Defoliation and gender effects on fitness components in three congeneric and sympatric understorey palms

Abstract

Rain forest understorey perennial plants can be frequently exposed to leaf area losses induced by herbivory or physical damage from falling canopy debris. In dioecious species, tolerance to defoliation may differ between genders (e.g. females may suffer more than males), but this topic has so far received little attention. Here, we quantified gender-dependent effects of increased levels (0-100%) of sustained defoliation (applied bi-annually for 2 years) on vital rates in three economically important dioecious understorey palm species in the genus Chamaedorea (C. elegans, C. ernesti-augustii and C. oblongata). We also quantified gender differences in functional and life-history traits and assessed the direct reproductive costs in terms of biomass allocation to reproduction. In the three species, non-defoliated (control) females were smaller and had three to seven times higher reproductive allocation than males. Defoliation did not affect survivorship in any of the three species, except in the 100% defoliation treatment. Stem growth (RGR) and especially reproduction (probability of reproduction and reproductive output) were negatively affected by defoliation. Females of C. ernesti-augustii suffered higher mortality than males at 100% defoliation, but this was not the case for the other two species. Also, only in C. ernesti-augustii females exhibited lower RGR than males. In all species, the probability of reproduction did not differ between genders. The reproductive output (production rate of inflorescences) differed among genders only in C. ernesti-augustii, where males were more productive than females. Interestingly, in most cases, defoliation effects on vital rates did not differ significantly between males and females, indicating that tolerance to defoliation was similar between genders. Such results were independent of plant size (stem length). Synthesis. Our results do not support the prevailing theory that the greater reproductive costs of females will lead to reduced tolerance to stresses such as defoliation. The implications of these results and their importance for designing sustainable leaf harvesting regimes are discussed. © 2012 The Authors. Journal of Ecology © 2012 British Ecological Society.