Competition

Species can compete for two resources and can coexist when 2 conditions are met:
1) The habitat must be such that one species is more limited by one resource and the other species is more limited by the other resource.
2) Each species must consume more of the resource that more limits its own growth.

Another look at plant strategies
– from Peter Grime

Grime’s C-S-R strategies
• Competitive - plants such as perennial herbs, shrubs and trees typically have dense leaf canopies, high growth rates, low seed production and relatively long life spans
•
Stressful -stress-tolerant plants that often have small evergreen leaves, low growth rates, low seed production and long life spans
• Disturbed environments - the plants are primarily
Ruderals
– plants which are usually small, grow rapidly, short life spans and produce many seeds

Grime’s C-S-R strategies

Fynbos – South African
Mediterranean shrubland

Competition in Nature – the Birth of Experimental Ecology
Joe Connell

Acorn barnacles growing on an old car tire

Acorn barnacles on the rocky coast

Sceloporus – Fence lizard

Urosaurus
– long tailed brush lizard aka tree lizard

• Competitive Release is a prediction from examining the competitive exclusion principle that in the absence of competition a species should expand its niche

Chalcophaps indica
– Emerald Dove

Chalcophaps stephani
–
Stephen’s
Dove

Gallicolumba rufigula

• Character displacement is a measurable physical difference between two species which has arisen by natural selection as a result of the selection pressure on one or both to avoid competition with each other - here we assume that environment is the same at all locations

Hydrobia ulvae
Hydrobia ventrosa

Hydrobia ulvae
– note size

The Ghost of Competition Past
Joe Connell

Patterns like character displacement or competitive release can be caused by several things:
1.
the pressure of current competition causes the pattern
2.
competition which occurred in the past may have driven natural selection to cause the pattern we see today - "the ghost of competition past"
3.
competition in the past eliminated a number of other species, leaving behind only those that were different in the use of habitat
4.
the species may have evolved independently and in different ways and have never competed with each other
5.
the species may differ in their niches, but not enough to coexist in a stable environment, however the environment varies and thus prevents competition from reaching its predicted end result

Blackburnian warbler
Cape May warbler
Black-throated green warbler
Bay-breasted warbler
Yellow-rumped warbler

Gerbillus allenbyi Meriones tristami