Informing disease models with temporal and spatial contact structure among GPS-collared individuals in wild populations.

Contacts between hosts are essential for transmission of many infectious agents. Understanding how contacts, and thus transmission rates, occur in space and time is critical to effectively responding to disease outbreaks in free-ranging animal populations. Contacts between animals in the wild are often difficult to observe or measure directly. Instead, one must infer contacts from metrics such as proximity in space and time. Our objective was to examine how contacts between white-tailed deer (Odocoileus virginianus) vary in space and among seasons. We used GPS movement data from 71 deer in central New York State to quantify potential direct contacts between deer and indirect overlap in space use across time and space. Daily probabilities of direct contact decreased from winter (0.05-0.14), to low levels post-parturition through summer (0.00-0.02), and increased during the rut to winter levels. The cumulative distribution for the spatial structure of direct and indirect contact probabilities around a hypothetical point of occurrence increased rapidly with distance for deer pairs separated by 1,000 m-7,000 m. Ninety-five percent of the probabilities of direct contact occurred among deer pairs within 8,500 m of one another, and 99% within 10,900 m. Probabilities of indirect contact accumulated across greater spatial extents: 95% at 11,900 m and 99% at 49,000 m. Contacts were spatially consistent across seasons, indicating that although contact rates differ seasonally, they occur proportionally across similar landscape extents. Distributions of contact probabilities across space can inform management decisions for assessing risk and allocating resources in response

Violin-box plots displaying the impact of habitat-specific positional error on medium-(A), large-(B), and small-scale (C) peaks in varFPT/area for 500 simulated movement paths of white-tailed deer in central New York in 2006–2007.

<p>Dashed lines indicate the location of the peak in varFPT/area for the observed path (resolution = 10 m).</p

Percent canopy cover across New York State (Homer et al. 2004).

<p>Stationary collars were located within Spafford Township (outlined in red within the study area inset).</p

Regression of predicted versus observed standard deviation of error for leave-one-out cross-validation of the logistic model describing the relationship between percentage canopy cover and the standard deviation of the positional error of stationary GPS collars in central New York (<i>R²</i> = 0.79).

<p>Regression of predicted versus observed standard deviation of error for leave-one-out cross-validation of the logistic model describing the relationship between percentage canopy cover and the standard deviation of the positional error of stationary GPS collars in central New York (<i>R²</i> = 0.79).</p

Plots of area adjusted variance in first-passage time (varFPT/area, s²/m²) as a function of the scale used to determine passage time along the observed movement path (radius of circle, m) for 4 white-tailed deer in central New York.

<p>Peaks in varFPT/area indicate the landscape scale(s) to which individuals are responding by altering time spent along their movement path.</p

Positional error (m) of stationary collars placed in varying percentages of canopy cover in the Town of Spafford, New York from mid-February to mid-March 2008 for two different fix schedules: a) 5 hr and b) 30 min.

<p>Dashed lines represent the 50% and 90% normal ellipse contours of position densities. Percent canopy cover increases from left to right (0–25%, 26–50%, 51–75%, 76–100%).</p

Plots of area adjusted variance in first-passage time (varFPT/area, s²/m²) as a function of the extent used to determine passage time along the observed movement path (radius of circle, m) for 3 white-tailed deer in central New York.

<p>Peaks in varFPT/area indicate the landscape scale(s) to which individuals are responding by altering time spent along their movement path.</p

Model comparisons for functional relationship between percent canopy cover and the standard deviation of positional error for stationary GPS collars, Spafford Township, NY.

<p>Model comparisons for functional relationship between percent canopy cover and the standard deviation of positional error for stationary GPS collars, Spafford Township, NY.</p

Characteristics (rank correlation, regression, and goodness-of-fit) of the accuracy of each fold for 5-fold cross validation of selected models predicting temporal contact probabilities among deer in central New York.

<p>^a Significantly different from 0.0.</p><p>^b Significantly different from 1.0.</p><p>Significant difference between observed and expected.</p