Functional traits explain variation in plant life history strategies

Abstract

Ecologists seek general explanations for the dramatic variation in species abundances in space and time. An increasingly popular solution is to predict species distributions, dynamics, and responses to environmental change based on easily measured anatomical and morphological traits. Trait-based approaches assume that simple functional traits influence fitness and life history evolution, but rigorous tests of this assumption are lacking, because they require quantitative information about the full lifecycles of many species representing different life histories. Here, we link a global traits database with empirical matrix population models for 222 species and report strong relationships between functional traits and plant life histories. Species with large seeds, long-lived leaves, or dense wood have slow life histories, with mean fitness (i.e., population growth rates) more strongly influenced by survival than by growth or fecundity, compared with fast life history species with small seeds, short-lived leaves, or soft wood. In contrast to measures of demographic contributions to fitness based on whole lifecycles, analyses focused on raw demographic rates may underestimate the strength of association between traits and mean fitness. Our results help establish the physiological basis for plant life history evolution and show the potential for trait-based approaches in population dynamics.

Keywords: elasticity; seed size; specific leaf area; vital rates; wood intensity.

Fig. 1.

Functional traits are related to vital rate elasticities. Relationships were estimated with Dirichlet regression. Dotted lines show nonsignificant functional trait effects, solid lines show significant functional trait effects, and dashed lines show functional trait effects that were not significant after growth form was added to the model.

Fig. 2.

Comparison of functional trait effects on vitals rate and vital rate elasticities. The standardized effect size is the Z (Dirichlet regression) or t value (PGLS regressions) for the following functional traits: (A) seed mass, (B) wood density, (C) leaf lifespan, (D) SLA, and (E) leaf N. Vital rates are survival (S), growth (G), and fecundity (F). Trait–elasticity relationships were fit using both Dirichlet and PGLS regressions, whereas trait–vital rate relationships were fit using only PGLS regression. The dashed lines show statistically significant effects at α=0.05.