Challenges in a changing climate : The effect of temperature variation on growth and competition in damselflies

Sammanfattning: Climate change is affecting biodiversity on multiple levels all over the world. Concomitant with a higher mean temperature, an increased amplitude of temperature variation is predicted. These fluctuations might be even more challenging for organisms than average temperature increases, as they have been demonstrated to decrease survival and physiological performance. However, little attention has been paid to the effects of thermal variation on species interactions. Temperature-dependence of interacting species might affect abundance and population dynamics of species and should be better understood to apply effective conservation measures.  I experimentally investigated the influence of thermal variation on growth, cannibalism, and intraguild predation in larvae of two damselfly species: Enallagma cyathigerum, which is a common species in Northern Europe, and Ischnura elegans, which is expanding to the north in Europe. The temperature treatment in the experiment included three different levels of amplitude between 20–26°C (average 23°C) and a constant temperature at 23°C. There was no difference between the temperature variation treatments and also no difference between the constant and the variation treatments in growth, cannibalism and intraguild predation. Hence, at the temperature variation used in this experiment, plastic mechanisms may allow individuals to adjust to temperature fluctuations, or short-term effects in the cold and warm-exposure periods cancel each other out. There was a significant positive correlation between cannibalism/predation and body size variation at the start of the experiment. E. cyathigerum had higher growth rates than I. elegans, but the latter showed higher survival in interspecific treatments. Interestingly, cannibalism was higher than intraguild predation. This study is an important contribution to our understanding of climate change impacts on biotic dynamics, and thus, our ability of making predictions on biodiversity changes in the future.