COMMUNITY ASSEMBLY of NEOTROPICAL FROGS ACROSS ECOLOGICAL SCALES a Dissertation by CHRISTOPHER MICHAEL SCHALK Submitted To
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COMMUNITY ASSEMBLY OF NEOTROPICAL FROGS ACROSS ECOLOGICAL SCALES A Dissertation by CHRISTOPHER MICHAEL SCHALK Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chair of Committee, Lee A. Fitzgerald Committee Members, Thomas E. Lacher Amanda Stronza Kirk O. Winemiller Head of Department, Michael Masser August 2016 Major Subject: Wildlife and Fisheries Sciences Copyright 2016 Christopher M. Schalk ABSTRACT Ecological communities are organized by historical, biotic, and abiotic factors and the strengths of these factors vary across multiple spatial and temporal scales. I sought to disentangle the drivers of community assembly in frogs of the Bolivian Gran Chaco. This research was conducted within the framework of Applied Biodiversity Science that incorporates collaborations with local institutions to achieve biodiversity conservation. I used functional traits to examine the relationship between species distribution in niche space and community diversity of post-metamorphic frogs. Community organization was non-random, and species-packing significantly increased with increasing community diversity, a pattern indicative of response to environmental filters. I quantified the spatiotemporal dynamics of pond food webs and observed that consumers were trophic generalists, with many species occupying more than one trophic position. Breeding ponds are patchy and ephemeral across the landscape, and being trophic generalists enables consumers to exploit various resources within a pond. I conducted an experiment to examine predator-induced plastic responses in tadpoles of an arid-adapted species, Leptodactylus bufonius, a species with terrestrial oviposition and aquatic development. Tadpoles in the predator treatments exhibited the strongest responses when exposed to both predator and conspecific alarm cues. Species adapted to breed in ephemeral ponds with terrestrial oviposition may be able to afford reduced growth rates by capitalizing on a head start in development. I examined the relationships between calling activity and environmental factors. Calling phenology of tropical ii anurans is the product of exogenous factors (i.e., climatic variables) and endogenous factors (i.e., reproductive modes). I also studied intra-specific variation in ambush site selection in metamorphs and adults of Ceratophrys cranwelli. Metamorphs selected a subset of available habitat, whereas adult frogs did not appear to select ambush sites based on variables I measured. This study provides insights to the trade-offs between foraging strategy and mortality risk. A synthesis of the diet in frogs of the Family Ceratophryidae revealed they are generalist, opportunistic predators. Contrary to previously published literature, there is little evidence of larval cannibalism in these species. The results of my dissertation provide important biological information useful in developing conservation strategies needed for habitat management and biodiversity conservation. iii DEDICATION To my family for sparking my interest in the natural world. And to my wife, Carmen, whose support is a constant source of inspiration in maintaining that spark. iv ACKNOWLEDGEMENTS I am grateful to my committee chair, Lee Fitzgerald, for accepting me into his laboratory, giving me the freedom in my academic pursuits, and helping me become a better scientist. I also thank my committee members, Drs. Tom Lacher, Amanda Stronza, and Kirk Winemiller for their advice that greatly improved the quality of the science. I am forever indebted to the number of colleagues and friends in the Herpetology Laboratory and Biodiversity Research and Teaching Collections that contributed to my growth as a scientist over the years. An invaluable source of constructive feedback and fruitful discussions came from Nicole Angeli, Drew Dittmer, Toby Hibbitts, Dan Leavitt, Heather Prestridge, Daren Riedle, Wade Ryberg, Nicole Smolensky, Mike “Dr. T.” Treglia, Danielle Walkup, and Megan Young. Beyond Texas A&M, I greatly benefited from discussions and feedback from Nathalie Aall, James Childress, Mike Cove, Marty Crump, Mo Donnelly, Brian Langerhans, Dan Saenz, and Erik Wild, who graciously offered their time, advice, and support. I thank the Capitania del Alto y Bajo Isoso (CABI) for permission to conduct research in Isoso and the Kaa-Iya National Park. This research would not be possible without the numerous friends and colleagues from Bolivia and beyond that assisted me during the course of my dissertation. These people include Ronald Sosa, Lorenzo Braga, Marco Senzano, Doris Ticona, Martin Jansen, Arne Schulze, Elio Iti, Alejandro Arambiza, and Florencio “Akori” Mendoza. Kathia Rivero at the Museo Noel Kempff Mercado assisted with permit support. I am particularly grateful to my colleague and v friend, Rosy Leny Cuellar, for assisting with logistical and permit support while in Bolivia, and for welcoming me into her family as I spent a year away from mine. This research would not be possible without the generous support from numerous organizations. Funding was provided by the Applied Biodiversity Science NSF-IGERT Program at Texas A&M University, the National Science Foundation’s Graduate Research Fellowship Program, Carolyn Wierichs Kelso and George Kelso via the International Sportfish Fund, the Ecology and Evolutionary Biology Program at Texas A&M University, and the U.S. Forest Service’s Southern Research Station. Some chapters from this dissertation are publication numbers 1473, 1501, 1503, 1508 of the Biodiversity Research and Teaching Collections at Texas A&M University. vi TABLE OF CONTENTS Page ABSTRACT........................................................................................................... ii DEDICATION ...................................................................................................... iv ACKNOWLEDGEMENTS .................................................................................. v TABLE OF CONTENTS....................................................................................... vii LIST OF FIGURES................................................................................................ ix LIST OF TABLES ................................................................................................ xii CHAPTER I INTRODUCTION ........................................................................... 1 CHAPTER II SPECIES PACKING, FUNCTIONAL TRAITS, AND COMMUNITY ORGANIZATION OF NEOTROPICAL FROG ASSEMBLAGES..............................................................................……. 6 Introduction ........................................................................................... 6 Materials and Methods ........................................................................... 9 Results ................................................................................................... 15 Discussion............................................................................................... 21 CHAPTER III TROPHIC PLASTICITY, ENVIRONMENTAL GRADIENTS, AND FOOD WEB STRUCTURE OF TROPICAL POND COMMUNITIES ..... 27 Introduction ........................................................................................... 27 Materials and Methods........................................................................... 29 Results ................................................................................................... 33 Discussion ............................................................................................. 40 CHAPTER IV ENVIRONMENTAL DRIVERS OF ANURAN CALLING PHENOLOGY IN A SEASONAL NEOTROPICAL ECOSYSTEM.................. 46 vii Introduction ........................................................................................... 46 Materials and Methods ......................................................................... 48 Results ................................................................................................... 52 Discussion .............................................................................................. 55 CHAPTER V PREDATOR-INDUCED PHENOTYPIC PLASTICITY IN AN ARID-ADAPTED TROPICAL TADPOLE........................................................ 73 Introduction ........................................................................................... 73 Materials and Methods ......................................................................... 76 Results ................................................................................................... 81 Discussion .............................................................................................. 85 CHAPTER VI ONTOGENETIC SHIFTS IN AMBUSH SITE SELECTION OF A SIT-AND-WAIT PREDATOR, THE CHACOAN HORNED FROG (CERATOPHRYS CRANWELLI) ........................................................................ 91 Introduction ........................................................................................... 91 Materials and Methods ......................................................................... 94 Results ................................................................................................... 98 Discussion .............................................................................................. 103 CHAPTER VII ON THE DIET OF THE FROGS OF THE CERATOPHRYIDAE: SYNOPSIS AND NEW CONTRIBUTIONS .............. 110 Introduction ..........................................................................................