Rainfall and host reproduction regulate population dynamics of a specialist seed predator

Abstract

1. Mast seeding is a widespread resource pulse caused by synchronized and intermittent production of a large seed crop by plant populations. The effects of masting on wildlife have been well documented in granivorous vertebrates, but less is known about its impact on population dynamics of insects.2. This study investigated, over 6 years, variation in abundance of a specialist weevil (Curculio elephas) preying on holm oak (Quercus ilex) acorns.3. An immediate bottom‐up effect of seed production on weevil larval abundance was detected, which was driven by an increase in realised fecundity and aggregation at seed‐rich trees. Moreover, trees producing on average more and larger acorns sustained larger weevil populations. However, no correlation was found between current and previous year adult abundance, suggesting that C. elephas did not capitalise on the reproductive bottom‐up effect.4. It was rainfall, not masting, that most strongly shaped the temporal variation in insect abundance. Rainfall facilitates emergence after diapause at underground earth cells and was also responsible for among‐tree synchronisation in adult weevil population dynamics.5. In spite of their trophic specialisation, not only food availability, but also weather affects weevil numbers. The present results indicate that moving beyond bottom‐up effects is required to better understand complex systems that involve masting plants and insects that consume their seeds.