Variation in vital‐rate sensitivity between populations of Texas horned lizards

Abstract

AbstractDemographic studies of imperiled populations can aid managers in planning conservation actions. However, applicability of findings for a single population across a species’ range is sometimes questionable. We conducted long‐term studies (8 and 9 years, respectively) of 2 populations of the lizard Phrynosoma cornutum separated by 1000 km within the historical distribution of the species. The sites were a 15‐ha urban wildlife reserve on Tinker Air Force Base (TAFB) in central Oklahoma and a 6000‐ha wildland site in southern Texas, the Chaparral Wildlife Management Area (CWMA). We predicted a trade‐off between the effect of adult survival and fecundity on population growth rate (λ), leading to population‐specific contributions of individual vital rates to λ and individualized strategies for conservation and management of this taxon. The CWMA population had lower adult survival and higher fecundity than TAFB. As predicted, there was a trade‐off in the effects of adult survival and fecundity on λ between the two sites; fecundity affected λ more at CWMA than at TAFB. However, adult survival had the smallest effect on λ in both populations. We found that recruitment in P. cornutum most affected λ at both sites, with hatchling survival having the strongest influence on λ. Management strategies focusing on hatchling survival would strongly benefit both populations. As a consequence, within the constraint of the need to more accurately estimate hatchling survival, managers across the range of species such as P. cornutum could adopt similar management priorities with respect to stage classes, despite intra‐population differences in population vital rates.