PARENT SESSION
Oral Session #74: Spatial Ecology: Models and Methods. Presiding: C. Loehle.
Friday, August 10, 2001. 8:00 AM to 11:30 AM. Hall of Ideas E.
The extinction debt revisited: population dynamics in a continuous space model.
Dietze, Michael1, Govindarajan, Sathish1, Clark, James1, Agarwal, Pankaj1, 1
ABSTRACT- Spatially implicit population models and cellular automata both predict the existence of an "extinction debt," the delayed but deterministic collapse of a population in response to habitat destruction. Extinction occurs, despite the presence of suitable habitat, because dispersal is unable to compensate for mortality. This result has implications both for conservation and for how we understand population dynamics, but it may be an artifact of treating space as a set of discrete patches. We re-evaluate the extinction debt, relaxing the assumption of discrete space, using a simple discrete-time point process model of plant population dynamics. In this model populations are regulated by local dispersal and neighborhood competition on a continuous homogeneous spatial domain. Spatially explicit populations are able to persist at levels of habitat destruction much greater than predicted by either spatially implicit models or cellular automata, even when the intrinsic dynamics of the population are chaotic. The response of population density to habitat fragmentation is nonlinear, and extinction is solely the result of demographic stochasticity at low densities. Population decline is strongly affected by whether density dependence is over-compensating or under-compensating. With over-compensating density dependence, populations are competition-limited at high fecundity while at low fecundity they are dispersal-limited. Competition-limited populations are more stable against loss of habitat than dispersal-limited populations because reduced neighborhood density results in increased survival of individuals.
KEY WORDS: extinction, fragmentation, dispersal, competition