title: Trade-offs in seedling growth and survival within and across tropical forest microhabitats.
abstract: For niche differences to maintain coexistence of sympatric species, each species must grow and/or survive better than each of the others in at least one set of conditions (i.e., performance trade-offs). However, the extent of niche differentiation in tropical forests remains highly debated. We present the first test of performance trade-offs for wild seedlings in a tropical forest. We measured seedling relative growth rate (RGR) and survival of four common native woody species across 18 light, substrate, and topography microhabitats over 2.5 years within Hawaiian montane wet forest, an ideal location due to its low species diversity and strong species habitat associations. All six species pairs exhibited significant performance trade-offs across microhabitats and for RGR versus survival within microhabitats. We also found some evidence of performance equivalence, with species pairs having similar performance in 26% of comparisons across microhabitats. Across species, survival under low light was generally positively associated with RGR under high light. When averaged over all species, topography (slope, aspect, and elevation) explained most of the variation in RGR attributable to microhabitat variables (51-53%) followed by substrate type (35-37%) and light (11-12%). However, the relative effects of microhabitat differed among species and RGR metric (i.e., RGR for height, biomass, or leaf area). These findings indicate that performance trade-offs among species during regeneration are common in low-diversity tropical forest, although other mechanisms may better explain the coexistence of species with small performance differences.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California 621 Charles E. Young Drive South, Los Angeles, California, 90095-1606.
authors.forename: Faith
authors.initials: F
authors.lastname: Inman-Narahari
authors.affiliation: Department of Biology, University of Hawaii 200 W. Kawili Street, Hilo, Hawaii, 96720.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Ostertag
authors.affiliation: Department of Global Ecology, Carnegie Institution for Science 260 Panama St., Stanford, California, 94305.
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Asner
authors.affiliation: USDA Forest Service, Institute of Pacific Islands Forestry 60 Nowelo Street, Hilo, Hawaii, 96720.
authors.forename: Susan
authors.initials: S
authors.lastname: Cordell
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California 621 Charles E. Young Drive South, Los Angeles, California, 90095-1606 ; Center for Tropical Forest Science, Smithsonian Tropical Research Institute Balboa, Republic of Panamá
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Hubbell
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California 621 Charles E. Young Drive South, Los Angeles, California, 90095-1606.
authors.forename: Lawren
authors.initials: L
authors.lastname: Sack
keywords: Determinants of plant community diversity and structure; light; performance rank changes; plant population and community dynamics; regeneration niche; relative growth rate; substrate; survival; topography; tropical forest diversity