An assessment of the role of roads in population demography and genetic structuring in two species of lizards in the northern Chihuahuan Desert

Kevin Wesley Floyd, University of Texas at El Paso


Roads can fragment habitat and increase mortality rates of wildlife, potentially reducing population sizes and gene flow, which in turn can reduce genetic diversity through genetic drift. Although negative road impacts have been found in a variety of taxa, not all species are impacted. For instance, species that move less and rarely encounter roads and those that avoid the roads are predicted to not be negatively affected. Yet tests of these predictions are uncommon, especially for reptiles and particularly lizards. Side-blotched lizards (Uta stansburiana) are small sit-and-wait predators, while the larger marbled whiptails (Aspidoscelis marmorata) are active foragers. Their responses to roads were tested in populations inhabiting areas near a large high volume road and a smaller local road. Whiptails were hypothesized to encounter roads frequently, decreasing survival rates and abundance near roads. Conversely, side-blotched lizards should encounter roads less often and have less mortality. Potentially lower abundance of whiptails near roads should also lead to decreased genetic diversity, and the lack of movement across roads should lead to increased genetic differentiation. Neither the abundance nor survival of either species was decreased near the roads. Both species crossed the smaller road less often than expected, and no individuals were found to have crossed the larger road. Genetic diversity was not correlated with distance to road and no divergence was detected. Both species were abundant at all sites, and some lizards crossed the small road, maintaining genetic connectivity. Although unlikely that lizards cross the larger road, the lack of differentiation is likely due to large populations where genetic drift acts slowly. Furthermore, the roads are relatively new, perhaps allowing insufficient time for detectable differentiation. Despite biological differences, these two lizard species do not appear to experience negative demographic or genetic effects of roads. Future studies should examine how lizard species with divergent life histories and behaviors respond to increasing road density. This study is the first on lizard road ecology in the desert Southwest, and one of the few studies that integrates demographic and genetic data to gain a better understanding of animal responses to roads.

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Recommended Citation

Floyd, Kevin Wesley, "An assessment of the role of roads in population demography and genetic structuring in two species of lizards in the northern Chihuahuan Desert" (2015). ETD Collection for University of Texas, El Paso. AAI3724920.