Abstract
Growth and body size play important roles in population demography. Differences in habitat and variation in local environmental conditions or resources can differentially affect growth rates between individuals and populations. Understanding this variation is crucial for applying demographic knowledge to species management. However, inappropriate selection of growth models and failure to account for individual variation can affect parameter estimates and understanding similarities or differences in growth between individuals or populations, potentially leading to misguided management decisions. Previous models of growth for the Sonoran Desert tortoise (Gopherus morafkai) did not select among competing models or incorporate individual variation, so I used an information-theoretic framework to apply hierarchical, mixed-effects models to the growth of individual tortoises over 25 yrs in a population in Arizona to provide a foundation for interpopulation studies. Females grew more rapidly early in life than males (k = 0.23 vs. 0.18) before slowing to a smaller asymptotic carapace length than males (251.6 mm vs. 262.5 mm). Females matured at slightly earlier ages than males (15.0 yrs vs. 16.8 yrs). Within years, gravid females invested less in growth than nongravid females, and smaller tortoises tended to grow more than larger ones; growth also generally increased following wetter winters. On average, tortoises ceased growing upon reaching 265.2 mm carapace length. Growth characteristics documented for this population differ from those reported elsewhere, which could affect demographic inferences and management attention to different populations across the range of this declining species. Therefore, a more detailed, population-specific study of individual growth and habitat conditions between G. morafkai populations may contribute to improved management and conservation trajectories for the species.
