Abstract
The lowland rainforest of north-eastern Costa Rica harbours an assemblage of large wandering spider species belonging to three habitat subguilds: 1) semi-aquatic, 2) forest-ground dwelling, and 3) vegetation dwelling species. We hypothesized that desiccation resistance should differ among species preferring different microhabitats and the associated microclimate. Desiccation resistance was assessed 1) by measuring water-loss rates of the spiders under relatively dry experimental conditions, and 2) by recording desiccation susceptibility, i.e., the reactions of the spiders to a relatively dry environment. High water-loss rates and desiccation susceptibility of the semi-aquatic and forest-ground dwelling subguilds clearly mirrored the relatively humid microclimate of the understory. Significantly lower water-loss rates and desiccation susceptibility of the vegetation-dwelling species reflected the highly variable, often dry and hot conditions of the rainforest canopy and forest edge habitats. Vegetation-dwelling wandering spiders are therefore physiologically better adapted to dry conditions than the semi-aquatic and forest-ground dwelling species. The results illustrate the significance of physiological characteristics for explaining species-specific habitat use, and in a larger context also for niche partitioning within a community.
