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lecture_notes_10_1_07 - Lecture Notes How predictable is...

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Lecture Notes 10-1-07 How predictable is community variation in space and through time? Communities are dynamic in space and time; no two are ever exactly alike. Spatial variation of community composition and structure is explained in part by the geographic variation of the physical environment, but also by the history of the site -- change through time ECOLOGICAL SUCCESSION A shift in the relative abundance of populations over time in a given location under a relatively stable climate such that replacement of communities occurs COMMUNITY CHANGE TIME SCALES Geological Daily/Seasonal Successional PRIMARY SUCCESSION Ecological succession in a location that has never supported a biotic community SECONDARY SUCCESSION Ecological succession in a location where an existing biological community has been disrupted by a DISTURBANCE The pattern of Old Field Succession often seems to be: Bare Ground Annual then Perennial Grasses and Herbs Shrubs Trees Is this always the case? What explains the pattern? Before addressing these questions, need some concepts and definitions, and a word about study methods. DISTURBANCE Discrete event Changes community structure and/or function
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Events vary in spatial scale and return time Same factor (fire, flood) can be a disturbance in one circumstance, not in others Approaches Used to Study Ecological Succession Longitudinal Studies Comparative studies Physical gradients CONTEMPORARY OR MULTIPLE STEADY STATES MODEL OF SUCCESSION Patterns of change happen differently on every site.
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