Body Size Differences Between Populations of the Chuckwalla, Sauromalus Obesus

Body size of chuckwallas, Sauromalus obesus (measured as the upper decile snout—vent length, UDL) at 12 locations throughout the species' range is highly correlated with average winter rainfall. The coefficient of variation of rainfall and average seasonal temperatures did not significantly aid winter rainfall in accounting for populational body size differences. Two populations with the highest (Little Lake) and the next to lowest (Amboy) UDL were studied in detail. The larger Little Lake chuckwallas appear to grow faster but do not live longer than chuckwallas at Amboy. This enhanced growth was allied to the more diverse and abundant food regime at Little Lake. Surprisingly, chuckwallas at Little Lake maintain relatively smaller fat bodies than animals at Amboy. This may be an adaptation to Amboy's more severe and less productive environment.