NATIVE MOSQUITOFISH AS BIOTIC RESISTANCE TO INVASION: PREDATION ON TWO NONINDIGENOUS POECILIIDS By KEVIN ALLEN THOMPSON A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2008 1 © 2008 Kevin Allen Thompson 2 To my Mom and Dad, for always encouraging my academic pursuits 3 ACKNOWLEDGMENTS I thank my chair, Dr. Jeffrey Hill for invaluable guidance and support throughout this research as well as my supervisory committee, Dr. Charles Cichra and Dr. Leo Nico for their roles as mentors. I thank Craig Watson, Dan Bury, Jonathan Foster, Scott Graves, Kathleen Hartman, Carlos Martinez, Debbie Pouder, and Amy Wood of the Tropical Aquaculture Lab for research support as well as Colin Calway of Happy Trails Aquatics for providing research animals. Gary Meffe provided information in this study and statistics consulting was provided by James Colee of the IFAS statistics consulting unit. I thank the faculty and students of the Department of Fisheries and Sciences as well as my friends and family that provided encouragement throughout this process. This research was supported in part by the University of Florida Institute of Food and Agricultural Sciences and a grant from the University of Florida School of Natural Resources and the Environment. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES...........................................................................................................................7 LIST OF FIGURES .........................................................................................................................8 ABSTRACT.....................................................................................................................................9 CHAPTER 1 INTRODUCTION ..................................................................................................................11 2 METHODS.............................................................................................................................19 Study Species..........................................................................................................................19 Mesocosm Overview ..............................................................................................................21 Experiment 1: Adult Introduction...........................................................................................22 Experiment 2: Stage-Structured Population ...........................................................................24 Experiment 3: Effects of Structural Complexity ....................................................................25 Experiment 4: Behavioral Measurements...............................................................................26 Analysis of Differing Stem Densities (4A) .....................................................................27 Analysis of Eastern Mosquitofish Presence (4B)............................................................27 Data Analysis..........................................................................................................................29 3 RESULTS...............................................................................................................................34 Experiment 1: Adult Introduction...........................................................................................34 Experiment 2: Stage-Structured Population ...........................................................................35 Experiment 3: Effects of Structural Complexity ....................................................................36 Experiment 4: Behavioral Measurements...............................................................................37 Analysis of Differing Stem Density (4A)........................................................................37 Day 1 ........................................................................................................................37 Day 3 ........................................................................................................................38 Analysis of Eastern Mosquitofish Presence (4B)............................................................39 Day 1 ........................................................................................................................39 Day 3 ........................................................................................................................39 4 DISCUSSION.........................................................................................................................50 5 APPENDIX A FRESHWATER FISH INTRODUCTIONS INTO FLORIDA..............................................61 B DATA SHOWN IN FIGURES FOR ALL EXPERIMENTS.................................................63 LIST OF REFERENCES...............................................................................................................66 BIOGRAPHICAL SKETCH .........................................................................................................73 6 LIST OF TABLES Table page 2-1 Overview of four different mesocosm experiments testing the effects of eastern mosquitofish (MF) predation on two nonindigenous poeciliids........................................32 3-1 Summary of caudal fin damage results for surviving adult variable platyfish in all experiments and treatments................................................................................................41 3-2 Summary of caudal fin damage results for surviving swordtails in all experiments and treatments. ...................................................................................................................42 A-1 Status of known freshwater fish species with maximum TL < 15cm introduced into the state of Florida. ............................................................................................................61 B-1 Survival data from all treatments of Experiments 1-3 for adults and juveniles of variable platyfish and swordtails. ......................................................................................63 B-2 Total attack data from all treatments of Experiments 4a and 4b for adults of variable platyfish and swordtails. ....................................................................................................64 B-3 Habitat use data from all treatments of Experiments 4a and 4b for adults of variable platyfish and swordtails. ....................................................................................................65 7 LIST OF FIGURES Figure page 2-1 Pictures of experimental tank and vegetation.. ..................................................................33 3-1 Results from Experiment 1.. ..............................................................................................43 3-2 Results from Experiment 2.. ..............................................................................................44 3-3 Results from Experiment 3.. ..............................................................................................45 3-4 Total attack results from Experiment 4a............................................................................46 3-5 Habitat use results from Experiment 4a.............................................................................47 3-6 Total attack results from Experiment 4b............................................................................48 3-7 Habitat use results from Experiment 4b.............................................................................49 8 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science NATIVE MOSQUITOFISH AS BIOTIC RESISTANCE TO INVASION: PREDATION ON TWO NONINDIGENOUS POECEILIIDS By Kevin Allen Thompson August 2008 Chair: Jeffrey E. Hill Major: Fisheries and Aquatic Sciences Widespread introduction of nonindigenous aquatic species by anthropogenic means has resulted in homogenization of worldwide faunas and some negative ecological and economic impacts. When a species is introduced outside of its natural range, various abiotic and biotic factors influence the ability of a nonindigenous species to successfully establish. Native predators can contribute to biotic resistance, the reduction of invasion success by the native biotic community. There have been numerous freshwater fish introductions into Florida, but few small-bodied freshwater species have maintained reproducing populations. Eastern mosquitofish Gambusia holbrooki, is a widespread and abundant native fish throughout the freshwater systems of Florida and is known to prey on small fish, and recent data have indicated that mosquitofish may consume fish similar to their own size. To test the hypothesis that eastern mosquitofish predation creates a biotic resistance to invasions of small-bodied freshwater fish, a series of mesocosm experiments were conducted using two nonindigenous species, variable platyfish Xiphophorus variatus and green swordtail X. hellerii. Both species are very common livebearers in the aquarium trade and aquacultured in Florida. Four experiments with both Xiphophorus species were conducted to test (1) the effect of eastern mosquitofish density on survival of nonindigenous adult fish following