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Lecture 7

Lecture 7 & 8

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University of Toronto St. George
Ingrid L.Stefanovic

Lectures 7 & 8 22:10 Partial Taxonomy of Species Interactions Types of Interactions: Consumer Resource (+-) Predator-prey Plant-herbivore Host-parasite Competition (--) as one individual gets more, another gets less) Mutualism (++) species benefit each other Foci of Study: Population dynamics (effects on numbers) Evolutionary dynamics (adaptation, co-evolution) Interspecific Competition: Basic model: Lotka-Volterra equations for two species competing for resources Simple extension of logistic equation: Logistic already has braking term for intra-specific variation Both species must inhibit own growth more than it inhibits growth of competitor; otherwise, competitor drops in population and allows other species to grow Alphas must be smallish (share less resources) (See lecture slides for equations): know the equations and the meanings of the terms Possible Outcomes of L-V competition: Expect now to solve for N1 and N2 as f(t), but. Instead, specify 4 possible equilibria: The two species may stably coexist Species 1 may always win (N1=K1, N2=0) Species 2 may always win (N2=K2, N1=0) Identity of winner may depend on starting Ns Outcomes depend on values of Ks and as (small alphas mean less sharing of resources = makes it easier for species to coexist) Coexistence requires both species to inhibit their own growth more than they inhibit each others Can expand to consider n species (Be able to write L-V equations and explain what the terms are) Law of Competitive Exclusion Complete competitors cannot coexist Will consider this later, under niche
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