Short–term effects of horse grazing on spider assemblages of a dry meadow (Western France)

Abstract

Short-term effects of horse grazing on spider assemblages of a dry meadow (Western France). In this study, the biodiversity impacts of a little studied herbivore, the horse, were assessed in a high conservation value habitat of dry meadows in Brittany (Western France). Spiders, a diversified and abundant group of predators, were used as bioindicators. Three complementary sampling techniques were used to assess changes in spider assemblages in both soil and vegetation strata, over time (diachronic comparison of managed unit before vs. after management) and space (synchronic comparison of managed vs. control units). Few effects of grazing, i.e. only one significantly indicative species, were found on assemblage composition (ANOSIM), and none on abundances, α-and β-diversities (GLM on pitfall trap data). On the contrary, important differences were found between units before management took place. The main effects of grazing management were revealed over time (after one year), and not between managed and control units (CCA on pitfall trap data and x²-tests on guilds from each sampling method), showing the relevance of a diachronic approach more than a synchronic approach in such management monitoring. Grazing by horses could be relevant to manage meadows because it creates a high spatial heterogeneity, but further (long-term) studies including other model groups are required.

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

“…high density of grazers) is related to negative impacts on spider diversity (Polchaninova et al, 2016;Hashemi et al, 2019;Torma et al, 2019). Yet, several authors were unable to link intense grazing to negative effects on spiders, showing no relationship between grazing and spider taxonomic and guild diversities (da Silva & Ott, 2017;Pétillon et al, 2018).…”