| Statistical Programs |
| College of Agriculture | University of Idaho |
| Seminar Announcement |
| "Applied Statistics in Agriculture" |
|
"What Minimal Numbers Are Necessary for a Species to Maintain
Itself in Nature?" Allee Effects in Stochastic Populations
Presented By |
| Dr. Brian C. Dennis |
|
Department of Fish and Wildlife Resources and Division of Statistics University of Idaho |
| Tuesday, November 6 3:30 P. M. Ag. Science 62 |
|
An Allee effect, or positive density dependence, could
seriously increase a population's risk of extinction. Theoretical studies of Allee effects
have been predominantly deterministic and have featured population models that typically
display a lower unstable equilibrium (critical population size) below which extinction is
certain. In this presentation, I discuss the combination of stochastic forces with Allee
effects, using general stochastic models. The probability of reaching a lower population
size 'a' before reaching an upper size 'b', when considered as a function of initial
population size, has an inflection point at the underlying deterministic unstable
equilibrium. The inflection represents a threshold in the probabilistic prospects for
the population and is independent of the type of stochastic fluctuations (e.g.
demographic or environmental). Demographic noise alone (absent Allee effects), although
considered an "extinction vortex," does not produce such threshold behavior. Formulating
the problem in a stochastic framework is a possible key to testing for an Allee effect in
species translocation or colonization data. The results provide a new understanding of the
interplay of stochastic and deterministic forces in ecological populations. |
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