Highlights

Community ecology seeks to generalize the effects of traits on performance across species, which may be possible if traits explain variation in population fitness.

Linking traits to a specific demographic rate, such as survival or reproduction, is an important step but can be misleading because trade-offs among demographic rates obscure the net effect on fitness.

Integrating demographic rates (survival, growth, and reproduction) and computing low density population growth rates incorporates these trade-offs into measures of fitness.

Several approaches can be used to quantify the net effect of traits on fitness, and these approaches span a trade-off of empirical rigor and logistical ease.

The adaptive value of traits is evident when intrinsic growth rates are explained by trait–environment interactions across multiple coexisting species spanning an environmental gradient.