Document: DER-3-51-13

Patch size-dependent migration and semi-synchronous extinction in a beetle metapopulation.

JOHNSON, D.M.*

University of Miami, Miami, FL 33124 USA ¹

Abstract:
Ecologists are increasingly using metapopulation models to address extinction probabilities and to predict the effects of habitat fragmentation. One such model, the Incidence Function Model, is promising as a predictive tool because it can be parameterized from one snapshot of presence/absence data, and is a reasonable predictor of patch occupancy. Two assumptions of the Incidence Function Model are addressed: 1) per capita migration rate is independent of patch size and 2) populations among patches have asynchronous extinction events. A mark-release-recapture study of the specialist beetle (Cephaloleia fenestrata) was conducted in 69 mapped patches of Pleiostachya pruinosa at La Selva Biological Station, Costa Rica in a lowland tropical rainforest. Over 1,200 beetles were uniquely marked, of which 42% were recaptured from one to seven times. Maximum likelihood analysis indicates that the per capita rate of emigration is negatively correlated with patch size, thus violating assumption number 1). Presence/absence data indicates high fluctuations in the percentage of occupied patches over a one-year period; 45%, 55%, 68%, and 48% in March, June, and September 1999, and January 2000, respectively. A December 1999 flood inundated some of the patches, causing synchronous extinctions between the third and fourth census, thus, assumption number 2) was also violated. Flooding events at La Selva occur seasonally most years. Simulations indicate that patch size-dependent migration and synchronous extinction events reduce the number of occupied patches at steady state and reduce the average persistence time of the metapopulation.

Keywords: metapopulation, migration, local extinction

This abstract is being presented at: 3:30 PM in session:
ANIMAL ECOLOGY