Indigenous forest edges increase habitat complexity and refuge opportunities for grassland butterflies

Abstract

Heterogeneity at local and landscape scales can promote insect diversity and moderate insect declines that stem from global change. Determining how species respond to different landscape components provides insight into the role of heterogeneity in landscapes undergoing change. We examine how indigenous forest-grassland edges are used by butterflies. We assessed butterfly diversity and behaviour at forest edges and adjoining grassland, and tested whether these patterns are influenced by differing weather conditions between seasons. Forest edges supported a species rich butterfly assemblage. Forest specialists were more diverse at forest edges than in grassland, whereas grassland specialists and habitat generalists were as diverse at forest edges as in grassland. All butterfly groups showed more inter- and intra-specific interactions and more patrolling behaviour at forest edges, but more feeding and transient behaviour in grassland. Occurrence and behavioural patterns were not mediated by season, suggesting that the influence of forests does not change with varying environmental conditions. Nonetheless, certain species preferentially utilized forest edges in the hot and windy season, indicating that shelter provided by forest edges influences butterfly habitat use. We found no evidence that complementary nectar sources influence butterfly distribution patterns. Implications for insect conservation: The diverse butterfly assemblages and range of behaviours supported by indigenous forest edges indicate that forest patches are an important habitat component for butterflies. Conserving forest patches in these coastal grasslands may help buffer butterfly populations against global change.