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Background Many tropical forest tree species delay greening their leaves until full expansion. This strategy is thought to provide newly flushing leaves with protection against damage by herbivores by keeping young leaves devoid of nutritive value. Because young leaves suffer the greatest predation from invertebrate herbivores, delayed greening could prevent costly tissue loss. Many species that delay greening also produce anthocyanin pigments in their new leaves, giving them a reddish tint. These anthocyanins may be fungicidal, protect leaves against UV damage or make leaves cryptic to herbivores blind to the red part of the spectrum. Methods A comprehensive survey was undertaken of seedlings, saplings and mature trees in two diverse tropical forests: a rain forest in western Amazonia (Yasuní National Park, Ecuador) and a deciduous forest in Central America (Barro Colorado Island, Panamá). A test was made of whether individuals and species with delayed greening or red-coloured young leaves showed lower mortality or higher relative growth rates than species that did not. Key results At both Yasuní and Barro Colorado Island, species with delayed greening or red young leaves comprised significant proportions of the seedling and tree communities. At both sites, significantly lower mortality was found in seedlings and trees with delayed greening and red-coloured young leaves. While there was little effect of leaf colour on the production of new leaves of seedlings, diameter relative growth rates of small trees were lower in species with delayed greening and red-coloured young leaves than in species with regular green leaves, and this effect remained when the trade-off between mortality and growth was accounted for. Conclusions Herbivores exert strong selection pressure on seedlings for the expression of defence traits. A delayed greening or red-coloured young leaf strategy in seedlings appears to be associated with higher survival for a given growth rate, and may thus influence the species composition of later life stages. [ABSTRACT FROM AUTHOR]

Leaf dark respiration (R) and its temperature sensitivity are essential for efforts to model carbon fluxes in tropical forests under current and future temperature regimes, but insufficient data exist to generalize patterns of R in species-rich tropical forests. Here, we tested the hypothesis that R and its temperature sensitivity (expressed as Q10, the proportional increase in R with a 10 °C rise in temperature) vary in relation to leaf functional traits, and among plant functional types (PFTs). We conducted in situ measurements of R of 461 leaves of 26 species of tree and liana in the upper canopy of a tropical forest in Panama. A construction crane allowed repeated non-destructive access to measure leaves kept in the dark since the previous night and equilibrated to the ambient temperature of 23–31 °C in the morning. R at 25 °C (R25) varied among species (mean 1.11 μmol m−2 s−1; range 0.72–1.79 μmol m−2 s−1) but did not differ significantly among PFTs. R25 correlated positively with photosynthetic capacity, leaf mass per unit area, concentrations of nitrogen and phosphorus, and negatively with leaf lifespan. Q10 estimated for each species was on average higher than the 2.0 often assumed in coupled climate–vegetation models (mean 2.19; range 1.24–3.66). Early-successional tree species had higher Q10 values than other functional types, but interspecific variation in Q10 values was not correlated with other leaf traits. Similarity in respiration characteristics across PFTs, and relatively strong correlations of R with other leaf functional traits offer potential for trait-based vegetation modeling in species-rich tropical forests. [ABSTRACT FROM PUBLISHER]

Heterostyly is a genetic polymorphism in which plant populations are composed of two or more morphs that differ in stigma and anther heights. The polymorphism promotes intermorph pollen transfer, thus outcrossing. Heterostyly has been reported in 28 angiosperm families and is frequently lost in heterostylous lineages. To assess ecological factors related to shifts from heterostyly to monomorphy, we examined the reproductive ecology of heterostylous tropical shrubs of Psychotria. Among 21 species at Barro Colorado Island and the nearby Parque Nacional Soberania, Panama, 14 species were heterostylous while seven were monomorphic. A molecular phylogeny and the existence elsewhere of heterostylous populations indicated that the breakdown of heterostyly had occurred independently. Heterostylous and monomorphic species were visited by the same bee species, although visit frequencies were lower in monomorphic species. Monomorphic species had significantly lower population density and greater fruit set than did heterostylous species. Autonomous autogamy made a large contribution to fruit set in monomorphic species and was only rarely observed in heterostylous species. The results indicate monomorphic and heterostylous species produce more seeds through selfing and outcrossing, respectively. The limitation of outcrossing as a result of low population density may be related to the breakdown of heterostyly and the evolution of selfing. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 125–134. [ABSTRACT FROM AUTHOR]