LTREB Renewal: Acorn pulses and the dynamics of rodents, ticks, and Lyme-disease risk in oak forests

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Lyme disease afflicts hundreds of thousands of Americans each year. There is no vaccine and both diagnostic methods and treatments remain problematic; avoidance of exposure to disease-bearing ticks is the primary means of protecting the public. This project will identify what regulates the abundance of ticks and the proportion of ticks that carry the disease agent, providing detailed knowledge about when and where people are most at risk of exposure to Lyme disease. Researchers will continue long-term collection of data on acorns, ticks, mice, other hosts, and climate in one of the most heavily affected portions of the United States. Results will facilitate reduced burden of disease though avoidance and management of high risk places and times. The project will contribute to K-12 classroom teaching, undergraduate education, and extensive public education through strong collaborations the researchers have developed over the course of this sixteen-year study. Public health benefits ensure widespread coverage of the research by public media. The project will train undergraduate and graduate students, as well as postdoctoral researchers, through their participation in the research. Lyme-disease risk can be predicted from past acorn production, yet the discovery of new patterns and mechanisms complicates these predictions. The investigators will continue research on 6 oak-forest plots to collect long-term data on acorn production; the population dynamics of mice, chipmunks, squirrels, and larval, nymphal, and adult blacklegged ticks; infection prevalence of ticks with Lyme disease bacteria; and tick responses to specific climatic variables. Five additional years of data encompassing a more extensive range of host abundances, tick burdens, resources, and climatic conditions will generate the empirical base for constructing robust models of all tick life stages, questing and attached, to address biotic and abiotic drivers of tick population dynamics. Models will also be extended to distinguish the effects of climatic variables from those of host abundances and host resources on Lyme disease risk. The importance of contingencies in acorn-mouse-tick interactions will be explored. Although most years of high mouse abundance are followed by high nymph abundance, a recent mouse peak was not followed by a nymph peak. More robust and predictive models of the mast-mouse-tick system require the exploration of specific contingencies, which are likely to be episodic. Long-term trends in acorn production will be analyzed to decompose temporal variation in the magnitude and timing of masting events by individual species into patterns due to individual variation in seed production versus changes in overall abundance and population size structure. Analyses of the seasonal timing of host-seeking by larvae and nymphs will be integrated with estimates of host population size to explain variation in nymphal infection prevalence and to improve predictions for this critical variable.