Browsing by Author "Chandler, Richard B."
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- Balancing carnivore conservation and sustainable hunting of a key prey species: A case study on the Florida panther and white-tailed deerBled, Florent; Cherry, Michael J.; Garrison, Elina P.; Miller, Karl, V; Conner, L. Mike; Abernathy, Heather N.; Ellsworth, W. Hunter; Margenau, Lydia L. S.; Crawford, Daniel A.; Engebretsen, Kristin N.; Kelly, Brian D.; Shindle, David B.; Chandler, Richard B. (Wiley, 2022-08)Large carnivore restoration programs are often promoted as capable of providing ecosystem services. However, these programs rarely measure effects of successful restoration on other economically and ecologically important species. In South Florida, while the endangered Florida panther Puma concolor coryi population has increased in recent years due to conservation efforts, the population of its main prey, the white-tailed deer Odocoileus virginianus, has declined in some regions. The extent to which panther predation has affected deer populations has been difficult to assess because several other factors have changed during this period, including hydrology and hunting regulations. We collected known-fate survival data on 241 GPS-collared adult deer (156 females and 85 males) from 2015 to 2018 in the Florida Panther National Wildlife Refuge and the Big Cypress National Preserve in Florida, USA, to assess effects of panther predation on the deer population, while also evaluating the impacts of hunting and hydrology. Predation was the primary cause of death (110 of 134 mortalities), and 87% of predation events were attributed to panthers, a much greater rate than reported by studies conducted before the panther genetic restoration effort initiated in 1995. One deer was legally harvested, and two were likely killed by poachers. Increasing water depth decreased female survival but had little impact on male survival, and drowning was never a cause of mortality. Females had greater survival probability than males, except during fawning season. From 2015 to 2018, annual survival rates increased from 0.61 (0.52-0.70) to 0.86 (0.79-0.91) for females, and from 0.45 (95% CI: 0.33-0.58) to 0.79 (0.69-0.86) for males. Synthesis and applications. High predation rates, coupled with previous evidence of low recruitment of deer in South Florida, suggest that it will be challenging to meet society's competing demands for large predator restoration and sustainable deer harvest. Deer hunting in the area must remain tightly controlled, for now, if it is to be sustainable, and managers should seek to mitigate effects of high waters and improve deer habitat quality to increase deer population viability. Future work should closely monitor the deer population to assess if management actions can increase vital rates and abundance in the context of high predation rates.
- Fire, flooding, and felids: Deer and puma spatial ecology and predator-prey interactions in dynamic, subtropical wildlandsAbernathy, Heather N. (Virginia Tech, 2021-04-06)Cyclic and extreme ecological disturbances have the capacity to alter resources and thereby animal populations. Interactions between disturbance and resource availability can influence predator-prey interactions. Predator-prey responses to ecological disturbance may be more pronounced in herbivores and their predators as herbivores track food resources that are often augmented by ecological disturbance. My objective with this dissertation was to examine how various forms of ecological disturbance influence predator-prey interactions through the lens of a case study – white-tailed deer (Odocoileus virginianus) and Florida panther (Puma concolor coryi) in southwestern Florida public and conservation lands. I quantified species-specific behavior of deer to an extreme disturbance event (i.e., Hurricane Irma), examined behavior of females with different fate outcomes to varied ecological disturbances and predation, investigated how ecological disturbance mediates the influence of human disturbance on predator-prey interactions, and quantified deer spatial ecology in response to fire, hydrology, panther and human activity. I found that deer behaviorally mediated the negative fitness impacts of Hurricane Irma. Further, I found that female deer with different fate outcomes selected areas of different ecological disturbance and the ecological disturbance type conferred different fitness costs (through differences in predation risk). Finally, I found that South Florida deer utilize diurnal times when humans are the most active to temporally reduce predation risk as panthers were more nocturnal in response to humans. My work here suggests that ecological disturbance regimes have the capacity to influence predator-prey interactions through nuanced mechanisms. Outcomes of these nuanced species-specific and predator-prey responses should be examined further. More practically, if disturbance influences aspects of animal fitness, a deeper understanding of species-specific and predator-prey responses to disturbance will improve management and conservation efforts as some regimes can be manipulated (e.g., prescribed fire). More broadly, consideration of ecological disturbance when examining predator-prey interactions may yield novel insight that deviates from predictions based on inference suggested in systems without disturbance. Highlighting nuanced predator-prey interactions mediated by ecological disturbances will improve predictions regarding species and community responses to global changes such as climate change and ecological restoration.
