Browsing by Author "Wright, S Joseph"

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    Functional traits and the growth-mortality tradeoff in tropical trees
    (Ecological Society of America, 2010) Wright, S Joseph; Kitajima, Kaoru; Kraft, Nathan J B; Reich, Peter B; Wright, Ian J; Bunker, Daniel E; Condit, Richard; Dalling, James W; Davies, Stuart J; Diaz, Sandra; Engelbrecht, Bettina M J; Harms, Kyle E; Hubbell, Stephen P; Marks, Christian O; Ruiz-Jaen, Maria C; Salvador, Cristina M; Zanne, Amy E
    A trade-off between growth and mortality rates characterizes tree species in closed canopy forests. This trade-off is maintained by inherent differences among species and spatial variation in light availability caused by canopy-opening disturbances. We evaluated conditions under which the trade-off is expressed and relationships with four key functional traits for 103 tree species from Barro Colorado Island, Panama. The trade-off is strongest for saplings for growth rates of the fastest growing individuals and mortality rates of the slowest growing individuals (r2 = 0.69), intermediate for saplings for average growth rates and overall mortality rates (r2 = 0.46), and much weaker for large trees (r2 ≤ 0.10). This parallels likely levels of spatial variation in light availability, which is greatest for fast- vs. slow-growing saplings and least for large trees with foliage in the forest canopy. Inherent attributes of species contributing to the trade-off include abilities to disperse, acquire resources, grow rapidly, and tolerate shade and other stresses. There is growing interest in the possibility that functional traits might provide insight into such ecological differences and a growing consensus that seed mass (SM), leaf mass per area (LMA), wood density (WD), and maximum height (Hmax) are key traits among forest trees. Seed mass, LMA, WD, and Hmax are predicted to be small for light-demanding species with rapid growth and mortality and large for shade-tolerant species with slow growth and mortality. Six of these trait–demographic rate predictions were realized for saplings; however, with the exception of WD, the relationships were weak (r2 < 0.1 for three and r2 < 0.2 for five of the six remaining relationships). The four traits together explained 43–44% of interspecific variation in species positions on the growth–mortality trade-off; however, WD alone accounted for >80% of the explained variation and, after WD was included, LMA and Hmax made insignificant contributions. Virtually the full range of values of SM, LMA, and Hmax occurred at all positions on the growth–mortality trade-off. Although WD provides a promising start, a successful trait-based ecology of tropical forest trees will require consideration of additional traits.
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    Species with greater seed mass are more tolerant of conspecific neighbours: a key driver of early survival and future abundances in a tropical forest
    (Wiley, 2016) Lebrija‐Trejos, Edwin; Reich, Peter B; Hernández, Andres; Wright, S Joseph
    Multiple niche‐based processes including conspecific negative density dependence (CNDD) determine plant regeneration and community structure. We ask how interspecific and intraspecific density‐dependent interactions relate to plant life histories and associated functional traits. Using hierarchical models, we analysed how such interactions affected first‐year survival of seedling recruits of 175 species in a tropical forest, and how species abundances and functional traits are related to interspecific variation in density‐dependent effects. Conspecific seedling neighbour effects prevailed over the effects of larger conspecific and all heterospecific neighbours. Tolerance of seedling CNDD enhanced recruit survival and subsequent abundance, all of which were greater among larger seeded, slow‐growing and well‐defended species. Niche differentiation along the growth–survival trade‐off and tolerance of seedling CNDD strongly correlated with regeneration success, with manifest consequences for community structure. The ability of larger seeded species to better tolerate CNDD suggests a novel mechanism for CNDD to contribute to seed‐size variation and promote species coexistence through a tolerance–fecundity trade‐off.