Mechanisms Altering Exotic-Native Proportions in Plant Communities, and Impacts on Biodiversity and Ecosystems Leanne M

Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2013 Mechanisms altering exotic-native proportions in plant communities, and impacts on biodiversity and ecosystems Leanne M. Martin Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Biology Commons, and the Ecology and Evolutionary Biology Commons Recommended Citation Martin, Leanne M., "Mechanisms altering exotic-native proportions in plant communities, and impacts on biodiversity and ecosystems" (2013). Graduate Theses and Dissertations. 13303. https://lib.dr.iastate.edu/etd/13303 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Mechanisms altering exotic-native proportions in plant communities, and impacts on biodiversity and ecosystems by Leanne Michelle Martin A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Ecology and Evolutionary Biology Program of Study Committee: Brian J. Wilsey, Major Professor Sue Fairbanks Mary Harris Kirk Moloney Lisa Schulte Moore Iowa State University Ames, Iowa 2013 Copyright © Leanne Michelle Martin, 2013. All rights reserved. ii TABLE OF CONTENTS ABSTRACT iv CHAPTER 1. GENERAL INTRODUCTION 1 Dissertation Organization 7 References 9 CHAPTER 2. ASSEMBLY HISTORY ALTERS ALPHA AND BETA DIVERSITY, EXOTIC-NATIVE PROPORTIONS AND FUNCTIONING OF RESTORED PRAIRIE PLANT COMMUNITIES 15 Summary 15 Introduction 16 Materials and Methods 20 Results 26 Discussion 28 Acknowledgments 33 References 33 Supporting Information 43 CHAPTER 3. NATIVE SPECIES SEED ADDITIONS DO NOT CAUSE RESTORED PRAIRIE PLANT COMMUNITIES TO SHIFT FROM EXOTIC TO NATIVE STATES 45 Abstract 45 Introduction 46 Methods 48 Results 52 Discussion 53 Acknowledgments 56 Literature Cited 56 Supplementary Information 62 CHAPTER 4. BIODIVERSITY, PHOTOSYNTHETIC MODE, AND ECOSYSTEM SERVICES DIFFER BETWEEN NATIVE AND NOVEL ECOSYSTEMS 64 Abstract 64 Introduction 65 Materials and Methods 68 Results 75 Discussion 78 Acknowledgments 81 References 82 Online Resources 93 iii CHAPTER 5. PHENOLOGY AND NICHE PARTITIONING DIFFER BETWEEN NOVEL, EXOTIC- AND NATIVE-DOMINATED GRASSLANDS FOR PLANTS, BUT NOT FOR POLLINATORS 104 Abstract 104 Introduction 105 Methods 108 Results 113 Discussion 114 Acknowledgments 120 References 120 CHAPTER 6. GENERAL CONCLUSIONS 129 Summary 129 Future Research 131 Conclusions 134 References 135 ACKNOWLEDGEMENTS 137 iv ABSTRACT Understanding the causes and consequences of variation in species composition and diversity across space and time are basic questions in ecology that have strong implications for conservation and restoration. However, exotic-dominated ecosystems, in which species with potentially novel interactions occur, are altering the context in which we ask these questions. The work presented here tested for the first time whether 1) experimental community assembly history manipulations of the seeds of native species could alter species composition, diversity, and ecosystem measures in grasslands dominated by exotic species, and 2) whether exotic- dominated grasslands differ from native-dominated grasslands for multiple aspects of diversity and ecosystems across a latitudinal gradient and over a growing season. Differences in community assembly history resulted in either a more diverse, native state when native seeds were added in spring and without priority effects, or a low-diversity, exotic-dominated state when seeds were added in summer or with priority effects. The exotic-dominated state persisted for eight years, even with an experimental seed addition of native species, and the differences resulted in altered productivity and fire temperatures. Across the latitudinal gradient, exotic- dominated grasslands had lower levels of species diversity, but had higher levels of tissue N concentrations. Productivity in exotic grasslands was higher in the south but it was lower in the north, where biomass peaked earlier in the growing season than in native grasslands. Exotic- dominated grasslands were more strongly dominated by C 4 species in the south and C 3 species in the north, with a strong shift at 34-36 degrees, implying that an important measure of functional diversity was altered. Experimental results from a common garden experiment indicated that the difference in functional diversity was at least partially caused by species themselves. Pollinator communities did not differ between exotic and native grasslands, implying that other factors may v be important in structuring pollinator communities. Overall, results from this work imply that novel ecosystems should be considered when testing ecological theory in the field and when considering impacts of species on ecosystems. Managing grasslands and restorations for high levels of species diversity will require understanding the impacts of multiple exotic species. 