Previous tick-borne disease studies in the U.S. have focused on the association between fragmentation and increased disease risk mediated by reduced host biodiversity. However, high levels of fragmentation, such as those encountered in urban areas, can potentially reduce risk if patches are too isolated for tick establishment and persistence due to limited host dispersal. We hypothesize there is a non-linear relationship between forest fragmentation and infection risk driven by urban forest connectivity and the movement of white-tailed deer (Odocoileus virginianus), the dispersal host for ticks. Individual host responses to the identity and permeability of the landscape matrix can scale up to population patterns shaping the distribution of ticks and their pathogens and driving human infection risk heterogeneity. Animal perception of the habitat determines movement decisions and the willingness to utilize habitat patches and corridors. Further, resource provisioning from humans may attract hosts to visit isolated habitat patches. Thus, integrating animal movement into disease ecology is essential to determine which movements and/or individuals are most important for sustaining enzootic transmission in an urban environment.
We examine how the movement decisions and resource utilization by deer determines the distribution of three Ixodid tick species that differentially depend on this host for dispersal (Ixodes scapularis, Amblyomma americanum, and Haemaphysalis longicornis) in the highly fragmented landscape of Staten Island, a borough of New York City. We use circuit theory modeling to identify corridors and determine the impact of connectivity on tick densities. We use GPS location data from Staten Island deer to examine movement responses to the urban landscape through step selection analysis and relate this to the distribution and density of ticks in public parks.
Results/Conclusions
Results showed the distance between urban parks was a significant predictor of I. scapularis presence and that centrality – an indicator of the park connectivity for deer – was an important driver of the density and infection prevalence of nymphs. This indicates that deer have a critical impact on enzootic dynamics within the parks through distributing adult ticks to establish new populations. We show that deer habitat use is clustered around urban parks but spills over into residential and urban areas. The next step is to identify covariates that predict resource selection and movement within, and surrounding, each park using step selection analysis. Our results emphasize that fragment connectivity and host movement is a neglected factor which is critical to consider in urban tick-borne disease systems.