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Chapter 13

BIOL 180 Chapter Notes - Chapter 13: Intraspecific Competition, Allele Frequency, Competitive Exclusion Principle

Course Code
BIOL 180
John W Parks

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BIOL 180 – Reading Notes 13
Competition: (-/-)
Lowers the fitness of both individuals involved
oTime and energy are limited
Energy is put into competition which reduces the amount available for
reproducing, foraging, and other activities that increase fitness
Intraspecific ("within-species") competition:
oOccurs between members of the same species
Competition for
Other resources
This competition intensifies as population's density increases
oMajor cause of density dependent growth
Interspecific ("between-species") competition:
oOccurs when individuals from different species use the same limiting resources
oMay be directly competing
Ex. Lion fighting off a hyena for control over zebra carcass
oMay be indirectly competing
Ex. Finch consumes all the available seeds on a bush, leaving no seeds for
species visiting the bush later
Using the Niche Concept to Analyze Interspecific Competition:
Niche: range of resources that the species is able to use or the range of conditions it can
oINTERSPECIFIC COMPETITION occurs when the niches of the two species overlap
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oIndividuals competing for the overlapped resource lowers in fitness
Expend extra time and energy trying to get these seeds and also most likely
acquire fewer seeds because of the presence of competing individuals
oSymmetric competition: both species experience a similar decrease in fitness due to the
overlap of their niches
What happens when One Species is a Better Competitor?
Asymmetric competition: one species suffers a greater fitness decline than the other species
oDepends on the amount of overlap in niches
oOnly the group that experiences less fitness decline continues logistic growth until
carrying capacity
Lower carrying capacity than if they were alone though
oOther species who suffers a greater fitness decline = driven to extinction
Competitive Exclusion Principle: two species that occupy the exact same niche (in both biotic
and abiotic dimensions) CANNOT COEXIST
When niches do not overlap completely:
oFundamental niche: total theoretical range of environmental conditions that a species
can tolerate
No other species / competition present
oRealized niche: portion of the fundamental niche that a species ACTUALLY occupies,
given limiting factors such as COMPETITION WITH OTHER SPECIES
Experimental Studies of Competition in Nature:
Fundamental niches of the two species partially overlap
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