Assessment of spatial genetic structure to identify populations at risk for infection of an emerging epizootic disease

1. Understanding the geographic extent and connectivity of wildlife populations can provide important insights into the management of disease outbreaks but defining patterns of population structure is difficult for widely distributed species. Landscape genetic analyses are powerful methods for identifying cryptic structure and movement patterns that may be associated with spatial epizootic patterns in such cases.
2. We characterized patterns of population substructure and connectivity using microsatellite genotypes from 2,222 white‐tailed deer (Odocoileus virginianus) in the Mid‐Atlantic region of the United States, a region where chronic wasting disease was first detected in 2009. The goal of this study was to evaluate the juxtaposition between population structure, landscape features that influence gene flow, and current disease management units.
3. Clustering analyses identified four to five subpopulations in this region, the edges of which corresponded to ecophysiographic provinces. Subpopulations were further partitioned into 11 clusters with subtle (F_ST ≤ 0.041), but significant genetic differentiation. Genetic differentiation was lower and migration rates were higher among neighboring genetic clusters, indicating an underlying genetic cline. Genetic discontinuities were associated with topographic barriers, however.
4. Resistance surface modeling indicated that gene flow was diffuse in homogenous landscapes, but the direction and extent of gene flow were influenced by forest cover, traffic volume, and elevational relief in subregions heterogeneous for these landscape features. Chronic wasting disease primarily occurred among genetic clusters within a single subpopulation and along corridors of high landscape connectivity.
5. These results may suggest a possible correlation between population substructure, landscape connectivity, and the occurrence of diseases for widespread species. Considering these factors may be useful in delineating effective management units, although only the largest features produced appreciable differences in subpopulation structure. Disease mitigation strategies implemented at the scale of ecophysiographic provinces are likely to be more effective than those implemented at finer scales.

     

Survival of white-tailed deer fawns on Marine Corps Base Quantico

Some jurisdictions in the eastern United States have reduced harvest of white-tailed deer (Odocoileus virginianus) because of perceived declines in recruitment and population size over the last decade. Although the restoration of American black bears (Ursus americanus) and the colonization of coyotes (Canis latrans) have increased fawn predation in some areas, limited information exists on how temporally dynamic resources and weather influence fawn survival. Therefore, we evaluated fawn survival probability, cause specific mortality, and if factors such as oak (Quercus spp.) mast abundance, winter severity, precipitation, and landscape composition influenced mortality risk on Marine Corps Base Quantico in northern Virginia, USA, from 2008 to 2019. We tracked 248 fawns outfitted with very high frequency radio-collars and predation was the leading cause of mortality (n = 42; 45%). We estimated survival to 133 days and survival pooling all years (2008–2019) was 0.50 (95% CI = 0.42–0.60). Increased annual red oak (Quercus spp.) mast abundance from the previous fall reduced mortality hazard for fawns. The longevity of our study revealed a link between fawn survival and a specific maternal resource (red oak mast) only available during gestation. Our results highlight the importance of oak mast in eastern deciduous forests and, more broadly, overwinter maternal condition on white-tailed deer recruitment.     

Assessing the impact of ancient Maya animal use

Tropical forest animals are at high risk worldwide as a result of over-exploitation and forest clearing. Zooarchaeological studies of animal use by the ancient Maya of the southern lowland regions of Guatemala, Honduras, Belize, and Mexico provide long-term historical information on animal populations under conditions of human population growth and climatic change that is valuable to both archaeology and conservation biology. In this paper, zooarchaeological data from 35 chronologically defined faunal sub-samples recovered from 25 ancient Maya archaeological sites are used to assess the effects of ancient hunting on animal populations of the Maya region between the Preclassic and Colonial periods (2000 BC–AD 1697). The variations in species abundance are used as a proxy for describing changes in ancient Maya hunting practices and hunted animal populations, interpreted on the basis of hunting efficiency models from foraging ecology. A significant reduction in the proportion of large mammals, particularly Odocoileus virginianus, in zooarchaeological assemblages between the Late Classic (AD 600–850) and Terminal Classic/Postclassic periods (AD 850–1519) suggest that over-hunting during the Late Classic may have led to a reduction in availability of these animals to the ancient Maya hunters in the later periods. This finding is discussed in relation to important social and environmental variations to evaluate the impact of hunting and other factors such as forest clearance and climate on ancient animal populations in the Maya region.     

