Effects of Nutrient Limitation on Understory Communities in a Tropical Forest
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EFFECTS OF NUTRIENT LIMITATION ON UNDERSTORY COMMUNITIES IN A TROPICAL FOREST BY JÉSSICA LIRA VIANA DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Plant Biology in the Graduate College of the University of Illinois at Urbana-Champaign, 2020 Urbana, Illinois Doctoral Committee: Professor James W. Dalling, Chair Associate Professor Anthony Yannarell Associate Professor Jennifer Fraterrigo Associate Professor Wendy Yang ABSTRACT Ferns are the second most diverse group of vascular plants whose diversity and abundance peak in mid-elevation tropical forests. Soil nutrient limitation is an important factor influencing plant communities and yet little is known about the factors influencing fern floristic composition and functional traits in montane tropical forests. My dissertation compares composition variation and decay-rates between terrestrial ferns and understory palms, since the extent to which their resource needs overlap has not been determined. Furthermore, ferns and palms are two essential components of forest understories that differ widely in physiology and reproductive traits, while competing for the same limited resources. I found that soil factors impacted compositional similarity of both ferns and palms, with fern compositional variation related to total soil nitrogen to phosphorus ratio (soil N:P) and light conditions (red:far read – RFR) and palm compositional variation related to bulk density. Distance–decay rates in compositional similarity were slightly higher for palms than ferns. In addition, the abundance of understory palms and tree ferns showed opposite trends with soil N:P and RFR compared to herbaceous ferns. I also analyzed the responses of functional composition and functional dispersion to soil and precipitation gradients, to determine to what degree environmental factors influence trait distribution and diversity of fern communities across their phylogeny. The examination of functional composition and functional dispersion of fern communities along the soil fertility gradient demonstrated that functional composition was affected by soil variables and dry season rainfall. Leaf traits contributed to most of the variation among all trait variables evaluated. Functional dispersion decreased with soil N:P and manganese (Mn), and increased with dry season soil moisture. Trait and phylogenetic diversity showed clustered patterns. Due to field collections, the fern species list of Fortuna is expanded. I give floristic details of species occurrence and extend the discussion on habitat preference of ii herbaceous ferns and tree ferns. Several indicator taxa associated with soil nutrient conditions related to parent material type were identified. By contrasting compositional and abundance patterns of similar groups with differing dispersal strategies in highly diverse ecosystems, this dissertation uncovers how distinctly terrestrial ferns and understory palms respond to soil nutrient limitation gradient. Incorporating edaphic gradients with the phylogenetic framework of the fern communities, this research reinforces the importance of eco-evolutionary information to better understand the mechanisms of assembly that maintain diversity in tropical forests. INDEX WORDS: tropical rainforest, nutrient limitation, environmental gradients, pteridophytes, ferns, understory palms, floristics, composition turnover, functional traits Fortuna Forest Reserve, Panama iii Dedicated with all my affection to my mother Maria Edileuza Lira, and sisters Jamily Lira Viana and Carla Jesseany Lira Viana, to my grandparents Pedro Vieira Lira, Maria Lina Vilar Lira; in loving memory of my father Carlos José Rodrigues Viana, and my grandparents José da Costa Viana and Maria Rodrigues Viana. I also dedicate this thesis with all my gratitude to Ernesto Machado. iv ACKNOWLEDGEMENTS Foremost, I would like to express my sincere gratitude to my advisor, Prof. James Dalling, for his patience, guidance, inspiration, comprehension, enthusiasm, tremendous expertise, and for the continuous support of my Ph.D. studies and research. Throughout the research and writing process of this thesis, his advice helped me to thrive and become a skilled researcher. For my Ph.D. thesis, I could not have imagined finding a better mentor. In addition to my advisor, I would like to thank the research committee, Prof. Wendy Yang, Prof. Anthony Yannarell, and Prof. Jennifer Fraterrigo, for their support, informative comments, and challenging questions. My sincere thanks go to Dr. Robbin Moran (New York Botanical Garden); Prof. Surangi Punyasena, Dr. Carol Augspurger and Dr. Astrid Ferrer (Plant Biology Department – University of Illinois); Dr. Ben Turner (Smithsonian Tropical Research Institute); Dr. Alfonso García Piñeres (Universidad de Costa Rica); Pedro Caballero (Universidad Autónoma de Chiriquí); and the staff from the Herbarium of the Universidad de Panama. Each of them has kindly helped me along my PhD studies, either teaching me or supporting me, or helped me in a crucial step of my research. I thank my labmates in the Dalling Lab: Adriana Corrales and Kate Heineman that received me in the lab with enthusiasm, Jennifer Jones, Cecilia Prada, Zarluis Mijango, and Sierra Brown for reviewing my talks and for sharing happy moments in the professional and personal life. I wish to all my labmates, including current and new ones (Manuel Flores and Taylor McClellan), a successful academic experience during their studies. This research could have been more difficult if not for the help from Carlos Espinosa and Evidelio Garcia during fieldwork. Thank you for walking with me countless times in muddy, steep and treacherous conditions in Fortuna, only because I saw a beautiful fern. v I feel extremely grateful for the funding I received from Brazil’s agency National Council for Scientific and Technological Development (CNPq), Center for Latin American and Caribbean Studies, Torrey Botanical Society, Smithsonian Tropical Research Institute, Govindjee and Rajni Govindjee, the School of Integrative Biology and the Plant Biology Department of the University of Illinois at Urbana-Champaign. I appreciate the initial help from Dr. Maria Regina Barbosa (Universidade Federal da Paraíba), my first postgraduate mentor and Dr. Wayt Thomas (New York Botanical Garden) for the support, and both for encouraging me to pursue this path. I recognize the immeasurable value of all my friends Ingrid Romero, Dessireé Zerpa, Georgia Seyfried and Cecilia Prada I thank Ernesto Machado, for endless encouragement, patience and emotional support. I have immense gratitude for my family, for allowing me time away to pursue my career. vi TABLE OF CONTENTS CHAPTER 1: AN OVERVIEW OF FERNS ..................................................................................1 CHAPTER 2: COMPOSITIONAL VARIATION IN UNDERSTORY FERN AND PALM COMMUNITIES ALONG A SOIL FERTILITY AND RAINFALL GRADIENT IN A LOWER MONTANE TROPICAL FOREST ...............................................................................................22 CHAPTER 3: DIVERSITY AND ECOLOGY OF THE FERNS IN FORTUNA .......................58 CHAPTER 4: TRAIT DISPERSION AND PHYLOGENETIC RELATEDNESS IN A GUILD OF TROPICAL TERRESTRIAL FERNS .....................................................................................93 CHAPTER 5: CONCLUSIONS .................................................................................................133 APPENDIX A: SUPPLEMENTARY MATERIAL FOR CHAPTER 2 .....................................138 APPENDIX B: SUPPLEMENTARY MATERIAL FOR CHAPTER 3 .....................................146 APPENDIX C: SUPPLEMENTARY MATERIAL FOR CHAPTER 4 .....................................153 PLATES ......................................................................................................................................164 vii CHAPTER 1. AN OVERVIEW OF FERNS Prominent ecological and evolutionary aspects among pteridophytes Ferns and lycophytes, also known collectively as pteridophytes, are distinguished from other vascular plants by the absence of seeds, flowers and fruits. In addition, the identity of pteridophytes is also linked to their life cycle, in which the gametophyte is free from sporophyte regulation. Although sharing these features, lycophytes and ferns are two evolutionary lineages of spore bearing vascular plants organized in two distinct classes, Lycopodiopsida and Polypodiopsida, respectively. Together, the two classes comprise approximately 12,000 species widely spread across the globe (PPG I, 2016). Richness and abundance are particularly high in tropical, subtropical, and southern temperate forested ecosystems where lycophytes and ferns coexist, whereas in northern temperate forests, terrestrial ferns from basal groups seem to be scarce (Kessler et al., 2016; Moran, 2008). Pteridophytes were a pervasive component of the terrestrial flora before the angiosperm diversification during the Cretaceous period, which is thought to be associated with a drop in pteridophyte diversity (Schneider et al., 2004). Although most of the extant ferns are restricted to herbaceous forms, fossil records indicate that pteridophytes were once comprised of a broad range of diverse life forms, including rhizomatous herbs, epiphytic herbs, shrubs, vines and trees of diverse growth architectures (Rothwell, 1996). Climate changes occurring between the Paleozoic and Mesozoic periods were likely to have caused a substantial decrease of specialized groups like arborescent