Investigation of how vegetation, small mammal interactions, and land-use determine blacklegged tick abundance

Abstract

Climate change and shifting land-use patterns have caused the expansion of tick ranges across much of the northeastern United States, which has serious implications for public health. Ticks serve as vectors for numerous tick-borne diseases, which can become more prevalent as tick ranges expand and their populations increase. Western New York is currently experiencing this range expansion as ticks are migrating in from southeastern New York, followed by an increase in incidence of tick-borne disease. The spatial distribution of ticks is dependent on both small-scale and regional-scale ecological interactions. The landscape-level land use mosaic can structure what habitats ticks and their hosts are found in: within those habitats, a moist microclimate provided by ample vegetative cover is necessary to ensure tick survival. My study examined the distribution of ticks in the greater Rochester, NY area at both of these spatial scales. In the first half of my project, I collected ticks from plots dominated by invasive pale swallowwort and compared their density to tick densities in control sites, where pale swallowwort was absent. In a subset of plots, I used data loggers to study the microclimatic conditions and sampled for white-footed mice, the primary host of juvenile blacklegged ticks. I found that swallowwort was able to alter the microclimate of a site by providing high relative humidities, low vapor pressure deficits, and small ranges for both variables. I found significantly more adult ticks in swallowwort patches as opposed to corresponding bare patches, although I did not find differences for nymphal ticks. Swallowwort patches seemed to harbor more white-footed mice, and white-footed mice captured in swallowwort plots often had more embedded ticks. Swallowwort seemed to have more of an effect on tick abundance in areas that lacked other vegetative cover in the understory. In the second part of my study, I collected ticks on public trails in parks across the greater Rochester area to see where ticks were most prevalent and how the landscape was affecting tick density. I found that latitude and longitude were the most important predictor variables for tick density, and that ticks were most likely to be found in the southeastern portion of my study area. I also found that in general, ticks were most likely found in areas with a higher proportion of forests and agricultural areas, and less likely to be found in developed areas. In summary, my first study provides support for the hypothesis that invasive plants can alter the surrounding microclimate in ways that support tick populations. The second half of my study documents the spatial distribution of ticks in public parks in the Rochester area, supports a northwesterly expansion of ticks across New York State, and suggests that ticks are most likely to occur in areas with high cover of forests and agriculture and less developed areas.