community structure new views

community structure new views - Community Structure Part 2:...

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Community Structure Part 2: A new view Old view: lots of evidence that birds compete. Therefore, competition has to be important. First, let’s back up and recall the goal : “The mission of community ecology, as of any scientific endeavor, is to detect the patterns and explain the causal processes that underlie them” (John Weins)
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There are two sets of challenges to the classic view of community structure The mission of community ecology, as of any scientific endeavor, is to detect the patterns and explain the causal processes that underlie them” (John Weins) 1) The patterns are not really there and so nothing needs to be explained… the theory has caused a generation of ecologists to waste a monumental amount of time ” ( Dan Simberloff ) 2) The patterns are there, but too much emphasis is placed on one process – competition. We’ll tackle #2 first
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How important is competition? How consistently are the conditions right for it? All scientists are biased; they tend to see what they believe is true. Competition is important. Here’s the evidence Example: Obvious differences in where and how tits forage. Competition is what caused those differences. But, the logic is deceptively simple (anectodal) - if you look hard enough, you’ll always find differences. (If you don’t, it’s a problem with you, not the theory.)
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It’s human nature … An example: http://www.dothetest.co.uk/
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Competition theory has two “hidden” assumptions 1. Natural selection is continuous and intense. ( Resources are constantly limiting ) If resources are often abundant, then competition may rarely come into play. 2. Communities are in equilibrium ( Population size grows until it becomes limited, then stays constant ) No “slop” in the system. Number of individuals and species is at carrying capacity.
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A case study of whether those 2 assumptions are met Grassland bird communities - two dimensional habitat; easy to study (vs. tits) - not many types of birds or prey
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community structure new views - Community Structure Part 2:...

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