- Population Dynamics and Spatial Ecology of White-tailed Deer in the Central Appalachian Mountains of VirginiaClevinger, Garrett Balee (Virginia Tech, 2022-11-17)White-tailed deer (Odocoileus virginianus) are a highly charismatic game species with considerable ecological and economic impacts across most of their range. In the Central Appalachian Mountains, deer are a keystone species in forested ecosystems. Regionally, populations vary in herd growth or decline. These fluctuations are important in that they often drive many aspects of population management and regulation, which are dependent on herd demographics. Some key population vital rates allowing better understanding of these changes in white-tailed deer herds are survival, cause-specific mortality, home-range variation, both broad and fine-scale resource selection, and ultimately population growth trends in response to changes in both population vital rates and hunter harvest regulations. In this study, I address each of these concepts within a deer population in Bath County, Virginia, that has presumably been in overall decline since the early 1990's. From June-September, 2019-2020, I monitored survival and cause specific mortality of 57 neonate white-tailed deer until 12 weeks of age. Fawn and adult female survival was 0.310 (95% CI = 0.210-0.475) and 0.871 (95%CI=0.790-0.961) respectively. During the study, I observed a total of 37 fawn mortalities and identified the cause of death using field evidence and through analyzing genetics from residual predator salvia recovered on deer carcasses. Mortalities included 28 predation events and 9 deaths from other causes (e.g., abandonment, malnutrition, or disease). Black bears accounted for 48.6% of all mortality and 64.2% of known predations within our study. My top model identified elevation as a significant predictor of fawn survival, with mortality risk increasing 20% for every 100m increase in elevation. My model using observed vital rates predicted an increasing population of λ = 1.10 (interquartile range, IQR 1.06-1.14). The population was predicted to increase by 2% with a 10% increase in doe harvest (λ = 1.02, IQR = 0.97-1.06) but declined by 7% at 20% harvest (λ = 0.93, IQR = 0.89-0.96). I found that fawning home ranges of females that successfully reared fawns to the end of the season had significantly larger home ranges than those that were unsuccessful at higher elevations. Fawning home ranges for females with fawns increased approximately 71ha in size for every 100m increase in mean home range elevation, whereas seasonal home ranges of females without fawns decreased approximately 1.5 ha for every 100m increase in mean home range elevation. Deer selected fawn-rearing areas nearer to forested edges, open habitats, and at higher elevations, while they avoided areas near disturbed and mature forests. Within the fawn rearing area, females selected locations closer to disturbed forest, open habitats, and forested edge, while avoiding mature forest habitats, and higher elevations. Females selected birth sites with higher levels of visual obstruction. Using a step-selection method for real-time resource selection across biological seasons, we found that female deer selected for open areas during the fawning, breeding, early gestational, and late gestational seasons. During the fall breeding season, females avoided forested edge, but selected for areas at higher elevations. During early gestational seasons females selected disturbed habitats and areas at higher elevations while again avoiding forested edge. Overall, my work highlights variations in population dynamics of white-tailed deer in areas of the Central Appalachian Mountains that are primarily characterized by poor habitat quality and provides novel insights into fine-scale spatial ecology of female deer across biological seasons within the region. Ultimately, while the deer population in our study was not predicted to be in decline, this work supports predation risk as being a significant factor associated with habitat quality.
- Space Use and Survival of White-Tailed Deer in a Disturbance-Driven System Containing a Restored Apex PredatorEllsworth, William Hunter (Virginia Tech, 2020-08-13)White-tailed deer (Odocoileus virginianus) in the Big Cypress Basin of South Florida must cope with top-down and bottom-up forces, including frequent pyrogenic and hydrological disturbances and the threat of predation. These forces affect their space use, behavior, and survival. Recent changes to the regional hydrology and increased abundances the Florida panther (Puma concolor coryi), their primary predator in this system, call for a renewed look at how these forces affect this deer herd. To assess the effects of these forces on seasonal space use, behavior, and survival of deer, I analyzed GPS telemetry and camera trap data, highlighting the factors influencing deer space use across hydrological and biological seasons, and connected behavioral data captured on camera traps to female deer survival. Space use is primarily a function of intrinsic sex affects and landscape composition and configuration, and varies as resources and reproductive cycles fluctuate across seasons. Disturbance has little effect on space use, suggesting deer are well adapted to these disturbance regimes. Temperament in foraging behavior in female deer impacted survival, influencing prey catchability and potentially buffering prey populations against cycles of predation.
