#16 - Spatial variation in male whitetail deer morphology across Georgia

Understanding morphological variation across space in large mammal species can provide insights into their overall ecology and evolutionary history. However, these analyses are frequently limited by the availability of high-resolution morphological data from individuals over a wide spatial scale. In this study, we compiled a large (N=2,092) sample of morphological characteristics from male whitetail deer (Odocoileus virginiana) harvested on Georgia Department of Natural Resources Wildlife Management Areas (N=40; DNR WMA) during the 2017 hunting season. We use these data to investigate spatial heterogeneity in the morphological characteristics (e.g., body weight, total antler spread, antler diameter) of this species. Our data indicate that: 1) most males harvested across these sites were 3.5 years of age or younger, 2) males harvested in northern Georgia WMA were significantly larger (i.e., higher body mass) on average and had longer antler beam length when controlling for age group. These data indicate significant variation in male whitetail deer populations at the state of Georgia spatial scale that may be driven by resource availability and hunting pressure. In the future, we plan to analyze similar patterns in female deer as well as evaluate the influence of agricultural practices and human-induced habitat change

#35 - Enamel isotopes reveal late Pleistocene ecosystem dynamics in southeastern North America

The end of the late Pleistocene (~10,000 years ago) witnessed the extinction of over seventy percent of North America’s megafaunal genera. Although this pattern has been extensively investigated, its causal mechanisms remain elusive. Much of this difficulty is related to the spatial and temporal discontinuity of sites dating to the period leading up to the extinctions. Due to its removal from glacial conditions, southeastern North America provides a unique window into ecosystem dynamics just prior to human arrival in the region. In this study, we present new stable carbon and oxygen isotope data from Mammuthus columbiand Bison latifronsteeth collected from a well-dated Last Glacial Maximum (~20,000 rcybp) locality called Clark Quarry in coastal Georgia, USA. We compare these data to those from similarly aged (middle and late Rancholabrean) localities from Florida and demonstrate the presence of a vegetation gradient with elevated levels of C3vegetation at higher latitudes. We hypothesize that this pattern may have contributed to previously described migratory patterns of mastodon (Mammut) populations in southeastern North America. Serially-sampled δ13C and δ18O values suggest that Clark Quarry Mammuthus and Bison changed their diet seasonally with the incorporation of elevated quantities of C4vegetation during warmer periods. Our data indicate more exaggerated seasonal dietary variability in these taxa at Clark Quarry relative to those collected from the interglacial locality of Waccasassa River in Florida, providing additional evidence for the significant influence of glacial dynamics in structuring North American ecosystems

25. Isotopic evidence of dietary variation in white-tailed deer: a model for Pleistocene herbivores in southeastern North America

Understanding the ecological factors that contributed to the late-Pleistocene large mammal extinction event (~10,000 years ago) has been particularly challenging due to the lack of a modern comparative framework. However, existing research suggests that changes in landscapes and the distribution of vegetation likely contributed to the downfall of megaherbivores. In this study, we create a dietary model for late-Pleistocene herbivores using enamel carbon (δ13C) and oxygen (δ18O) isotope values from extant white-tailed deer (Odocoileus virginianus). More specifically, we investigate the isotopic signature of enamel during the formation of M1, M2 and M3 as a means of considering annual variation in diet as well as variation across the life of the individual. The δ13C value of enamel apatite reflects the δ13C value of ingested foodstuffs, offset by a diet-tissue fractionation factor. Based upon this scheme, herbivorous mammals can be divided into three different dietary categories: C3 browsers (3/C4 mixed-feeders (\u3e-8‰ to 4 grazers (\u3e-1‰). Variability in δ18O values within a single tooth are indicative of seasonal changes in precipitation or temperature given the relationship between enamel δ18O values and ingested water. Higher δ18O values are suggestive of elevated evaporation or decreased precipitation, frequently induced by warm/dry conditions. With this information, we will be able to better understand existing isotopic data collected from mammoth (Mammuthus columbi) and long-horned bison (Bison latifrons) in southeastern North America. Finally, these data (particularly oxygen isotopes) will be valuable for considering modern and ancient changes in rainfall across southeastern North America

