Evolutionary ecology focuses on optimal traits to provide a mechanistic understanding of ecological patterns. For some issues, however, It might be a mismatch to marry optimality and ecology. Given that many ecological questions involve limits (to species distributions and abundances; to species diversity), it might be useful to focus on `limiting traits' rather than optimal traits; that is, to understand ecological limits it might be useful to identify the things that organisms do poorly, and to study constraints on the evolution of these limiting traits. While a limiting-traits approach has a long history in ecology, relatively few studies have fully applied the approach, and some ecological issues have only recently been examined from this view.