Fig. 2.

Empirical fitness landscape for San Salvador pupfishes. Heat map in 3-D and 2-D shows probability of F2 hybrid survival in a high-density field enclosure for 3 months. The surface is estimated using generalized cross-validation of a thin-plate spline fit to the raw survival data using the Fields package (Fields Development Team 2006) in R (R Development Core Team 2011). Each F2 hybrid (survivor: black; death: gray)) is plotted within a linear discriminant morphospace for 16 traits separating the lab-reared phenotypes of the three parental species, indicated by 95% confidence ellipses and photographs/arrow, on two discriminant axes with dominant loadings of lower jaw length on the x-axis and nasal protrusion distance and angle on the y-axis. Modified from Martin and Wainwright (2013c).