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Lecture 7

lecture 7 notes from prof. Thomson

Course Code
Jon Abbatt

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Lecture 7: Species interactions: From 2-species population models to community structure
Types of interaction classified by who pays and who benefits
Consumer-resource (+/-, Ricklefs treats first)
o Predator-prey
o Plant-herbivore
o Host-parasite
Competition (-/-, I treat first)
Mutualism (+/+)
Lotka-Volterra equations
intraspecific competition: competition between individuals of same species
interspecific competition: competition between individuals of different species
Outcomes of L-V competition
The two species may stably coexist
o Coexistence requires both species to inhibit their own growth more than they
inhibit each other’s
Species 1 may always win (N1 = K1, N2 = 0)
o Can expand to consider n species
Species 2 may always win (N2 = K2, N1 = 0)
Identity of winner may depend on starting N’s.

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Law of Competitive Exclusion
Stated that two species cannot coexist indefinitely when the same resource limits both
species (两个吃同样食物的物种不能共存)
o ONLY TRUE for math model, COEXIST DO EXIST in nature!!!!
Experiments by Gause
Experiment with protozoa.
Depends on species, he can get
both stable coexist, and
competitive exclusion.
In reality..
Competitve exclusion is less likely to go extinction
o Species can hide in different places
o Biological effects interact with physical effects.
o Natural selection favors better competitors
Experiment by Tensely
G.sylvestre grows better in base soil
G. saxatile grows better in acid soil
When the two put together, sylvestre
wins saxatile in base soil, saxatile wins
sylvestre in base soil.
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