Community ecology: History and theory
Dr. Dan Simberloff region
landscape
population individual
Main goal of community ecologists: to understand why particular species do or do not coexist in the same community, and to relate this to how many species are in a community.
Series of related theories or ideas based on the notion that species that are very similar cannot coexist in the same local community.
Definition and measurement of “similarity” varies, as does meaning of “very.”
a) Darwin’s naturalization hypothesis
In The Origin of Species, Darwin (1859) drew attention to observations by Alphonse de Candolle (1855) that floras gain by naturalization far more species belonging to new genera than species belonging to native genera. Darwin (1859, p. 86) goes on to give a specific example: “In the last edition of Dr. Asa Gray's `Manual of the Flora of the United States' … out of the 162 naturalised genera, no less than 100 genera are not there indigenous.” “As the species of the same genus usually have, though by no means invariably, much similarity in habits and constitution, and always in structure, the struggle will generally be more severe between them” (Darwin 1859, p. 60). a) Darwin’s naturalization hypothesis b) species/genus ratios and related statistics – islands
Charles Elton
1927 1958 Letter from Charles Elton to Aldo Leopold, 1941 1946, J. Anim. Ecol. 15:54
a) Darwin’s naturalization hypothesis b) species/genus ratios and related statistics - islands c) Gause’s competitive exclusion principle
Georgyi Gause 1910-1986
1934 G. Gause, 1930s, experiments on Paramecium and yeast.
Joseph Grinnell, 1904: "Two species of approximately the same food habits are not likely to remain long evenly balanced in numbers in the same region. One will crowd out the other.”
(Image from: http://www.slideshare.net/docsawyer/11-ecology) 1934
(Images from: https://www.studyblue.com/notes/note/n/exam-3/deck/15957221) (Images from: https://www.studyblue.com/notes/note/n/exam-3/deck/15957221) Ecology 1958 by D. Kaspari a) Darwin’s naturalization hypothesis b) species/genus ratios and related statistics - islands c) Gause’s competitive exclusion principle d) limiting similarity - invasion
Robert MacArthur Richard Levins 1930-1972 1930 - “species packing”
2 species can coexist only if α (the per capita effect of each species on the other) is less than 0.544. And a 3rd species can invade only if its α with each of the 2 existing species is less than 0.544. Key results: 1) Harder for a new species to invade a community the more species are originally present. 2) A species that would be a superior competitor if it invaded cannot invade if α among resident species is high enough 3) “PRIORITY EFFECT” a) Darwin’s naturalization hypothesis b) species/genus ratios and related statistics - islands c) Gause’s competitive exclusion principle d) limiting similarity - invasion e) priority effects
Jim Drake Tad Fukami “priority effects” = “historical contingency”