Global warming will likely be accompanied by an intensification of climate extremes, such as more frequent and intense heavy rain spells. How such combined, multiple climatic drivers will affect endangered species with special habitat requirements and a narrow ecological niche is largely unknown. However, such knowledge is crucial for species conservation. In a mesocosm experiment in Bayreuth, Germany, we investigated how winter warming and heavy rain spells affect development and survival of the rare butterfly Erebia medusa. E. medusa lives in nutrient poor, extensively used or fallow mountain meadows. Festuca ovina, one of the main food plants of the caterpillars of E. medusa, grows on such meadows. Caterpillars hatch in spring and feed throughout the summer until the beginning of autumn. During winter they survive in litter, pupate in early spring and adults hatch on average from mid of May till mid of June. Eggs were collected in May/early June of 2010 and were placed in mesocosms planted with Festuca ovina and associated herbaceous species. Two different treatments, matching climate projections for Germany plus a control treatment, were applied: i) mesocosms were subjected to heavy irrigation in September/October for 3 weeks ii) mesocosms were warmed during winter using infrared lamps additionally to heavy rain spells, and iii) a control treatment with no climate manipulation was applied.
Results/Conclusions
We found that warming with rain drastically shortened the developmental time of the caterpillars and decreased larval mortality. Adults hatched significantly earlier out of pupae in the warmed mesocosms, however, female weight and oviposition was reduced. Extreme rain without warming surprisingly increased mortality of adults. Our findings imply that heavy rain spells that are projected to become more frequent in Germany under climate change might lead to a reduction of fitness in E. medusa populations. As warming advances adult eclosion, this might make adults more susceptible to die from late frosts. Hence current habitats might not be suited to fit the needs of E. medusa in the future. Such findings should be taken into account for conservation actions.