1 CHAPTER 1: GENERAL INTRODUCTION High levels of variation in species composition and biodiversity exist across space and time on Earth. Some of the most basic questions in community and ecosystem ecology, therefore, try to address 1) the causes of variation in species composition and biodiversity across space and time and 2) the ecosystem consequences of this variation (e.g., Whittaker 1960, Anderson et al. 2011). A deeper understanding of these basic questions could have important implications for how we conserve and restore the variation of biota on Earth, and how those activities will affect species diversity, the functional diversity that is related to ecosystem functioning, and ecosystem services, or “the benefits people receive from ecosystems” (Millennium Ecosystem Assessement 2005). For example, mounting evidence suggests that higher amounts of biodiversity can provide higher levels of ecosystem services and functioning over longer time frames and across many places (e.g., Naeem et al. 1994, Isbell et al. 2011). Declines in biodiversity worldwide, therefore, generate a need to understand what generates and maintains biodiversity, its patterns of variation, and its role in sustaining ecosystem functioning and services (Naeem et al. 1994, Symstad et al. 2003, Gamfeldt et al. 2008). Ecologists, however, now face the important task of addressing these important questions in ecosystems that are highly altered by anthropogenic activities. Specifically, little work has been conducted on how both biodiversity and variation in species composition arise in the now common condition of exotic-dominated ecosystems, in which multiple exotic species with novel ecological interactions occur. Consequently, we have little knowledge of how novel ecosystems in general impact ecosystem functioning and services. Therefore, we need to address the most basic questions in community and ecosystem ecology in the context of novel ecosystems. 2 Biodiversity is composed of multiple spatial components, including alpha, beta, and gamma diversity. All of these components contribute to global biodiversity, and understanding how they are generated at high levels may help conserve current and restore lost species diversity. Alpha, or local, diversity is important because it is the scale at which species interactions of plants and many resulting ecosystem functions occur (Martin et al. 2005, Wilsey 2010). Mechanisms generating beta diversity, defined as turnover or variation in species composition across space, have been of theoretical and practical interest to ecologists for half a century (Whittaker 1960, Gering 2003, Martin et al. 2005, Wilsey et al. 2005, Legendre et al. 2009, Chase 2010, Anderson et al. 2011). Theoretically, beta diversity allows us to link alpha (local) and regional (gamma) diversity (Wilsey 2010). High levels of beta diversity can also reduce rates of extinction in fragmented landscapes to levels below those predicted by island biogeography theory, and conservation biologists increasingly recognize that conserving beta diversity across many sites may sometimes preserve more species than will conserving one large site (Gering 2003, Wilsey et al. 2005). However, despite its importance to ecosystems, we lack an understanding of the relative importance of alternative mechanisms generating beta diversity, as well as the generation of community composition and diversity of the local communities (alpha diversity) therein. Several different processes can generate beta diversity, but the relative importance of these processes remains poorly understood (Chase 2003). Abiotic conditions, dispersal limitation, and differences in community assembly history are all mechanisms by which beta diversity can be generated. First, species could sort deterministically according to differences in abiotic environments, such as soil type or amount of precipitation (Whittaker 1960). Second, dispersal limitation could generate beta diversity because all species would not be found 3 everywhere if dispersal were limited. Thus, differences in community composition across space could emerge (Mouquet and Loreau 2003). Finally, the theory of community assembly history predicts that the order and timing of arrival of species after a disturbance can impact species diversity and community composition,

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