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.

Moth persistence in enemy-occupied space: The interaction between prey dispersal and spatially heterogeneous predation risk.

Goodwin, Brett¹, Jones, Clive¹, Schauber, Eric¹, ¹

ABSTRACT- Gypsy moth (Lymantria dispar) has persisted in the US Northeast for over 100 years. At low densities the primary moth predator is the white-footed mouse (Peromyscus leucopus). Voracious consumers of gypsy moth pupae, mice should be capable of driving moth populations extinct. Yet, twenty-one years of monitoring moth populations on the IES property have yet to produce a detectable extinction, though densities of less than 10 egg masses per ha occurred in nine of those years. How are moths surviving periods of low density? The interaction between gypsy moth larval dispersal and spatially heterogeneous pupal predation risk (due to mice) may allow for moth survival at low density. We investigated this possibility using empirically parameterized, individual-based, spatially explicit simulation modeling. In our simulations restricting dispersal (e.g., limited dispersal distance vs. complete redistribution) reduced extinction probability by at least two orders of magnitude, halved the time until outbreak, and reduced the initial number of gypsy moths necessary to avoid extinction five-fold. Furthermore, these effects became more apparent as mouse density increased (e.g., moth pupal predation increased). These results suggest that the interaction between dispersal and spatially heterogeneous predation risk is important for population persistence, particularly at low densities when extinction is most likely. Data on gypsy moth dispersal and the spatial patterning of mouse predation risk will be necessary to understand low-density gypsy moth population dynamics.

KEY WORDS: Gypsy moth, white-footed mice, dispersal, population persistence