Effects of Distance from Invasive Lythrum Salicaria On
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EFFECTS OF DISTANCE FROM INVASIVE LYTHRUM SALICARIA ON POLLINATOR VISITATION RATE AND REPRODUCTIVE SUCCESS IN NATIVE LYTHRUM ALATUM A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Anthony Steven Kinyo August, 2005 EFFECTS OF DISTANCE FROM INVASIVE LYTHRUM SALICARIA ON POLLINATOR VISITATION RATE AND REPRODUCTIVE SUCCESS IN NATIVE LYTHRUM ALATUM Anthony Kinyo Thesis Approved: Accepted: ______________________________ _____________________________ Advisor Department Chair Dr. Randall J. Mitchell ______________________________ ______________________________ Committee Member Dean of the College Dr. Stephen C. Weeks Dr. Charles B. Monroe ______________________________ ______________________________ Committee Member Dean of the Graduate School Dr. Peter H. Niewiarowski Dr. George R. Newkome ______________________________ Date ii ACKNOWLEDGEMENTS Numerous people have helped me during this project and I could not have completed the research without all of their generous support. I would like to begin by thanking Dr. Randy Mitchell for his constant enthusiasm and positive encouragement throughout the research process. Thanks Randy, you have helped me to become a better scientist and researcher and I appreciate all that you have done for me. I would also like to thank my committee members Dr. Steve Weeks and Dr. Peter Niewiarowski, who provided feedback and assistance throughout the research process. Next, I would like to the Cuyahoga Valley National Park, Summit County Metroparks, and Ottawa National Wildlife Refuge for allowing me to pursue my research on their land. The University of Akron Biology Department provided financial assistance. Robert Jean, Donald Webb, Martin Hauser, and John Ascher deserve thanks for helping me to identify the numerous pollinators collected during the experiment. I could not have grown my study plants without the expertise of Dr. Warren Stoutamire, whose knowledge of plant biology is unparalled. I would also like to thank Jeff Dunlap and Jesi Chaney for helping with the field work. Jesi, you helped me get through many trying times and I appreciate you listening to me talk about plants and pollinators incessantly. Last but definitely not least I would like to thank my parents Steve and Tammy Kinyo. Dad, your strong work ethic has inspired me many times and I hope that I can be as great a father to my children as iii you have been to me. Mom, your constant support has helped me to get through many tough times and I cannot thank you enough for being so caring and loving. Without both of you I wouldn’t be the person I am today, thanks. iv TABLE OF CONTENTS Page LIST OF TABLES………………………………………………………………...vii LIST OF FIGURES……………………………………………………………… viii CHAPTER I. INTRODUCTION....................................................................................................1 II. METHODS..............................................................................................................4 Study Species and Study System........................................................................4 Study Area and Experimental Design.................................................................5 Experimental Plants............................................................................................5 Insect Visitation..................................................................................................6 Reproductive Success.........................................................................................7 Germination........................................................................................................7 Statistical Analyses.............................................................................................8 III. RESULTS..............................................................................................................10 Characterizing the Pollinator Community.........................................................10 Overall Response...............................................................................................10 Visitation............................................................................................................10 Reproductive Success.........................................................................................12 v Germination........................................................................................................12 V. DISCUSSION..........................................................................................................17 VI. SUMMARY...........................................................................................................23 REFERENCES...............................................................................................................24 APPENDICES...............................................................................................................29 APPENDIX A. TOTAL VISITATION......................................................30 APPENDIX B. COMPLETE INDIVIDUAL ANOVAS FOR POLLINATOR VISITATION..........................................31 APPENDIX C. COMPLETE INDIVIDUAL ANOVAS FOR SEED SET AND GERMINATION .................................33 APPENDIX D. GROWTH AND CARE OF LYTHRUM SPECIES...........34 vi LIST OF TABLES Table Page 1. List of pollinator species identified foraging during experimental period.......13 2. MANOVA for four response variables.............................................................14 3. Individual ANOVAs..........................................................................................14 vii LIST OF FIGURES Figure Page 1. Experiment design...................................................................................9 2. Average visitation rate to Lythrum alatum as a function of distance from Lythrum salicaria..........................................................................15 3. Number of seeds per fruit in Lythrum alatum as a function of distance from Lythrum salicaria.............................................................16 4. Proportion of seeds sired by Lythrum alatum germinated as a function of distance from Lythrum salicaria.........................................................16 viii CHAPTER I INTRODUCTION Invasive non-native plants have received increasing attention recently due to the negative effects these exotic species can cause on native plants and animals (Mooney and Drake 1986, Usher 1988, Pimm et al. 1995, Pysek 1995). Aggressive invasive plants often create large monotypic stands with a corresponding decrease in overall plant and animal biodiversity (Thompson et al. 1987, White et al. 1997, Mullin 1998, Van Driesche et al. 2002). Many studies have shown that exotic plants often out-compete native plants for resources such as light (Weihe and Neely 1987), space (Rawinski and Malecki 1984), water (Delph 1986), and nutrients (Vitousek and Walker 1989). However, research into the possible reproductive competitive abilities of invasive plant species has not received as much study (but see Grabas and Laverty 1999, Brown and Mitchell 2001, Chittka and Schurkens 2001, Brown et al. 2002, Niovi Jones 2004). Waser (1983) defines competition for pollination as any interaction in which co- occurring plant species suffer reduced reproductive success because they share pollinators. This can happen in two ways. First, an invasive plant may reduce the number of pollinator visits to native plants by being more attractive to potential pollinators by having a larger floral display or nectar reward (Heinrich 1979). This decreased visitation rate can reduce pollen transfer between flowering plants and cause a 1 pollen deficiency such that plants are unable to set normal amounts of seed in the presence of the invasive plant species (Chittka and Schurkens 2001, Brown et al. 2002). Another mechanism by which there may be competition is through interspecific transfer of pollen (IPT). IPT can cause numerous problems for plants including a reduction in seed set due to chemical or physical interference induced by the foreign pollen (Thompson et al. 1981, Waser 1983, Brown et al. 2002), wasted maternal energy and effort by producing sterile hybrids (Waser 1978), and reduced male fitness due to the deposition and loss of pollen on flowers of a different species. Competition is not the only possible outcome when two flowering plant species interact. There may also be a facilitative effect where plant species A does not negatively affect the pollinator visitation and reproductive output of species B but it actually increases pollinator visitation and reproductive output of species B (Rathcke 1983). This can also be termed the “magnet species effect” (Thompson 1978). A magnet species may draw pollinators into an area by having a large floral reward, and facilitative interactions with co-occurring plants may arise if the benefits of having more pollinators are greater than any negative effects caused by reproductive interference (Johnson et al. 2003). Examples of facilitation are rare but a few studies (Thompson 1981, Laverty 1992, Johnson et al. 2003, Moeller 2004) have demonstrated a facilitative effect. Competitive and facilitative effects may even exist concurrently. There may be an aggregate facilitative affect bringing in more potential pollinators through increased attractiveness to an area and competition among individuals once pollinators are drawn into the area (Rathcke 1983). 2 Unlike vegetative