Department

University College CoursesCourse Code

UNI101Y1Professor

Spencer BarrettThis

**preview**shows half of the first page. to view the full**1 pages of the document.**chapter 12: TEMPORAL AND SPATIAL DYNAMICS OF POPULATIONS

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 > rτ : 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.

cycles

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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