BIOB50Winter2012 Lecture 22.docx - includes images and relevant textbook notes!

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12 Apr 2012

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BIOB50Winter2012 Lecture 22: Lottery Competition and Neutral Theory (Chapter 18)
o The competitive exclusion principle : two species that use a limiting resource in the same way cannot coexist
o Joseph Grinnell first used the term “niche” in 1917 as: no two species of birds or mammals will be found to
occupy precisely the same niche
o Figure 18.4 Community membership: A series of Filters species end up in a local community by passing through
a series of filters that determine community membership. Species are lost at each filter so local communities
contain only a fraction of species in the regional pool. In practice, all filter work at the same time, rather than in
a series as the figure suggests
Community Membership
o Species diversity differs among communities due to variation in regional species pools, abiotic conditions and
species interactions
o There are three schools of thought about what controls community diversity
o 1) Equilibrium Theory: ecological and evolutionary compromises lead to resource partitioning
o 2) Nonequilibrium Theory: fluctuating conditions keep dominant species from monopolizing resources
o 3) Neutral Theory: species do not differ and diversity patterns are product of dispersa, speciation and
demographic stochasticity
Equilibrium Theories Resource Partitioning
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