Distribution map of Stegodyphus spp. on a continental gradient of two environmental predictors, (a) vegetation productivity (unitless ratio) and (b) precipitation seasonality (coefficient of variation of monthly means, mm) (b). Three regions, defined to separate the distributions of the social species, are indicated by circles (region 1), triangles (region 2) and rectangles (region 3). Empty and filled symbols indicate the occurrences of social and solitary species, respectively (n = 366 occurrences in total). For inserts of species maps in the South African region where the spider distribution records are very dense, see Additional file1: Figure S1. The darker the green in (a), the more productive the continental area is. Likewise, the bluer the continental area in (b), the more seasonal it is in precipitation patterns.