ABSTRACT
Population cycles occur frequently in forest insects. Time-series analysis of fluctuations in one such insect, the southern pine beetle (Dendroctonus frontalis), suggests that beetle dynamics are dominated by an ecological process acting in a delayed density-dependent manner. The hypothesis that delayed density dependence in this insect results from its interaction with predators was tested with a long-term predator-exclusion experiment. Predator-imposed mortality was negligible during the increase phase, grew during the year of peak population, and reached a maximum during the period of population decline. The delayed nature of the impact of predation suggests that predation is an important process that contributes significantly to southern pine beetle oscillations.
ABSTRACT
Parasitoid-host metapopulation models (after Reeve) were simulated with varying amounts of spatio-temporal or spatial environmental variability, as well as varying dispersal rates and instability of within-population dynamics. Persistence with environmental variability occurred over broad ranges of low dispersal rates, the amount of variability required for persistence increased with increasing dispersal, and the range of values giving persistence was less when within-population dynamics where more unstable. Fixed spatial variation was found to be sometimes more effective than spatio-temporal variability at producing persistence, but with greater variance among replicates. Metapopulations also could persist without environmental variability (as found by Adler), but this occurred at very particular dispersal rates, quite different from those allowing persistence with environmental variability. Copyright 1998 Academic Press.
