Community assembly in time and space: the case of Lepidoptera in a Quercus ilex L. savannah‐like landscape

Abstract

Abstract 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. 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. 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. 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.