The Restoration of Plant-Pollinator Mutualsims on a Reclaimed Strip-Mine
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The Restoration of Plant-Pollinator Mutualsims on a Reclaimed Strip-Mine Thesis Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Sarah Cusser, B.A. Graduate Programs in Evolution Ecology and Organismal Biology The Ohio State University 2012 Thesis Committee: Karen Goodell, Advisor Allison Snow Elizabeth Marschell Mary Gardiner Copyright by Sarah Cusser 2012 2 Abstract Plant-pollinator mutualisms are one of several functional relationships that must be reinstated to ensure the long-term success of habitat restoration projects. However, these mutualisms are not likely to reinstate themselves until the very particular resource requirements of pollinators have been met. By giving special attention to these requirements, habitat restoration projects are more likely to be successful in the long- term. I used network analysis to determine how aspects of the restoration effort itself influence the reestablishment and organization of plant-pollinator communities at an experimentally restored site in Central Ohio. Specifically, I investigate the influence of landscapes factors, floral diversity and the role of non-native plants on the structure and stability of plant-pollinator networks. I found that the diversity and distribution of floral resources affect the organization and stability of plant pollinator networks. Plots with high floral diversity far from remnant habitat compensated for loses in pollinator diversity by attracting generalized pollinators, which increase network redundancy and robustness. I also found that non-native plants play a central role in the structure of networks. I conclude that aspects of the restoration effort itself can be successfully tailored to incorporate the restoration of pollinators. ii 3 Dedication Dedicated to my beautiful bunnies Moose and Edie ii4i Acknowledgments Special thanks to Ryan Martyn, Reem Najjar, and Carol Brown for help in the field. To Chia Hau Lin, Amy McKinney, and Jessie Lanterman, as well as Joseph Pipia for technical advice and support. Thanks to Jenise Bauman for help coding in R and to Nicole Cavender, Shana Byrd, The Wilds staff for logistical help. iv5 Vita 2002…………………………………………………….…………….……..Pembroke Hill School 2006…………………………………………………….……………….…..B.A. Biology, Pomona College 2009- present……………………………………………………….……Graduate Teaching and Research Associate, Department of Evolution Ecology and Organismal Biology, The Ohio State University Fields of Study Major Field: Evolution Ecology and Organismal Biology v6 Table of Contents Abstract……………………………………………………………………………………..…iii Dedication………………………………………………………………………………….…iv Acknowledgements………..………………………………………………….…………v Vita……………………………………………………………………………………….………vi List of Tables…………………………………………………………………………….…..vii List of Figures…………….…………………………………………………….……………viii Chapter 1: The influence of floral distribution and richness on the restoration of robust plant-pollinator networks on a reclaimed strip mine. ……..…1 Chapter 2: The role of non-native plants in the restoration of plant-pollinator mutualisms in a constructed prairie. …………………………………29 References………………………………………………………………………………..…..49 Appendix A: Figures and Tables………………………………………………….…56 vi7 List of Tables Table 1.Comparison of Pollinator Communities……………………………..57 Table 2.Pollinator Generalization…………………………………………………..61 Table 3.Comparison Network Structure and Stability………………..…..62 Table 4. Floral Community Constituents……………………………………..…64-65 Table 5. Comparison of Centrality Indices…………………………………..…67 Table 6.Seed Mixtures………………………………………………………………..…70 Table 7. Centrality Indices……………………………………………………………..71-72 Table 8. Centrality Indices Continued…………………………………………….72-73 vii8 List of Figures Figure 1. Map of the Wilds……………………………………………………………56 Figure 2. Comparison of Pollinator Community …………………………….58 Figure 3. NMDS of High Floral Diversity Plots………………………………...59 Figure 4.NMDS of Low Floral Diversity Plots………………………………….60 Figure 5. Comparison of Network Structure and Stability……………...63 Figure 6. Schematic of Centrality Indices.…………………………………..…65 Figure 7.Comparison of Floral Community…………………………...…..