28. Spatial variation in white-tailed deer morphology across southeastern North America

Morphological variation across space in large mammal species can provide insights into their overall ecology and evolutionary history. However, these analyses are frequently limited by the availability of high-resolution morphological data from a large number of individuals over a wide spatial scale. In this study, we compiled morphological data (\u3e700,000 individuals; \u3e600 localities) spanning two decades collected from white-tailed deer (Odocoileus virginiana) across Georgia, Virginia, South Carolina, North Carolina and Tennessee. We use these data to investigate spatial heterogeneity in the morphological characteristics (e.g., body weight, total antler spread, antler diameter) of this species across southeastern North America. Preliminary analysis indicates 1) significant variation in body size across the space considered here, and 2) the potential of this large data set to provide unprecedented insights into the ecology and biogeography of this important species. Finally, the patterns identified here could serve as a model for evaluating extinct mammal herbivores in the paleontological record of this region. Future analysis will incorporate morphological data from additional localities outside of southeastern North America

TESTING THE FIDELITY OF ENAMEL ISOTOPIC, ENVIRONMENTAL AND CLIMATIC VARIATION IN A LOCALIZED POPULATION OF WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS)

Stable isotopes from tooth enamel have long been used to gain better insight into modern and ancient environmental dynamics. Carbon isotopes are used to determine the ratio of 13C/12C within tooth enamel and can be used to infer the relative proportion of C3 (e.g., trees, shrubs, cool growing season grasses) and C4 (e.g., warm growing season grasses and sedges) plants consumed by the animal during the time period of the tooth’s mineralization. Oxygen isotopes are used to determine the ratio of 18O/16O consumed, typically in the form of drinking water or water contained in plant tissues, by the animal during tooth mineralization. Due to this relationship, oxygen isotopes can be used to infer whether the animal lived in a more evaporative (i.e., warm, decreased rainfall) or less evaporative (i.e., cool, more rainfall) environment. Although a commonly used method, there is currently a lack of modern comparative frameworks testing the precision of these relationships. In this study, we sampled three molars (m1, m2, and m3) from 6 individual male deer (18 teeth total) of known age and life history collected from the Piedmont National Wildlife Refuge (PNWR). These teeth were serially sampled (multiple samples along the growth axis of the tooth) to elucidate any isotopic variation between individuals and between molars. These isotopic signatures were compared to climate data (e.g., temperature, precipitation) gathered from around PNWR during the time of tooth mineralization. Our study indicates a complex relationship between climatic variables and their reflection in the isotopic composition of deer enamel. We observe significant inter-individual variation in isotopic signature, which suggests a complex relationship between climate variables and the universality of their representation in mammalian enamel

Enamel isotopes reveal late Pleistocene ecosystem dynamics in southeastern North America

The end of the late Pleistocene (∼10,000 years ago) witnessed the extinction of over seventy percent of North America\u27s megafaunal genera. Although this pattern has been extensively investigated, its causal mechanisms remain elusive. Much of this difficulty is related to the spatial and temporal discontinuity of sites dating to the period leading up to the extinctions. In this study, we present new stable carbon and oxygen isotope data from Mammuthus columbi and Bison latifrons teeth collected from a well-dated Last Glacial Maximum (∼20,000 rcybp) locality called Clark Quarry in coastal Georgia, USA. This site lies in direct proximity to where Sir Charles Lyell collected the type specimen of M. columbi in 1846 and therefore is of added historical significance. We compare these data to those from similarly aged (Sangamonian interglacial and Wisconsin glacial intervals) localities from Florida and demonstrate the presence of a vegetation gradient with elevated levels of C3 vegetation at higher latitudes. Serially-sampled δ13C and δ18O values suggest that Clark Quarry Mammuthus and Bison changed their diet seasonally with the incorporation of elevated quantities of C4 vegetation during warmer periods. Our data indicate more exaggerated seasonal dietary variability in these taxa at Clark Quarry relative to those collected from the Sangamonian interglacial locality of Waccasassa River in Florida, providing additional evidence for the significant influence of glacial dynamics in structuring North American ecosystems. These high-resolution ecological patterns should be incorporated into hypotheses focused on extinction dynamics in southeastern North America and more broadly