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School of Environment and Natural Resources


TWEL Allison Williams Thesis

The State of Species Distribution Modeling Efforts for Ixodes scapularis and a Comprehensive Approach to Predict Their Occurrence and Abundance in Ohio, USA

Allison Kaitlyn Williams, MS

Advisor: William E. Peterman


Ixodes scapularis, otherwise known as the blacklegged tick, has rapidly expanded across eastern North America in the last 50 years due to changing climate, land use change, and associated shifts in host distribution across the landscape.  Blacklegged ticks are major vectors of disease agents, including those that cause Lyme disease, the most common vector-borne disease in the United States, leading to public health concerns in the USA and Canada.  Species distribution models (SDMs) can help assess blacklegged tick occurrence and abundance, avoiding extensive time or funding that would otherwise be needed for active surveillance.  Additionally, SDMs can reveal important ecological drivers of expansion and highlight areas where blacklegged ticks are likely to spread.  To understand the ecological drivers of blacklegged tick occurrence and abundance, we reviewed all published blacklegged tick SDMs as of December 2022, and identified common traits of SDMs and areas for improvement.  Next, we studied the spatial distribution and abundance of blacklegged ticks in Ohio, a midwestern state in the USA where the northeastern and upper midwestern ranges of the blacklegged tick are converging over the Ohio River Valley.  To develop comprehensive models, we considered climate, landscape, and host covariates in a spatially explicit framework.  Additionally, we considered several spatial scales for landscape covariates to identify possible cross-scale linkages between blacklegged ticks and their hosts.  With these considerations, we developed the first predictive occurrence and abundance models for blacklegged ticks in Ohio, USA, identifying key drivers of blacklegged tick abundance and areas of high disease risk.