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BIO120H1 (1,171)
Jon Abbatt (10)
Lecture 8

lecture 8 notes from prof. Thomson

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University of Toronto St. George
Jon Abbatt

Lecture 8: Metapopulations, plant community composition Fender’s Blue butterfly  Was native in prairies; rely on special habitat caterpillars survive only in prairie. Population decrease to extinction, rediscovered.  Annual pulses of reproduction followed by heavy larval mortality o Ecobeaker  Explicit spatial map of habitat with two types of vegetation, prairie and farm  Butterflies undergo annual cycles of reproduction, then disperse across habitat  Butterflies must discover prairie or will die without reproducing Bodie Pika (Pika from Bodi,Californiamining ghost town)  Tailing piles from hard-rock mining create many small replicated parches of pika habitat.  % patch occupancy (1972-1991) o North: high,stable,anchored by big reservoirs o Middle: low, no reservoirs; extinction/renewal o South: marginal, in decline. Stochastic VS. Deterministic models  Deterministic: outcomes can be predict with certainty.  Stochastic: resulting from chance events o EX: probability of getting from age 0 to age 1 is 0.5 Deterministic Stochastic L1=0.5  constant Consider each newborn individually, flip a coin to see whether it survives or dies; repeat many times Outcome: 100 newborns X 0.5 = 50 Outcome: Get a frequency distribution one-year old of # survivors; average = 50, but each 100 flips can be different  Stochastic metapopulation model for Bodie pikas o Estimate patch extinction rates and dispersal rates, simulate occupancy rates o Findings:  North zone has stable, high occupancy, is a net exporter (source) to Middle  South zone is a sink, needs stream of new colonists (“rescue effect”)  Middle: Sink, but also a steppingstone, providing a flow from N to S Models describe the spatial structure of populations  Source-Sink models: growing populations in high-quality habitat patches (source populations) produce excess individuals. These individuals disperse to less suitable habitat patches, where immigration maintains less productive sick population.  Metapopulation: a set of subpopulations occupying patches of a particular habitat type between which individuals move occasionally. Stability and coexistence  Model
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