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 fagiglandana) 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 predation rates in well-connected old forests vs. isolated new forests). K E Y W O R D Sacorn predation, biotic interactions, forest regeneration, landscape structure, life-history traits, spatiotemporal effects, zero-sum effects

1. The factors governing community assemblages in fragmented habitats remain a challenging topic in ecology, especially in the present context of global change. We studied the colonisation of holm oak (Quercus ilex L.) woodland by specialist Lepidoptera in an afforested savannah-like landscape that has emerged as a result of the abandonment of croplands. We sampled herbivorous caterpillars for 5 years to assess the interplay between tree age and structure (canopy size and connectivity) on Lepidoptera species abundance, richness, diversity and composition.2. 1336 individuals belonging to 24 species of Lepidoptera were collected. Species abundance, richness and diversity increased in the best connected large trees and in the best connected young ones, probably because of the greater likelihood of colonisation and the existence of colonisation credits, respectively. Although species abundance, richness and diversity varied significantly between years in all trees, there were no effects for tree age, canopy size, or connectivity.3. Although tree age and structure had little effect on species composition (alpha and beta diversity), thereby revealing a predominant random effect, the relative abundance of Noctuids and Pyralids was significantly affected by tree age, suggesting that differences in dispersal abilities exist between these families.4. These findings suggest that habitat age and structural interactions play a significant role in the accumulation of Lepidoptera species but have little importance in determining their identities. From a conservation point of view, the results highlight the need to preserve old, large and well-connected holm oak trees in agricultural landscapes as refuges for specialist insects.

& Key message Insect herbivory in novel Quercus ilex L. forests is a highly context-and scale-dependent process. We show that forest composition, tree height and fine-scale spatial location, as well as tree genetic relatedness and ontogeny, can all influence herbivore activity at local to landscape scale. & Context Understanding the intrinsic and extrinsic drivers of herbivory in novel expanding forests is essential to envisage their role for biodiversity conservation. & Aims To analyse the effects of landscape attributes, forest composition, genetic relatedness, ontogeny and leaf traits on insect herbivory in novel Q. ilex forest stands. & Methods In 15 forest patches, we examined effects of patch size and connectivity, forest composition, tree height, specific leaf area (SLA) and nitrogen content on herbivory. In 3 forest patches, we assessed effects of tree genetic relatedness, ontogeny and spatial distribution. & Results Herbivory was lower in pine-oak than in mixed-oak forests owing to the shorter tree height in the former with no effects of patch size or connectivity. Herbivory increased with SLA whereas nitrogen content had no effect. Within patches, herbivory differed among genetic clusters and was reduced in saplings growing near mature oaks and individuals near the forest edge. & Conclusion We illustrate the strong context and scale dependence of tree-herbivore interactions that renders predictions for dynamic systems such as novel oak forests extremely challenging. It implies, however, that the structural heterogeneity of such unmanaged forests allows their function as stepping stones for insect herbivore diversity in fragmented landscapes.

1. Woody vegetation spread over former croplands in Europe has created new unexploited habitats for forest organisms. Their ability to colonise them and thrive depends on life-history traits including fecundity, dormancy and dispersal ability.2. The effects of these traits on species distribution, abundance and community assembly have been extensively studied in fragmented landscapes. However, their consequences for genetic diversity and connectivity in local populations remain largely unknown.3. We investigated the genetic population structure and diversity of Curculio elephas and Curculio glandium (Coleoptera: Curculionidae), two sympatric acorn weevils with contrasting life-history strategies, in a landscape with mature oak stands and plots of new expanding forests.4. Using a fragment of a mitochondrial gene cytochrome oxidase subunit 1 and nuclear DNA (80 single nucleotide polymorphisms [SNPs]), we found that gene flow between populations was significantly weaker in the poor disperser C. elephas, especially in isolated new forests. However, genetic neutrality tests did show population expansion in C. elephas, which suffers frequent population bottlenecks (probably linked to extended dormancy) and is a poor coloniser of isolated new forests. However, its greater fecundity allows it to recovery quickly if the number of reproductive individuals falls. Its populations are thus larger but genetically less diverse than those of C. glandium 5. Within foraging guilds, the most fecund species will outcompete the others under a context of constrained dispersal. Hence, new landscapes of expanding forests represent a good opportunity for more mobile but less fecund species to colonise new habitats and so be temporarily released from competition.