Are Functional Traits Good Predictors of Demographic Rates? Evidence From Five Neotropical Forests

Abstract

Abstract. A central goal of comparative plant ecology is to understand how functional traits vary among species and to what extent this variation has adaptive value. Here we evaluate relationships between four functional traits (seed volume, specific leaf area, wood density, and adult stature) and two demographic attributes (diameter growth and tree mortality) for large trees of 240 tree species from five Neotropical forests. We evaluate how these key functional traits are related to survival and growth and whether similar relationships between traits and demography hold across different tropical forests.There was a tendency for a trade-off between growth and survival across rain forest tree species. Wood density, seed volume, and adult stature were significant predictors of growth and/or mortality. Both growth and mortality rates declined with an increase in wood density. This is consistent with greater construction costs and greater resistance to stem damage for denser wood. Growth and mortality rates also declined as seed volume increased. This is consistent with an adaptive syndrome in which species tolerant of low resource availability (in this case shade-tolerant species) have large seeds to establish successfully and low inherent growth and mortality rates. Growth increased and mortality decreased with an increase in adult stature, because taller species have a greater access to light and longer life spans. Specific leaf area was, surprisingly, only modestly informative for the performance of large trees and had ambiguous relationships with growth and survival.Single traits accounted for 9-55% of the interspecific variation in growth and mortality rates at individual sites. Significant correlations with demographic rates tended to be similar across forests and for phylogenetically independent contrasts as well as for cross-species analyses that treated each species as an independent observation. In combination, the morphological traits explained 41% of the variation in growth rate and 54% of the variation in mortality rate, with wood density being the best predictor of growth and mortality. Relationships between functional traits and demographic rates were statistically similar across a wide range of Neotropical forests. The consistency of these results strongly suggests that tropical rain forest species face similar trade-offs in different sites and converge on similar sets of solutions.

Intraspecific trait variation can weaken interspecific trait correlations when assessing the whole‐plant economic spectrum

“…Surprisingly, our data do not strongly support the predictions and observations that WD will be correlated with growth rates of both juveniles and mature trees (Falster et al., 2011; Gibert et al., 2016; Poorter et al., 2008; Wright et al., 2010). We detected a weak negative correlation between WD and growth rate among mature tree species, but the correlation disappeared in the PICs, suggesting that the generality of this relationship occurs across, rather than within, clades.…”

“…We detected a weak negative correlation between WD and growth rate among mature tree species, but the correlation disappeared in the PICs, suggesting that the generality of this relationship occurs across, rather than within, clades. To complement previous field studies (Poorter et al., 2008; Wright et al., 2010), future studies could clarify the potential role of ontogenetic effects by comparing cultivated juveniles with mature trees grown in standard environments. This task will pose significant challenges, but arboreta and monocultures of trees grown in biodiversity–ecosystem function experiments probably offer the best chance of comparing mature trees of different species grown under conditions that approach the level of standardization achieved in common‐garden experiments.…”

“…On the other hand, several other studies have reported weak correlations among leaf, stem, and root traits, or no correlation at all (Baraloto et al., 2010; Fortunel, Fine, & Baraloto, 2012; Jager, Richardson, Bellingham, Clearwater, & Laughlin, 2015; Pietsch et al., 2014; Weemstra et al., 2016; Wright et al., 2007), indicating that interspecific correlations across organs are not consistently observed. Moreover, while substantial volumes of theory and data support relationships between morphological functional traits and RGRs (Hunt & Cornelissen, 1997; Reich, Tjoelker, Walters, Vanderklein, & Buschena, 1998; Shipley, 2006), correlations observed in the field are sometimes weak or nonexistent (Paine et al., 2015; Poorter et al., 2008; Wright et al., 2010). What can explain these discrepancies?…”

The role of breeding system in community dynamics: Growth and mortality in forests of different successional stages

“…Demographic variation within communities have been linked to a number of functional traits (Poorter et al., 2008; Wright et al., 2010; Lida et al. 2014) and ecological processes (e.g., seed dispersal and density‐dependence, Ma et al.…”

“…In terms of understanding the multiple traits driving successional differences, seed mass, leaf mass per area, woody density, and maximum height of trees received a great deal of attention (Westoby et al. 2002, Westoby & Wright 2006; Poorter et al., 2008; Chave et al. 2009; Norden, Letcher, Boukili, Swenson, & Chazdon, 2012; Buzzard, Hulshof, Birt, Violle, & Enquist, 2016).…”