Community ecology: History and theory

Dr. Dan Simberloff

region

landscape

ecosystem

community

population

individual

Main goal of community ecologists: to understand why particular species do or do not coexist in the same community, and torelate this to how many species are in acommunity.

Series of related theories or ideas based onthe 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 hypothesisb) 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 hypothesisb) species/genus ratios and related

statistics - islandsc) Gause’s competitive exclusion principle

Georgyi Gause1910-1986

1934

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)

G. Gause, 1930s,experiments onParamecium and yeast.

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 hypothesisb) species/genus ratios and related

statistics - islandsc) Gause’s competitive exclusion principled) limiting similarity

- invasion

Robert MacArthur1930-1972

Richard Levins1930 -

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 the2 existing species is less than 0.544.

“species packing”

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 hypothesisb) species/genus ratios and related statistics - islandsc) Gause’s competitive exclusion principled) limiting similarity - invasion

e) priority effects

Jim Drake Tad Fukami

“priority effects” = “historical contingency”