About

W. David Walter, Ph.D., is an Adjunct Associate Professor of Wildlife Ecology and an Assistant Unit Leader at the Pennsylvania Cooperative Fish and Wildlife Research Unit. He is based at the Department of Ecosystem Science and Management at Pennsylvania State University. His areas of expertise include Applied Spatial Ecology, Disease Epidemiology, and Stable Isotope Ecology. Dr. Walter holds a Ph.D. from Oklahoma State University obtained in 2006, an M.S. from the University of New Hampshire earned in 2000, and a B.S. from SUNY - College of Environmental Science and Forestry completed in 1995. He is involved in research and outreach activities related to ecosystem analytics, conservation, restoration, climate change solutions, and harmful species ecology. His professional profile includes participation in regional and national conferences, and he maintains a laboratory focused on applied spatial ecology.

Research topics

• Medicine
• Biology
• Ecology
• Geography
• Genetics
• Evolutionary biology
• Demography
• Environmental health
• Pathology

Selected publications

• Home range and resource selection by American crow

  USGS DOI Tool Production Environment · 2026-04-30

  otherOpen access1st authorCorresponding

  This project contains 4 R Markdown scripts and requires a valid Movebank login is to access the data needed for these scripts. The purpose of this script is to import crow location data from movebank and group it by individual animal and season, run estimators of home range, and conducted integrated step selection function analysis.

  PublisherDOI

• Author response for "Viral outbreak dynamics and evolution in wildlife at the interface with humans"

  2025-10-16

  peer-reviewSenior author
  PublisherDOI

• Development of High‐Throughput Genomic Resources to Inform White‐Tailed Deer Population and Disease Management

  Molecular Ecology Resources · 2025-11-26 · 1 citations

  articleOpen access

  White-tailed deer (Odocoileus virginianus) are the most abundant and widespread cervid in North America. Genetic data are used as a tool to monitor populations and make management decisions for this game species. However, the development and use of genomic tools that can generate a set of markers suitable for longitudinal genomic data collection, whether for management purposes or to study the demographic and evolutionary processes of widely distributed species, have been challenging. This is mainly due to the cost required to fully implement and interpret the data produced. Here, we generated whole genome resequencing data for 44 free-ranging deer from three regions in their central and eastern North American range and identified over 89 million single nucleotide polymorphisms (SNPs). We used a subset of these SNPs to develop two nested SNP tools, a high-density array (702,183 SNPs) and a medium-density array (72,723 SNPs) to support deer and chronic wasting disease (CWD) management and research. SNPs were selected to ensure an even distribution across scaffolds of the reference genome and include SNPs associated with CWD susceptibility. Using genotyping results for 469 deer from 15 states in the US and Mexico generated by the high-density array and 1335 deer from 18 states generated by the medium-density array, we assessed genotyping success across different populations and explored some insights into population structure. These genomic tools offer a standard set of markers that will enable researchers and managers to address important questions related to white-tailed deer and CWD management. Our SNP arrays also offer the opportunity to examine aspects of white-tailed deer ecology and evolutionary history that were previously difficult to address.

  PublisherOA PDFDOI

• Accounting for non‐random samples with distance sampling to estimate population density

  Journal of Applied Ecology · 2025-02-12 · 2 citations

  articleOpen access

  Abstract A critical assumption of standard distance sampling is that sampling lines are located such that animals are uniformly distributed as a function of distance from the line. Failure to meet this assumption can introduce bias in the estimator. Many studies have used landscape features, such as roads or rivers, as lines, which can violate assumptions of distance sampling in two ways. First, animals may be attracted or repelled by the landscape feature due to human activity (e.g. along roads) or habitat characteristics associated with the feature (e.g. rivers). Second, sampling along landscape features may not be representative of the larger area of interest. We used auxiliary data to generalize the distance sampling estimator and relax assumptions of a uniform distribution of animals relative to distance from the line (i.e. density gradient) and to allow the distribution of animals to differ by habitat type. The generalized estimator provides unbiased estimates of density within the area sampled but may not be representative of the study area. To address the problem of landscape features providing unrepresentative sampling, we used a resource selection model to estimate the proportion of the population that occurred within the surveyed area to obtain an estimate of abundance for the desired area of inference. We demonstrate our modified distance sampling estimator using white‐tailed deer ( Odocoileus virginianus ) in a 972‐km 2 study area. We conducted infrared surveys of deer from roads to collect distance‐to‐transect data. We used locations of radio‐collared deer to model the distribution of deer relative to the transects and to develop a resource selection model of deer based on distance to roads, habitat type, elevation and slope to account for roads being a non‐representative sample of the study area. Synthesis and applications . When using landscape features as survey lines, the density gradient and deer distribution can introduce either positive or negative bias, which makes it impossible to assess the bias introduced without auxiliary data. The estimator we developed can improve precision because we obtained a better fit to distance observations and accounts for non‐random placement of transects with minimal loss of precision.

