The effect of climate change on the life-history of long-lived vertebrates

Background/Question/Methods

Understanding the effect of climate change on fitness of long-lived ectotherms is extremely difficult given their extended lifespans. It is well-established that warm temperature increases growth rate in ectotherms, and although theory generally suggests that faster growth rates driven by increases in food supply should increase both size at maturity and fitness, empirical data show that when warmer temperatures drive increased growth rate, fitness may be reduced, as evidenced by a smaller size a maturity. Both temperature and food availability vary together in wild environments, and so the fitness consequences of a warming environment need to be explored empirically, especially in long-lived species with protracted reproductive lifespans. Here, we use a 33-year mark-recapture study of wild, free-ranging painted turtles in Edwin S. George Reserve, Michigan, USA, to understand how a warming climate may influence the life-history strategy of these long-lived vertebrates. We fit hierarchical von Bertalanffy growth models in a Bayesian framework. In this model, we include a temperature effect on the size-independent growth term to understand the effect of temperature on growth. This framework will be expanded to model temperature and size effects on survival and longevity.

Results/Conclusions

We fit a hierarchical von Bertalanffy growth model for 504 mature individuals (n female = 336, n male = 168) across 33-years. Asymptotic size in this population is 12.27cm (95% CR: 11.84 – 12.73cm) for females and 11.78cm (95% CR: 11.21 – 12.35cm) for males. We found that temperature had a positive, albeit weak, effect on growth. For a one standard deviation increase in temperature of the growing season (0.79℃), the growth rate increased by 0.13 (-0.64 – 0.93), on the log-scale. There was considerable variation in both asymptotic size and growth rate at the individual level, standard deviation = 0.13 and 0.42 on the log-scale. Overall, we show that temperature has only a weak positive effect on growth rate. Thus, it seems unlikely that climate change will have a strong effect on the life-history strategy of turtles, as growth is only weakly affected by temperature.