Recent experimental studies have found evidence for three mechanisms determining seedling performance with contrasting soil nutrient availability in tropical forests: trade-offs in biomass allocation, resource use efficiency, and anti-herbivore defense. Here we examine the relative contribution of each of these trade-offs in determining seedling performance of understory palm species along a soil nutrient gradient in a lower montane forest in western Panama. We examined seedling performance of 13 understory palm taxa transplanted to five sites along a soil nutrient gradient and exposed to and protected from herbivores.
Results/Conclusions
We found strong species and species by site interactions for traits related to biomass allocation, resource use efficiency, and anti-herbivore defense. However, the relative importance of these trade-offs differed among sites. In general, biomass allocation and nutrient-use efficiency were more strongly related to seedling performance at lower nutrient sites, whereas water-use efficiency and herbivory were more strongly related to seedling performance at higher nutrient sites. In addition, pest pressure indirectly affected seedling performance by increasing leaf area damage with increasing leaf quality at intermediate and high nutrient sites and by reducing aboveground biomass at low nutrient sites. Thus, different sets of trade-offs were involved in determining palm seedling performance and, thus, ecological filtering along the soil nutrient gradient in this lower montane forest.