Friend and foe? The effects of grassland management on global patterns of spider diversity

Abstract

1. Grassland ecosystems have been used worldwide for food production through pastoral and cropping activities. In these ecosystems, spiders constitute important mesopredators, which are affected by grassland management in opposite ways. Historically, the spider taxonomic diversity has been the main focus in studies of grazing impacts in grassland ecosystems, while the intrinsic variability of traits within spiders have been neglected, which may have led to mistaken conclusions. Our objective is to reanalyse the effects of grazing on spider taxonomic and functional guilds on worldwide grasslands.2. We conducted a systematic review of the literature from the last 10 years, to assess the influence of grazing on the taxonomic and functional guild diversity of spiders worldwide. Using Generalised Linear Mixed Models, we assessed the effects of grazing pressure and type of herd on abundance, richness of spider species, and guilds.3. In the taxonomic perspective, we found no evidence of grazing impact on the abundance and richness of spiders. However, in the functional guild perspective, high grazing pressure reduced the diversity of web building spiders and enhanced diversity of ground dwelling spiders. Moreover, pastures containing more than one grazing species enhanced the diversity of ambush spiders.4. Overall, the functional guild diversity of spiders in grassland ecosystems seems to be more influenced by grazing intensity. Our results suggest that grazing intensity can change the guild composition of the araneofauna in grasslands, with guilds responding differently to grazing.