title: Drivers of morphological diversity and distribution in the Hawaiian fern flora: trait associations with size, growth form, and environment.
abstract: OBJECTIVE
  Hawaii is home to 238 native and 35 alien fern and lycophyte taxa distributed across steep gradients in elevation and resource availability. The fern flora spans a wide range of growth forms, with extraordinary diversity in morphology and plant size. Yet the potential factors underlying this diversity have remained enigmatic.
  
  
  METHODS
  We used a trait database generated from the most recent and comprehensive survey of Hawaiian ferns and lycophytes to test hypotheses of size-scaling and trait associations with environment and growth form as factors underlying this diversity. We also tested relationships among morphology, taxon abundance and distribution and identified key differences between native and alien taxa.
  
  
  RESULTS
  Strong trait-trait relationships included geometric scaling of plant dimensions with a tendency for more divided fronds in larger ferns. Trait-environment relationships independent of size included more divided fronds at higher elevation, longer blades in shaded habitats, and fronds with shorter stipes and fewer pinnae in drier habitats. Growth forms differed in mean size with epiphytic and epipetric taxa smaller than terrestrial ferns. Plant size was independent of taxon abundance and distribution across islands, and native and alien ferns did not differ in mean size. Alien taxa were more abundant, especially at lower elevations, apparently due to human land use.
  
  
  CONCLUSIONS
  These relationships point to linkages of fern form and demography with biogeography and highlight potential flora-scale physiological and morphological adaptations in ferns across contrasting environments.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California Los Angeles, 621 Charles E. Young Drive South Box 951606, Los Angeles, California 90095-1606, USA. czerniak@ucla.edu
authors.forename: Chris
authors.initials: C
authors.lastname: Creese
authors.forename: Albert
authors.initials: A
authors.lastname: Lee
authors.forename: Lawren
authors.initials: L
authors.lastname: Sack
mesh_terms: D000531:Altitude; D044822:Biodiversity; D029624:Ferns / Q000033:anatomy & histology* / Q000145:classification / Q000254:growth & development*; D006254:Hawaii; D006813:Humidity; D058865:Introduced Species; D008954:Models, Biological; D010802:Phylogeny; D011157:Population Dynamics; D019655:Quantitative Trait, Heritable