THE SPATIAL ECOLOGY OF THE COMANCHE HARVESTER ANT POGONOMYRMEX COMANCHE (HYMENOPTERA: FORMICIDAE) by ANN BURGESS MAYO 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 Ann Burgess Mayo 2015 All Rights Reserved ii Dedication This work is respectfully dedicated to Joe Kuban (1950 – 2009) and Tony Burgess for the love of place. Acknowledgements My dissertation committee consisted of Dr. Esther Betrán (Supervising Professor), Drs. Jonathan Campbell, Paul Chippindale, Sophia Passy, and Walter Tschinkel (Florida State University), supervising committee members. I wish to thank them for their patience and guidance. I also want to thank Dr. Daniel Formanowicz, my original Supervising Professor, for input and feedback on this project as well as lab space and equipment and Dr. Raymond Jones, former manager of the Genomics Core Facility, for use of the dissecting microscope which was essential for ant identification. I wish to thank Joshua Been and Mitch Stepanovich of the UTA library for assistance with the ArcGIS program and Dr. Colin MacLeod of GIS in Ecology (Scotland) for assistance with the ArcGIS program, spatial ecology methods and spatial analysis. I wish to thank Dave General of the Museum of Natural History at the University of the Philippines, Dr. Robert Johnson of Arizona State University, Dr. Gail Kampmeier of the Illinois Natural History Survey, and Dr. James Trager of the Shaw Nature Reserve of the Missouri Botanical Garden for providing feedback on drafts of my proposal. I want to thank Dave General, Dr. Danny McDonald of Sam Houston State University, Dr. James Trager, and Chris Wilson of the University of North Texas for help with ant identification. I wish to thank the city of Fort Worth Parks and Community Services Department and the staff of the Fort Worth Nature Center and Refuge in Fort Worth, Texas for access to the Fort Worth Nature Center and Refuge and the Tandy Hills Natural Area. I especially wish to thank the Staff of the Fort Worth Nature Center for assistance on site. I wish to thank the city of Arlington Parks and Recreation Department in Arlington, Texas for access to the Southwest Nature Preserve and sharing geological and historical information about this site. iv I produced most of the maps using ArcGIS® software by Esri (Esri 2012). ArcGIS® and ArcMap™ are the intellectual property of Esri which I used under license, copyright © 2014 Esri, all rights reserved. (For more information about Esri® software, please visit www.esri.com.) I used their World Imagery Basemap in some maps. I wish to thank Dr. Stephen W. Taber (Saginaw Valley State University) and Texas A & M Press for permission to use Dr. Taber’s distribution map of P. comanche (Taber 1998). Finally, I wish to express gratitude to my family and the many friends, both professional and personal, who kept me going. I couldn’t have done it without all of you. Thank you! May 6, 2015 v Abstract THE SPATIAL ECOLOGY OF THE COMANCHE HARVESTER ANT POGONOMYRMEX COMANCHE (HYMENOPTERA: FORMICIDAE) Ann Burgess Mayo, PhD The University of Texas at Arlington, 2015 Supervising Professor: Esther Betrán Because of the diverse roles ants play, it has been suggested that ants may be ecosystem engineers and so, may be useful in monitoring ecosystem function and health. Because ant activities are localized around their nests, ant colony spatial patterns may have important ecological impacts on their own populations, other organisms and the environment. While some species in the harvester ant genus Pogonomyrmex are well studied, little is known about the Comanche harvester ant, Pogonomyrmex comanche. The goal of this study was to characterize the spatial pattern of local populations of P. comanche and investigate possible influences on this pattern. The examination of its local distribution and factors that influence that distribution may contribute to understanding P.comanche biogeography, population biology, ecological relationships and because of their movement between prairie and wooded habitats, may contribute to understanding some of the ecosystem processes important in the Cross Timbers Ecoregion. I hypothesized that the spatial pattern of P. comanche colonies is regular. Such a pattern implies the influence of competition and aggression among colonies as a driving vi force for population organization. I further hypothesized that the important influences on this spatial pattern include habitat characteristics, the presence of other ant species and colony interactions involving nestmate discrimination via aggression. I assessed the colony spatial pattern by mapping colonies in five areas from 2009 – 2013 and analyzing the pattern with a spatial point process, Ripley’s K function. To investigate habitat characteristics and other ant species, I assessed the ground active ant assemblage and environmental variables in 21 sites. I collected ants with pitfall traps in June, July, and August 2012 and measured environmental variables when the ants were collected. I calculated several diversity indices and used a redundancy analysis (RDA) to assess the differences in ant species among sites and ant response to environmental variables. Finally, I used a behavioral assay to test P. comanche’s ability to discern nestmates from non-nestmates in order to investigate aggression as a factor influencing the colony spatial pattern. I found that P. comanche colonies are randomly distributed at spatial scales up to 50 m, the ant assemblage differs among sites, species diversity is higher in prairie habitats compared to wooded habitats and P. comanche does discriminate nestmates from non-nestmates. However, I found no evidence that aggression is a significant factor in colony location or spatial pattern. vii Table of Contents Acknowledgements ........................................................................................................ iv Abstract ......................................................................................................................... vi List of Illustrations .......................................................................................................... xi List of Tables ................................................................................................................ xii Introduction .....................................................................................................1 Animal Spatial Patterns ...............................................................................................1 Seed Harvesting Ants of the Genus Pogonomyrmex ...................................................6 Pogonomyrmex comanche..........................................................................................9 Hypotheses to Test ...................................................................................................10 Study Site Description ...............................................................................................11 Plant Community ..................................................................................................12 Fort Worth Nature Center Sites (FWNC) ...............................................................13 Southwest Nature Preserve Site (SWNP) ..............................................................15 Tandy Hills Natural Area (THNA) ..........................................................................17 The Spatial Pattern of P. comanche Colonies................................................18 Introduction ...............................................................................................................18 Materials and Methods ..............................................................................................21 Field Methods .......................................................................................................21 Data Analysis Methods .........................................................................................24 Results .....................................................................................................................28 Population Stability ...............................................................................................29 Spatial Pattern ......................................................................................................30 Discussion ................................................................................................................36 Environmental and Species Impacts on P. comanche ...................................39 viii Introduction ...............................................................................................................39 Materials and Methods ..............................................................................................41 Field Methods .......................................................................................................41 Site Information ................................................................................................42 Environmental Variable Sampling .....................................................................43 Ant Sampling ....................................................................................................46 Data Analysis Methods .........................................................................................48 Ant Diversity