BIOGEOGRAPHICAL AND EVOLUTIONARY PROCESSES INFLUENCING THE ASSEMBLY OF DECIDUOUS FOREST PLANT COMMUNITIES A Dissertation Presented to the Faculty of the Graduate School of Cornell University In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Jesse Lee Bellemare February 2010 © 2010 Jesse Lee Bellemare BIOGEOGRAPHICAL AND EVOLUTIONARY PROCESSES INFLUENCING THE ASSEMBLY OF DECIDUOUS FOREST PLANT COMMUNITIES Jesse Lee Bellemare, Ph. D. Cornell University 2010 Ecological theories of community assembly and structuring are often predicated on the overriding importance of small-scale processes operating over short periods of time. However, it is becoming increasingly clear that longer-term, larger-scale processes, such as migration and the diversification of evolutionary lineages, are also important factors influencing the distributions of individual species and the diversity of communities. In this investigation, I first examined the geographic distribution of an ant-dispersed forest plant, Jeffersonia diphylla, to assess whether the population structure of its geographic range in eastern North America exhibited patterns consistent with a distribution in equilibrium with the environment, or whether the species’ limited dispersal ability on local scales might lead to a non-equilibrial distribution at large geographic scales. Population size and performance did not decline toward the northern range edge and seed sowing within and beyond the species’ northeastern range edge demonstrated potentially suitable habitat up to 300 km outside its range. As such, the range of J. diphylla may not be in equilibrium with the environment and its restricted distribution in the Northeast may trace to limited post-glacial migration. These findings highlight the potential for limited migratory responses of plant species to climate change, raising the possibility that human intervention or ‘assisted colonization’ may be necessary to aid some species in tracking modern climate change. Finally, I investigated a prominent plant species richness gradient in the forests of the northeastern U.S. to determine whether long- term evolutionary processes, including phylogenetic niche conservatism, may contribute to high species richness in communities on fertile, calcium-rich soils. Analyses of the phylogenetic ‘depth’ of communities along this gradient demonstrated that species-rich communities on calcium-rich soils included a disproportionate representation of Basal Angiosperm and Lower Eudicot angiosperm taxa. Parsimony- based reconstructions of the ancestral calcium niche of lineages present in the study also suggested a key role for fertile soils in the early diversification of angiosperms in Temperate Deciduous Forests. These patterns suggest that calcium-rich soils may be an ecological ‘zone of origin’ for angiosperms and highlight the potential for long- term evolutionary processes to influence species diversity in contemporary communities. BIOGRAPHICAL SKETCH Jesse L. Bellemare was born on September 30, 1976 in Northampton, Massachusetts, son of Susan and Robert E. Bellemare, Jr. He attended public schools in Whately and Deerfield, Massachusetts prior to enrolling at the University of Massachusetts in Amherst in 1994. While at the University of Massachusetts, Jesse worked as a research assistant to botanist Dr. Karen Searcy and ecologist Matt Hickler. Jesse graduated in 1998 with a B.S. in Biology and a minor in Portuguese. In 1999, Jesse began research in the Master of Forest Science (MFS) program at Harvard University’s Harvard Forest in Petersham, Massachusetts, where he was advised by Dr. David Foster and Glenn Motzkin. For his thesis research, Jesse developed a project investigating environmental and historical factors influencing the distribution of Rich Mesic Forest plant species in western Massachusetts. Following the completion of the MFS degree in 2002, Jesse was accepted to the doctoral program in Ecology and Evolutionary Biology at Cornell University in Ithaca, New York, where he was co-advised by Drs. Monica Geber and Peter Marks. While at Cornell University, Jesse developed research projects focusing on plant migration and community assembly. In July 2006, he married Sarah Ahearn, of Greenfield, Massachusetts. In 2009, Jesse completed his Ph.D. research at Cornell University and began work as a faculty member in the Department of Biological Sciences at Smith College in Northampton, Massachusetts. iii to Sarah iv ACKNOWLEDGMENTS I would like to thank J. M. Baskin and C. C. Baskin, P. Cantino, K. Clay, S. Gardescu, and D. J. Leopold for assistance in locating several of the J. diphylla populations on which research described in Chapters 1 and 2 is based. In addition, the collections of the University of Kentucky