Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2003 Distribution, Spread, Activity Patterns, and Foraging Behaviors of the Introduced Ant Pheidole Obscurithorax in the Southeastern United States Shonna R. Storz Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] THE FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES DISTRIBUTION, SPREAD, ACTIVITY PATTERNS, AND FORAGING BEHAVIORS OF THE INTRODUCED ANT PHEIDOLE OBSCURITHORAX IN THE SOUTHEASTERN UNITED STATES By SHONNA R. STORZ A Thesis submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Masters of Science Degree Awarded: Summer Semester, 2003 The members of the Committee approve the thesis of Shonna R. Storz defended on June 13, 2003 Walter R. Tschinkel Professor Directing Thesis Thomas E. Miller Committee Member Laura R. Keller Committee Member Approved: Thomas M. Roberts, Chairperson, Department of Biological Science Donald Foss, Dean, College of Arts and Science The Office of Graduate Studies has verified and approved the above named committee members. ii I’d like to dedicate this work to my husband, Brian L. Storz, for his never-ending belief in me and for his ability to always make me laugh. iii ACKNOWLEDGMENTS This study would not have been possible without the support and field assistance of B. L. Storz who spent an immeasurable amount of time with me driving across the southeast and collecting data. I’d like to thank my advisor, W. R. Tschinkel, for his not-so-gentle prodding and demand for progress, countless hours of help on Statistica, comments and suggestions on manuscripts and grants, and for his brilliant insights into what it all means. Thanks to my committee members, T. E. Miller and L. R. Keller for gentle prodding and valuable discussion. Thanks also to T. E. Miller for lending me numerous items from his lab. Thanks to my lab mates, K. L. Haight, A. S. Mikheyev, J. N. Seal, and C. R. Smith, for helpful discussions and assistance, and for making my time spent in the lab enjoyable; they are a great bunch of guys. Thanks to N. Plowes for getting me started with ant identifications and making it seem less daunting. Special thanks to M. Deyrup for assistance with ant species identifications while at the Ant Course; without his help I would likely have taken two more years to complete this research. I am thankful for spending my tenure in graduate school at FSU; my fellow graduate students and the faculty have made my experience very rewarding and enjoyable. FSU undergraduates T. Ballinger, N. Dix, M. Fisher, R. Moore, and T. Rhoades helped with specimen sorting and counting. I appreciate the hard work of two dedicated high school students, M. Ponce and S. Mendenhall, in the FSU Young Scholars Program who helped monitor activity at nests. I thank the more than 86,000 ants who passed from this world in the name of science. This project was iv partially funded by the Theodore Roosevelt Memorial Fund through the American Museum of Natural History and by the Department of Biological Science at Florida State University. v TABLE OF CONTENTS List of Tables ………………………………………………………………………… vii List of Figures ………………………………………………………………………... viii Abstract ………………………………………………………………………... x INTRODUCTION ..……………………………………………………………………… 1 1. DISTRIBUTION, SPREAD, AND ECOLOGICAL ASSOCIATIONS OF THE INTRODUCED ANT PHEIDOLE OBSCURITHORAX NAVES IN THE SOUTHEASTERN UNITED STATES ….………………………………………….... 3 2. ACTIVITY RHYTHMS AND FORAGING TACTICS OF THE INTRODUCED ANT PHEIDOLE OBSCURITHORAX NAVES ………………….………………….. 24 CONCLUSION …………………………………………..……………………………… 46 APPENDICES …….…………………………………………………………….……..… 48 REFERENCES …………………………………………………………………………… 53 BIOGRAPHICAL SKETCH ……………………………………………………………… 59 vi LIST OF TABLES Table 1.1 Site characteristics at sites with P. obscurithorax present and absent ……… 11 Table 1.2 Mann-Whitney U tests of the abundances of the six most common ant species at sites with P. obscurithorax present and absent …………………………..… 13 Table 1.3 Spearman rank order correlations of the abundances of the six most common ant species and P. obscurithorax nest density ……………………………… 13 Table 2.1 Means and 95% confidence intervals for the activities represented in figure 2.6. ……………………………………………………………………………… 34 Table 2.2 Repeated measures ANOVA table for foraging activity vs. bait type ..……. 38 vii LIST OF FIGURES Figure 1.1 Pheidole obscurithorax nest densities at each site plotted on a map of the southeastern United States …………………………………………………………….. 10 Figure 1.2 Collection frequencies of 19 bait-collected ant species …………………… 12 Figure 1.3 Rarefaction curve for southeast survey …………………………………… 14 Figure 1.4 Frequency of 26 ant species collected in pitfall traps …………………….. 