PROXIMATE BEHAVIORAL AND MORPHOLOGICAL MECHANISMS THAT MAY MEDIATE INTRAGUILD PREDATION STABILITY IN THE ANISOPTERA By BENJAMIN THOMAS ALLEN Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS AT ARLINGTON August 2015 Copyright © by Benjamin Thomas Allen 2015 All Rights Reserved ii Acknowledgments I would like to acknowledge Paul Chippindale and Matthew Walsh for taking over faculty advising and content editing of this dissertation after my former advisor retired. Without them, finishing would have been impossible. I would also like to thank Trey Fondon and Sophia Passy for their feedback and unflagging support, as well as for asking difficult questions that keep me on my toes. Esther Betrán and Eric Smith also deserve thanks and acknowledgement for being there when things got “interesting”. Jürgen Gadau, Jürgen Liebig, Rick Overson, Oliver Niehuis, Bert Hölldobler, Adam Siegel, Adam Dolezal, Kevin McGraw, Melissa Meadows and Dan Formanowicz also warrant mention for giving me the foundation in entomology and behavioral ecology necessary for this work to be completed. For helping keep me sane, I would also like to thank the following individuals; Ann Mayo, Patrick Stinson, Courtney Schmier-Davis, Becky Robinson, Michael Natishyn, Cameron Johnson, Garvin Anders, Jason Berman, Tyson Sueret, Julian Matson, Sean McFarlane, Russell Bruce and Michelle Davis, Jack Randy and Jennifer Lennox, Garrett Craft, Valerie Liege, Justin Morris, Robert and Laura Barker, Rachel and Neal Coleman, Björn Paulsen and Alva Lindval. Last but certainly not least, I would like to thank my immediate family for emotional support, and I must admit no small amount of financial assistance during a rough patch. My mother Marianne Allen, my brother Dustin Allen, my sister Emily Sutton and brother-in-law Jesse Sutton. They are all awesome. May 22, 2015 iii Abstract PROXIMATE BEHAVIORAL AND MORPHOLOGICAL MECHANISMS THAT MAY MEDIATE INTRAGUILD PREDATION STABILITY IN THE ANISOPTERA Benjamin Thomas Allen, PhD The University of Texas at Arlington, 2015 Supervising Professors: Paul T. Chippindale and Matthew R. Walsh Intraguild Predation (IGP) is a form of interference competition characterized by an intraguild predator consuming interspecific competitors, the intraguild prey. This interaction is extremely common in nature, but mechanistic and descriptive models usually predict that it is unstable with either the IG prey or IG predator becoming locally extinct, dependent on initial conditions. Only intermediate shared prey availability leads to IGP stability in these models, and this condition is not common. In this work, I used dragonfly nymphs to examine behavioral and morphological aspects of consumptive competition and predator avoidance that may act to stabilize IGP, particularly in systems with more than two predators. There are two primary hypotheses in this treatment. The first is that prey capture is morphologically mediated and that this leads to differences in diet composition that can promote IGP stability by allowing prey specialization. The second is that there is a behavioral tradeoff that leads to disproportionate feeding on competitively superior IG prey by an IG predator that may lead to IGP stability. This tradeoff was hypothesized to exist in terms of direct prey capture as well as movement and space use patterns. Both of these mechanisms were found to exist, with variation in mortality being explained by behavior, in spite of morphological defenses compensating for the lack of behavioral defenses in some species. While the effect of this possible mechanism on IGP stability was not directly examined, further long-term study should elucidate it. iv Table of Contents Acknowledgments…………………………………………………………………...……………………..iii Abstract………………………………………………………………………………………………….….iv List of Illustrations…..………...……………………………………………………………..…...….…....vii List of Tables..……………………………………………………………………………………..……….xi Chapter 1 Overall Question and Introduction to Dissertation .......................................................... 1 Intraguild Predation .................................................................................................................. 1 Chapter 2 Mouthparts and Prey Specialization ............................................................................... 6 Introduction ............................................................................................................................... 6 Methods and Results .............................................................................................................. 14 Discussion .............................................................................................................................. 40 Chapter 3 Prey Consumption, Diet Choice, and Predator Attraction. ........................................... 49 Introduction ............................................................................................................................. 49 Methods and Results .............................................................................................................. 53 Discussion .............................................................................................................................. 78 Chapter 4 Movement and Space Use ........................................................................................... 86 Introduction ............................................................................................................................. 86 Methods and Results .............................................................................................................. 90 Discussion ............................................................................................................................ 114 Chapter 5 Defensive Morphology ................................................................................................ 125 v Introduction ........................................................................................................................... 125 Methods and Results ............................................................................................................ 128 Discussion ............................................................................................................................ 151 Chapter 6 Conclusion and Prospectus ........................................................................................ 157 References .................................................................................................................................. 160 Biographical Information .............................................................................................................. 177 vi List of Illustrations Figure 1-1. Predicted forms of intraguild predation. ........................................................................ 1 Figure 2-1. Stages of predation and points of predatory failure for generalized predator-prey encounter. ........................................................................................................................................ 6 Figure 2-2. Variation in dragonfly nymph labial mask morphologies. .............................................. 8 Figure 2-3. Comparison of odonate labial masks and major morphological features. .................... 9 Figure 2-4. Head width and palpal setae by species..................................................................... 12 Figure 2-5. Head width and mental setae by species. .................................................................. 13 Figure 2-6. Initial capture success varies by prey type. ................................................................ 16 Figure 2-7. Prey escape success varies by prey type and odonate species. ............................... 17 Figure 2-8. Total prey capture success varies little by species and prey type. ............................. 18 Figure 2-9. Palpal lobe width positively affects Gammarus consumption. .................................... 20 Figure 2-10. Gammarus capture by Anax varies negatively with Anax head width. ..................... 21 Figure 2-11. Head width is positively related to total Gammarus capture success. ...................... 22 Figure 2-12. Capture of Daphia is positively related to palpal lobe length. ................................... 23 Figure 2-13. Total Daphnia capture success is positively related to strike speed. ....................... 24 Figure 2-14. Within-subjects initial prey capture was affected by both species and prey type. .... 27 Figure 2-15. Within-subjects prey escape varied by species and prey type. ................................ 29 Figure 2-16. Total prey capture success varies by prey and species. .......................................... 32 Figure 2-17. Strike speed differs between species and individuals shift strike speed. ................. 34 Figure 2-18. Anax head width negatively affects initial capture of Gammarus. ............................ 35 Figure 2-19. Total Gammarus capture success by Anax varies positively with strike speed........ 36 Figure 2-20. Gammarus capture success by non-Anax species varies with head width. ............. 37 Figure 2-21. Pooled Gammarus captures by non-Anax varies negatively with mental setae. ...... 38 Figure 2-22. Total Gammarus capture success by all non-Anax varies positively with