Interspecific Competition Chapter 6 Interspecific Competition n Individuals

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Interspecific Competition Chapter 6

Interspecific Competition Chapter 6

Interspecific Competition n Individuals of one species suffer reduction in fecundity, survivorship, or growth

Interspecific Competition n Individuals of one species suffer reduction in fecundity, survivorship, or growth as a result of exploitation of resources or interference by individuals from another species

Interspecific Competition n n May exclude one another from particular habitats (no coexistence) Or

Interspecific Competition n n May exclude one another from particular habitats (no coexistence) Or may coexist (utilize slightly different habitats)

Interspecific Competition n Exploitation or interference

Interspecific Competition n Exploitation or interference

Exploitation - diatoms n n n OK when alone, but one disappears when together

Exploitation - diatoms n n n OK when alone, but one disappears when together More effective exploiters exclude less effective ones Depresses resources so low other species can’t survive

Interference - barnacles One species pushes other off rock surfaces

Interference - barnacles One species pushes other off rock surfaces

Highly Assymetric n n Consequences not same for both species One harmed greatly, other

Highly Assymetric n n Consequences not same for both species One harmed greatly, other less so or not much at all

More Effects n n Competition for one resource affects competition for other resources E.

More Effects n n Competition for one resource affects competition for other resources E. g. , plants competing for light have ability to compete for nutrients affected

Competition Models n n Lotka-Volterra model Examines changes in abundance of one species while

Competition Models n n Lotka-Volterra model Examines changes in abundance of one species while in competition with another species

Competition Models

Competition Models

Competition Models 4 possible outcomes

Competition Models 4 possible outcomes

Competition Models n n Species 1 is stronger competitor, so 1 wins Species 2

Competition Models n n Species 1 is stronger competitor, so 1 wins Species 2 is stronger competitor, so 2 wins Both species are stronger competitors on each other than on themselves, so may exist in unstable coexistence Both species are weak competitors, so exist in stable coexistence

Coexistence n n Partitioning of resources, differentiation of realized niches Species deprived of realized

Coexistence n n Partitioning of resources, differentiation of realized niches Species deprived of realized niche by a competitor is driven to extinction

Competitive Exclusion Principle n n If two competing species coexist in stable environment, then

Competitive Exclusion Principle n n If two competing species coexist in stable environment, then they do so as a result of niche differentiation. If there is no such differentiation, one competing species will eliminate the other.

Niche Differentiation n How much niche differentiation is necessary for species to coexist?

Niche Differentiation n How much niche differentiation is necessary for species to coexist?

Niche Differentiation n Interspecific competition tends to increase separation along gradient (reduce overlap) to

Niche Differentiation n Interspecific competition tends to increase separation along gradient (reduce overlap) to reduce the effects of the competition

Niche Differentiation n Intraspecific competition tends to decrease separation along gradient by expanding each

Niche Differentiation n Intraspecific competition tends to decrease separation along gradient by expanding each species’ use of the gradient

Niche Differentiation n Niche differentiation results from interaction of the effects of intra- and

Niche Differentiation n Niche differentiation results from interaction of the effects of intra- and interspecific competition

End result? n n Environment may not be constant enough for effects of competition

End result? n n Environment may not be constant enough for effects of competition to reach final conclusion Environment may change before one competitor wins

Evidence for interspecific comp. n n n Laboratory experiments Controlled conditions Simple environment, unlike

Evidence for interspecific comp. n n n Laboratory experiments Controlled conditions Simple environment, unlike natural

Evidence for interspecific comp. n n n Manipulative field experiments Reduce density of one,

Evidence for interspecific comp. n n n Manipulative field experiments Reduce density of one, see how other responds Best for sessile organisms

Evidence for interspecific comp. n n Natural experiments Competitive release expansion of niche in

Evidence for interspecific comp. n n Natural experiments Competitive release expansion of niche in absence of competitor compared to size in presence of competitor

Evidence for interspecific comp. n n Natural experiments Character displacement morphological difference between allopatric

Evidence for interspecific comp. n n Natural experiments Character displacement morphological difference between allopatric (species alone) and sympatric (species together) populations