lecture+15+community+ecology

Species 1 2 3 4 5 1 0 2 0 0 3 0 4 0 0 0 5 0 0

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Species 1 2 3 4 5 1 - + + 0 2 - + 0 0 3 - + 0 + 4 + 0 0 0 5 0 0 - 0 Remember - a minus indicates that the growth of the other species’ population in the pair causes a decrease in the target species, a plus indicates that growth of the other species’ population causes an increase in the target species.
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Algae Grazers on Algae Small Fish that eat Grazers Big Fish that eat Small Fish
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Indirect Effects Through Competition Indirect mutualism also is possible through competition if three species use a resource, divide it up but overlap in its use, then the two “extreme” species may be (in effect) indirect mutualists
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Keystone Species Keystone species are defined as species that are not very abundant or apparent, but that exert a lot of leverage on the functioning of the system - Wolves in Yellowstone There are multiple examples of high-level predators that function as keystones . (Losing top predators to extinction therefore can be a disruption with lots of cascading effects as we are seeing in many marine ecosystems)
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Keystone Mutualists? Fig trees have been suggested as “keystone mutualists ” in tropical American forests. Often, they aren’t abundant – but they produce fruit as at a season when very few other plants do, they do so reliably, and so they carry the fruit-eating animals through a time when their populations might otherwise crash to the detriment of the many other fruit-producing trees in the area
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Collective Properties A complementary way of thinking about ecological communities is to evaluate the
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