Identifying the Substrate and Vegetation Characteristics Driving Population Densities in the Buckspoor Spider, Seothyra schreineri

Abstract

Buckspoor spiders (Araneae: Eresidae: Seothyra Purcell) are a distinct lineage of burrow-inhabiting web-building spiders endemic to the arid and semi-arid parts of southern Africa. We investigated the role of substrate and vegetation characteristics on site selection in Seothyra schreineri Purcell in the xeric Nama Karoo of the western Free State Province, South Africa. We studied web densities in two 0.5 ha plots in an open habitat grazed by sheep and found declining web densities with increasing distance from the border fence. Web densities in the 1 m² plots were negatively correlated with increasing grass density, positively correlated with increasing percentage fine gravel, whereas shrub cover, litter, hard soil and stones had a very weak effect. Our results indicate that the spatial distribution of fine gravel in Nama Karoo landscapes is a key factor determining the occurrence of S. schreineri, a finding that can guide future sampling efforts, leading to a more complete prediction of the species' distribution and, ultimately, its overall conservation status.