Interactions of Avian Frugivores and Invasive Trees in French Polynesia

Interactions of Avian Frugivores and Invasive Trees in French Polynesia By Erica Noelle Spotswood A dissertation submitted in partial satisfaction of the requirement for the degree of Doctor of Philosophy in Environmental Science, Policy and Management in the Graduate Division of the University of California, Berkeley Committee in charge: Professor James W. Bartolome, Chair Professor John Battles Professor Brent Mishler Dr. Jean-Yves Meyer Fall 2011 ABSTRACT Interactions of Avian Frugivores and Invasive Trees in French Polynesia by Erica Noelle Spotswood Doctor of Philosophy in Environmental Science, Policy and Management University of California, Berkeley Professor James W. Bartolome, Chair Invasive species pose a threat to the persistence of the sensitive endemic biotic communities on oceanic islands. The direct ecological, social and economic effects of invasions have been well documented and can be significant on both islands and continents. The indirect effects on the interactions between species has received less attention despite being of critical importance to the long term stability of ecosystems facing multiple threats from anthropogenic impacts. In this dissertation, I examined how seed dispersal relationships are modified by the presence of multiple introduced species on the islands of Tahiti and Moorea in the Society archipelago of French Polynesia. Additionally, I evaluated the risks associated with one of my research methods; the use of mist nets to capture wild birds. I first evaluated how the local abundance of the invasive Miconia calvescens modifies seed dispersal relationships between birds and plants. The species is an invasive fruit-bearing tree that currently covers much of the island of Tahiti and is present at much lower densities on Moorea. I found that while the overall size of networks was similar across sites, networks on the highly invaded island of Tahiti were less diverse and less even because birds concentrated a greater proportion of their foraging on Miconia calvescens. There were fewer links between birds and native plants at highly invaded sites where birds switched their diets away from a broader range of fruit and insects. The endemic Grey-green Fruit Dove (Ptilinopus purpuratus) consumed native fruit in larger quantities and more total species than two introduced frugivores. This study demonstrates that the impacts of invasive fruit-bearing plants on seed dispersal networks depends in part on their abundance, and are likely to increase as a species becomes increasingly dominant in a community. Additionally, the dispersal of native plants continues to depend heavily on the single extant native fruit dove on these islands despite the presence of multiple introduced frugivores. The impact of invasive plants on seed dispersal networks is the result of the cumulative effects of foraging decisions by birds. The available evidence suggests that birds choose which fruit to consume based on the complementarity between fruit traits and their own preferences as well as the relative abundance of fruit in a community. I used fruit choice experiments with captive Red-vented Bulbuls (Pycnonotus cafer) to uncouple fruit preferences from the effects of abundance to determine which operates more strongly on foraging decisions in birds. Birds 1 showed both reliable and consistent preferences for some fruits over others and a strong response to abundance. However, when included simultaneously in the same experiment, the patterns of preference remained intact while the effect of abundance disappeared. Taken together, experimental and field data suggest that foraging decisions are highly context-dependent, and neutral models that consider only the relative abundance of fruit in the community are unlikely to provide reliable predictions about how seed dispersal networks will change in response to invasion. In the final study of my thesis, I evaluated the risks associated with one of my primary research methods; the use of mist nets to capture birds. Mist nets are used widely for monitoring avian populations. While the method is assumed to be safe, very few studies have addressed how frequently injuries and mortalities occur, and no large-scale comprehensive evaluation has been conducted to determine the associated risks. In collaboration with several banding organizations, I quantified the rates of mortality and injury at 22 banding organizations in the United States and Canada and used capture data from five organizations to determine what kinds of incidents occur most frequently. I compiled a dataset including nearly 350,000 records of capture over a 22 year period and evaluated what makes birds most at risk to incident. I found that the risks varied among species and factors such as body mass and the number of previous captures were related to the probability of an incident. Additionally, I found that birds that were released back into the wild after an injury were recaptured at similar rates compared to birds that were released without an injury, indicating that injured birds survived in similar numbers as those released uninjured. This study fills a gap by providing the first comprehensive evaluation of the risks associated with mist netting and concludes that while overall risks are low, species and traits can predict a bird’s susceptibility to incident. These results can be useful for organizations that use mist netting, and should be incorporated into protocols aimed at minimizing injury and mortality. Finally, I emphasize that projects using mist nets should monitor their performance and compare their results to those of other organizations. I conclude that the indirect effect of species invasions are variable and depend in part on the abundance of the invasive species. Thus, consequences for seed dispersal networks are likely to be most pronounced at the highest levels of invasion. Despite the effects of abundance, birds also showed strong preferences for certain kinds of fruits. Thus, the integration of novel fruit into native seed dispersal networks is likely to depend not only on the relative abundance of fruit but also on the preferences for each fruit relative to others that are available. The Grey-green Fruit Dove is the sole disperser for several native plants, and the maintenance of viable populations of these plants is likely to depend on conservation of this protected and sensitive endemic species. Similarly, it is likely that the Fruit Dove also depends on native plants despite the integration of many exotic fruit into its diet. There is an urgent need for more research evaluating the habitat requirements and population dynamics of this frugivore in order to ensure the long term persistence of the species. 2 This dissertation is dedicated to the endemic flora and fauna of French Polynesia I am willing to sacrifice elegance for reality, knowing just how muddy reality can be. ~ David Steadman (2006) i TABLE OF CONTENTS ACKNOWLEDGEMENTS…………………………………………………………………iii CHAPTER 1 General Introduction……………………………………………………………….…1 CHAPTER 2 Abundance of invasive trees alters the structure of seed dispersal networks in French Polynesia…………………………………………………………………..19 CHAPTER 3 Fruit choice in birds is influenced by abundance and fruit type but not invasion status in French Polynesia ……………………………………………………………46 CHAPTER 4 How safe is mist netting? Evaluating the risk of injury and mortality to birds……….70 CHAPTER 5 Conclusions & Directions for Future Research……………………………………….89 LITERATURE CITED………………………………………………………………………..97 APPENDICES………………………………………………………………………………..118 ii ACKNOWLEDGMENTS I am grateful to many people that helped me during the course of my dissertation research. First, I am grateful for the opportunity to work with my advisor, James Bartolome, whose support and advice was critical to the success of my project, and who was extraordinarily patient for the duration of the time that I have worked with him. This dissertation would also not have been possible without the assistance of Jean-Yves Meyer, who guided me towards the idea that became my dissertation, and provided an enormous amount of advice and expertise along the way. I thank John Battles, who was a member of my orals and dissertation committee and who gave excellent feedback and advice and challenged me to think deeply about my data and my project. I thank Brent Mishler, also a member of my orals and dissertation committee who encouraged me with positive energy and enthusiasm and pushed me to think about evolution and phylogenies even when I was resistant. A number of other Berkeley faculty were also tremendously supportive and generous with their time. The faculty that participate in the Moorea course Biology and Geomorphology of Tropical Islands were excellent sources of support and advice, including my advisor, Vince Resh, Brent Mishler, George Roderick, Jere Lipps, and Carole Hickman. Steve Beissinger allowed me to attend his lab meetings, read my papers, watched my talks and generally acted as an additional advisor to me and deserves an enormous thank you for all of it. Perry DeValpine taught me almost everything I know about statistics, and gave advice on data analysis numerous times even though I was no longer his student. Maggi Kelly helped me understand landscape ecology, served on my orals committee, and taught me everything I know about GIS. George Roderick and Rosie Gillespie helped secure funding for me through the NSF GK-12 program in Moorea, and were present through the course of my dissertation providing advice and

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