Ectoparasites Influenced Woodrat Survival and Recruitment in a California Oak Woodland

Anne Y. Polyakov, Department of Environmental Science, Policy, and Management, University of California, Berkeley

William D. Tietje, Department of Environmental Science, Policy, and Management, University of California, Berkeley

An understanding of host-parasite relationships underpins the management of host species and public health concerns. During 2005-2014, we indexed the abundance of botfly warbles (Diptera: Oestridae), and ticks (Acari: Ixodidae) on big eared woodrats (Neotoma macrotis) live-trapped during October and May in a blue oak (Quercus douglasii)-coast live oak (Q. agrifolia) woodland in coastal-central California. During our 18 live-trapping sessions, the proportion of 4,367 unique woodrats on which we detected one or more specimens from these ectoparasite groups (parasite prevalence) was 13%. Tick prevalence (proportion infested) and intensity (number of parasites per individual) was higher in males than females, whereas no differences between sexes were detected for bot fly prevalence and load. Adult woodrats had higher tick intensities than juveniles, but bot fly warble prevalence was greater on juveniles than adults. Elevated tick and bot fly intensities predict a negative effect on big-eared woodrat survival, and a positive effect on woodrat recruitment, suggesting that high ectoparasite intensities favor a life history strategy with higher recruitment and lower survival. Furthermore, tick intensities increased with higher temperatures, suggesting that a warming climate in California could ultimately shift the life history strategy of the woodrat to a more r-selected strategy, where population growth is influenced more by recruitment than survival. Our results provide insight into the interplay between parasites, hosts, and a changing environment.