  PublisherOA PDFDOI

• Viral outbreak dynamics and evolution in wildlife at the interface with humans

  Biology Letters · 2025-12-01 · 1 citations

  articleOpen accessSenior author

  In this study, we used a multi-faceted approach to understand patterns of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission and persistence in a wild white-tailed deer (Odocoileus virginianus) population. Serology data indicated transmission of SARS-CoV-2 and persistence during the seven-month sampling period. Traditional disease modelling based on deer-to-deer transmission indicated relatively low prevalence with an R0 of 1.9 and recovery period of 7 days; however, individual-based modelling informed by GPS tracked-movement data captured a potential transmission event. Phylogenetic analyses revealed a recurring pattern of divergent groups of deer-derived sequences with human-derived sequences falling close to each deer-derived cluster. Further, human-derived sequences were frequently sampled months prior to the deer-derived sequences, indicating repeated human to deer spillover. Using multiple types of data as well as both fine and broad scale analyses, we have characterized a pattern of localized outbreaks of SARS-CoV-2 within white-tailed deer populations that are likely recurring due to frequent spillover events. Our results suggest that while deer-to-deer transmission occurs over small spatiotemporal scales, SARS-CoV-2 persistence over longer periods and across larger regions is likely driven by repeated spillover from human populations.

  PublisherOA PDFDOI

• Relatedness of White-Tailed Deer from Culling Efforts Within Chronic Wasting Disease Management Zones in Minnesota

  Pathogens · 2025-01-13 · 1 citations

  articleOpen accessSenior author

  ), closely related females form social groups, avoiding other social groups. Consequently, females infected with chronic wasting disease (CWD) are more likely to infect social group members. Culling has been used to reduce CWD transmission in high-risk areas; however, its effectiveness in removing related individuals has not been assessed. We analyzed 11 microsatellites and a mitochondrial DNA fragment to assess: (1) the genetic structure in white-tailed deer in Minnesota, USA and (2) the effectiveness of localized culling to remove related deer. For (1), we genotyped deer culled in 2019 and 2021 in three CWD management zones, and deer collected in between zones. For (2), we only included culled deer, defining "culled groups" as deer obtained in the same township-range-section and year. We compared mean relatedness among deer from the same culled group (intra-group relatedness) and among deer from different culled groups (inter-group relatedness). We did not find evidence of genetic structure, suggesting that an outbreak in any of the management zones could naturally spread to the others. Culling removed deer that were on average more related than expected by chance (intra-group relatedness > inter-group relatedness), and most highly-related deer were culled in the same bait site.

  PublisherOA PDFDOI

• White-Tailed Deer Odocoileus virginianus (E. A. W. von Zimmerman, 1780)

  Fascinating life sciences · 2025-01-01

  book-chapterSenior author
  PublisherDOI

• Workflow to predict geochemical distributions of soil

  USGS DOI Tool Production Environment · 2025-12-19

  otherOpen access1st authorCorresponding

  Mapping soil geochemistry across large spatial extents is essential for understanding mineral distributions and their environmental implications. However, rasters of soil geochemical distributions for the United States are limited. We present a Bayesian modeling framework for generating predictive geochemical distribution maps using integrated nested Laplace approximation in R (R-INLA).

  PublisherDOI

• Evaluation of SARS-CoV-2 antibody detection methods for wild Cervidae

  Preventive Veterinary Medicine · 2025-03-30 · 4 citations

  articleOpen access

  Wildlife surveillance programs often use serological data to monitor exposure to pathogens. Diagnostic sensitivity and specificity of a serological assay quantify the true positive and negative rates of the diagnostic assay, respectively. However, an assay's accuracy can be affected by wild animals' pathogen exposure history and quality of the sample collected, requiring separate estimates of an assay's detection ability for wild-sampled animals where an animal's true disease status is unknown (referred to hereafter as sampling sensitivity and specificity). We assessed the sampling sensitivity and specificity of a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) surrogate virus neutralization test (sVNT) and conventional virus neutralization tests (cVNT) to detect antibodies for ancestral and Omicron B.1.1.529 variants of SARS-CoV-2 in wild white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus). We studied the influence of sample collection method using paired blood samples collected in serum separator tubes and on Nobuto strips from the same animal. Mean estimates of sampling sensitivity and specificity ranged from 0.21-0.95 and 0.94-1.00, respectively, varying by sample collection method, host species, and SARS-CoV-2 variant targeted by the assay. Broadly, sampling sensitivity was estimated to be higher for 1) sera collected in tubes, 2) detecting pre-Omicron SARS-CoV-2 variants, and 3) sVNT relative to cVNT assays. Sampling specificity tended to be high for all tests. We augmented our study with SARS-CoV-2 spike protein sequences derived from sampling locations and times coincident with white-tailed deer captures, finding common amino acid mutations relative to the sVNT Omicron antigen variant. The mutations may indicate that the SARS-CoV-2 variants circulating in cervids from 2021 through 2024 may be better adapted to cervid hosts and more closely related to variants that circulated in humans prior to Omicron variants. We conclude our study with an inter-test comparison of sVNT results, revealing that 40 % inhibition is an optimal threshold for test positivity when testing deer sera for responses to Omicron variant B.1.1.529, compared to the 30 % inhibition recommended for ancestral variants.

  PublisherDOI

• Author response for "Viral outbreak dynamics and evolution in wildlife at the interface with humans"

  2025-09-25

  peer-reviewSenior author
  PublisherDOI

Frequent coauthors

• Kurt C. VerCauteren

  Animal and Plant Health Inspection Service

  63 shared

• Justin W. Fischer

  United States Department of Agriculture

  43 shared

• Charles W. Anderson

  Colorado State University

  33 shared

• Tyler S. Evans

  Texas A&M University

  20 shared

• Krysten L. Schuler

  Cornell University

  20 shared

• Christopher S. Rosenberry

  Pennsylvania Fish and Boat Commission

  20 shared

• William L. Miller

  Day Family Medicine

  18 shared

• Matthew J. Lovallo

  Pennsylvania Game Commission

  16 shared

Labs

• Walter Applied Spatial Ecology LaboratoryPI