Presented by Dr. Lee Fitzgerald, Professor of Wildlife and Fisheries Sciences, Texas A&M University
Abstract: A central question in conservation biology is “What allows a species to persist and what causes it to disappear?” The answer depends on the species’ life history and behavioral constraints, its role in ecological communities, and its sensitivity to landscape change. Our research on the Dunes Sagebrush Lizard (Sceloporus arenicolus) carried out over the last 18 years has revealed how their populations are organized from local neighborhoods of interacting individuals up to the distribution of the species across its geographic range. Dunes Sagebrush Lizards are habitat specialists, endemic to the Mescalero-Monahans shinnery oak sand dunes in southeastern New Mexico and adjacent Texas. They occur only in and around wind-hollowed “blowouts” in a matrix of dwarf shinnery oak trees (Quercus havardii). The quality and quantity of habitat are correlated; high quality habitat consists of many interconnected large blowouts. At the scale of habitat patches, lizards live in “neighborhoods”. Larger neighborhoods are found in higher quality habitat and produce an excess of recruits that disperse across the interconnected landscape. Poor quality habitat supports smaller neighborhoods, where recruitment fails to balance mortality. At the landscape scale, the species’ presence is associated with contiguous areas of dunes, and its absence is associated with dunes infiltrated by mesquite.
How does land-use affect the lizards and their habitat? Our results are converging on the conclusion that landscape fragmentation disrupts both the hierarchy of organization of populations and the self-organizing dynamic that maintains the shinnery dune landform. Daniel Leavitt’s dissertation research is showing that Dunes Sagebrush Lizards practically disappear from sites fragmented by dense networks of caliche roads. In this system, top-down disturbance disrupts the relationships between habitat quality, neighborhood size, and connectivity among populations.
The Dunes Sagebrush Lizard is proposed for listing as Endangered by the US Fish and Wildlife Service because of perceived threats of habitat loss from shinnery oak removal and landscape fragmentation associated with oil and gas development (and because FWS was sued by the Center for Biological Diversity). The lizard’s range lies in the Permian Basin, which produces about 20% of USA domestic oil supply. Not surprisingly, the proposed listing has propagated concerns that if it is listed, oil supplies and jobs will be threatened with devastating economic consequences. Candidate Conservation Agreements have been put into place in New Mexico, and are being enacted in Texas. To date, land use policies are aimed at small-scale practices such as placement of individual well pads, or pasture-by-pasture shinnery oak removal. To preserve the dynamic processes that maintain the unique landform in this system and the resulting hierarchical scaling of populations, land use policies should recognize the potential for hierarchical effects and conserve large contiguous areas of shinnery dunes.
Loading more stuff…
Hmm…it looks like things are taking a while to load. Try again?