TEMPERATURE, ACTIVITY, AND LIZARD LIFE-HISTORIES

Lizard life-history characteristics vary widely among species and popu lations. Most authors seek adaptive or phylogenetic explanations for l ife-history patterns, which are usually presumed to reflect genetic di fferences. However, lizard life histories arc often phenotypically pla stic, varying in response to temperature, food availability, and other environmental factors. Despite the importance of temperature to lizar d ecology and physiology, its effects on life histories have received relatively little attention. We present a theoretical model predicting the proximate consequences of the thermal environment for lizard life histories. Temperature, by affecting activity times, can cause variat ion in annual survival rate and fecundity, leading to a negative corre lation between survival rate and fecundity among populations in differ ent thermal environments. Thus, physiological and evolutionary models predict the same qualitative pattern of life-history variation in liza rds. We tested our model with published life-history data from field s tudies of the lizard Sceloporus undulatus, using climate and geographi cal data to reconstruct estimated annual activity seasons. Among popul ations, annual activity times were negatively correlated with annual s urvival rate and positively correlated with annual fecundity. Proximat e effects of temperature may confound comparative analyses of lizard l ife-history variation and should be included in future evolutionary mo dels.