Fig. 4.

The ΔI surface. As explained in detail in Shuster and Wade (5), simultaneous consideration of the mean spatial crowding of matings, m*, and the mean temporal crowding of matings, t*, provides opportunities to visualize how spatial and temporal distributions of matings influence the opportunity for sexual selection, ΔI, as well as the dynamic nature of mating system evolution. Changes in mating system character occur as a result of modifications in the spatial and temporal distribution of matings. When m* is low and t* is high, males are likely to seek out, remain with, and provide parental care for isolated, synchronously receptive females, forming persistent pairs (green rectangle); when m* is moderate to high, t* is high, males are expected to defend individual females, but breeding is expected to occur in large aggregations or mass matings (red rectangle). Polygamy is likely when m* and the mean temporal crowding of matings, t* are both moderate (blue rectangle).