Biology 146L ECOLOGY - Claremont...
Transcript of Biology 146L ECOLOGY - Claremont...
BIOTIC INTERACTIONSCompetitionMutualismPredationHerbivoryParasitismDisease
Species 2
Species 1 ‐ / ‐
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This lead to Gause’s COMPETITIVE EXCLUSION PRINCIPLE
No two species can coexist indefinitely on the same limiting resource
Many similar species DO coexist; therefore the CEP requires that these species have different NICHES
Monteverde, Costa Rica: 12 species of hummingbirds
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Modelling Competition
ΔN = r1 N1 ( K1 ‐ N1 ) = Logistic growth in a single speciesΔt K1
But for 2 competing species the K value (resources) is impacted not only by N1 but also by N2
If the impact of one individual of N1 = one individual of N2, then:
ΔN1 = r1 N1 ( K1 ‐ (N1 + N2 )) which is r1 N1 ( K1 ‐ N1 ‐N2 )Δt K1 K1
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However the per capita impact of Species 2 on K may differ from the impact of Species 1 :
ΔN1 = r1 N1 ( K ‐ N1 – α1,2 N2 )Δt K
Where α1,2 is the competition coefficient
Elephant M ~ 5000 kgGiraffe M ~ 1000 kg
ΔN2 = r2 N2 ( K ‐ N2 – α2,1 N1 )Δt K
ele, gir = 0.2 8
In nature, there are three possibilities:
• Competition is prevalent
• Competition is rare, because of COMPETITIVE DISPLACEMENT
• Predation, disease etc hold the population below levels at which competition would become significant.
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Species sympatric allopatric Sym. ratio
Allop.ratio
Weasels(skull)
Mustelanivalis
39.3 42.9 1.28 1.07
Mustelaerminea
50.4 46.0
Darwinsfinches(beak)
Geospizafortis
12.0 10.5 1.43 1.13
Geospizafuliginosa
8.4 9.3
The Hutchinsonian ratio
Mean separation resulting from competitive displacement is 1.28
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