Stable carbon isotope analysis of modern leporids to assess their usefulness as fine-grained ecological proxies to reconstruct local paleoecology

This thesis focused on developing appropriate scales to measure environmental variability at temporal and spatial increments meaningful to hunter gatherer adaptation. Most ecological proxies operate at scales too coarse-grained for reconstructing hunter-gatherer adaptive decisions. To investigate the problem, I focused on stable carbon isotope of 66 modern leporids to assess the potential to use leporids as ecological proxies to reconstruct local paleoecology. Leporids should make good local proxies. They eat a diverse diet of vegetation, have small home ranges, live short-life spans, and are commonly found in the archaeological record. Stable carbon isotopic values in the bone collagen of jackrabbits and cottontails are made of a mix of the plant types (C3, C 4, and CAM) they consume. The short lifespan and low mobility of these animals make it clear their collagen reflect local, short term vegetation. Environmental parameters, such as temperature and rainfall, interact to produce different mixes of plants in local settings. We do not understand how these different mixes become expressed in leporids' collagen. To remedy this gap in knowledge, I studied modern leporids to permit comparing the results to known vegetation and environment conditions.

I selected three environmentally diverse regions in Texas to obtain leporids specimens and focused on reconstructing changes in vegetation using stable carbon isotopic compositions preserved in 66 modern bone collagen of jackrabbits (Lepus sp.) and cottontails (Sylvilagus sp.) collected from these three different ecological settings in Texas. The three areas were far El Paso, Big Bend, and Kerr Co. Carbon isotopic values in the Big Bend had the heaviest 13Ccollagen values (mean = -16.37). The next heaviest 13Ccollagen values is the El Paso (mean = -18.83). Kerr County specimens have the lightest 13Ccollagen values (mean = -20.17).

Big Bend specimen values reflect a desert habitat lower in elevation and hotter than El Paso or Kerr County. El Paso specimens reflect a desert environment that is higher in elevation more northern latitude. In El Paso, C3 shrubs are available year round including summer. Vegetation transects data from El Paso show even in summer C3 forbs and shrubs are available. While elevation transects data from Big Bend, suggest an environment dominated in summer by CAM (approximately 70% of the total ground cover) to the near exclusion of C3 plants. The Big Bend transects did not consider annuals or forbs. Kerr Co specimens reflect much higher rainfall and an area dominated by C3 forest and woodlands. Clearly, the isotopic values of these specimens reflect the three different environments. However, this study raises difficult questions regarding the complexity of this the use of the method in reconstructing paleoenvironment. Future studies should focus on environmental factors, such as evaportranspiration and the seasonality and timing of rainfall, and their direct correlation to delta 13Ccollagen values in leporids bone.