A species’ ecological traits determine the role it plays in ecosystem functioning. Identifying and quantifying these traits is paramount to explain natural patterns of biodiversity, how biodiversity changes in the face of anthropogenic impacts, and how ecosystems provide services to humanity. Functional diversity (FD) describes the variety of traits exhibited by an assemblage of species. As FD increases, ecosystem functioning increases, yet the strength of this relationship requires measuring the proper traits that determine the ecosystem processes under study. How can these traits be properly chosen? Here, we propose that by estimating the dynamics and constraints of trait macroevolution, traits that underlie ecosystem functioning and service provisioning can be identified. We provide a framework that integrates trait-evolution theory with functional ecology to obtain a detailed picture of how FD is structured, how it influences ecosystem services, and how the relationship between FD and ecosystem services is altered by humans.
Adaptive landscape theory provides a useful framework for understanding how trait evolution determines FD. The macroevolutionary adaptive landscape is a metaphorical multivariate-trait surface across which lineages evolve towards trait combinations that confer the best matching for a particular niche (i.e., adaptive peaks). Under this metaphor, assemblages that contain species exhibiting more adaptive peaks should function at a higher rate than those exhibiting fewer adaptive peaks. Species can therefore be quantified in terms of how distant they are from identified adaptive peaks, and these distances used to determine FD. This adaptive landscape argument, however, makes two assumptions. First, in the terms of coexistence theory, adaptive peaks conifer “stabilizing”, and not “equalizing” differences. Second, adaptive peaks are directly related to the effects that species have on ecosystem functioning—in other words, there is a direct relationship between “response” and “effect” traits.
We explore the validity of these two assumptions and how these assumptions can be relaxed when identifying adaptive peaks that determine ecosystem services. We provide empirical and theoretical examples of our framework including estimates of how adaptive landscapes have formed spatially across the past millions of years. With the rapid increase of phylogenetic and trait databases for many taxonomic groups, the identification of macroevolutionary adaptive peaks to determine the effect of biodiversity on ecosystem services is now possible.