Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology, Ecology

Date of Defense

6-8-2007

Graduate Advisor

Bette A. Loiselle, PhD

Committee

Mathews, Sarah

John G. Blake, Ph.D.

Pedro Jordano, Ph.D.

William Connett, Ph.D.

Abstract

Seed dispersal contributes significantly to tropical forest maintenance, influencing processes, such as metapopulation dynamics and population persistence. Although several hypotheses have been debated regarding the contribution of seed dispersal to tropical forest diversity, recent work suggests that dispersal limitation is a major component in determining plant population patterns. This dissertation research broadly addresses hypotheses that seed dispersal behaviour of frugivores influences dispersal limitation of a Neotropical tree, Virola flexuosa (Myristicaceae). To test these hypotheses, I studied how different frugivores influenced seed dispersal of V. flexuosa at two sites in Amazonia Ecuador. General research objectives were to estimate fruit removal by all dispersers, model toucan-generated dispersal curves, and determine effective dispersal distances using molecular markers. By using a combination of ecological and genetic methods, this project contributes to our understanding of how dispersal processes influence spatial distribution patterns of seeds, seedlings, and saplings. Research was conducted at the Tiputini Biodiversity Station (non-hunted) and Yasun¿ Research Station (hunted), Ecuador. I conducted observations of frugivore behaviour and seed removal at fruiting Virola trees. Radio-telemetry and seed retention rates were used to estimate toucan-generated dispersal curves. I used microsatellites to identify relatedness between seedlings and saplings with maternal Virola trees. Probability models of toucan dispersal suggested the majority of seeds were dispersed away from parent plants; up to 84% of seeds were predicted to fall >100 m from trees. Between-site comparisons revealed that fewer seeds were dispersed from fruiting trees at the hunted site; furthermore, fewer large-bodied dispersers visited trees at that site. Using genetic methods, I also demonstrated significantly reduced dispersal distances at the hunted site compared to the non-hunted site. Consequently, I found that dispersal was limited in a site where large frugivores were hunted. Conservation in Amazonia Ecuador faces many severe threats. Of primary concern are an increase in hunting activities and habitat degradation. As these pressures intensify, the influence of seed dispersers on forest regeneration may become increasingly important. This research provides new data on the contribution of frugivores to the process of seed dispersal and the degree to which disturbance alters the ecological function of these seed dispersers.

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