Effects of Dispersal and Insect Herbivory on Seedling Recruitment of Dipteryx Oleifera Benth (Fabaceae) a Tropical Tree.

Abstract

ABSTRACT

EFFECTS OF DISPERSAL AND INSECT HERBIVORY ON SEEDLING RECRUITMENT OF DIPTERYX OLEIFERA BENTH (FABACEAE) A TROPICAL TREE

by

Javier Enrique Ruiz

Chair: John H. Vandermeer

This dissertation provides evidence for the relative contribution of primary and secondary seed dispersal and insect herbivory on seedling recruitment of D. oleifera. I tested the Janzen-Connell and the recruitment limitation hypotheses using seedlings of Dipteryx oleifera within a prermanent plot (6.5 ha), located in eastern Nicaragua. Results show that seedling insect herbivory decreases with the distance to the nearest conspecific adult (r2 = 0.79, p =0.000). As a consequence seedling survival was higher away from as oppose to near to a conspecific adult (r2 =0.80, p <0.05). Bat primary seed dispersal, while removing seeds from the immediate vicinity of adult trees, nevertheless had the effect of congregating seeds below roosting sites usually located far away from adult conspecifics (79% of the cases, n=70 roosts). Bats preferred to roost in two palm species (Welfia regia and Cryosophila warscewiczii). Rodent secondary seed dispersal from these seed concentrations was required to release seed from seed predators and insect herbivores (Z =3.3, df =2, p<0.005). The presence of unviable seeds at the seed concentrations “masked” the availability of viable seeds, confused rodents and increased secondary seed dispersal. Per each additional unviable seed moved by bats into the seed concentrations, seed predation rate decreased by a factor of ~1.9% (p<0.001), and increased seedling recruitment rate by a factor of ~1.8% (p<0.001). The distribution of Dipteryx oleifera seedlings is consistent with the Janzen-Connell hypothesis and depends on primary dispersal by bats, secondary dispersal by rodents and the constant threat of insect herbivores acting on the seedlings.