title: Sources of variation in foliar secondary chemistry in a tropical forest tree community.
abstract: Specialist herbivores and pathogens could induce negative conspecific density dependence among their hosts and thereby contribute to the diversity of plant communities. A small number of hyperdiverse genera comprise a large portion of tree diversity in tropical forests. These closely related congeners are likely to share natural enemies. Diverse defenses could still allow congeners to partition niche space defined by natural enemies, but interspecific differences in defenses would have to exceed intraspecific variation in defenses. We ask whether interspecific variation in secondary chemistry exceeds intraspecific variation for species from four hyperdiverse tropical tree genera. We used novel methods to quantify chemical structural similarity for all compounds present in methanol extracts of leaf tissue. We sought to maximize intraspecific variation by selecting conspecific leaves from different ontogenetic stages (expanding immature vs. fully hardened mature), different light environments (deep understory shade vs. large forest gaps), and different seasons (dry vs. wet). Chemical structural similarity differed with ontogeny, light environment, and season, but interspecific differences including those among congeneric species were much larger. Our results suggest that species differences in secondary chemistry are large relative to within-species variation, perhaps sufficiently large to permit niche segregation among congeneric tree species based on chemical defenses.
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Ancón, Panama.|Center for Biodiversity and Drug Discovery, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología, Apartado 0843-01103, Ciudad del Saber, Ancón, Panama.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Sedio
authors.affiliation: Center for Biodiversity and Drug Discovery, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología, Apartado 0843-01103, Ciudad del Saber, Ancón, Panama.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Rojas Echeverri
authors.affiliation: Center for Biodiversity and Drug Discovery, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología, Apartado 0843-01103, Ciudad del Saber, Ancón, Panama.|Department of Biotechnology, Acharya Nagarjuna University, Nagarjuna Nagar, Guntur, 522 510, India.
authors.forename: Cristopher A
authors.initials: CA
authors.lastname: Boya P
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Ancón, Panama.
authors.forename: S Joseph
authors.initials: SJ
authors.lastname: Wright
mesh_terms: D065928:Forests; D060434:Herbivory; D018515:Plant Leaves / Q000737:chemistry*; D012621:Seasons; D014197:Trees / Q000737:chemistry*; D014329:Tropical Climate
keywords: 
  Eugenia
  ; 
  Inga
  ; 
  Ocotea
  ; 
  Psychotria
  ; anti-herbivore defense; chemical ecology; intraspecific variation; leaf ontogeny; mass spectrometry; molecular network; species coexistence