Incidence of Extra-Floral Nectaries and their Effect on the Growth and Survival of Lowland Tropical Rain Forest Trees

Abstract

Mutualistic relationships between organisms have long captivated biologists, and extra-floral nectaries (EFNs), or nectar-producing glands, found on many plants are a good example. The nectar produced from these glands serves as food for ants which attack intruders that may threaten their free meal, preventing herbivory. However, relatively little is known about their impact on the growth and survival of plants that exhibit EFNs. To better understand the ecological significance of EFNs, I examined their incidence on 896 species of lowland tropical rain forest tree in Yasuni National Park in Amazonian Ecuador. Of those species that were observed in the field, EFNs were found on 96 species (11.2%), widely distributed among different angiosperm families. This rate of incidence is high but consistent with other locations in tropical regions. Furthermore, this study adds 13 new genera and 2 new families (Urticaceae and Caricaceae) to the list of trees exhibiting EFNs. Using demographic data from a long-term forest dynamics plot, I compared the growth and survival rates of species that have nectaries with those that do not. This same process was also done with EFN incidence previously recorded at two different locations, Barro Colorado Island, Panama and Pasoh Forest Reserve, Malaysia. Results show that while species with EFNs have generally higher diameter growth rates, they also have higher mortality rates than species without, suggesting a cost to this ecological strategy.