Effects of different grazing intensities on spider diversity in saihanwula grassland

Abstract

Aims: As the main consumers of grassland ecosystem, spiders are of great significance to maintain biodiversity and ecosystem function in grasslands. Grazing is the most common way for humans to exploit grasslands, so it is ecologically important to understand the effects of grazing on the spider diversity. In this study, we selected five sample plots that varied in their grazing intensity in the Saihanwula Grassland in Inner Mongolia. Methods: We analyzed differences in spider diversity and species composition among these five sample sites using one-way analysis of variance tests and non-metric multidimensional scale analysis (NMDS) and analysis of similarities (ANOSIM), respectively. We also evaluated the effect of vegetation height on spider biodiversity using a correlation analysis. Results: Spider biodiversity in heavily grazed sites is significantly lower than in non-grazed and lightly grazed sites. Grazing intensity also had a significant effect on spider richness and the abundance of garden spiders, but not on the number of wolf and jumping spiders. Web-building spiders were mainly affected by vegetation structure, while hunting spiders were more likely to be affected by potential prey availability. NMDS analysis revealed that species composition significantly varied across sites of different grazing intensities. Sites with lower grazing intensities had more similar composition to non-grazed sites than sites that were heavily grazed. The correlation analysis showed that the height of grassland vegetation was positively related to spider biodiversity. Spiders from the family Araneidae (which build webs on plants), Thomisidae and Philodromidae (which ambush prey on the upper layer of plants) were highly correlated with vegetation height. Conclusions: Our results suggest that available resources and spatial heterogeneity of habitat could play a leading role in supporting high grassland spider diversity. Therefore, reducing grazing intensity can contribute to the maintenance of grassland spider diversity community composition, especially for web-building spiders that depend on the vegetation structure provided by intact grasslands.