Nitrogen fertilization and high plant growing temperature increase herbivore performance

Global environmental change exerts growing pressure on biodiversity. Anthropogenic climate and land use change are particularly important drivers of biodiversity loss. While their effects on biodiversity have been widely studied individually, interactions among them are poorly understood. Here, we investigate the effects of two common drivers of global change, increased temperature and nitrogen fertilization, on host-plant quality and herbivore performance in the butterfly Lycaena tityrus. We show that butterfly performance was positively affected by plants grown at increased temperatures and nitrogen fertilization, the latter being in line with the nitrogen limitation hypothesis. Effects were largely consistent across treatments, i.e. nitrogen deposition and temperature did not interact strongly to affect herbivore performance. Overall, females suffered more strongly than males from poor host-plant quality. Our study demonstrates changes in host-plant quality caused by variation in temperature and nitrogen availability, which induced indirect effects in an herbivore. Such indirect effects of global environmental change are an important source of variation and should be considered in order to reduce uncertainties with regard to the effects of global change on biodiversity.