Recovery of Insectivorous Bird Ecological Function in Tropical Forest Restorations

RECOVERY OF INSECTIVOROUS BIRD ECOLOGICAL FUNCTION IN TROPICAL FOREST RESTORATIONS By Steven Michael Roels A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Integrative Biology—Doctor of Philosophy Environmental Science and Policy—Dual Major Ecology, Evolutionary Biology and Behavior—Dual Major 2018 ABSTRACT RECOVERY OF INSECTIVOROUS BIRD ECOLOGICAL FUNCTION IN TROPICAL FOREST RESTORATIONS By Steven Michael Roels Recovery of animal-dependent ecosystem functions is a key component of ecological restoration on degraded tropical forest lands. One of these functions, regulation of herbivorous insects by birds, shapes tropical communities through trophic cascades that protect trees from insect damage. Understanding how bird-driven trophic cascades vary with environmental context, reforestation strategy, and management would guide restoration practitioners seeking to facilitate beneficial relationships between birds and plants. My dissertation examines the speed of bird community recovery following restoration action, the effects of climate dynamism on bird-driven trophic cascades, the mechanisms by which bird-driven trophic cascades occur, and insectivorous bird ecological function in forest restorations relative to other land cover types. In Chapter 1, I studied temporal trends and spatial patterns in bird activity and diversity over a five-year period at a forest restoration in Panama. Four years after tree planting, bird activity had increased three-fold and species richness eleven-fold, compared to pre-planting. However, species richness differed strongly between experimental plots within the field site. Using a multi-species hierarchical occurrence model, I considered possible reasons for this variation. Features within plots, such as the number of tree species planted, did not explain differences in the number of species observed. However, neighborhood context did explain differences; there were more species in plots with more adjacent woodland and farther from pasture. My results demonstrate that native tree planting can generate rapid responses from tropical bird communities but the surrounding matrix will mediate bird responses to restoration. In Chapter 2, I considered the ecological significance of insectivorous bird and bat activity in tropical forest restorations. I conducted bird and bat exclosure experiments in a Panamanian forest restoration during a typical wet season, dry season, and wet season with an El Niño drought. A trophic cascade was present on one of two tree species studied but only during a wet season with normal rainfall. These results highlight the importance of resident bird species for regulation of damaging insects in forest restorations and also point to the ability of regular seasonality and irregular El Niño events to alter trophic relationships in restoration ecosystems. In Chapter 3, I more closely inspected the mechanisms that produced the trophic cascade described in Chapter 2. On the tree species featuring a trophic cascade, predation by birds and bats during the normal wet season reduced biomass for five folivorous insect orders and reduced numbers of individuals for four of the five orders. Birds and bat effects were especially noticeable for larger-bodied arthropods. These patterns were weaker or absent on the tree species where a trophic cascade was not observed. In Chapter 4, I compared predation pressure by birds on artificial caterpillars in six land cover types, including the plantation-style forest restoration featured in Chapters 2 and 3. Bird predation pressure was lowest in intensively managed tree plantations and highest in land covers with structurally complex vegetation, such as successional forest and residential countryside. My results suggest insectivorous bird ecosystem function can be enhanced on reforestation lands by incorporating unmanaged areas and tolerating non-planted understory vegetation. Facilitation of bird-driven trophic cascades is potentially a useful tool for tropical forest restoration but the presence of a substantial trophic cascade cannot be assumed or taken for granted. I recommend that land managers adopt a holistic approach to reforestation that restores bird habitat and encourages recovery of animal-dependent ecosystem functions. This dissertation is dedicated to my parents, who encouraged me to play in the dirt, catch bugs, and chase birds, and to my wife, who still does. iv ACKNOWLEDGEMENTS I thank my committee members, Catherine Lindell, Peggy Ostrom, Gary Roloff, and Tom Getty, for their patient guidance, encouragement, and editorial assistance. Their support and high standards pushed me to expand my scientific horizons. I especially thank Catherine, my advisor, and Peggy, my co-advisor, for their efforts to keep me on track, even though the project completion timelines we created so often fell by the wayside due to statistical roadblocks or irresistible opportunities that had nothing to do with actually finishing my degree. I am also grateful to Catherine for assembling a fine lab group of ornithologists, scientists, and friends. The intellectual support and camaraderie provided by Melissa Brady Hannay, Rachael Eaton, Megan Shave, Olivia Utley, and Sean Williams were key to my growth as a scientist and surviving to tell about it. Many other members of the IBIO, EEBB, and ESPP communities were friends, classmates, and even fellow softball champions. The statistical rigor in this dissertation would not have been possible without the support of the MSU Center for Statistical Training and Consulting. Andrew Dennhardt was my essential guide during the statistical odysseys that lie behind Chapters 1 and 2. Alex Wright and Elise Zipkin also generously gave statistical advice on Chapter 1. Brian Maurer pushed my statistical training to a new level and forced me to learn R, a skill that became valued two years later. Funding for this dissertation came from many academic units within Michigan State University including: the Department of Integrative Biology; George J. and Martha C. Wallace Endowed Scholarship; College of Natural Science; Ecology, Evolutionary Biology, and Behavior Program; Caribbean and Latin American Studies Program; and School of Graduate Studies. A Dissertation Continuation grant from the College of Natural Science came at a critical time when v not much was going right. That grant was secured on my behalf by my advisor, Catherine Lindell, and I am especially thankful for her tangible support during that period. Funding was also provided by the Smithsonian Tropical Research Institute (STRI) and Daystar Research. Access and logistical support in the Mamoní Valley was thanks to the Earth Train Foundation. Jefferson Hall and the Agua Salud Project (ASP) took me in when I needed a new field site. Katherine Sinacore’s warm welcome and orientation tips made me feel quickly feel at home at the ASP. Federico Davis and Aristoteles Villegas provided logistical support at the ASP, especially those months we had no running water. Many fellow students in the ASP community provided friendship and excellent group cooking; some even gave a couple days of field assistance when I was in a pinch. Steve Paton’s regular weather updates and explanations of Panama’s climate helped make sense of the El Niño. The ASP is a collaboration between STRI, the Panama Canal Authority, and the Ministry of the Environment of Panama. Jade Porter was my assistant, co-explorer, and chief safety officer for three field seasons in Panama. Her positive attitude and humor got me through exhaustion, droughts, floods, and Panama City traffic. Her delight in the natural world reminded me every day that biology is fun. Finally, I thank my family for their love and support. My parents and my wife’s parents are proud of their son, even if they are not always sure what I do. Will, Lori, and Julie are friends that are family and I had the assurance that my wife was well-cared for during my long absences. Flora, my Chowbrador extraordinaire, has never known at least one of her humans not in graduate school, but loves us anyway and always greeted me with a happy tail, whether I was gone for two hours or two months. My wife, Dr. Sarah Bodbyl, is my best friend, best critic, and keen-eyed editor. Her spirit of determination in all things inspires me and her willingness to put up with a total of nine years in graduate school humbles me. Thank you. vi TABLE OF CONTENTS LIST OF TABLES ..................................................................................................................... ix LIST OF FIGURES ................................................................................................................... xi KEY TO ABBREVIATIONS ................................................................................................. xiii CHAPTER 1: Recovery of Bird Activity and Species Richness in an Early-stage Tropical Forest Restoration ....................................................................................................................... 1 ABSTRACT .......................................................................................................................... 2 INTRODUCTION ................................................................................................................. 3 METHODS ........................................................................................................................... 8 Study site ........................................................................................................................

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