The effect of climate on oak-based species interactions : annual number of leaf flushes and insect voltinism

Abstract: Plants interact with a large diversity of organisms, including insects and microorganisms. These species interactions are strongly influenced by climate, as illustrated by the advances in plant and insect phenology in response to increasing temperatures. Beyond changes in phenology, climate might also affect the number of times certain events take place during the same year, such as the number of leaf flushes of plants and the number of generations of insects (voltinism). In this thesis, I investigated the impact of the number of leaf flushes and insect voltinism on the oak food web. I focussed on the pedunculate oak Quercus robur and the community of herbivores and fungi that share oaks as a common resource. In the first half of my thesis, I looked into the impact of the co-existence of multiple leaf flushes on plant chemistry, insect attack, pathogen infection and the structure of the foliar fungal community along the distributional range of oaks in Europe. In the second half of my thesis, I examined the impact of temperature and species traits on the voltinism of the oak-associated herbivore community, as well as the joint impact of plant spring phenology and pathogen infection on the preference and performance of multigenerational attackers during the growing season. Overall, my findings showed that I) plant chemistry, insect attack and pathogen infection differ between leaf flushes, II) the foliar fungal community is strongly affected by oak leaf flush and latitude, III) temperature and resource specialisation are the main drivers for changes in voltinism within the oak-associated community of herbivores, and IV) spring phenology and pathogen infection affect the preference and performance of multigenerational attackers. Taken together, my thesis contributes to our understanding of the effects of climate-induced changes in the number of leaf flushes and voltinism on the structure and dynamics of the oak food web.