title: Can evolutionary constraints explain the rarity of nitrogen-fixing trees in high-latitude forests?
abstract: Contents 1195 I. 1195 II. 1196 III. 1196 IV. 1200 1200 References 1200 SUMMARY: The rarity of symbiotic nitrogen (N)-fixing trees in temperate and boreal ('high-latitude') forests is curious. One explanation - the evolutionary constraints hypothesis - posits that high-latitude N-fixing trees are rare because few have evolved. Here, we consider traits necessary for high-latitude N-fixing trees. We then use recent developments in trait evolution to estimate that > 2000 and > 500 species could have evolved from low-latitude N-fixing trees and high-latitude N-fixing herbs, respectively. Evolution of N-fixing from nonfixing trees is an unlikely source of diversity. Dispersal limitation seems unlikely to limit high-latitude N-fixer diversity. The greater number of N-fixing species predicted to evolve than currently inhabit high-latitude forests suggests a greater role for ecological than evolutionary constraints.
authors.affiliation: Department of Ecology, Evolution and Environmental Biology, Columbia University, 1200 Amsterdam Ave, New York, NY, 10027, USA.
authors.forename: Duncan N L
authors.initials: DN
authors.lastname: Menge
authors.affiliation: The Land Institute, 2440 E. Water Well Road, Salina, KS, 67401, USA.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Crews
mesh_terms: D044822:Biodiversity; D005075:Biological Evolution; D065928:Forests; D009586:Nitrogen Fixation / Q000502:physiology*; D013559:Symbiosis / Q000502:physiology; D014197:Trees / Q000502:physiology*
keywords: forest; latitudinal gradient; legume; symbiotic nitrogen fixation; trait evolution