Butterfly diversity at the ecotone between agricultural and semi-natural habitats across a climatic gradient

Aim Understanding the response of species to ecotones and habitat edges is essential to designing conservation management, especially in mosaic agricultural landscapes. This study examines how species diversity and composition change with distance from semi-natural habitats, over ecotones into agricultural fields, and how within-site patterns of community transition change across a climatic gradient and differ between crop types. Location A total of 19 sites in Israel where semi-natural habitats border agricultural fields (wheat fields or olive groves) distributed along a sharp climatic gradient ranging between 100 and 800 mm mean annual rainfall. Methods We performed butterfly surveys in 2006. We analysed species richness (alpha-diversity), diversity, community nestedness and species turnover (beta-diversity) within sites and between sites (gamma-diversity). We also assessed where species of conservation concern occurred. Results In wheat sites, richness and diversity declined abruptly from ecotones to fields and remained homogenously poor throughout the fields, regardless of climate. In olive sites, despite the sharp structural boundary, richness and diversity remained high from the semi-natural habitat to the grove margins and then declined gradually into groves. Species of conservation concern occurred across all habitats at olive sites, but none were found inside wheat fields or at their ecotones. The contrast in community structure between semi-natural habitats and fields was affected by both climate and field type. Irrigation in arid regions did not augment species diversity. Main conclusions Our results indicate that consideration of crop type, within a climatic context, should receive high priority in biodiversity conservation in agricultural areas. In 'hostile' crops, such as wheat, we suggest favouring a combination of high-intensity management and wide margins over less intensive management without margins, which may merely aid generalist butterfly species. The scarcity of butterflies in arid irrigated fields suggests a need to carefully assess the effects of irrigation and agrochemicals on species' communities.