Effects of size, isolation and grazing intensity of sandy grasslands on vegetation-dwelling spider assemblages
Abstract
Vegetation-dwelling spider assemblages were investigated in eight sandy grassland fragments with different size, isolation and grazing intensity in 2008 (East Hungary, Nyírség). Spiders were sampled by sweep-netting in each habitat at a fixed sampling site from April to October fortnightly. The following hypotheses were tested: the rules of classical island biogeography are assessed for grassland fragments: the number of species increases with the size and decreases with the isolation of the fragment. Species richness of spiders decreases by the intensity of grazing. Grazing may have a negative influence on the large, web-builder spiders and on the diurnal hunters associated with the vegetation. During the study, altogether 2369 individuals belonging to 82 species were collected from the eight sandy grassland fragments. There was no significant relationship neither between the sizes nor the isolation of grassland fragments with the number of species. There was a positive correlation of the average height of vegetation with the total number of spider species, as well as with the number of vegetation-dwelling species. The results of indicator species analysis (IndVal) showed that the abundance of the large, web-builder spiders and also those diurnal hunters decreased significantly in the sites which had lower average height of the vegetation, therefore the grazing had a negative influence primarily on these species.
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