…..66 Figure 8.Comparison of Centrality Indices……………………………………..68 Figure 9. Network Diagram……………………………………………………………69 vi9ii Chapter 1: The influence of floral distribution and richness on the restoration of robust plant-pollinator networks on a reclaimed strip mine. Introduction The primary goal of restoration is to return degraded ecosystems to pre- disturbance composition, structure, and function (Jordan et al. 1999). In principal, the composition and structure of a plant community can be restored relatively simply with the addition of native plants and the removal or control of invasive ones (Hobbs and Norton 1996, Ried 2009). However, how to restore functional relationships between plants and the other organisms they interact with in a community is less well established. Pollination is one of several functional relationships that must be reinstated for ecological restoration to be successful (Dixon 2009). Animal pollinators play a fundamental role in the maintenance of plant communities and contribute to the reproduction of somewhere between 70% and 90% of flowering plant species (Buchmann and Nabhan 1996, Kearns et al. 1998). Pollination mutualisms are not likely to reinstate themselves in degraded plant communities until the floral, nesting, and over-wintering resource requirements of pollinators have been met (Exeler et al. 2009, Roulston and Goodell 2011). By giving special attention to these habitat requirements, restoration is more likely to succeed in reinstating pollination services in plant communities (Forup and Memmott 2005, Forup et al. 2008, Menz et al. 2010). 110 When considering how to restore pollination service in plant communities, special care should be directed towards promoting pollinator richness (Murray et al. 2009, Potts et al. 2009). Pollinator richness has been shown to promote the reproductive output (Gomez et al. 2007, Hoehn et al. 2008), genetic resilience (Bowles et al. 1994, Linhart 1995, Wilcock and Neiland 2002), and community stability (Steffan- Dewenter et al. 2005, Steffan-Dewenter and Westphal 2008) of a variety of ecosystems. Closely linked to pollinator richness is the distribution and richness of floral resources (Steffan-Dewenter et al. 2001, Potts et al. 2003, Steffan-Dewenter 2003, Kremen et al. 2007). Potts et al. (2003) found that aspects of the floral community directly shape the composition of the pollinator communities they support. Consequently, to restore pollinator richness, ecologists must consider the distribution and richness of floral resources in a community. As pollinator communities are taxonomically and ecologically diverse, the distribution of floral resources can affect subsets of the community differently. Bees, an important group of pollinators, are central-place foragers and require suitable floral resources within the flight range of their nesting habitat (Michener 2000). Flight range varies with species and is correlated with body size (Greenleaf et al. 2007). In the case of some of the smallest bees, foraging is limited to within a couple of hundred meters of the nesting habitat (Zurbuchen et al. 2011). Thus, even relatively short distances can serve as a filter, eliminating potential pollinators from a community (Klein 2009, Vergara and Badano 2009, Carvalheiro et al. 2010). Situations where floral and nesting resources 11 do not overlap in space are considered “partial habitats” (Westrich 1996). Partial habitats contain only some of the needed resources of bees and function either as a nesting area or a foraging area, but not both. As a result, these habitats are not likely to support diverse bee communities (Matheson et al. 1996). Lepidopteran and Dipteran pollinator species on the other hand are not central place foragers, but rather they require specific ovipositing and larval substrates to be distributed throughout the habitat (Scott 1986, Schweiger et al. 2007). Most butterflies are specialised in there requirements, each species having particular needs in respect to temperature, humidity, larval food plants and adult food sources. Thus, butterfly and hoverfly communities respond to the distribution of floral resources very differently than bee communities (Steffan-Dewenter and Tscharntke 2000, Bergman et al. 2004, Krauss et al. 2005, Biesmeijer and Schaffers 2006, Ghazoul 2006, Schweiger et al. 2007, Jauker et al. 2009). Along with the distribution of floral resources in a community, the richness of resources can also directly influence pollinator richness. For example, Steffan-Dewenter et al. (1999) found a positive relationship between floral richness and abundance and pollinator richness. Similarly, Hegland et al. (2006) found that floral composition, in part, determines the richness and abundance of pollinators and the carrying capacity of the community. Ecologists are increasingly interested in understanding plant-pollinator interactions in a community context (Memmott 1999). Using network analysis allows 12 ecologists to transcend the narrow habitat and taxonomic boundaries of species-specific approaches, and allows for the development of overarching descriptions of diverse pollinator assemblages. The approach provides powerful quantitative tools to explore the influence of ecological factors on pollinator community structure and function (Dunne et al. 2002a, Bascompte 2007). In restoration, network statistics