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Kp.QS&K THE BIOLOGY AND ECOLOGY OF CO-EXISTING SPECIES OF POLYCENTROPUS (TRICHOPTERA: POLYCENTROPODIDAE) IN A MICHIGAN BOG LAKE Alice J. Loesch Anderson A Dissertation Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY June 1979 il ABSTRACT An analysis of the life history, morphology, behavior and niche separation of coexisting species of Polycentropus caddisflies was performed on data collected over three years, 1976, 1977, and 1978. Collections were made from a bog lake to simplify the potential inter actions in the community. It was found from adult emergence data that three species were present, P_. interruptus, P_. remotus, and P. flavus, and that differing emergence time was adequate to separate the niche of only P_. flavus from the other two species. From analysis of the larval collection data, it was found that P^ interruptus dominated at stations which were in open water and free from vegetation, and that P_. remotus larvae dominated at stations close to shore, or in deep flocculent peat with vegetation. Further analysis of these differences showed that P_. remotus actually had two color types, one with spots on the parietal sclerites of the head, and one without, and that these two color types were separated by differential utilization of substrate. The light- colored P_. remotus utilized aquatic plants for net-building almost exclusively, thus influencing the difference in substrate utilization between P_. remotus and P_. interruptus considerably. In multivariate analyses of morphological characters and two environmental characters, it was found that P^. interruptus and P_. remotus were most clearly separated morphologically by a difference in setal pattern on the pronotum. P. interruptus, and the two color variants Ill of P_. remotus were separated most clearly by setal pattern on the pronotum, color pattern, and collection site. Collection site was important because transects of lily pads where hand picking was carried out were included in the analysis, and these were where the light color variant of P_. remotus were dominant. More data on physical and bio logical characteristics at different stations, and at different levels at each station need to be collected to distinguish the exact mechanism of separation between the dark color variant of P_. remotus and P^. inter- rùptus. From observational data, it is hypothesized that the P_. interruptus larvae utilized a deeper level within the detritus for net building and feeding as well as pupating than did the dark color variant of 1?. remotus. If 3?. interruptus were able to tolerate lower C>2 conditions found within the detritus, an interesting and unusual niche separating mechanism would be exemplified for lentie species. Scanning electron microscopy and gut analysis yielded inconclusive results. No differences were found in the net structure and attachment sites between species, but subtle differences in mouthpart structure were found. Gut analysis indicated that P_. interruptus was more exclusively a predator, and more often a predator of Chironomidae. P_. remotus was found to contain parts of Corrixidae, which were in young stages and plentiful at the time of collection of the larvae. IV ACKNOWLEDGEMENTS Many people helped and influenced me during the course of this project. I would like to acknowledge the able assistance of the following people in identifying insects, ecological problems, techniques, and statistical analyses: Dr. Todd Harris, Dr. G. Wiggins, Dr. R. Mackay, Dr. R. Stein, Dr. J. R. Voshell, Dr. R. Loesch, Dr. R. K. Tucker, Dr. R. C. Graves, Dr. R. Lowe, Dr. M. H. Hohn, Dr. W. Easterly, Di. R. E. Crang,, and Dr. G. Heberlein. I also wish to specially thank the following fellow graduate students and friends for encouragement and help: G. Bernon, B. Peck-Lewis, M. Bruno, R. Grimm, B. Walker, Dr. Win. Baxter, B. Silcox, H. Silcox, and all the Beaver Island crew, particularly P. Cupp. The intangible support of these and many others can only be thanked by my deepest appreciation, and the knowledge that I have come a long way, which would not have been possible without them. V TABLE OF CONTENTS Page INTRODUCTION..................... ................................ 1 Life History Importance in Ecological Studies............... 1 Bog Lakes: A Simpler System......... i...................... 3 Polycentropus Information in the Literature................. 4 Predation in Polycentropus.................................. 5 Niche Analysis..................... ......................... 7 Multivariate Statistical Analysis........................... 9 Summary..................................................... 10 MATERIALS AND METHODS............................................ 