Research
Landscape Fragmentation Effects on the Dunes Sagebrush Lizard and the Lizards of the Mescalero-Monahans Shinnery Sands
Currently, I am analyzing the effects of landscape fragmentation on lizards in Mescalero-Monahans Shinnery Sands Ecosystem in southeastern New Mexico.
This ecosystem, situated at the base of the llano estacado, is undergoing heavy development related to oil and gas extraction. The animals found in this ecosystem represent a unique mixture of generalists and a few specialized endemic species occur here (Henderson 2006, Leavitt 2012). Many of my questions focus on how this development affects biodiversity.
I have analyzed the impacts of fragmentation on the lizard community structure. This community, which includes the dunes sagebrush lizard (Sceloporus arenicolus), is demonstrating signs of non-directional and random disassembly. Major differences exist in the diversity and evenness between heavily developed sites and those not yet developed (Leavitt and Fitzgerald, In prep; 2009a; 2010; Leavitt et al. 2011). In addition to this, patterns of species loss appear to be more stochastic and less predictable than the patterns that structure these communities (Leavitt and Fitzgerald, In prep).
I am beginning analysis directed towards determining if specialist lizards are more susceptible to fragmentation than generalist lizards. After comparing their habitat selection, I will assess the differences in environmental variation between non-fragmented landscape and fragmented landscape. Ultimately I will be able to evaluate the cross correlations between lizard traits, lizard abundance on the landscape, and landscape fragmentation.
Eventually, I will assess the use of the dunes sagebrush lizard as an "Umbrella" for the diversity of this ecosystem. This analysis will provide insights for resource managers and conservation practitioners in this region.
This research was funded by the Bureau of Land Management, the Alfred P. Sloan Foundation, the Tom Slick Graduate Fellowship, the Herpetologists League, and the section on Ecology and Evolutionary Biology at Texas A&M.
Consequences of Green Treefrog Range Expansion
This research is focused on a small population of Green Treefrogs (Hyla cinerea) which arrived in a remote wetland in west Texas, a range expansion of more than 300 miles. Thus far, I have focused my research on the colonizing potential of this species. Results of a dietary analysis demonstrated few differences exists in consumption patterns when compared with regions where they are native (Leavitt and Fitzgerald, 2009b). Future research will attempt to uncover their ecological position and importance in this remote wetland.
Lizard Community Responses to Vegetative Shifts
In 2005 and 2006, I conducted this research to evaluate trends in lizard communities in the Chihuahuan Desert at Big Bend National Park. Following protocol designed and implemented in the 1950s (Degenhardt, 1966; 1977) I followed up on a previous study and found some rather drastic changes in the lizard community compositions. This research was conducted on an elevation gradient between the Rosillos and Chisos Mountains.
Gross vegetation compositions changed markedly at all elevations (840 m - 1470 m) (Leavitt et al, 2010). Likewise, shifts in the saurian faunas were recorded by this study. In the 1950s, the study areas were much more open. As the landscape was turned from cattle and goat grazing to park management, brush encroachment ensued. The result for lizards was, a overall decrease in Southwestern Earless Lizards (Cophosaurus texanus) and an increase in the Big Bend Whiptail (Aspidoscelis septemvittata).
I hope to revisit this survey in the future.
Literature cited
Degenhardt, W. G. 1960. An ecological study of the lizard genera Holbrookia and Cnemidophorus in the Big Bend National Park, with a checklist of the reptiles and amphibians. Ph.D. Dissertation. Texas A&M University, College Station, Texas.
Degenhardt, W. G. 1966. A method of counting some diurnal ground lizards of the Genera Holbrookia and Cnemidophorus with results from the Big Bend National Park. American Midland Naturalist 75:61-100.
Degenhardt, W. G. 1977. A changing environment: documentation of lizards and plants over a decade. Pages 533-555 in R. H. Wauer and D. H. Riskind, editors. Transactions of the symposium on the biological resources of the Chihuahuan desert region. National Park Service Transactions and Proceedings Series, Alpine, Texas.
Henderson, D. 2006. An introduction to the Mescalero sands ecosystem. Thesis. Texas A&M University, College Station, Texas. pdf
Leavitt, D. J. and L. A. Fitzgerald. 2009a. Results from the first year of research: effects of management practices for oil and gas development on the mescalero dune landscape and populations of the endemic dunes sagebrush lizard, Sceloporus arenicolus. Pages 1-9.
Leavitt, D. J. and L. A. Fitzgerald. 2009b. Diet of non-native Hyla cinerea, in a Chihuahuan desert wetland. Journal of Herpetology 43:541-545. pdf
Leavitt, D. J. and L. A. Fitzgerald. 2010. Results from the second year of research: effects of management practices for oil and gas development on the mescalero dune landscape and populations of the endemic dunes sagebrush lizard, Sceloporus arenicolus. Pages 1-9.
Leavitt, D. J., A. F. Leavitt, and C. M. Ritzi. 2010. Post-grazing vegetational change in Big Bend National Park, Texas: a 50-year perspective. Southwestern Naturalist 55:493-500. pdf
Leavitt, D. J., D. K. Walkup, K. E. Narum, and L. A. Fitzgerald. 2011. Results from the second year of research: effects of management practices for oil and gas development on the mescalero dune landscape and populations of the endemic dunes sagebrush lizard, Sceloporus arenicolus. Pages 1-11.
Leavitt, D. J. 2012. The Dunes Sagebrush Lizard: an endemic species in an endangered ecosystem. Partners in Amphibian and Reptile Conservation: Year of the Lizard Newsletter. 1:4-5. pdf
