Figure 2.

Contour plots of selection, showing positive associations between the six phenotypic traits and annual fitness, with trait–fitness associations generally strongest at higher population density. (A–D and F) Each point on plots represents a single individual measured at a given combination of the trait (x-axis) and population density (y-axis). Round points are females and crosses are males. Contours show predicted annual fitness at different combinations of the trait and density (with darker shading indicating higher fitness values). (E) Plot shows selection on horn growth, which did not vary with population density, so we simply show the relationship between horn growth and annual fitness. Each point shows an individual male’s fitness at a measurement of horn growth. The solid line shows the predicted change in annual fitness with increasing horn growth; the broken lines show the prediction ± 1 SE.