Predation by coyotes on white-tailed deer neonates in South Carolina

Coyotes (Canis latrans) are novel predators throughout the southeastern United States and their depredation of white-tailed deer (Odocoileus virginianus) neonates may explain observed declines in some deer populations in the region, but direct evidence for such a relationship is lacking. Our objective was to quantify neonate survival rates and causes of mortality at the United States Department of Energy's Savannah River Site (SRS), South Carolina to directly evaluate degree of predation in this deer population. From 2006 to 2009, we radio-monitored 91 neonates captured with the aid of vaginal implant transmitters in pregnant adult females and opportunistic searches. Overall Kaplan–Meier survival rate to 16 weeks of age was 0.230 (95% CI = 0.155–0.328), and it varied little among years. Our best-fitting model estimated survival at 0.220 (95% CI = 0.144–0.320). This model included a quadratic time trend variable (lowest survival rate during the first week of life and increasing to near 1.000 around week 10), and Julian date of birth (survival probability declining as date of birth increased). Predation by coyotes was the most frequent cause of death among the 70 monitored neonates that died, definitively accounting for 37% of all mortalities and potentially accounting for as much as 80% when also including probable coyote predation. Predation by bobcats (Felis rufus) accounted for 7% (definitive) to 9% (including probable bobcat predation) of mortalities. The level of coyote-induced mortality we observed is consistent with the low recruitment rates exhibited in the SRS deer population since establishment of coyotes at the site. If representative of recruitment rates across South Carolina, current harvest levels appear unsustainable. This understanding is consistent with the recent declining trend in the statewide deer population. The effects of coyote predation on recruitment should be considered when setting harvest goals, regardless of whether local deer population size is currently above or below desired levels, because coyotes can substantially reduce fawn recruitment. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

Influence of habitat features and hunter behavior on white-tailed deer harvest

Sport hunting may help in controlling cervid populations over large areas. As with natural predators, several environmental factors can influence sport harvest. A better understanding of the environmental variables that limit the efficiency of sport hunting could provide guidelines for more efficient wildlife management using hunting. We studied white-tailed deer (Odocoileus virginianus) hunting on a high deer density island where hunting was the sole form of predation. Our objective was to study the behavior of sport hunters and determine the habitat characteristics (e.g., abundance of deer forage, visibility of the deer from the hunter's point of view, and accessibility of the territory to hunters) that are associated with a successful harvest. We collected movements and harvest site location data from 477 hunters equipped with handheld Global Positioning System (GPS) units. Harvest sites were visited and characterized, along with a paired random site, to determine the environmental conditions associated with a successful hunt. We also developed a model to predict the daily number of deer seen by hunters considering weather conditions, hunter characteristics (e.g., age, experience), and date of hunting. We used the mean number of deer seen per hunter per day as a relative index of local density in each hunted territory. At both the site and landscape scales, the combination of visibility and access had a positive effect on the distribution of harvested deer. Habitat types with less visual obstruction from vegetation enabled hunters to see more deer in a given day. At the site scale, harvested deer were located in areas with a lower density of access routes compared to areas where hunters travelled throughout the day. Using an innovative approach of studying hunter behavior with GPS technology, digital maps, and questionnaires, we highlighted the factors associated with hunter success. Our study suggests that habitat characteristics could be modified to increase harvest by improving accessibility and visibility near roads. Creating openings in mature and regenerating forest near access roads could make sport hunting a more efficient management tool, but the potential impact of increased forage availability in forest openings should not be overlooked. © 2012 The Wildlife Society.     

Lack of Mother—Offspring Relationships in White-Tailed Deer Capture Groups

ABSTRACT Behavioral studies of white-tailed deer (Odocoileus virginianus) often assign mother-offspring relationships based on common capture of juveniles with adult deer, assuming that fawns associate closely with mothers. We tested this assumption using genetic parentage to assess mother-offspring relationships within capture groups based on data from 10 polymorphic microsatellite loci. At the 80% confidence level, we assigned maternity to 43% and 51% of juveniles captured with an adult female in 2 respective study areas. Capture with their mother did not differ by sex of juveniles in either study area, and limiting our analysis to capture groups that most represent family groups (i.e., one ad F with 1–3 juv) did not increase maternity assignment (35%). Our results indicate that common capture may be a poor indicator of mother-offspring relationships in many field settings. We recommend genetic verification of family relationships.     

