One time only: determining spider diversity along a latitudinal gradient in South Africa's arid Succulent Karoo and Desert biomes using a rapid sampling protocol

Abstract

The Succulent Karoo Biome (SKB) is distributed in the western and southern parts of South Africa and is an entirely arid global biodiversity hotspot, but it is severely undersampled for spiders. To address this gap, we used a standardized sampling protocol to collect arachnids from four biotopes (open plain, riparian vegetation, east- and west-facing mountain slopes) using three methods along a latitudinal gradient of five adjacent degree-squares in South Africa's arid western interior to determine how latitude, biotopes, sampling methods and climate affect spider assemblages and diversity. A total of 6497 spiders were collected, representing 305 species and 39 families. Beating yielded the most individuals but the fewest species (n = 3710, S = 130), hand collecting in litter the most species and intermediate numbers (n = 1646, S = 213) and hand collecting from rocks collected the lowest numbers and intermediate species richness (n = 1141, S = 150). Abundance and species richness showed a general bell-shaped pattern along the transect, peaking at Akkerendam Nature Reserve (n = 1839, S = 129). Hand collecting from leaf litter was the most important contributor to spider species richness, with a lower species accumulation rate than beating or hand collecting from rocks. Spider composition from rocks and leaf litter showed some overlap, whereas beating sampled a highly distinct fauna across sites. In total, 519 specimens were sequenced (cytochrome c oxidase subunit I, COI), and this data is publicly available on the SPIZA project on the Barcode of Life Data System (BOLD).