Figure 2.

Individual traits are characterized by cost–benefit ratios (C/B).

C/B < 1 is required for a trait to be adaptive. However, cost–benefit ratio is a function of the environment, and a given change in the environmental factor can affect C/B of different traits to different degrees. Here Trait₁ is less sensitive than Trait₂ to a given environmental change. (A) In environment E, Trait₁ has C/B₁ and Trait₂ has C/B₂, both of which are less than 1. (B) Environmental change, E′ → E″, causes a shift in the C/B ratio for both traits. Trait₁ remains adaptive, with C″/B₁ < 1, but Trait₂ becomes maladaptive, with C″/B₂ > 1.