Intraspecific leaf trait variability along a boreal-to-tropical community diversity gradient

Disentangling the mechanisms that shape community assembly across diversity gradients is a central matter in ecology. While many studies have explored community assembly through species average trait values, there is a growing understanding that intraspecific trait variation (ITV) can also play a critical role in species coexistence. Classic biodiversity theory hypothesizes that higher diversity at species-rich sites can arise from narrower niches relative to species-poor sites, which would be reflected in reduced ITV as species richness increases. To explore how ITV in woody plant communities changes with species richness, we compiled leaf trait data (leaf size and specific leaf area) in a total of 521 woody plant species from 21 forest communities that differed dramatically in species richness, ranging from boreal to tropical rainforests. At each forest, we assessed ITV as an estimate of species niche breadth and we quantified the degree of trait overlap among co-occurring species as a measure of species functional similarity. We found ITV was relatively invariant across the species richness gradient. In addition, we found that species functional similarity increased with diversity. Contrary to the expectation from classic biodiversity theory, our results rather suggest that neutral processes or equalizing mechanisms can be acting as potential drivers shaping community assembly in hyperdiverse forests.Leaf data used to come to this manuscript resulted from many different studies involving different funding sources: European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 265171; Spanish-funded project REMEDINAL3eCM (S2013/MAE-2719); Ecometas excellence network (CGL2014-53840-REDT); a FPU grant by the Spanish Government (AP2010-5600); a Marie Curie IEF fellowship (FP7-PEOPLE-2011-IEF. no. 302445);Peer Reviewe

Summary table of the GLMM testing the change in the extent of ITV with species richness (SR), mean annual temperature (Mean.

<p>Ann. T^ra) and annual precipitation (Pp) for both leaf size and SLA.</p

Intraspecific leaf trait variability along a boreal-to-tropical community diversity gradient - Fig 3

<p><b>Linear regression models of the median values of trait overlap (panel A, B) and the proportion of low (less than 0.25; panel C, D) and high (> 0.75; panel E, F) values of degree of trait overlap between species for each forest community against species richness for both leaf size (left) and SLA (right).</b> Trait similarity was calculated by assuming normal trait distribution of species with ≥ 5 individuals measured. (***): p-value <0.001; (**): p-value <0.01; (*): p-value < 0.05; (.): p-value <0.1.</p

Intraspecific leaf trait variability along a boreal-to-tropical community diversity gradient - Fig 2

<p><b>Effect of species richness on the extent of ITV (estimated as coefficient of variation, CV) for (A) leaf size and (B) SLA.</b> n = number of species measured for each forest community with ≥ 5 individuals measured. Empty circles indicate the average of ITV values for each forest community and richness level. The number of sampled species (n) may be both lower than the species richness of the community since we sub-sampled a forest layer, but also, potentially larger than the species richness of that community since the arrival of seeds from neighbor canopies may result in the establishment of new individuals that previously were not part of the main canopy of the focal community.</p

Description of each forest community included in the study.

<p>Description of each forest community included in the study.</p