The Evolution of Functional Traits in Plants: Is the Giant Still Sleeping?

In the field of plant ecophysiology, the term “functional trait” has multiple overlapping definitions (table 1). However, functional traits are generally considered aspects of plant phenotypes that influence growth, survival, and reproduction by mediating interactions with the biotic and abiotic environment; examples include leaf mass per unit area (LMA), which estimates the construction cost for light interception, and photosynthetic capacity (Amax), which estimates the maximum rate of carbon fixation when light is not limiting. As such, functional traits are expected to evolve in response to natural selection, and intraand interspecific variation in functional traits is often interpreted as being adaptive. One milestone in the effort to understand the evolution of functional traits in plants was the publication in 2003 of a special issue of the International Journal of Plant Sciences. This special issue included papers that have been repeatedly cited in subsequent studies of the evolution of functional traits: examples include Reich et al.’s (2003) reviewof themechanisms that affect the evolution of functional trait spectra and Geber and Griffen’s (2003) quantitative meta-analysis of estimates of natural selection on and heritability of functional traits. But in the introduction to the 2003 special issue, the guest editors had a “tough love”message for plant functional biologists (Ackerly andMonson 2003, p. S1):