) have the highest species diversity and stability ± In many cases, it turns out that diversity actually highest in intermediate period (between early and late succession stages) ± Evidence suggests that many late-succession habitats are leVV stable than earlier phases Ecological stability = likelihood that a system (e.g., habitat, set of interacting species) will remain unchanged over time ± Stability ultimately depends on frequency and magnitude of disturbances Ecological UeVilience = likelihood that a system will return to roughly same state (species diversity, ecological function) following disturbance ± Disturbances = physical (e.g., fires, floods, hurricanes, volcanic eruptions) or biological (e.g., predation, disease, overgrazing) ± Biological causes include anthropogenic (human-caused) ones: fire, clearing, harvesting, etc.
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