Date of Award

Spring 5-2020

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Advisor

Allison Gardner

Second Committee Member

Eleanor Groden

Third Committee Member

Pauline Kamath

Abstract

National park areas represent unique disease transmission settings compared to other private and public lands, limiting our capacity to understand tick-borne disease exposure risk using traditional approaches. These challenges may be overcome by using ecological metrics to develop spatial models of disease vector density and to identify areas of highest vector exposure risk within a park. The blacklegged tick and the infectious diseases of humans and wildlife that it transmits, including Lyme disease, anaplasmosis and babesiosis, have been expanding in the eastern United States within recent decades. Acadia National Park (ANP) located on Mount Desert Island, ME is highly visited, with more than 3 million visitors per year, and largely has not been assessed for tick-borne disease exposure risk. To determine the broad scale patterns of blacklegged tick densities in ANP, field surveys of blacklegged ticks were conducted at a total of 114 sites across the park between the months of June and August during two consecutive years. Using field-observed nymphal tick densities and geospatial landscape feature data (i.e., land cover, elevation, forest fragmentation, aspect, and UTM coordinates) a random forest model was created to model nymphal tick density across Mount Desert Island. We found that nymphal tick densities vary significantly across the island and are particularly high in areas characterized by deciduous forest cover, relatively low elevations and northerly and easterly locations. To investigate the causal mechanisms driving spatial patterns of tick density, a subset of 19 sites were assessed for microclimate conditions (relative humidity and temperature), host activity (small mammal trapping and deer scat surveys), and vegetation metrics (percent canopy cover and leaf litter depth). Multivariate analysis of variance indicated that there are significant differences in microclimate conditions across landscape features but not among host activity or vegetation metrics. Generalized linear models indicated that mean temperature and mean humidity are significantly correlated to nymphal densities and therefore may provide a mechanistic link between landscape features and blacklegged tick densities. This project emphasizes the importance of using ecological metrics to estimate risk of exposure to vector-borne diseases, provides new insight into habitat characteristics that may drive tick-borne disease exposure risk across spatial scales, and demonstrates the design and effort required to operationalize similar vector-borne disease risk assessment protocols in other National Parks.

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