Doctor of Philosophy (PhD)


Biological Sciences

Document Type



In tropical forests, forest fragmentation that alters species interactions between plants and animals, especially mutualisms, will affect the regeneration of trees. Fragmentation reduced Duckeodendron cestroides seed dispersal quantity and quality. The percent and distance of dispersed seeds were twice as great in continuous forest (31%, 4.9 m) as in fragments (15%, 2.5 m). Differences were even more exaggerated for each tree's furthest dispersed seeds. Distributions of dispersed seeds across distance showed more seeds at all distances in continuous forest than in fragments. Dispersal differences were strongest in years when fruit production was high and resulted in a greater number of first-year seedlings at distances far from the parent tree in continuous forests. Fruit production and post-dispersal seed fate of Duckeodendron were also different between fragments and continuous forest. Fruit production, measured by fruit fall, was reduced in fragments, more dramatically in years when fruit production was high. In continuous forest, seeds protected from mammal seed predators or secondary dispersers had high rates of seedling establishment (55%), but the majority of unprotected seeds were rapidly removed (77%). Seed predation was 17 times greater in continuous forest (53%) than in fragments (3%). More seeds in fragments had delayed germination than in continuous forest, resulting in seedlings half as tall as their continuous forest counterparts. Despite these differences in the processes leading up to seedling establishment, there was no difference between the percent of seedlings that established in fragments or continuous forest. Although fragmentation had dramatic effects on D. cestroides, responses of species interactions to fragmentation can vary. Although the number, percentage, distance, and distributions of dispersed seeds were reduced in fragments for the large-seeded Duckeodendron, they were not for the small-seeded Bocageopsis multiflora. Seed dispersal of large-seeded species may be more susceptible to fragmentation than small-seeded species because large-seeded species rely on fewer, extinction prone dispersers. Three lines of evidence from other tropical fragmentation research support this hypothesis. A rapid survey failed to detect differences in fruit production between fragments and continuous forest, probably because small sample sizes and high intraspecific variability caused a Type II error.



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Committee Chair

G. Bruce Williamson