Revisiting Darwin's hypothesis: Does greater intraspecific variability increase species’ ecological breadth?

 Premise of the study: Darwin fi rst proposed that species with larger ecological breadth have greater phenotypic variation. We tested this hypothesis by comparing intraspecifi c variation in specifi c leaf area (SLA) to species’ local elevational range and by assessing how external (abiotic) fi lters may infl uence observed differences in ecological breadth among species. Understanding the patterns of individual variation within and between populations will help evaluate differing hypotheses for structuring of communities and distribution of species.  Methods: We selected 21 species with varying elevational ranges and compared the coeffi cient of variation of SLA for each species against its local elevational range. We examined the infl uence of external fi lters on local trait composition by determining if intraspecifi c changes in SLA with elevation have the same direction and similar rates of change as the change in community mean SLA value.  Key results: In support of Darwin’s hypothesis, we found a positive relationship between species’ coeffi cient of variation for SLA with species’ local elevational range. Intraspecifi c changes in SLA had the same sign, but generally lower magnitude than the community mean SLA.  Conclusions: The results indicate that wide-ranging species are indeed characterized by greater intraspecifi c variation and that species’ phenotypes shift along environmental gradients in the same direction as the community phenotypes. However, across species, the rate of intraspecifi c trait change, refl ecting plastic and/or adaptive changes across populations, is limited and prevents species from adjusting to environmental gradients as quickly as interspecifi c changes resulting from community assembly.