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UNI101Y1 Study Guide - Metapopulation, Calliphoridae, Sub Pop

University College Courses
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Spencer Barrett

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1. pop. fluctuate in response to:
envmtal variations
unstable intrinsic properties
pop. of species w/ larger bodies and longer life spans respond less rapidly to changes in
their envmts
the age structure of a pop. often indicates variations in recruitment over time
ex. seedlings of a certain tree species tend to become established in forests primarily
following a major disturbance
2. discrete-time models of density-dependant populations:
show pop. sizes tend to oscillate when disturbed
behaviour depends on the proportional rate of increase (R) per unit of time
0 < R < 1 : pop. size approach equilibrium (K) w/o oscillation
1 < R < 2 : pop. size undergoes damped oscillations and eventually settles down to K
R > 2 : pop. size oscillates in increasing amplitude (limit cycles) until
a stable limit cycle is achieved or;
the pop fluctuates irregularly (chaos)
3. continuous-time models of density-dependant pop.:
predict pop. cycles when there are time delays
behaviour depends on the product of the intrinsic rate of increase (r) and the time
delay (τ)
0 < rτ < 1/e (0.37) : no oscillation
rτ < π/2 (1.6) : damped oscillations
π/2 > : limit cycles w/ amplitude > 4τ
4. time delays result from indiv’s. responses to pop. density; related to:
the period of development
may be enhanced by storage of nutrients
A. J. Nicholson sheep blowflies
he experimentally circumvented a time delay, and was thereby able to eliminate pop.
5. metapopulations are pops. that are dubdivided into discrete subpops. occupying patches
of suitable habitat
dynamics of metapops. depend on:
pop. growth
regulation within patches
migration of indiv. b/w patches
when the rate of extinction of subpop. < rate of colonization of unoccupied patches
a metapopulation exists as a changing mosaic of an equilibrium # of occupied patches
6. migration of indiv. dispersing from large, productive subpops. can rescue declining
subpops. from extinction
this rescue effect demonstrates the importance of maintaining connectivity b/w
habitat patches in metapops.
dynamics of small pops. depend to a large degree on chance events
stochastic models demonstrate that the prob. of extinction due to random fluctuations
in pop. size is greater in smaller pop.
the median time to extinction for small density-independent pop. when BR (b) = DR is
~1.4N/b where N is pop. size
small density-dependant pops. are also vulnerable to extinction
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