Identifying Disruptions of Population Processes in Fragmented Landscapes for an Endemic Habitat Specialist, the Dunes Sagebrush Lizard (Sceloporus Arenicolus)
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Habitat fragmentation and habitat loss are two of the main drivers of biodiversity loss. This anthropogenic reduction of habitat and the corresponding increasing isolation can lead to negative consequences for biodiversity including species loss, changes in community composition, and reduced species diversity at multiple levels of organization. Understanding how a species is distributed across the landscape is especially important in conservation contexts, as variations in habitat quality can drive population persistence. My dissertation focused on Sceloporus arenicolus (dunes sagebrush lizard) a habitat specialist endemic to the Mescalero Monahans Sandhills ecosystem threatened by loss and degradation of shinnery oak dunes. Extensive development of well-pad and road networks has led to fragmentation of shinnery oak dunes, negatively impacting S. arenciolus populations. I utilized data from three different studies to elucidate responses of S. arenicolus populations in highly fragmented areas, understanding how S. arenicolus use and move through habitat, and finally estimating occupancy probabilities across part of its Texas range. To understand how populations of S. arenicolus and other dune-dwelling lizards in the community were impacted by landscape fragmentation, we captured lizards on 27 independent trapping grids located in unfragmented (N=18) and fragmented (N=9) sites in southeastern New Mexico from 2009 to 2013. Using a two-way ANOVA, we tested for effects of fragmentation and year on capture rates for each species. Capture rates of S. arenicolus decreased to zero in all fragmented sites. Before extirpation, the demographic structure of S. arenicolus and Holbrookia maculata (common lesser earless lizard), were severely disrupted at fragmented sites, with proportions of juveniles, adult males or adult females being over or under represented during sample months. To understand patterns in use, settlement, and vacancy at both the microhabitat and landscape scales at two different sites, we trapped S. arenicolus at two different trapping sites (~14 ha each). For each site individually, we modeled use, settlement, vacancy, and detection as functions of microhabitat and landscape variables in separate analyses. I showed that microhabitat and landscape context influence use, settlement, and vacancy patterns in complex ways; these patterns were dynamic and no single variable consistently predicted the dynamics among the patterns. Microhabitat variables better predicted the probability of use, while landscape-scale variables better predicted probabilities of settlement and vacancy. Finally, to gain a baseline understanding of occupancy in parts of the range of S. arenicolus in Texas using the range map from the Texas Conservation Plan, 100 16-ha sites were surveyed multiple times (336 surveys total) from May to August 2014–2016. Thirty-three S. arenicolus were detected during 17 surveys at nine sites in areas classified as Very High likelihood of occurrence. Occupancy probability for S. arenicolus in the Very High likelihood of occurrence areas was 0.32 ± 0.09 (SE), with a detection probability of 0.52 ± 0.12. Local extinction probabilities were low at 0.12 ± 0.18, with the colonization probability fixed at zero. No S. arenicolus were detected in the 54% of surveys that occurred outside the currently recognized range.
Walkup, Danielle Kathryn (2018). Identifying Disruptions of Population Processes in Fragmented Landscapes for an Endemic Habitat Specialist, the Dunes Sagebrush Lizard (Sceloporus Arenicolus). Doctoral dissertation, Texas A & M University. Available electronically from