High species turnover and guild shifts in spider communities between two contrasting dryland ecoregions of Catamarca, Argentina

Spider (Araneae) assemblages are sensitive indicators of environmental filtering, yet remain poorly studied in drylands worldwide, particularly in north-western Argentina. We compared alpha and beta diversity of spider communities between two contrasting ecoregions of Catamarca Province: the arid Monte de Sierras y Bolsones and the high-altitude Puna. Spiders were sampled at 12 sites across three seasons using pitfall traps and vacuum sampling on ground and vegetation strata. A total of 1195 individuals from 109 species and 28 families were collected. The Monte showed higher abundance and richness (N = 653, S = 68) than the Puna (N = 542, S = 59), with only 18 species shared. Hill-number profiles confirmed greater diversity in the Monte. Beta diversity was high and dominated by species turnover (96.98%) rather than nestedness. PCoA and PERMANOVA revealed complete separation of assemblages along a gradient of vegetation structure, temperature and substrate cover (Axis 1: 60.17% of variance). Indicator value analysis identified 23 species with strong fidelity to either ecoregion, reflecting a shift from web-building guilds in the Monte to ground-hunting guilds in the Puna. These results highlight strong environmental filtering over a short distance and underscore the value of spiders as sensitive indicators of ecoregional integrity.