Both local and landscape-level factors are important drivers in shaping ground-dwelling spider assemblages of sandy grasslands

Abstract

Earlier studies emphasized that landscape-level factors were essential in shaping arthropod assemblages of semi-natural grasslands. Recently, several studies demonstrated that local factors were more important than landscape-level factors. We examined the importance of several local and landscape-level factors on spider assemblages using pitfall traps from eight sandy grassland fragments between 2001 and 2003. We tested three hypotheses: (i) species richness decreases with grazing intensity; (ii) species richness increasing with fragment size; (iii) the higher isolation of fragments results in decreasing species richness. We found that species richness of spiders did not depend on the grazing intensity, but there were changes in species composition and abundance of species among the variously grazed fragments. Out of the other two studied local factors (fragment size, and the shape of fragment), only the fragment size was a significant predictor of the diversity of specialist spiders, since the number of these species increased significantly with fragment size. Out of the four investigated landscape-level factors (isolation, total area of croplands in the landscape, total area of forests in the landscape, and landscape diversity), only the isolation was a significant predictor influencing spider diversity. The total number of species, the number of generalist species and the number of hunting species increased significantly with the isolation of fragments. Our results suggest that both local and landscape-level factors are important drivers in maintaining spider diversity in sandy grasslands; therefore, these factors should be considered simultaneously during the restoration and/or management of grasslands.