White-tailed deer (Odocoileus virginianus) fecal pellet decomposition is accelerated by the invasive earthworm Lumbricus terrestris

Exotic European earthworms have expanded into worm-free forests of the United States. Concurrently, populations of the white-tailed deer, Odocoileus virginianus, have also increased. During winter, deer use hemlock stands for cover while browsing elsewhere, creating a net organic matter flux into these stands. Deer fecal pellets can provide annual inputs of 48.1 kg C, 1.4 kg N, and 1.3 kg Ca per hectare. We tested the hypothesis that these pellets were readily consumed by invading earthworms. The litter-feeding anecic earthworm Lumbricus terrestris redistributed fecal pellets and accelerated mass and nutrient loss rates. These losses are likely due to the combination of enhanced fragmentation and decomposition as earthworms drag pellets into their burrows for consumption. This nutrient subsidy may be an important source of high quality “litter” input to hemlock stands, which may in turn facilitate the invasion of these stands by earthworms under high deer densities.     

Revisions of Rump Fat and Body Scoring Indices for Deer,Elk, and Moose

Abstract: Because they do not require sacrificing animals, body condition scores (BCS), thickness of rump fat (MAXFAT), and other similar predictors of body fat have advanced estimating nutritional condition of ungulates and their use has proliferated in North America in the last decade. However, initial testing of these predictors was too limited to assess their reliability among diverse habitats, ecotypes, subspecies, and populations across the continent. With data collected from mule deer (Odocoileus hemionus), elk (Cervus elaphus), and moose (Alces alces) during initial model development and data collected subsequently from free-ranging mule deer and elk herds across much of the western United States, we evaluated reliability across a broader range of conditions than were initially available. First, to more rigorously test reliability of the MAXFAT index, we evaluated its robustness across the 3 species, using an allometric scaling function to adjust for differences in animal size. We then evaluated MAXFAT, rump body condition score (rBCS), rLIVINDEX (an arithmetic combination of MAXFAT and rBCS), and our new allometrically scaled rump-fat thickness index using data from 815 free-ranging female Roosevelt and Rocky Mountain elk (C. e. roosevelti and C. e. nelsoni) from 19 populations encompassing 4 geographic regions and 250 free-ranging female mule deer from 7 populations and 2 regions. We tested for effects of subspecies, geographic region, and captive versus free-ranging existence. Rump-fat thickness, when scaled allometrically with body mass, was related to ingesta-free body fat over a 38–522-kg range of body mass (r² = 0.87; P < 0.001), indicating the technique is remarkably robust among at least the 3 cervid species of our analysis. However, we found an underscoring bias with the rBCS for elk that had >12% body fat. This bias translated into a difference between subspecies, because Rocky Mountain elk tended to be fatter than Roosevelt elk in our sample. Effects of observer error with the rBCS also existed for mule deer with moderate to high levels of body fat, and deer body size significantly affected accuracy of the MAXFAT predictor. Our analyses confirm robustness of the rump-fat index for these 3 species but highlight the potential for bias due to differences in body size and to observer error with BCS scoring. We present alternative LIVINDEX equations where potential bias from rBCS and bias due to body size are eliminated or reduced. These modifications improve the accuracy of estimating body fat for projects intended to monitor nutritional status of herds or to evaluate nutrition's influence on population demographics.     

Survival and fidelity of an enclosed white-tailed deer population using capture–recapture-reporting data

The number of animal populations enclosed by impermeable fences has increased, which poses issues related to the behavior of individuals and populations. Despite the increased number of fenced enclosures, there is a paucity of survival and fidelity data on white-tailed deer (Odocoileus virginianus) from fenced enclosures. Therefore, we examined marked deer recaptures and resightings over 13 years for an enclosed population of white-tailed deer in Oklahoma, USA, to estimate survival and fidelity parameters. We found that a step model was the best model of survival for both sexes. Survival of females and males was greater after hunting was suspended. Average female survival was 77% before hunting was suspended but increased to 98% after. Male survival was also greater after (99%) hunting was suspended compared to before (58%). Females exhibited greater site fidelity (84–94%) than males for all age groups except old individuals, which showed similar site fidelities for males and females. Fidelity was highest for old males (85%), followed by adult (74%), fawn (61%), and yearling males (56%). Our high-tensile electric fence allowed management goals to be achieved through increased survival while potentially maintaining genetic diversity through the exchange of limited numbers of individuals from surrounding areas. However, if the goal is to confine deer to limit disease spread or protect sensitive areas (e.g., airports) from deer encroachment, then other fence designs may be necessary, because our fence was not completely effective at controlling deer movements for these purposes.