Incidence of Extrafloral Nectaries and Their Relationship with Growth and Survival of Lowland Tropical Rain Forest Trees

Mutualistic relationships between organisms have long captivated biologists, and extrafloral nectaries, or nectar-producing glands, found on many plants are a good example. The nectar produced from these glands provides food for ants, which may defend the plant from potential herbivores in turn. However, relatively little is known about their impact on the long-term growth and survival of plants that produce them. To better understand the ecological significance of extrafloral nectaries, we examined their incidence on lowland tropical rain forest trees in Yasuní National Park in Amazonian Ecuador, and collated data from two other tropical lowland forest sites (Barro Colorado Island, Panamá and Pasoh Forest Reserve, Malaysia). At Yasuní, extrafloral nectaries were found on 137 of 1123 species censused (12.2%), widely distributed among different angiosperm families. This rate of incidence is high but consistent with other tropical locations. Furthermore, this study adds 18 new genera and two new families (Urticaceae and Caricaceae) to the list of taxa exhibiting extrafloral nectaries. Using demographic data from long-term forest dynamics plots at each site, we compared the growth and mortality rates of species with extrafloral nectaries to those without. After controlling for phylogeny, no general relationship between extrafloral nectary presence and demographic rates could be detected, suggesting little demographic signal from any community-wide ecological effects.