Landscape type and variation in landscape heterogeneity cause species turnover rather than loss in agricultural landscapes

Abstract

Biodiversity in agroecosystems is known to be reduced by agricultural intensification and the concomitant decline in landscape heterogeneity. In order to assess the impact of heterogeneity on biodiversity, we conducted a study in which we compared spider assemblages in three pairs of landscapes, each including a highly intensified, fragmented ‘modern’ landscape and a less intensified, heterogeneous ‘traditional’ landscape. Throughout, spiders were sampled in (fragments of) wet meadows by pitfall trapping. We examined the impact of landscape composition and configuration at different spatial scales on the taxonomic diversity and functional composition of spider assemblages in our target patches. Overall, we did not observe differences in species richness or total abundance of spiders between modern and traditional agricultural landscapes. However, functional composition and community structure differed strongly between landscape types, and were also affected by compositional and configurational heterogeneity. In particular, the size and configuration of crop fields was an important factor in shaping spider assemblages. This suggests that modern agricultural landscapes may result in species turnover due to species-specific responses rather than declines in species richness. Therefore, species numbers alone may not be a good indicator of intensification. In order to preserve spider diversity in agricultural landscapes it is necessary to consider the effects of compositional and configurational heterogeneity on taxonomic diversity as well as functional traits and community structure.