Aquatic and Terrestrial Vegetation Influence
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AQUATIC AND TERRESTRIAL VEGETATION INFLUENCE LACUSTRINE DRAGONFLY (ORDER ODONATA) ASSEMBLAGES AT MULTIPLE LIFE STAGES By Alysa J. Remsburg A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Zoology) at the UNIVERSITY OF WISCONSIN – MADISON 2007 i ACKNOWLEDGMENTS Reflecting on the contributions of my colleagues and friends during my graduate studies gives me a strong sense of gratitude for the community of support that I have enjoyed. The people who surround and support me deserve more thanks than I can describe here. Friends and family have supported my graduate studies by generously accommodating my tight schedule and warmly offering encouragement throughout the process. Monica Turner guided my graduate studies in numerous ways. It was her trust in my abilities and willingness to learn about a new study organism that first made this research possible. She encouraged me to pursue the research questions that most interested and inspired me, although it meant charting territory that was new to both of us. Monica served as the ideal mentor for me by requiring clear communication, modeling an efficient and balanced work ethic, providing critical reviews, and listening compassionately. This research benefited from the expertise and generosity of outstanding Wisconsin ecologists. Members of my graduate research committee, Steve Carpenter, Claudio Gratton, Tony Ives, Bobbi Peckarsky, and Joy Zedler, all offered useful suggestions and critiques on experimental design, pressing research questions, and the manuscripts. Cecile Ane provided additional statistical advice and smiles. Bill Smith, Bob DuBois, and Robert Bohanan answered (or reassured me that I should try to answer) many questions about field methods, Odonata biology, and species identification. ii The kindness of my colleagues encouraged me to ask frequently for help or second opinions. The graduate students and post-doctoral researchers working with Monica have been great friends, reviewers, trouble-shooters, cooks, and sharers of table space. Coworkers at the Center for Limnology’s Trout Lake research station introduced me to aquatic communities and taught me how to launch a boat. Trout Lake station graduate students and staff not only shared their field equipment, data, and study sites, but also lured me away from the bug-picking table when I needed breaks. My decision to research odonates was made, in part, because I hoped it would attract and enable many undergraduate students to participate in the research. Neither the odonates nor the students have let me down. I enjoyed and benefited from working in the field with Jasmine Batten, Bridget Henning, Melissa Theis, and Phil Winkler. Students who diligently counted labial palp setae in the lab with me for species identification were Josh Estreen, Josie Iacarella, Debbie Hong, Anh Duong, and Cecilia Leugers. I thank each of them for helping to investigate the nitty-gritty details that underlie much of ecological research. Anders Olson, my outstanding field assistant and coauthor for the South Africa research, deserves many thanks. Anders helped design and conduct the field experiments on hot South African days (including re-hanging shade cloth after the ‘Cape Doctor’ blew through, fixing flat bike tires, and countless other efforts). On all of my research chapters, he offered detailed reviews and patiently listened to practice presentations. In addition to ecological contributions, the moral support and understanding he provided have ultimately helped me to reach this stage with peace of mind. We are blessed to have each other as coauthors in life. iii TABLE OF CONTENTS Abstract of dissertation vi I. Dissertation introduction 1 Literature Cited 4 II. Aquatic and terrestrial drivers of dragonfly (order Odonata) assemblages within and among north-temperate lakes 7 Abstract 7 Introduction 8 Methods Study Area 12 Aquatic and terrestrial drivers of Odonata larval density 13 Effects of riparian vegetation on adult abundance 18 Macrophyte effects on larval densities within sites 20 Results Aquatic and terrestrial drivers of Odonata larval density 22 Effects of riparian vegetation on adult abundance 24 Macrophyte effects on larval densities within sites 25 Discussion 26 Acknowledgments 31 Literature cited 32 Tables 42 Figures 54 iv Appendix 63 III. Gomphidae densities among three life stages: Oviposition site selection overrides post-recruitment spatial variation 66 Abstract 66 Introduction 67 Methods Study sites 72 Odonata surveys 72 Habitat variables 74 Data analysis 75 Results 78 Discussion 79 Acknowledgments 85 Literature Cited 86 Tables 95 Figures 101 Appendix 107 IV. Shade alone from invasive riparian trees reduces dragonfly abundance 