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Competition
Chapter 13
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http://www.youtube.com/watch?v=h6nhOChpMck
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Modes of Competition
• Interference:
–
• Intraspecific:
–
• Interspecific:
–
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Bart’s hay field…
http://www.gardenseeker.com/herbs/images/alfalfa_sprouted.jpg
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Intraspecific Competition Among
Herbaceous Plants
• Plants compete for…
• Competition is more intense at …
• Self-Thinning (-3/2 or -1/2 slope rule)
¿How does this explain influence spacing in
plants?
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Intraspecific Competition Among
Herbaceous Plants
What pattern is
present? Why?
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Niches
• Niche:
• Gause:
– Two species with identical niches cannot coexist
indefinitely.
• One will be a better competitor and thus have higher
fitness and eventually exclude the other.
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Niches
• Hutchinson defined niche as:
–
• n equates the number of environmental factors
important to survival and reproduction of a species.
–
–
- hypervolume
includes interactions
such as competition that may restrict
environments where a species may live.
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Feeding Niches of Galapagos Finches
How have these finches partitioned the
seed resources available?
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Feeding Niches of Galapagos Finches
– Grant found differences in beak size among
ground finches translates directly into diet.
• Size of seeds eaten can be estimated by measuring
beak depths.
– Individuals with deepest beaks fed on hardest seeds.
• After 1977 drought, the remaining seeds were very
hard. Thus, mortality was most heavy in birds with
smaller beaks.
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Mathematical and Laboratory Models
• Metz summarized models:
– Abstractions and simplifications, not facsimiles of
nature.
– Man-made construct; partly empirical and partly
deductive.
– Used to provide insights into natural phenomena.
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Lotka Volterra
• In general, LV predicts coexistence of two
species when, for both species, interspecific
competition is ___________ than
intraspecific competition.
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Paramecia Lab Experiments
What happened
when grown
together?
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Paramecia Lab Experiments
• Gause demonstrated resource limitation with
Paramecium caudatum and Paramecium
aurelia in presence of two different
concentrations of Bacillus pyocyaneus.
– When grown alone, carrying capacity determined
by intraspecific competition.
– When grown together, P. caudatum
quickly
?
declined.
• Reduced resource supplies increased competition.
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Competition and Niches
• Competition can restrict species to their
realized niches.
– But if competitive interactions are strong and
pervasive enough, they may produce an
evolutionary response in the competitor
population.
• Changes _______________________.
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Niches and Competition Among Plants
• Tansley suggested
interspecific competition
restricts realized niche of
each of two species of
bedstraw (Galium spp.)
to a narrower range of
soil types.
• Can you think of other
variables/resources that
could be partitioned?
http://www.onrcd.org/bedstraw.html
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What limits
Chthamalus
here?
What limits
Chthamalus
here?
What limits
Chthamalus
here?
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What effect did
Balanus
removal have?
What effect did
Balanus removal
have?
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Competition and Niches of Small
Rodents
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Competition and Niches of Small
Rodents
• Brown studied competition among rodents in
Chihuahuan Desert.
– Predicted if competition among rodents is mainly
for food, then small granivorous rodent
populations would increase in response to
removal of larger granivorous rodents.
• Insectivorous rodents would show little or no response.
• Results supported hypothesis.
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Character Displacement
• Because degree of competition is assumed to
depend upon degree of niche overlap,
interspecific competition has been predicted
to lead to directional selection for reduced
niche overlap.
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Character Displacement
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Character Displacement
• Taper and Case: Necessary criteria:
– Morphological differences between __________
___________ are statistically greater than
differences between ___________ ___________.
– Differences between sympatric and allopatric
populations have ___________ _______.
– Differences between sympatric and allopatric
populations evolved in place, and are ____ _____
____________ __________ __________ already
differing in the character.
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Taper and Case: Characteristics
– Variation in the character must have a ______
____________ on use of resources.
– Must be demonstrated ______________ for the
resource and competition must be directly
correlated with character similarity.
– Differences in character cannot be explained by
differences in resources available to each of the
populations.
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