No abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Turtles provide excellent models for studies of life history strategies, but terrestrial species are underrepresented in these analyses. We present a life table and demographic parameters of an inland population of Gopherus berlandieri to contribute to the study of evolution of turtle life histories. Data were gathered during a mark-recapture and radiotelemetry study in the Tamaulipan Biotic Province in southern Texas, USA. A total of 835 individuals were captured, measured, and their ages estimated. Females matured at 131 mm carapace length at an average of 5 yr of age (range: 4-8 yr). Clutch size, as determined by ultrasound, averaged 2.07 ?+ 0.15 eggs (n = 49). No nests were found, and we estimated clutch frequency with a quadratic model to be 1.34 clutches-female-t-year-1. Survival was estimated from age frequency regression and telemetry. Annual male survival (0.828, 0.834) differed (P < 0.05) from female survival (0.728, 0.774) for both techniques of estimation. Age-specific female survival ranged from 0.62 to 0.83 for 5-to 15-yr-old tortoises. Differential mortality of sexes led to a male-biased sex ratio in older age classes. Age structures of captured individuals did not vary (P > 0.05) among years, and population estimates did not differ among years; therefore, we constructed a life table under the assumption of a stationary population (r = 0.0). Under this assumption, survival from nest to age 4 yr must be at least 0.245, with hatchling survival of 0.528 to maintain a stationary population. Gopherus berlandieri matured at an earlier age, had smaller clutch sizes, and exhibited lower rates of female survival than other Gopherus species. We propose a physiological mechanism for lower female survival that implies trade-offs among egg size, subsequent hatchling survival, and female health. We maintain that high hatchling survival is necessary for population persistence. In an evolutionary context, we theorize that the selective advantages of small size and the life history strategies of G. berlandieri have been and are critical to its persistence.

The ecological effects of land‐use practices on reptiles, especially endangered or threatened species, are of conservation and scientific interest. We describe the effects of rotational livestock grazing and prescribed winter burning on resources and survival of the Texas horned lizard (Phrynosoma cornutum) during the summers of 1998 to 2001 in southern Texas, USA. We evaluated survival rates of Texas horned lizards (n = 111) on 6 study sites encompassing 5 different burning and grazing treatments. We also measured indices of cover (i.e., vegetation) and food abundance (i.e., harvester ants [Pogonomyrmex rugosus]). We telemetered and relocated adult lizards daily. We divided the study into 2 seasons, spring (15 Apr–30 Jun) and summer (1 Jul–15 Aug), corresponding to the relative activity of horned lizards. Winter burning provided an increase in food resources and led to increased survival of Texas horned lizards in the second growing season after fire, but grazing‐induced changes in vegetation cover reduced survival, likely by increasing lizard vulnerability. Fire and grazing reduced litter and increased bare ground and forb cover but did not affect woody vegetation. Ant activity was greater in burned sites and varied with grazing level, season, and year. Summer survival functions of horned lizards varied by burning treatment, with higher survival observed on burned sites in the second year after burning. Survival rates were ordered from highest in ungrazed sites to lowest in heavily grazed sites. We recognize the limitations of our work resulting from a lack of spatial replication of treatments. However, our mensurative study provides fertile ground for future hypothesis testing regarding the effects of land management on shrubland and grassland reptiles. We propose that future studies focus on the population consequences of variation in burn frequency, burn timing, and grazing intensity.

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Demographic 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 (k), leading to population-specific contributions of individual vital rates to k 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 k between the two sites; fecundity affected k more at CWMA than at TAFB. However, adult survival had the smallest effect on k in both populations. We found that recruitment in P. cornutum most affected k at both sites, with hatchling survival having the strongest influence on k. 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.