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
Explicit spatial map of habitat with two types of vegetation, prairie
Butterflies undergo annual cycles of reproduction, then disperse
Butterflies must discover prairie or will die without reproducing
Bodie Pika (Pika from Bodi,Californiamining ghost town)
Tailing piles from hard-rock mining create many small replicated parches of pika
% 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
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
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