Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1989 Habitat Differentiation of Iris Fulva Ker Gawler, Iris Hexagona Walter, and Their yH brids. Bobby Dale Bennett Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Bennett, Bobby Dale, "Habitat Differentiation of Iris Fulva Ker Gawler, Iris Hexagona Walter, and Their yH brids." (1989). LSU Historical Dissertations and Theses. 4832. https://digitalcommons.lsu.edu/gradschool_disstheses/4832 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. INFORMATION TO USERS The most advanced technology has been used to photo­ graph and reproduce this manuscript from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are re­ produced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. These are also available as one exposure on a standard 35mm slide or as a 17" x 23" black and white photographic print for an additional charge. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. University Microfilms International A Bell & Howell Information Company 300 North Zeeb Road, Ann Arbor, Ml 48106-1346 USA 313/761-4700 800/521-0600 Order Number 9025202 Habitat differentiation ofIris fulva Ker Gawler, Iris hexagona Walter, and their hybrids Bennett, Bobby Dale, Ph.D. The Louisiana State University and Agricultural and Mechanical Col., 1989 UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106 HABITAT DIFFERENTIATION OF IRIS FULVA KER GAWLER, IRIS HEXAGONA WALTER, AND THEIR HYBRIDS A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in ■ The Department of Botany by Bobby D. Bennett A.S., Lake City Community College, 1971, A.A., Lake City Community College, 1972, B.S., Elmira College, 1977 December 1989 ACKNOWLEDGEMENTS This research would not have been possible without Florence Givens's invaluable assistance in locating and identifying populations of irises. I would like to thank the members of the Society for Louisiana Irises and The American Iris Society for their support and encouragement; in particular Joseph Mertzweiller and Marie Caillet. I am grateful to anonymous landowners in southern Louisiana for their permission to carry out this research on their property. I would like to extend my deep appreciation to Dr. James B. Grace for giving me the opportunity to work with him. I would also like to thank the members of my committee for their help and advice throughout this research. Finally, I would like to thank Karen Bennett for her unwavering support and sacrifice which enabled me to pursue a dream. i i PREFACE This dissertation is comprised of a series of experiments along with data on the growth characteristics of natural populations of two species of Louisiana Iris and their hybrids. Each chapter considers a particular factor that may affect the zonation of the two parental species and their hybrids. All chapters have been prepared in manuscript form for the purposes of publication. Table of Contents Page Abstract............................................ vi Introduction....................................... viii I. Niche Differentiation of Iris fvlvaf Iris, hexagona, and their Hybrids............................... 1 Abstract............ 2 Introduction.................................... 3 Materials and Methods.......................... 6 Results.......................................... 9 Discussion......................... ............. 12 Literature Cited................................ 16 II. Shade Tolerance and its Effect on Habitat Differentiation of Iris fulva. Iris hexagona. and their Hybrids.................................... 29 Abstract........................................ 30 Introduction................................... 31 Materials and Methods......................... 34 Results........................ ................ 37 Discussion....................................... 42 Literature Cited ............................... 48 III. Competition and its Effect on the Zonation of Iris fulva, I r i s hexagona/ and their Hybrids. 59 Abstract........................ ............... 60 Introduction.................... ................ 61 Materials and Methods........................... 63 Results........................................... 66 Discussion...... 67 Literature Cited.................................. 71 IV. Salt Tolerance and its Effect on the Zonation of Iris fulva. Iris hexagona. and their Hybrids.......... 81 Abstract......................................... 82 Introduction..................................... 84 Materials and Methods................ 85 Results................................ 88 Discussion....................................... 90 Literature Cited................................ 93 Summary.......... 100 V i t a .................................................... 104 V ABSTRACT Iris fulva and Iris hexaoona have overlapping geographic ranges in Louisiana; in areas of overlap hybrids are fairly common. Iris hexaoona occupies the borders of freshwater marshes of southern Louisiana while fulva can be found farther north along edges of natural levees, canals and swamps. An area of hybridization (hybrid zone) can be found where bayous penetrate the freshwater marsh. The objective of this research was to investigate some of the factors affecting habitat differentiation of fulva. I. hexaoona. and their natural hybrids ("Hybrid Purple" and "Hybrid Red”). A three year field study was conducted to determine the survival, growth, and reproductive characteristics of these taxa. Additionally, three greenhouse experiments were undertaken to examine shade tolerance, competitive ability, and salt tolerance. Results from field data found that hybrids had the highest survival rate while X l. fulva had the lowest. Iris hexaoona generally had the highest clonal growth rate. Hybrids were generally intermediate morphologically. Iris fulva and X*. hexagona were not significantly different in reproductive fitness and both had greater reproductive capacity than the hybrids. The shade tolerance experiment revealed X*. fulva to be more tolerant of shading than X*. hexaoona and the two hybrids. Iris hexaoona was greatly affected by all levels of shade. The competition experiment demonstrated that X±. fulva was a weaker competitor than either X*. hexagona or a natural hybrid. Iris hexagona and the hybrid were equally competitive. Results from the salt tolerance experiment indicated that X* fulva was less salt tolerant than X j. hexagona and the hybrids. In sum, results indicate that the taxa are segregated across a complex environmental gradient. It is hypothesized that X*. fulva with its greater shade tolerance, weaker competitive ability, lesser salt tolerance, and reduced clonal growth is displaced from the marsh by X*. hexagona and confined to the natural levee. Iris hexagona with its greater clonal growth, competitive ability, and salt tolerance but lesser shade tolerance appears to be best adapted to the freshwater marsh habitat. The hybrid zone appears to represent an ecotone between parental habitats where there may be a selective advantage for the hybrid taxon. INTRODUCTION For more than 50 years, the Louisiana iris has been included in discussions on the process of natural hybridization of plants. In 1931, J. K. Small published his "Botanical Interpretation of Iridaceous Plants of the Gulf States" in which he described 96 different species of Iris. Later taxonomic treatments reduced most of these species to the non-specific status with a large number of species being hybrids between Iris fulva and Iris hexaoona. This work was done primarily by Viosca, Riley, and Foster in the mid 1930’s. In 193 6, Edgar Anderson published a taxonomic treatment of the northern blue flags. Later in 194 9, in his classic book, Introoressive Hybridization, Anderson cited the Louisiana irises, .L_ fulva. I. hexaoona and their natural hybrids, as a paradigm of the process of introgressive hybridization. To date, the only ecological