title: Revisiting Darwin's hypothesis: Does greater intraspecific variability increase species' ecological breadth?
abstract: OBJECTIVE
  Darwin first proposed that species with larger ecological breadth have greater phenotypic variation. We tested this hypothesis by comparing intraspecific variation in specific leaf area (SLA) to species' local elevational range and by assessing how external (abiotic) filters may influence 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 coefficient of variation of SLA for each species against its local elevational range. We examined the influence of external filters on local trait composition by determining if intraspecific changes in SLA with elevation have the same direction and similar rates of change as the change in community mean SLA value.
  
  
  RESULTS
  In support of Darwin's hypothesis, we found a positive relationship between species' coefficient of variation for SLA with species' local elevational range. Intraspecific 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 intraspecific variation and that species' phenotypes shift along environmental gradients in the same direction as the community phenotypes. However, across species, the rate of intraspecific trait change, reflecting plastic and/or adaptive changes across populations, is limited and prevents species from adjusting to environmental gradients as quickly as interspecific changes resulting from community assembly.
authors.affiliation: The Department of Ecology and Evolutionary Biology, The University of Arizona, 1041 Lowell Street, Tucson, Arizona 85719 USA.
authors.forename: Colby B
authors.initials: CB
authors.lastname: Sides
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Enquist
authors.forename: James J
authors.initials: JJ
authors.lastname: Ebersole
authors.forename: Marielle N
authors.initials: MN
authors.lastname: Smith
authors.forename: Amanda N
authors.initials: AN
authors.lastname: Henderson
authors.forename: Lindsey L
authors.initials: LL
authors.lastname: Sloat
mesh_terms: D000531:Altitude; D003120:Colorado; D055669:Ecological and Environmental Phenomena; D014644:Genetic Variation; D016014:Linear Models; D008954:Models, Biological; D018515:Plant Leaves / Q000033:anatomy & histology; D012621:Seasons; D013045:Species Specificity
keywords: community assembly; functional traits; intraspecific variation; species ecological breadth; specific leaf area