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Rapid aggregative and reproductive responses of weevils to masting of North American oaks counteract predator satiation

Bogdziewicz, Michał, Marino, Shealyn, Bonal, Raul, Zwolak, Rafał, Steele, Michael A.
Ecology 2018 v.99 no.11 pp. 2575-2582
Curculio, Quercus alba, Quercus montana, Quercus rubra, crops, data collection, fruits, insects, predators, prediction, reproductive performance, satiety, seed predation, sowing, starvation, trees
The predator satiation hypothesis posits that masting helps plants escape seed predation through starvation of predators in lean years, followed by satiation of predators in mast years. Importantly, successful satiation requires sufficiently delayed bottom‐up effects of seed availability on seed consumers. However, some seed consumers may be capable of quick aggregative and reproductive responses to masting, which may jeopardize positive density dependence of seed survival. We used a 17‐yr data set on seed production and insect (Curculio weevils) infestation of three North American oaks species (northern red Quercus rubra, white Q. alba, and chestnut oak Q. montana) to test predictions of the predation satiation hypothesis. Furthermore, we tested for the unlagged numerical response of Curculio to acorn production. We found that masting results in a bottom‐up effect on the insect population; both through increased reproductive output and aggregation at seed‐rich trees. Consequently, mast seeding in two out of three studied oaks (white and chestnut oak) did not help to escape insect seed predation, whereas, in the red oak, the escape depended on the synchronization of mast crops within the population. Bottom‐up effects of masting on seed consumer populations are assumed to be delayed, and therefore to have negligible effects on seed survival in mast years. Our research suggests that insect populations may be able to mount rapid reproductive and aggregative responses when seed availability increases, possibly hindering satiation effects of masting. Many insect species are able to quickly benefit from pulsed resources, making mechanisms described here potentially relevant in many other systems.