Biogeog_3_4_5_2009

Biogeog_3_4_5_2009 - GEOG102:BIOGEOGRAPHY3 COMMUNITIES...

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GEOG 102: BIOGEOGRAPHY 3 COMMUNITIES Ch 19, p 650­653, Old Version Ch 19, p 655­659, New Version Community ­ groups of populations of different species in the same place at the same time A. COMMUNITY DISTRIBUTIONS 1. Toposequence ­ a series of communities that differ in topography or soils characteristics ­ no successional relationship to one another 2. Chronosequence ­ a series of communities at one location that differ in stage of development ­ stage of development depends on time since last disturbance and the type and severity of that disturbance ­ chronosequence studies – compare sites with the same abiotic characteristics that differ in time since disturbance and disturbance history
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B. PATTERNS IN TIME: SUCCESSION AND DISTURBANCE 1. Succession ­ change in species composition over time ­ other community characteristics, structure and environment, also change ­ ongoing process that never ends a. primary succession b. secondary succession 2. Disturbance ­ any relatively discrete event in time that disrupts ecosystem, community or population structure and changes resources, substrate availability, or the physical environment ­ severe disturbances initiate successional sequences a. direct disturbance b. indirect disturbance
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3. Post­disturbance changes = successional change ­ 4 categories of change a. modification of the environment by plants b. modification of the environment by animals c. differences between species d. modification of the environment by new disturbances 4. “Climax = vegetation that exists at the “end” of succession ­ implies complexity and stability ­ three problems with the climax concept: a. b. c. 5. Patch Dynamics ­ combination of patches of vegetation in a landscape with different disturbance histories that are in different stages of succession ­ each patch is undergoing succession and change ­ combined, the patches create a dynamic mosaic or dynamic equilibrium
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Example: Coastal Forest in British Columbia
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