BIOB50H3 Lecture Notes - Lecture 7: Flea Beetle, Interspecific Competition, Intraspecific Competition

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2 Aug 2016
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Lec 7
competition
An antagonistic interaction (- / -) in which both parties are harmed by their shared use of a limiting
resource, reducing their ability to survive, grow, or reproduce.
Intraspecific competition: Competition between individuals of the same species.
Interspecific competition: Competition between members of different species.
The more limiting the resource, the more intensive the competition.
The principle of competitive exclusion
Gause’s Principle of Competitive Exclusion: Two species that use a limiting resource in the same
way cannot coexist indefinitely; one species will outcompete (exclude) the other, driving it to
extinction.
Forms of competition
Exploitation
Species impact each other by depleting a shared resource.
“Scramble” competition, they can coexist since they use this resource differently, some on day,
some on night
e.g. Mice are a shared prey resource for coyotes, foxes, and owls.
Interference
Species directly interact and “fight” over a shared resource.
“Contest” competition, actually fighting
Outcomes of competition
1. Competitive exclusion – local extinction!
2. Occupying a realized niche.
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Reduced abundance throughout your niche.
Occupy a small part of your resource niche.
3. Stable coexistence via intraspecific competition
Each species limits itself more than each other
4. Evolution
Resource partitioning
Competitive reversal
Character displacement
5. External factors regulate superior competitors
Disturbance
Herbivory/Predation
6. No pattern (other processes more important!)
The fundamental vs realized niche
Fundamental niche: the range of conditions and resources an organism can tolerate and use.
Can: biological capable
Some species tolerate / use a broad range (generalists for that resource/condition), while others
utilize only a small range (specialists)!
Reduced abundances may limit competition between species
Realized niche: the range of conditions and resources the organism actually uses due to
restrictions that occur in nature. (we can only measure realized niche)
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