Spatial and demographic ecology of Texas horned lizards within a conservation framework

Abstract

Disturbance due to habitat restoration and urbanization can threaten populations of sensitive wildlife species. I examined 2 aspects of the ecology of Texas horned lizards (Phrynosoma cornutum), a Species of Special Concern in Oklahoma. I studied the effects of native prairie restoration and urban development on a population of P. cornutum on an urban wildlife reserve at Tinker Air Force Base, Oklahoma. I also studied population vital rate variation in 2 populations of P. cornutum using deterministic elasticity and life-stage simulation analyses. My research on the effects of habitat disturbance on urban P. cornutum focused on Wildlife Reserve 3 (WR3) at Tinker Air Force Base, which has a population of P. cornutum that has persisted for many years. I quantified daily movement rates, home-range size, changes in spatial distribution, survival rates, and population size and density over 9 years (2003-2011). Movement rates of P. cornutum were affected by a 3-way interaction of sex, period (reproductive vs. non-reproductive), and study stage (2004-2005, 2007-2008, and 2009-2011). Stages represented variation in the type and level of anthropogenic disturbance on the site. Home-range size did not vary by sex, but was smaller during the non-reproductive period than the reproductive period. Spatial analyses indicated that disturbances due to restoration activities had little effect on the spatial distribution of P. cornutum on WR3. Survival was affected by season (inactive-season survival was higher), stage (declining survival in later stages with more disturbance), an interaction of season and stage, and disturbance (covariate of proportion of an individual\u27s home range in disturbed areas for a given year; small negative effect), with little evidence for variation in survival by sex. Major causes of mortality included depredation and anthropogenic causes. I estimated a population size of 32.9 ± 4.7 (95% CI of 28.1-49.0) individuals (excluding hatchlings) with a corresponding density of 2.68 lizards/ha. Spatial analyses did not support the hypothesis that disturbance associated with restoration activities affected the spatial ecology of P. cornutum on WR3. However, these results were not entirely conclusive, due to the logistical constraints of working on a single site with an uncommon species. Size and density of the P. cornutum population has apparently declined since 2005. This decline is likely a consequence of 2 factors: the 2008 translocation of 17 adult lizards from an area adjacent to WR3 impacted by housing development coupled with a decrease in the annual survival rate of adults over time. I compared the vital rates of the population of P. cornutum on WR3 to a site in south Texas, the Chaparral Wildlife Management Area (CWMA). The Chaparral WMA population had lower adult survival and higher fecundity than WR3. I predicted a trade-off between the effect of adult survival and fecundity on population growth rate (&lambda). I found that recruitment in P. cornutum most affected &lambda at both sites. Stochastic life-stage simulation analysis indicated that hatchling survival most affected &lambda in both populations. There was a trade-off in effect on &lambda between juvenile survival and fecundity between the two sites; fecundity affected &lambda more at the CWMA. Adult survival had minimal effects on &lambda in both populations. My study suggests that managers can address P. cornutum declines in similar ways across the species\u27 range

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This paper was published in OpenSIUC.

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