Interactions between abiotic gradients determine functional and phylogenetic diversity patterns in Mediterranean-type climate mountains in the Andes

Abstract

Questions: How do phylogenetic and functional trait dispersions respond to multiple abiotic gradients? Are functional trait and phylogenetic dispersions coupled across different spatial scales? Does phylogenetic signal on functional trait data help to elucidate the degree to which phylogenetic information is providing novel information?. Location: Three massifs in mediterranean-type climate zone of the high Andes, central Chile. Methods: We sampled plant species composition in 20 alpine sites above the tree line at three different spatial scales: plot (20 m × 20 m), subplot (2.4 m × 2.4 m) and cell (30 cm × 30 cm). Functional and phylogenetic mean pair-wise distances (MPD) calculated using data on six functional traits (maximum plant height, plant size, leaf area, specific leaf area, leaf dry matter content and leaf thickness) and a molecular phylogeny (rbcL and matK) were compared to the patterns expected under a null model to characterize the functional and phylogenetic dispersion along interacting elevation and potential solar radiation gradients. Results: Our results show that functional and phylogenetic dispersion were related and influenced by potential solar radiation, but the effect of this factor varied with elevation. Overdispersion was found in the most stressful sites, while clustering was observed where the conditions were milder, suggesting a relevant role of facilitation and competitive interactions, respectively. While Blomberg's K statistic indicated no phylogenetic signal for the studied plant traits, Pagel's λ indicated phylogenetic signal, but not of strong intensity (<1), suggesting that the correlation between the functional and phylogenetic diversities was low and that additional unmeasured traits with phylogenetic signal were likely to be important in determining the structure of the studied communities. Conclusions: Our results support the hypothesis that biotic interactions modulated by environmental conditions are important for alpine plant community assembly. Moreover, they reinforce the notion that multiple processes shape community structure, and this can be elucidated by examining interacting environmental gradients, such as elevation and potential solar radiation, and taking into account multiple spatial scales. Our results reinforce the use of both functional and phylogenetic diversities simultaneously and discourage the use of phylogenetic diversity as a surrogate of functional structure.