Does trait variation within broadly distributed species mirror patterns across species? A case study in Puerto Rico

Abstract

Although populations are phenotypically diverse, the majority of trait-based studies have focused on examining differences among species. The justification for this broadly applied approach is based on the assumption that differences among species are always greater than within species. This is likely true for local communities, but species are often broadly distributed across a wide range of environments and patterns of intraspecific variation might surpass differences among species. Therefore, an appropriate interpretation of the functional diversity requires an assessment of patterns of trait variation across different ecological scales. In this study, we examine and characterize patterns of leaf trait variation for species that are broadly distributed along an elevational gradient. We focus on seven leaf traits that represent a main axis of functional differentiation in plants reflecting the balance between photosynthetic efficiency, display, and stomatal conductance. We evaluated patterns of trait variance across ecological scales (elevation, species, populations, and individuals) and examined trait covariance at both within species and across species levels, along the elevation gradient. Our results show three key patterns: (1) intraspecific leaf trait variation for broadly distributed species is comparable to the interspecific trait variation, (2) the trait variance structure is highly variable across species, and (3) trait coordination between pairs of leaf traits is evident across species along the gradient, but not always within species. Combined, our results show that trait coordination and covariance are highly idiosyncratic across broadly distributed and co-occurring species, indicating that species may achieve similar functional roles even when exhibiting different phenotypes. This result challenges the traditional paradigm of functional ecology that assumes single trait values as optimal solutions for environments. In conclusion, patterns of trait variation both across and within species should be considered in future studies that assess trade-offs among traits over environmental gradients.

Intraspecific perspective of phenotypic coordination of functional traits in Scots pine

“…Within WS, wood density works as an integrator of wood properties, related to the mechanical support and resistance to embolism in drought periods [14]. As a result of the interaction of the different traits belonging to distinct plant organs, different phenotypes are displayed at the individual level [15,16], which is likely to have a profound adaptive significance in contrasting environments [17,18].…”

Could the environment limit dispersal between Sunda and Sahul?

“…Elevation data from the Shuttle Radar Topography Mission. The lowland cut-off point used in (c) is 400 m because environmental shifts shape plant traits at these elevations (Umaña & Swenson, 2019a;Umaña & Swenson, 2019b) and in the most remote mountains of the archipelago, montane flora can be found at these elevations (Holthuis & Lam, 1942; Trethowan personal observation). In the larger islands that dominate Sunda and Sahul lowland flora is found at higher elevations (MacKinnon et al, 1996;Utteridge & Edwards, 2009;Marshall & Beehler, 2012); therefore, the pattern of less lowland in Wallacea should be even greater than seen in (c).…”

The importance of intraspecific trait variability in promoting functional niche dimensionality

“…Alternatively, if intraspecific trait variation is caused by local adaption and/or phenotypic plasticity due to site‐specific environmental stress (Albert et al 2010, Messier et al 2017a), trait integration quantified from both inter‐ and intraspecific variances should be weaker than that from only interspecific variance. This is because species can individualistically fulfill local environmental requirements through differential adjustment of their phenotypes (Fajardo and Siefert 2018, Umaña and Swenson 2019), and consequentially co‐occurring species are represented by many alternative strategies with functional equivalency (Marks and Lechowicz 2006). Thus, viable strategies in a community representing good solutions to local environmental pressures might not necessarily be optimized around axes of interspecific tradeoffs, but rather stem largely from flexible functional designs within species.…”