- Spatial capture-recapture for categorically marked populations with an application to genetic capture-recaptureAugustine, Ben C.; Royle, J. Andrew; Murphy, Sean M.; Chandler, Richard B.; Cox, John J.; Kelly, Marcella J. (Ecological Society of America, 2019-04)Recently introduced unmarked spatial capture-recapture (SCR), spatial mark-resight (SMR), and 2-flank spatial partial identity models (SPIMs) extend the domain of SCR to populations or observation systems that do not always allow for individual identity to be determined with certainty. For example, some species do not have natural marks that can reliably produce individual identities from photographs, and some methods of observation produce partial identity samples as is the case with remote cameras that sometimes produce single-flank photographs. Unmarked SCR, SMR, and SPIM share the feature that they probabilistically resolve the uncertainty in individual identity using the spatial location where samples were collected. Spatial location is informative of individual identity in spatially structured populations because a sample is more likely to have been produced by an individual living near the trap where it was recorded than an individual living further away from the trap. Further, the level of information about individual identity that a spatial location contains is related to two key ecological concepts, population density and home range size, which we quantify using a proposed Identity Diversity Index (IDI). We show that latent and partial identity SCR models produce imprecise and biased density estimates in many high IDI scenarios when data are sparse. We then extend the unmarked SCR model to incorporate categorical, partially identifying covariates, which reduce the level of uncertainty in individual identity, increasing the reliability and precision of density estimates, and allowing reliable density estimation in scenarios with higher IDI values and with more sparse data. We illustrate the performance of this "categorical SPIM" via simulations and by applying it to a black bear data set using microsatellite loci as categorical covariates, where we reproduce the full data set estimates with only slightly less precision using fewer loci than necessary for confident individual identification. We then discuss how the categorical SPIM can be applied to other wildlife sampling scenarios such as remote camera surveys, where natural or researcher-applied partial marks can be observed in photographs. Finally, we discuss how the categorical SPIM can be added to SMR, 2-flank SPIM, or other latent identity SCR models.
- The Spatial Ecology of Wild Pigs (Sus scrofa) in Southwest FloridaSatter, Christopher Blake (Virginia Tech, 2023-01-23)Wild pigs (Sus scrofa) are among the world's most destructive mammalian invasive species, and mitigating farther range expansion will require a thorough understanding of movement behavior, diel activity patterns, space use, and resource selection. Currently, limited empirical evidence is available on the ecology of wild pigs in Southwest Florida. Therefore, I examined how wild pigs behaviorally modified their movements and diel activity patterns in response to individual and environmental covariates. I investigated space use dynamics (e.g., home range size and seasonal variation) and evaluated how individual and environmental variation influenced home range size. Next, I determined how fine-scale movement patterns and resource selection of wild pigs are affected by temperature and time of day, and how those resources changed at broad and fine-scales, given their availability. I found that as temperature increased, the probability of foraging increased while the probability of traveling decreased. Foraging behavior occurred predominately between 8:00 and 17:00, and traveling behavior occurred predominately between 18:00 and 7:00, thereby indicating wild pigs were cathemeral. Home range size ranged from 2.6 to 35.8 km2 and averaged 13.0 km2 (n=16). Finally, home range size increased as the proportion of pasture increased and decreased as the proportion of wetlands increased, indicating that resources in agricultural areas were more diffuse than in natural habitats. At the broad (i.e., home range selection) and fine-scale (i.e., within home range) wild pigs selected for wetlands, forests, and pastures. Wild pig movement tended to be tortuous in forested and cropland habitats, but more directed in pasture habitats. Slower movements (i.e., smaller steps) and more directed (i.e., fewer turning) steps were observed during warmer temperatures, particularly avoiding croplands when temperatures were warmer. Wild pigs avoided wetland habitats during dusk and night hours and cropland habitats during dawn hours. Wild pigs selected for forested habitats during night and dawn hours, possibly in response to human activity. In addition, I found that wild pigs were less likely to step into a location with a daily temperature of 35.7°C than 16.1 C°. Wild pigs were less likely to choose warmer locations and more likely to select intermediate temperatures, thus avoiding locations with extremely low or high daily temperatures. Also, I found that wild pigs were more likely to select home ranges nearer to wetlands, forests, and pastures, while avoiding areas near cropland habitats. However, within their home ranges they were more likely to select habitats farther from croplands, forests, and wetlands. My findings reinforce the importance of wetlands, forests and pastures to wild pig selection of home ranges, where they likely utilize these landcover types for thermoregulation (e.g. forests and wetlands) and for foraging resources (e.g. pastures). Within their home ranges wild pigs may avoid forests and wetlands due to perceived predation risk being higher in those habitats, thus causing wild pigs to forgo higher quality resources to reduce risk. These results contribute information useful to wildlife managers to better predict which landcover types provide refuge (e.g., wetlands and forests) or potential movement corridors (e.g., pasture and cropland habitats) for wild pigs. In Southwest Florida, wild pigs have broad inter-individual variation in home range size, are strongly regulated by temperature, and are largely dependent on wetlands and forests to meet their energetic demands.