BeetlemaniaThis resource ain’t big enough for two of us

© Steven Begin CC-BY-NC-SA

Darwinian Competition

‘As the species of the same genus usually have, though by no means invariably, much similarity in habitats and constitution, and always in structure, the struggle will generally be more severe between them, if they come into competition with each other, than between the species of distinct genera.’

(Darwin 1959)

Ecological effects of

one species on the other

Species 2

+ -

Species 1+ Mutualism Predation

- Predation Competition

Competition occurs when two species each require the same limited resource. The availability of the resource to one species is negatively influenced by the presence of the other species. It is a "-/-" interaction.

Triboliumconfusum

Triboliumcastaneum

Park, Thomas (1948) Interspecies Competition in Populations of Trilobium confusum Duval and Trilobium castaneum Herbst. Ecological Monographs 18(2):265-307http://www.jstor.org/stable/1948641

Images” © Sarefo CC-BY-SA from http://commons.wikimedia.org

Gause’s Competitive Exclusion Principle:When two species make similar demands

on a limited resource, then one or the other species will go extinct as a result of

competition for the resource.

In Park’s experimentsone species won and the other went extinct in every

one of the 170 Tribolium competition populations, providing strong support for Gause’s principle.

Equilibrium population size when reared ALONE Predict the

winner of the competition

Climate T. castaneum T. confusum

Cold-Dry 21 208

Cold-Wet 99 225

Warm-Dry 150 237

Warm-Wet 401 264

Hot-Dry 77 190

Hot-Wet 306 329

Equilibrium population sizes when reared ALONE

Winner in COMPETITION

ClimateT.

castaneumT. confusum T. castaneum T. confusum

Cold-Dry 21 208 0% 100%

Cold-Wet 99 225 30% 70%

Warm-Dry 150 237 13% 87%

Warm-Wet 401 264 86% 14%

Hot-Dry 77 190 10% 90%

Hot-Wet 306 329 100% 0%

Environment dependenceIn the Cold-Dry climate, T. confusum

eliminated T. castaneum in every two-species replicate.

In the Hot-Wet climate, T. castaneum always eliminated T. confusum.

StochasticityIn the intermediate environments, each species won in some of the

replicates.The outcome of competition is not

deterministic.