Irrigation effects on arthropod communities in Mediterranean cereal agro-ecosystems

Agricultural intensification has strongly affected the environment in recent decades. Intensification by irrigation is a common transformation worldwide, particularly in Mediterranean countries, but its effects on biodiversity have rarely been studied. We evaluated the effects of farming system and habitat structure on arthropod abundance, richness, diversity and species composition in irrigated and rainfed winter wheat fields in a Mediterranean farmland in NW Spain. To gain a more complete insight of the arthropod response to irrigation, we studied six groups with different ecological needs (i.e. Aphididae, Aphidiinae, Coccinellidae, Formicidae, Heteroptera and Syrphidae) at species level (147 species). Irrigated fields held higher arthropod abundance (Aphididae and Coccinellidae), species richness (Aphididae, Aphidiinae and Coccinellidae) and diversity (Aphidiinae, Coccinellidae and Syrphidae), while dry fields held higher species richness of only Formicidae. Species composition differed between farming systems for Coccinellidae, Formicidae and Heteroptera. The mean size of the surrounding fields positively influenced abundance and richness of Coccinellidae and Heteroptera and diversity of Coccinellidae. Our results suggest that irrigation boosted diversity of most arthropod groups by enhancing plant production during the summer drought.