Reading: On the Origin of Ecological Structure
Scientists debate what dictates species composition in biological communities
-Alexander von Humbolt (1800s) - Essay on the Geography of Plants described how vegetation varies with altitude, climate, etc.
-gave evidence to physical determinants of ecological structure
-Charles Darwin (mid-1800s) - noted that species composition in a community changes through time
-There is still no consensus on the relative importance of various factors affecting ecological structure, but new research may point to importance of evolution
Species abundance and composition define a biological community
-Physical factors ("environmental filters") broadly determine which species can live where
-Gause's (1930s) experiments with Paramecium and other organisms suggested competitive exclusion, since when competing for a limited resource, Paramecium always won
-real communities are more complicated
-Keystone predators - eat strong competitors, help weaker competitors to persist
-Some species also alter the physical environment, affecting species composition (ex. beavers build dams in rivers)
Other explanations of ecological structure
-Jared Diamond (1975) - "assembly rules"
-only some of the possible combinations of species actually coexist in nature
-there are some "forbidden species combinations"
-Stephen Hubbell (1997) - "unified neutral theroy of biodiversity"
-all organisms of the same trophic level are demographically identical (competition between species not important)
-species composition determined by random dispersal, speciation, extinction
-some scientists disagree with Hubbell because there are functional differences between species, but it is true that some events are random (ex. colonization)
Conclusion: general community rules can be useful, but may not be able to make predictions on smaller scale or on unstudied communities.