Abstract. 1. The Iberian Peninsula is one of the most relevant areas in terms of species richness, rarity and endemism in the Mediterranean Basin. Using spiders as a model, we studied the relative importance of environmental and non-environmental spatial variation along a gradient of mediterraneity on the western coast of the Iberian Peninsula.
2. We performed a spatially explicit analysis to evaluate the contribution of pure environmental and pure spatial effects and their shared influence on spider species richness by variation partitioning and principal coordinates of neighbour matrices (PCNM). We dissect the spatial variation of species richness into additive scale-specific models through PCNM analysis and estimate the relative importance of environmental variables for each model.
3. Variation partitioning revealed that 72.8% of species richness variation could be explained by the environmental (climate and dune stability) and spatial variables. Most of this variation (51.3%) corresponds to the environmental spatially structured component.
4. The influence of environmental variables was scale-dependent. At the broadest scales, the latitudinal-climatic gradient was the dominant factor that influenced spider species richness variation. At the finest scale, stability of the dune system was the most important component.
5. In conclusion, spider species richness patterns were determined mostly by spatially structured environmental variation. More importantly, this study shows that different environmental factors act at multiple scales. Hence, our results reinforce the importance of the incorporation of both local and broad-scale factors when examining species richness patterns.