Transcript Interspecific Competition

Interspecific Competition
Chapter 6
Interspecific Competition
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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
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May exclude one
another from particular
habitats (no
coexistence)
Or may coexist (utilize
slightly different
habitats)
Interspecific Competition
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Exploitation or
interference
Exploitation - diatoms
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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
Highly Assymetric
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Consequences not
same for both species
One harmed greatly,
other less so or not
much at all
More Effects
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Competition for one
resource affects
competition for other
resources
E.g., plants
competing for light
have ability to
compete for nutrients
affected
Competition Models
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Lotka-Volterra model
Examines changes in
abundance of one
species while in
competition with
another species
Competition Models
Competition Models
4 possible
outcomes
Competition Models
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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
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Partitioning of resources, differentiation of
realized niches
Species deprived of realized niche by a
competitor is driven to extinction
Competitive Exclusion Principle
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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
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How much niche
differentiation is
necessary for species
to coexist?
Niche Differentiation
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Interspecific
competition tends to
increase separation
along gradient
(reduce overlap) to
reduce the effects of
the competition
Niche Differentiation
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Intraspecific
competition tends to
decrease separation
along gradient by
expanding each
species’ use of the
gradient
Niche Differentiation
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Niche differentiation
results from
interaction of the
effects of intra- and
interspecific
competition
End result?
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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.
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Laboratory
experiments
Controlled conditions
Simple environment,
unlike natural
Evidence for interspecific comp.
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Manipulative field
experiments
Reduce density of
one, see how other
responds
Best for sessile
organisms
Evidence for interspecific comp.
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Natural experiments
Competitive release expansion of niche in
absence of competitor
compared to size in
presence of
competitor
Evidence for interspecific comp.
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Natural experiments
Character
displacement morphological
difference between
allopatric (species
alone) and sympatric
(species together)
populations