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Beetlemania
This 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)
Species 2
Ecological effects of
one species on the other
+
-
+
Mutualism
Predation
-
Predation
Competition
Species 1
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.
Tribolium Tribolium
confusum castaneum
Park, Thomas (1948) Interspecies
Competition in Populations of Trilobium
confusum Duval and Trilobium castaneum
Herbst. Ecological Monographs 18(2):265-307
http://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 experiments
one 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
Climate
T. castaneum
T. confusum
Cold-Dry
21
208
Cold-Wet
99
225
150
237
401
264
Hot-Dry
77
190
Hot-Wet
306
329
Warm-Dry
Warm-Wet
Predict the
winner of the
competition
Equilibrium population
sizes when reared ALONE
Winner in COMPETITION
Climate
T. castaneum
T. 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 dependence
In the Cold-Dry climate, T. confusum
eliminated T. castaneum in every twospecies replicate.
In the Hot-Wet climate, T. castaneum
always eliminated T. confusum.
Stochasticity
In the intermediate environments,
each species won in some of the
replicates.
The outcome of competition is not
deterministic.