Dissertation Research: Dispersal Distance, Deposition Site,and Survivorship of Cassowary-Dispersed Seeds

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Zoochory is the predominant dispersal syndrome in most tropical forests. Few studies directly address what selective advantages tropical plants gain from zoochory or what the demographic effects of frugivore-mediated seed dispersal are to tropical trees. The paucity of empirical data on tropical zoochory after removal stems from the extreme difficulty of finding seeds where they have been deposited by frugivorous dispersers. Seed dispersal by cassowaries is an ideal system for study because cassowaries are specialist frugivores, virtually the sole disperser for many large-seeded trees and lianas, and are commonly found in the vast undisturbed forests of New Guinea. Most importantly, their droppings which contain dispersed seeds are numerous and conspicuous at the study site. Seeds will be marked with tags or small radio-transmitters before cassowaries disperse them. Tagged seeds found in visual searches and transmitter-seeds found by radio tracking will reveal dispersal distances, including those seeds carried long distances. Within- dropping parameters (e.g. parameters (e.g. insolation) will be measured for every dropping found. Droppings will be monitored up to three years for germination, seedling growth, and survivorship. The effects of within-dropping parameters and site parameters on germination, growth and survivorship of seedlings will be analyzed. Data on dispersal distances, within-dropping parameters and site parameters will be pooled in probability matrices to test published hypotheses regarding the consequences of vertebrate mediated seed dispersal. In the second half of the study the effects of dispersal will be experimentally examined. Seeds voided by a captive cassowary to make "pseudo-droppings" to test hypotheses based on observations of naturally-dispersed seeds will be used.