Agricultural land use affects the heterogeneity of Odonata communities in the Brazilian Pampa

Abstract

Farming expansion has negative impacts on freshwater biodiversity. However, the effects of agricultural land use are not similar across taxa and depend on local context. For instance, the impacts of agricultural expansion are understudied in the Neotropics (one of the leading regions in cropland expansion). Knowledge of the effects of agricultural land use on aquatic insects from South American subtropical grasslands (Pampa) is even more incipient. We tested whether landscape modification related to increased agricultural land use was associated with taxonomic homogenization in odonate communities in waterbodies in the Brazilian Pampa. Odonates were collected in waterbodies differing in the main land-use class in their surroundings (cropland or grassland). Cropland and grassland sites differed with respect to their abiotic conditions (water chemistry) and species composition of Odonata. Additionally, we found higher variation in the composition of Odonata (and suborders Anisoptera and Zygoptera separately) in grassland than cropland sites. We found an interplay between agricultural and grassland land uses and the variation in the composition of odonate communities in the Brazilian Pampa. Specifically, landscape modification by agriculture modified the abiotic conditions in the waterbodies, which may have favored species able to establish as larvae under harsher environmental conditions. We suggest that the maintenance of mixed-grassland and cropland land uses in the fields adjacent to waterbodies can limit the negative effects of agricultural encroachment on Odonata communities with respect to biotic homogenization in the Brazilian Pampa.