Increased temperatures due to climate change are impacting the demographic rates and phenology of ectothermic organisms that rely on external warmth to develop. Potential nonlinear impacts of temperature on demography, phenology and development make it difficult to predict population level responses of species to climate change needed to plan wildlife management and conservation actions for the future. We investigated these impacts directly by measuring the survivorship and the timing of lifecycle events at several life stages of a wetland butterfly, the Appalachian Brown. We carried out manipulative warming experiments in a greenhouse and under field conditions at Fort Bragg, NC. We measured egg and larval survival over 3 generations during 2016-17 by raising butterflies from eggs to adults under increased temperature scenarios (+1-6 degrees Celsius) using infrared heating bulbs in greenhouse enclosures, and using open-top warming chambers at field sites. We estimated adult survival by using a multi-state mark and recapture survey in plots that varied in temperature due to experimental restoration. We investigated the potential for phenological shifts by recording the timing of adult emergence in spring alongside growing degree days (cumulative temperature) experienced by individuals in the experimental warming enclosures.
Results/Conclusions
Our results indicate that egg hatching rates in the greenhouse experiment decreased with increasing temperatures beyond 29 degrees Celsius (logistic regression p<0.001.) In our field experiment we found that increased temperatures were negatively correlated with the probability that at least one larvae per enclosure survived to adulthood (logistic regression p<0.001.) Our results demonstrate negative impacts of increased temperatures on the demographic rates of Appalachian Brown eggs and larvae. The results also suggest a potential maximum temperature threshold for egg survival. Our findings ultimately suggest that wildlife management strategies must take into account the future effects of temperature increases and the potential nonlinear response of ectotherms to warming.