15 Figure 1.5 Rarefaction curves for pitfall-trap study ………………………………….. 16 Figure 1.6 Relationship between Pheidole obscurithorax nest densities measured at 21 sites in Tallahassee in two years ………………………………………………… 17 Figure 1.7 Pheidole obscurithorax presence at each of 21 sites in Tallahassee, Florida, in two years …………………………………………………………………… 18 Figure 1.8 Pheidole obscurithorax nest densities at 21 sites in Tallahassee, Florida, in June 2002 …………………………………………………...………………….….. 19 Figure 2.1 Relationship between numbers of outbound and inbound foragers counted for two minutes ……………………………………………………………….. 28 Figure 2.2 Relationship between numbers of outbound and inbound nest-surface tenders counted for two minutes …………………………………………………….… 29 Figure 2.3 Relationship between total nest-surface tenders (outbound plus inbound nest-surface tenders) and total foragers (outbound plus inbound foragers) counted for two minutes ……………………………………………………………………..… 29 Figure 2.4 Relationships between time of day and ground temperature, total numbers of scouts, total numbers of foragers, and total numbers of nest-surface tenders …….. 31 Figure 2.5 Relationships between temperature and total numbers of scouts, total numbers of foragers, and total numbers of nest-surface tenders ……………………... 32 viii Figure 2.6 Relationship between time and ground temperature for each of three non-consecutive days of observation ……………………………………………..…… 33 Figure 2.7 Activity levels during three time periods plotted for each of three days …. 34 Figure 2.8 Proportions of workers that are minors performing three tasks ……..……. 35 Figure 2.9 Relationships between nest size and total numbers of scouts, total numbers of foragers, and total numbers of nest-surface tenders ………………..…….. 36 Figure 2.10 Typical relationship between time and the numbers of minors recruited to a bait counted during 10-second intervals ……………………………………..…… 37 Figure 2.11 Relationships between bait type (sm = small, lg = large, and lgst = large staked) and (a) time to remove bait (small and large only), (b) numbers of minors at the bait, and (c) numbers of majors at the bait ……………………..……. 40 ix ABSTRACT A field survey of the southeastern United States showed that Pheidole obscurithorax Naves, an ant introduced from South America, inhabits a 50-mile-wide band along the coast between Mobile, Alabama, and Tallahassee, Florida, and is continuing to increase its range. Evidence suggests that P. obscurithorax has spread mostly by diffusion by natural means. It coexists with the fire ant Solenopsis invicta Buren, appears to be part of a largely exotic community of ants that are tolerant of highly disturbed habitats, and seems to have little negative effect on the ant communities that it invades. In Tallahassee P. obscurithorax is rapidly spreading, and its nest density increased by a factor of 6.4 over a two-year period. P. obscurithorax summer activity patterns appear to be regulated by time of day rather than by temperature, but they do not appear to be active above ground at temperatures over 36˚C. Evidence suggests that foragers and nest-surface tenders are two separate populations and their activity is shifted in time relative to each other. The group prey retrieval tactics of P. obscurithorax related to prey size and mobility do not conform to predictions of central place foraging theory. x INTRODUCTION Natural ecosystems are disappearing at increasing rates, largely as a result of human disturbance. Along with the decline in natural habitats comes an increase in the amount of disturbed habitat such as open fields, urban areas, and roadsides. Documenting the communities that inhabit these ever increasing disturbed areas is an important step for conservation efforts. Human activity is also increasing the transfer rate of exotic species across the globe. Introduced species are often associated with disturbed habitat (Elton, 1958; Case, 1996), and many introduced species are thought to have negative effects on the communities that they invade. Invasion biology has historically focused on identifying common characteristics of highly invadable habitats as well as of successful invasive species in order to predict the outcome of invasions (Mooney and Drake, 1986; Vinson, 1986; Drake et al., 1989; Williams, 1994; Kareiva, 1996; Simberloff et al., 1997). While there has been progress in these areas, most research has focused on a small subset of introduced species. In order to better understand what characteristics make an invader successful, it is important to study a multitude of introduced species for comparisons. The ant, Pheidole obscurithorax, was introduced to the southeastern United States over 50 years ago (Naves 1985).