Effects of Rainfall and the Potential Influence of Climate Change on Two Congeneric Tortoise Species

Comparison of the resource accumulation patterns exhibited by related species inhabiting disparate hydrological conditions can provide insight into how they are affected by and respond to different environments. We compared the seasonal body condition of the desert tortoise (Gopherus agassizii) in the Mojave Desert with that of the gopher tortoise (Gopherus polyphemus) in central Florida. We assessed body condition indirectly, with indices derived from the relationship between body mass and size. In turtles, variation in body mass largely reflects tissue hydration, water stored in the bladder, and food stored in the gut. Mean body condition was lower and seasonal fluctuations were of lesser amplitude in the gopher tortoise than in the desert tortoise. Over the short term, body condition of the desert tortoise is correlated strongly with rainfall, but body condition of the gopher tortoise is not. These differences between the two species are consistent with what is known about their physiology and behavior under current climatic conditions. Changing rainfall patterns may severely affect the desert tortoise. The physiological reaction of the gopher tortoise to drought conditions also may put it at substantial potential risk from climate change.