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BIOL208 Lecture Notes - Isocline, Logistic Function, Directional Selection

Biology (Biological Sciences)
Course Code
Kurt Illerbrun

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Lecture 19
Lotka-Volterra Model of competition- realtion to logistic growth
Competition coefficients
K-N1-N2K N1= Old population N2= New additions… aka K-(N1+N2)K
Due to the new individuals in this new competition, its addition of
intraspecies competition. If theres more than one species this doesn’t
Competition Coefficient must be used α. This implies how much of a
species is equated to the other eg. 1/100 of and elephant=mouse so then N2 would be the
number of added individuals x α
α12= effect 2 has on species 1
α21= effect 1 has on species 2
Population growth will stop when N1 = K1 – α12N2 h
Isocline of zero population growth
On the graph, whichever species isocline of zero population
growth is on the top will win
If they cross and come towards it, the intercept=coexist But if
they go away from the center they both win
If both species are at the center theres an unstable equilibrium
and if one starts winning, it will ust keep on winning
Measuring Competition Coefficent
Big REALIZED niche overlap=exclusion
Small REAILZED niche overlap= coexistence
Niche Overlap
Fundamental niche overlap permitted because species…
Specialize on over resources- resources partitioning which
Avoids exclusion
Allows coexistence
Creates communities
Their fundamental niches are the
same but their realized niche is different eliminating exclusion and
competition… MacArthurs warbler
3 Main Niche Axis- Food, Time, habitat
Evolutionary Consequences of Competition- Natural Selection
Resource Paritioning Directional selection divergent species
Character displacement= evolutionary separation of two species in
morphology and physiology when in sympatry (together) vs alopatry (apart)
Aka: Three Spined StickleBacks
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