Patterns of spatio-temporal variation in the survival rates of a viviparous lizard: the interacting effects of sex, reproductive trade-offs, aridity, and human-induced disturbance

Examination of the spatial and temporal variation in survival rates provides insight on how the action of natural selection varies among populations of single species. In this study, we used mark-recapture data from seven populations of the viviparous lizard Sceloporus grammicus in Central Mexico and a multi-model inference framework to examine interpopulation variation in the survival of adult males and females. We aimed to analyze the potential effects of aridity, human-induced disturbance, and reproductive costs on the survival rates of these lizards. For females in particular, we also searched for a negative relationship between litter size (adjusted for female size) and female survival. Our results demonstrate seasonal changes in survival for males and females. In three out of our seven study sites female survival decreased during the birthing season. In contrast, male survival did not appear to decrease during the mating season. We found an interaction between site-specific aridity and reproductive season affecting female survival. A decrease in female survival during the birthing season was observed in relatively arid sites. In one of these arid sites we found a negative effect of size-adjusted litter size on female survival: females producing more offspring than those expected for their size were more likely to die. This result represents evidence of a physiological trade-off for gravid females occurring in at least one of the studied populations. Interpopulation variation in the degree of human-induced disturbance could not explain the observed patterns of spatial variation in survival rates. Our results demonstrate wide variation in sex-specific survival patterns of this viviparous lizard and provide evidence that negative associations between reproduction and survival are highly dependent on the local environmental conditions.