Proposal summary
| Tree defense, community interactions, and the population dynamics of Dendroctonus frontalis USDA Competitive Grant: 2000-2003. |
| Understanding why some species regularly attain very high abundance is a central problem in theoretical population ecology and applied entomology. We will test for the contributions of two biological processes to the outbreak population dynamics of the southern pine beetle (Dendroctonus frontalis): destabilizing positive density-dependence (allee effect) from effects of beetle attack rate on tree defense systems; and inverse density-dependence from community interactions involving mutualistic mycangial fungi, a bluestain fungus that competes with the mycangial fungi, and mites, which are phoretic on the beetles, that transport, propagate, and feed on the bluestain fungus. The first mechanism would tend to increase the peak of cyclical highs while the second would tend to limit the duration of outbreaks (and contribute to cycles if there is a delay in the feedback). We will characterize variation within and among pine species in characteristics of the oleoresin defense system and parameterize a model that predicts beetle attack success as a function of attack rate and tree resin systems. The model will validated through field studies and then extended to predict outbreak probabilities under different scenarios of forest composition, tree physiological status, and beetle abundance. This is likely to have applied value for forest managers because it will permit predictions using measurements that are cheap and easy. We will test the role of fungal interactions with a combination of experiments and field surveys will allow us to distinguish between alternative mechanisms by which density-dependent feedback could occur and test if the feedback includes a delay that would contribute to 2nd order population dynamics. Finally, we will integrate our understanding of density-dependence from tree defenses and fungal interactions with knowledge of density-dependence from intraspecific competition and specialist predators to develop synthetic models of endogenous population dynamics and test the hypothesis that combined effects from different sources of endogenous feedback produce population dynamics qualitatively different from those of the individual components. |
| Investigators: Matthew P. Ayres, Kier Klepzig, John Moser, Peter L. Lorio, Richard Hofstetter |