Zero-sum landscape effects on acorn predation associated with shifts in granivore insect community in new holm oak (Quercus ilex) forests

Aim: Landscape attributes can determine plant-animal interactions via effects on the identity and abundance of the involved species. As most studies have been conducted in a context of habitat loss and fragmentation, we know very little about interaction assembly in new habitats from a landscape approach. This study aimed to test the effect of forest age and connectivity on acorn predation by a guild of predator insects differing in dispersal ability and resilience mechanisms: two weevils (Curculio elephas and C. glandium) and one moth (Cydia fagiglandano) in expanding Quercus ilex forests. Location: Barcelona, Spain. Methods: We assessed the proportion of infested acorns and identified the predator at the species level in five patches of connected old forests, connected new forests and isolated new forests. Effects of habitat age and connectivity at three scales (tree, patch and landscape) were analysed using generalized linear mixed-effects models. Results: Predation by weevils was positively associated with old connected forests, while moths, with better dispersal ability, were able to predate upon all patches equally. Moreover, C. elephas, the weevil with lower dispersal ability, exhibited colonization credits in the new isolated patches. In spite of these changes in the guild of seed predators, the proportion of infested acorns was non-significantly different among forests. Main conclusions: The guild of seed predators may vary depending on forest age and connectivity. However, because those with higher dispersal ability may replace less mobile species, this resulted in zero-sum effects of landscape attributes on acorn predation (i.e., similar prédation rates in well-connected old forests vs. isolated new forests).