108 Abstract 108 Introduction 109 Methods Study area 111 v Field methods 112 Statistical methods 114 Results 116 Discussion 117 Acknowledgments 119 Literature Cited 120 Figures 125 vi AQUATIC AND TERRESTRIAL VEGETATION INFLUENCE LACUSTRINE DRAGONFLY (ORDER ODONATA) ASSEMBLAGES AT MULTIPLE LIFE STAGES Alysa J. Remsburg Under the supervision of Professor Monica G. Turner At the University of Wisconsin-Madison Abstract Understanding how animals respond to habitat structure is a fundamental objective in ecology, but is particularly challenging when the animals require distinct habitats for different life stages. Although the majority of animals have spatially segregated life stages, research on habitat associations has generally been restricted to only one of the life stages. The relative importance of aquatic and terrestrial habitat structure is not well known for the order Odonata (dragonflies and damselflies). In northern Wisconsin (USA) lakes, housing development contributes to heterogeneity in riparian and littoral vegetation structure. I surveyed odonate larval assemblages at 41 sites across 17 lakes. Based on mixed-effects multiple regressions, model selection identified site-level littoral macrophyte abundance as a key driver of larval odonate species richness, and riparian wetland plant abundance as the best predictor for odonate density. Subsequent field experiments on larval predation and adult site selection helped explain these patterns. Additional surveys of the most abundant family (Gomphidae) at 22 lake sites indicated that local larval densities depend most on vii recruitment, which I estimated from adult densities during the previous year. Densities of emergent Gomphidae skins (exuviae) were most related to densities of the later-instar (second-year) larvae, further suggesting that larval survivorship and movement are less variable spatially than recruitment from the previous life stage. Field experiments conducted at two South African lakes demonstrated how riparian tree structures alter adult odonate abundances. Riparian shade reduced the abundance of odonates at these potential breeding sites. Perch structures, added to separate experimental plots, supported locally higher adult abundances, but dragonflies were not sensitive to perch structure density or diversity. Thus shade is the critical habitat component that should be addressed for odonate conservation in South Africa. Collectively, this research describes the role of habitat structure during multiple life stages. Field experiments demonstrate that generalist predators are sensitive to vegetation structure. The results suggest that riparian habitat selection by animals with complex life cycles can influence aquatic communities. 1 CHAPTER I Dissertation introduction Understanding how habitat structure influences animal distributions is an important challenge faced by both ecologists and land managers. Natural and anthropogenic disturbances frequently alter vegetation physical structure. Fires, pest outbreaks, and land-use changes all alter foliage cover. By contrast, invasive plant species can add dense foliage layers having different architectures from native plant communities. Vegetation structure directly affects animal densities by controlling physical habitat attributes: microclimate, visibility, and permeability. Identifying which habitat components are most infuential for animal diversity and density can facilitate effective habitat conservation or restoration. Researchers have long investigated how vegetation structure affects animal diversity. Several empirical studies suggest that species richness of arthropods (Lawton 1983, Gardner et al. 1995, Halaj et al. 2000, Langellotto and Denno 2004), birds (MacArthur and MacArthur 1961, Karr and Roth 1971), rodents (M'Closkey 1976), and lizards (Pianka 1967) increase with greater vegetation complexity. From a theoretical perspective, increasing diversity of habitat structure was one of several hypotheses proposed for the accumulation of more species with increased sampling area (Connor and McCoy 1979, McGuinness 1984). Vegetation structure can influence trophic interactions of Odonata species (dragonflies and damselflies) in water or on land (e.g., Crowder and Cooper 1982, Wissinger 1988, Diehl 1992). The > 5000 Odonata species worldwide each have a 2 unique spatial, temporal, and/or behavioral niche, but all members of this order are generalist predators. Adults and larvae both detect prey visually, although larvae also rely somewhat on mechanoreceptors (Gaino and Rebora 2001, Rebora et al. 2004, Olberg et al. 2005). Many larvae fall prey to fish or other odonates, including conspecifics (Wright 1946, Kennedy 1950, Larochelle 1977, Crowder and Cooper 1982, Johnson 1991, Momot 1995, Stoks and McPeek 2003).