Quantifying landscape connectivity between locations of CWD detection

The composition and configuration of local landscapes influences animal behavior and may lead to directionally-biased movement patterns for free-ranging wild animals. Such landscape mediated animal movements may influence the directionality of emergent disease spread. Chronic wasting disease (CWD) was first discovered in free-ranging white-tailed deer of Michigan in 2015, and at the time of our analyses had been detected in nine animals from seven unique locations. Understanding the spread of CWD within this context has been a goal of state wildlife managers. We evaluated an assumed association between CWD positive animals to model potential disease spread direction using least cost path analysis and the nine detected animals. We evaluated the connectivity of habitat between CWD detection locations and assessed the potential for landscape-induced directionality of animal movement within a use-available framework. Results of this analysis showed significantly higher landscape connectivity of travel paths in an easterly direction relative to the westerly direction. Further, landscape connectivity in the easterly direction was significantly greater than expected assuming equal connectivity in all directions, while the degree of connectivity in the westerly direction was significantly lower than expected. As the distribution of CWD is associated with deer movement patterns, CWD is likely to have spread in an easterly direction across our study area, opposite the direction of detection. We provide a landscape-modeling framework for evaluating potential directional biases in ecological processes such as animal movement or disease spread.