Examining variation in the leaf mass per area of dominant species across two contrasting tropical gradients in light of community assembly

Abstract

Understanding variation in key functional traits across gradients in high diversity systems and the ecology of community changes along gradients in these systems is crucial in light of conservation and climate change. We examined inter‐ and intraspecific variation in leaf mass per area (LMA) of sun and shade leaves along a 3330‐m elevation gradient in Peru, and in sun leaves across a forest–savanna vegetation gradient in Brazil. We also compared LMA variance ratios (T‐statistics metrics) to null models to explore internal (i.e., abiotic) and environmental filtering on community structure along the gradients. Community‐weighted LMA increased with decreasing forest cover in Brazil, likely due to increased light availability and water stress, and increased with elevation in Peru, consistent with the leaf economic spectrum strategy expected in colder, less productive environments. A very high species turnover was observed along both environmental gradients, and consequently, the first source of variation in LMA was species turnover. Variation in LMA at the genus or family levels was greater in Peru than in Brazil. Using dominant trees to examine possible filters on community assembly, we found that in Brazil, internal filtering was strongest in the forest, while environmental filtering was observed in the dry savanna. In Peru, internal filtering was observed along 80% of the gradient, perhaps due to variation in taxa or interspecific competition. Environmental filtering was observed at cloud zone edges and in lowlands, possibly due to water and nutrient availability, respectively. These results related to variation in LMA indicate that biodiversity in species rich tropical assemblages may be structured by differential niche‐based processes. In the future, specific mechanisms generating these patterns of variation in leaf functional traits across tropical environmental gradients should be explored.

Trait variation and functional diversity maintenance of understory herbaceous species coexisting along an elevational gradient in Yulong Mountain, Southwest China

“…Using trait variance ratios of the understory herbaceous species, the presence of internal and environmental filtering on these communities were able to be determined ( Violle et al., 2012 , Taudiere and Violle, 2015 ). The magnitude of T IP/IC indicated the strength of internal filters ( Violle et al., 2012 , Neyret et al., 2016 ), and in our case the observed T IP/IC was significantly lower than randomized values for all four traits. Thus, we conclude that species exhibit more packing in trait space than null expectations, and this indicates that biotic interactions (such as competition) or micro-environmental heterogeneity is determining local community composition.…”

Effect of environmental gradients on leaf morphological traits in the Fandoghlo forest region (NW Iran)

“…At higher light environments, SLA tended to decrease (Li et al 2014, Larcher et al 2015, as observed in the present study. LMA increases with decreasing forest cover, likely due to the increased light availability and water stress (Neyret et al 2016). The results of this study also showed a significant increase in LMA with increasing light at the isolated trees, similar to the findings of previous studies (Sprugel et al 1996, Wang et al 2006.…”

The Influence of Taxonomy and Environment on Leaf Trait Variation Along Tropical Abiotic Gradients

“…In order to compare traits among plots and abiotic gradients, we derived community weighted means based on basal area at the plot level (CWM; Violle et al, 2007;Neyret et al, 2016) of each trait as well as the community weighted effect size (CWE).…”

“…Importantly, it is not just the values of functional traits that are used to understand and predict the structure and functioning of plant communities, but the variation within and co-variation between and among traits (Violle et al, 2007(Violle et al, , 2012Albert et al, 2011;Taudiere and Violle, 2015;Neyret et al, 2016). The role of leaf functional trait variation and co-variation at different ecological scales has received renewed attention in the last decades, with efforts searching for general trait syndromes or spectra reflecting differences in ecological strategies, which are considered the result of natural selection (Grime, 1977;Coley et al, 1985;Westoby et al, 2002;Reich et al, 2003;Wright et al, 2004;Agrawal and Fishbein, 2006;Craine, 2009;Díaz et al, 2016).…”