Strong persistent growth differences govern individual performance and population dynamics in a tropical forest understorey palm

Abstract

Summary Persistent variation in growth rate between individual plants can have strong effects on population dynamics as fast growers reach the reproductive size at an earlier age and thus potentially contribute more to population growth than slow growers. In tropical forests, such persistent growth differences have so far been documented for canopy tree species, where they are primarily associated with forest gap dynamics, but not for forest understorey species which are less responsive to gaps. Here, we study persistent growth differences and their demographic consequences for a tropical forest understorey palm, Chamaedorea elegans. We measured internodes along stems and annual leaf production rates to reconstruct lifetime growth trajectories. Using regression analysis, we determined the relative effect of stem length and past growth rate on vital rates (survival, growth and reproduction). We then simulated population dynamics using integral projection models (IPMs), in which individuals were categorized by both stem length and lifetime past growth rate. Stem growth differences among individual palms persisted over most of their lifetime. Past growth rate averaged over the palm's lifetime proved to be a very good predictor of growth, reproduction probability and seed production, often much better than stem length or age. The effects of past growth rate were positive, indicating that fast growers maintain high rates of growth and reproduction. Projected population growth rate (λ) was 1.056, and stable stage distributions closely resembled observed population structures. Separating individuals with above‐median and below‐median past growth rates in IPMs revealed substantial differences in elasticity values. The 50% fastest growers had a 1.8 times higher elasticity, and thus a 1.8 times higher contribution to population growth, compared to slow growers. Synthesis. Strong and persistent growth differences that are probably associated with environmental (edaphic) and/or genetic factors govern individual performance and population dynamics of a tropical forest understorey palm. Overall, our study shows that strong inter‐individual growth variation is not limited to canopy trees and that it can be generated by other factors than canopy dynamics. It is likely that persistently fast‐growing ‘super performers’ govern population growth of many long‐lived species.