Intraspecific Trait Variation Predicts Species Distributions and Niche Occupancy of Seedlings in a Tropical Wet Forest

Abstract

Functional traits enable comparison among species to elucidate general patterns and processes. While most work on trait-mediated ecology employs variation among species, recent studies show that intraspecific trait variation (ITV) can significantly affect community dynamics. We examined the extent of ITV in seedlings of woody plants and its influence on abundance patterns and niche parameters in a tropical wet forest. Using 14 species that had at least 5 individuals across 150 2 × 2-m plots arrayed across a gradient of light and water availability, we estimated species' niche properties (breadth and position) and abundance. We measured eight functional traits corresponding to morphological and allocational features of leaves, stems and roots, from which we estimated ITV and functional position of species. We used variance partitioning to determine the relative extent of trait variation at different ecological levels and used linear models to assess the relationship between ITV, abundance, and niche properties. ITV accounted for 30–100% of trait variation. Only leaf dry matter content showed a significant link between abundance and ITV via niche breadth along light and soil moisture gradients and via niche position along soil organic carbon gradients. While ITV of no other trait correlated with abundance, root, stem, and leaf mass fractions showed significant relations with niche breadth. Overall, ITV in seedlings was substantial and shaped niche properties, but this did not consistently translate to patterns in abundance. Future work should link ITV to species' performance to better comprehend the mechanisms underlying plant community dynamics.