Herbarium, Ohio State University Herbarium, New York State Museum Herbarium, and the Bailey Hortorium at Cornell University provided an invaluable resource for documenting the distribution of J. diphylla in the study areas investigated. In New York, C. Sheviak at the NYS Museum Herbarium provided access to the region-level map of extant and historical J. diphylla population occurrences on which Figure 2.1 was based; F. Cowett provided invaluable assistance in creating Figure 2.1. Access to J. diphylla population sites was provided by Raven Run Nature Sanctuary in Lexington, KY, the Indiana University Research and Teaching Forest near Bloomington, IN, and the New York chapter of The Nature Conservancy, as well as a number of private landowners. My research on the geographic range and range edges of J. diphylla was supported in part by a grant from the Andrew W. Mellon Foundation (no. 49900645). The manuscript on which Chapter 3 is based was greatly improved by comments from M.A. Geber, P.L. Marks, A.A. Agrawal, D. Moeller, J.C. Svenning, M. Vellend, K. Verheyen, M. Hermy, P. Somers, D. Sax, H. Tomimatsu and D.R. Foster. Study sites for the research described in Chapter 4 were located with the assistance of C. Cogbill, C. Canham, P.L. Marks, and T. Fahey, among others. The following public agencies and private organizations provided access to some of the research sites described in Chapter 4: Massachusetts Department of Conservation and Recreation, Vermont Department of Forests, Parks and Recreation, New York Department of Environmental Conservation, Albany Pine Bush Preserve Commission, The Nature Conservancy, USDA Forest Service, Black v Rock Forest Consortium, Cary Institute of Ecosystem Studies, and the Huyck Preserve; several private landowners also provided access to important study sites. The research described in Chapter 4 was supported in part by a grant from the Kieckhefer Adirondack Fellowship program, administered by the Cornell University College of Agricultural and Life Sciences. Numerous discussions with the Geber, Marks, and Agrawal lab groups at Cornell University provided valuable feedback on the development and interpretation of the research projects described here. vi TABLE OF CONTENTS Biographical Sketch iii Dedication iv Acknowledgements v List of Figures viii List of Tables ix Chapter 1. The Geographic Range of Jeffersonia diphylla, Part I: 1 Population Structure and Individual Performance in Range Center versus Range Edge Populations Chapter 2. The Geographic Range of Jeffersonia diphylla, Part II: Seed 45 Dispersal Limits the Local Distribution and Geographic Range of an Ant-Dispersed Forest Plant Species Appendix to Chapter 2 86 Chapter 3. The Prospects for ‘Assisted Colonization’ in the Temperate 94 Deciduous Forest Biome: Will Endemic Plant Species Require Human Intervention to Survive Climate Change? Chapter 4. Proximate Environmental Correlates and Ultimate Evolutionary 130 Sources of Species Richness Gradients in Temperate Deciduous Forests vii LIST OF FIGURES Figure 1.1. Geographic range of Jeffersonia diphylla in eastern North 8 America. Figure 2.1. Northeastern range edge of J. diphylla 55 Figure 2.2. Distribution of J. diphylla seedlings relative to adults 60 Figure 2.3. Jeffersonia diphylla seed germination with distance to adults 63 Figure 2.4. Germination of J. diphylla seeds in relation to soil bulk density 67 Figure 2.5. Germination of J. diphylla seeds in relation to soil pH 68 Figure 4.1. Locations of fifty vegetation plots in northeastern United States 138 Figure 4.2. Relationship between soil calcium and angiosperm species 144 richness Figure 4.3. Linear regression of natural log-transformed angiosperm 145 species richness and soil calcium content Figure 4.4. Relationship between native and exotic angiosperm species 147 richness in fifty 0.1 ha plots Figure 4.5. Relationship between Mean Community-Level Phylogenetic 150 Depth and soil calcium content in fifty 0.1 ha plots Figure 4.6. Relationship between Abundance Weighted Mean Phylogenetic 152 Depth and soil calcium content in fifty 0.1 ha plots Figure 4.7. Abundance-weighted soil calcium niche of angiosperm families 154 and inferred ancestral character states viii LIST OF TABLES Table 1.1. Locations and characteristics of 16 Jeffersonia diphylla 10 populations. Table 1.2. Characteristics, structure and performance of J. diphylla 18 populations near the species’ range center and northeastern range edge. Table 1.3. Individual-based performance of J. diphylla near its range center 21 and northeastern range edge. Table 1.4. Environmental characteristics of J. diphylla population sites. 23 Table 2.1. Abiotic characteristics of experimental sites within and beyond 64 the northeastern range edge of J. dihylla.