Year of Award

2021

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology, Ecology, and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Jedediah F. Brodie

Commitee Members

John L. Maron, Joshua J. Millspaugh, Kim R. McConkey

Keywords

Defaunation, Mast-fruiting, Seed dispersal, Seed predation, Southeast Asia, Sus barbatus

Abstract

Plant-consumer interactions can be critical for regulating populations of both plants and animals. In the tropics, many trees rely on animals to disperse their seeds, but many of these dispersers are disappearing, with potentially disastrous consequences for tropical tree species and global carbon storage. Defaunation—the loss of large animals due to factors such as overhunting—can also affect seed fates, either by increasing or decreasing seed predation. We know that defaunation alters these plant-animal interactions, but we still do not know how these changes at early life stages will ultimately affect tropical tree populations. Furthermore, we do not understand how defaunation will affect overall seed survival because we do not know the extent to which other seed enemies will compensate when large seed predators are removed.

Besides the effects of animals on plants, plants provide food resources that influence the ecology of consumers. In tropical Southeast Asia, dipterocarp mast fruiting results in highly variable fruit and seed resources over time, and logging alters the abundance and distribution of resources in different areas. These changes in resources may affect the behavior and co-occurrence of consumers, but it is unclear how other species will respond given the presence of key mast consumers. To study this, we would want to measure species’ responses to each other at fine spatiotemporal scales, but co-occurrence studies usually consider spatial or temporal co-occurrence separately.

In Chapter One of this dissertation, I review the literature on how defaunation affects tropical trees. Then I explore how defaunation may ultimately affect population dynamics by applying defaunation effects to matrix population models of tropical tree species. In Chapter Two, I use experimental treatments in a tropical forest in Borneo to test for functional redundancy among four key groups of seed predators—large mammals, small rodents, insects, and fungi—in terms of their impacts on seed mortality and germination. Finally, in Chapter Three, I develop a novel method of analyzing co-occurrence in space and time concurrently, which I use to assess how associations among frugivore-granivore vertebrate species differ according to resource conditions. For this analysis, I use camera trap and fruit abundance data from a tropical forest in Malaysian Borneo.

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