How does the management of rice in natural ponds alter aquatic insect community functional structure?

Abstract

Changes to biodiversity have mainly been assessed using taxonomic diversity indices. Although these approaches contribute to our scientific understanding of species richness and composition patterns, trait-based metrics may be more useful for detecting responses to land-use change. We compared functional diversity of aquatic insect communities along a gradient of agricultural intensification. Our goal was to compare functional redundancy, functional richness, functional evenness and functional divergence among natural ponds, and organic and conventional rice fields. We recorded 15606 aquatic insects distributed across 61 genera. The highest functional redundancy and richness were observed in the natural ponds, followed by organic rice fields and conventional ones. The functional composition varied among natural ponds and rice fields, and differed between organic and conventional rice fields. Organic management favoured the establishment of some pond insect traits, such as predatory taxa, in rice agroecosystems. Our analysis suggests that the conversion of ponds to rice fields results in a shift to less specialised aquatic insect communities with altered functional composition groups. Nevertheless, this result should not be seen as a negative reflection on organic rice fields, because organic rice production affords a better compromise between agricultural production and ecosystem function than conventional agriculture.