11 Field Location.............................................. 11 Field Methods........... 16 Sampling Methods........................................... 26 Laboratory Methods.......................................... 31 Behavioral Observations..................................... 35 RESULTS AND DISCUSSION........................................... 38 Barneys Lake and Greens Lake Comparison..................... 39 Adults of P_. interruptus, P_. remotus, and P^. flavus......... 41 Morphology of Polycentropus Adults.......................... 48 Niche Separation Based on Adult Emergence................... 49 Morphology of Polycentropus Larvae.......................... 49 Life History Analysis of P_. interruptus and P_. remotus...... 63 Statistical Analysis of Morphological and Ecological Data.... 64 Factor Analysis, Discriminant Analysis of Morphological and Ecological Variables........................ ................ 74 VI Page Scanning Electron Microscopy: Mouthpart Morphology........ 35 Scanning Electron Microscopy: Net Structure and Attachment Sites.................. 114 Feeding Behavior and Territorialism....................... 117 Feeding Behavior and Gut Analysis.... ...................... 123 Summary of Results.......... .............................. 130 Discussion of Evolution and Adaptation in Polycentropus.... 133 CONCLUS IONS............... .............. ........................ 139 LITERATURE CITED................................................ 144 Vll LIST OF TABLES Table Page 1. Families of Trichoptera found in Barneys Lake and Greens Lake, 1976...... .............. .................... ... 40 2. Numbers of Polycentropus larvae collected stations in Barneys Lake, 1976..................................... 42 3. Numbers of Polycentropus adults collected at stations in Greens Lake, 1976............ ............ .......... 44 4. Number of Polycentropus adults collected at stations in Greens Lake, 1977...................... ............... 46 5. Larval instars head capsule sizes for interruptus and P_. remotus............................................. 67 6. Station types and station numbers in GreensL ake, 1977.. 68 7. Numbers of Polycentropus species in four collection types.................................................. 73 8. Principal components analysis factor loadings.......... 78 9. Discriminant analysis DF coefficients.................. 83 10. Analysis two: Two taxonomic groups................ 84 10a. Density of Polycentropus larvae on artificial substrate 2 samplers (per cm )..................................... 121 11. Frequency of larvae in lily pad areas.................. 122 12. Average spacing distances of Polycentropus larvae.... , . 123 13. Types of food materials in gut of Polycentropus larvae.. 127 viii LIST OF FIGURES Figure Page 1. Outline map of Beaver Island with location of the two lakes sampled for Polycentropus: Greens Lake, an acid bog lake, and Barneys Lake, an alkaline bog lake. Inset map shows location of Beaver Island in northern Lake Michigan.......................................... 13 2. Greens Lake showing one depth contour, within which a depth of more than 1 m is reach. An extensive bog mat is also indicated...................................... 15 3. Barneys Lake showing a less extensive bog mat than Greens Lake. Survey sampling only was done at this lake.................................................. 18 4. Location of stations in Greens Lake, 1976 and 1977. Outlined areas in and around the lake are bog mats.... 20 5. Sampling types and times in 1976 and 1977. Artificial substrates were in place for five weeks. The beginning of the bar represents the set-up time; the end repre sents removal time. Other squares represent weeks during which sampling took place............. ......... 22 6. Detailed habitat map of "Boat Launch Bay" in Greens Lake. Extensive sampling along transects was done in May, 1978................... ......................... 25 7a. Artificial substrate samplers were constructed of small and medium cottage cheese containers cut into slats. Two 2x2 cm. squares of conservation webbing were placed inside................................ ................ 30 7b. Emergence trap samplers were constructed of plastic and screen cones with removable museum jar tops. These were submerged with a 5-7 cm. bubble of air left in the jar for emerging insects.................................. 30 8-1. Aerial photograph of Greens Lake "Boat Launch Bay" from the southeast. Note the areas of bog-building and vegetation............................................ 33 8-2. Aerial photograph of Greens Lake "Boat Launch Bay" from the northwest. Note the bog edge on the east side of the island (top of picture) 33 Figure Page 8- 3. Emergence