Figure 1.

Directional selection through two fitness components. The first component of selection is frequency‐independent towards an environmental optimum (top), and the second is frequency‐dependent in favour of individuals with larger traits (bottom). In the left‐hand panel, FD selection is aligned with the direction of change in the environmental optimum (b > 0, where b defines the rate and direction of change of the environmental optimum). As such, FD selection can promote adaptation and population persistence. In the right‐hand panel, FD selection is misaligned with the direction of change in the environmental optimum (b < 0) and therefore hinders adaptation and population persistence. For additional details, see Box 3 and the main text. Prior to either episode of selection, the probability density function for the trait is f(z), with a population mean of $\overline{z}$. Following frequency‐independent selection but prior to frequency‐independent selection, the probability density function is f(z _V), with a trait mean of ${\overline{z}}_v$. θ denotes the environmental optimum, and 1 – P represents the fraction of adults (those that survived frequency‐independent selection) that are selectively removed from the breeding population