PARENT SESSION
Oral Session #18: Predator-Prey Interactions: Plants and animals. Presiding: B. Goodwin.
Monday, August 6, 2001. 1:00 PM to 5:00 PM. Hall of Ideas I.
Modeling the indirect effects of acorn masting on gypsy moth population dynamics.
Schauber, Eric1,2, Turchin, Peter2, Ostfeld, Richard1, Jones, Clive1, Wolff, Jerry3, 1 2 3
ABSTRACT- Through direct effects on the abundance of generalist white-footed mice, acorn masting hast been hypothesized to indirectly control the initiation of gypsy moth outbreaks. To more rigorously evaluate the potential effects of acorn masting on gypsy moth dynamics, we constructed a stochastic model of the linkages from acorns to mice to gypsy moths. Acorn masting was simulated by stochastic autoregressive models, and midsummer white-footed mouse density was simulated as a simple function of acorns the previous autumn. Then, predation on gypsy moth pupae was simulated using an empirically parameterized functional response model that incorporates spacing behavior of white-footed mice. We coupled these components with two models of gypsy moth dynamics: a simple model of population growth at low density, and delayed density-dependent model that produces oscillatory dynamics. For the both model types, home range area had a greater effect on gypsy moth dynamics than any other mouse-related parameter. Increasing mouse home range size extended the interval between outbreaks, decreased the periodicity of moth fluctuations, and increased both the mean time to outbreak and the probability of local extinction. For both models, gypsy moth dynamics were also highly sensitive to duration of the vulnerable pupa stage. Our modeling results indicate that occasional peaks in acorn production and mouse density may delay or reverse an incipient outbreak, but gypsy moth outbreaks need not be preceded by mast failure and unusually low mouse densities.
KEY WORDS: predation, masting, modeling, gypsy moth