Determinants of local spider (Araneidae and Thomisidae) species richness on a regional scale:: climate and altitude vs. habitat structure

1. The habitat heterogeneity hypothesis states that the more complex the habitat, the higher the species richness. The present study analyzes the effect of local factors on regional spider (Araneidae and Thomisidae) richness. The main objective is to disentangle the relative importance of habitat structure and other environmental variables. 2. Fifteen territorial units of 1 km(2) were sampled to obtain reliable and comparable inventories of the two spider families. Richness values were modelled using general regression models and a set of climate, topographic and vegetation structure variables. Pure and joint effects were computed via variation partitioning. 3. The results highlight the great importance of vegetation complexity, especially of grass and sub-shrub cover, in determining spider species richness. 4. The maximum temperature is the only climate variable significantly related to species richness, although its effect is combined with that of spatial and vegetation structure variables. 5. These results support the habitat heterogeneity hypothesis, and highlight the importance of taking vegetation complexity into account when managing habitats and where spider conservation is desired.