This page intentionally left blank The Ecology of Freshwater Molluscs This book provides a comprehensive review of the ecology of freshwater bivalves and gastropods worldwide. It deals with the ecology of these species in its broadest sense, including diet, habitat and reproductive biology, emphasizing in particular the tremendous diversity of these freshwater invertebrates. Following on from these introductory themes, the author develops a new life history model that unifies them, and serves as a basis for reviews of their population and community ecology, including treatments of competiton, predation, para- sitism, and biogeography. Extensively referenced and providing a synthesis of work from the nineteenth century through to the present day, this book includes original analyses that seek to unify previous work into a coherent whole. It will appeal pri- marily to professional ecologists and evolutionary biologists, as well as to parasitologists. . is Associate Professor in the Department of Biology, College of Charleston, South Carolina. He has published widely on the ecology, evolution and genetics of molluscs for 20 years. The Ecology of Freshwater Molluscs ROBERT T. DILLON, JR Department of Biology,College of Charleston The Pitt Building, Trumpington Street, Cambridge, United Kingdom The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, New York, NY 10011-4211, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcón 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa http://www.cambridge.org © Cambridge University Press 2004 First published in printed format 2000 ISBN 0-511-03715-5 eBook (Adobe Reader) ISBN 0-521-35210-X hardback To the memory of my mother, Viola Turner Dillon Let every creature rise and bring Peculiar honours to our King; Angels descend with songs again, And earth repeat the loud Amen! Isaac Watts Contents Prefacepage xi 1Introduction1 2Bivalve autecology8 Feeding and digestion9 Digestive anatomy9 Particle retention11 Particle ingestion14 Assimilation16 Non-particulate dietary components19 Feeding period20 Habitat22 Unionoids22 Corbiculoids28 Dreissena34 Reproduction35 Unionoid gonochorism35 Unionoid hermaphroditism40 The unionoid larval stage42 Dreissena51 Corbiculoids52 Summary55 3Gastropod autecology57 Feeding and digestion58 Pulmonate diet and habitat61 Planorbidae61 Physidae66 Lymnaeidae70 Acroloxidae and Ancylidae76 viii · Contents Pulmonate reproduction79 Outcrossing79 Selfing83 Prosobranch diet and habitat85 Neritidae85 Pleuroceridae86 Pomatiopsidae91 Hydrobiidae94 Ampullariidae97 Viviparidae99 Bithyniidae100 Valvatidae101 Prosobranch reproduction101 Gonochorism101 Parthenogenesis109 Hermaphroditism113 Summary114 4Life history117 Genetics, environment, and demography118 Environment119 Population studies121 Reproductive effort123 Pisidium124 General survey126 The USR model131 Size at birth135 Pisidiids136 General survey138 Maturity140 Life cycle pattern150 Unionoids150 Corbiculoids and Dreissena154 Gastropods156 Modelling life cycles162 Summary168 5Population dynamics and competition171 Population growth172 Laboratory studies173 Field studies182 Contents · ix Crowding186 Population regulation191 Experimental approaches192 Perturbations199 Long-term trends202 Interspecific competition207 Natural situations207 Corbiculaand the North American bivalves210 Dreissenaand the unionids212 Helisomaduryi214 The ampullariids215 The thiarids219 Summary223 6Parasitism227 The digenetic trematodes228 Prevalence230 Consequences239 Schistosomes240 Fasciola245 Echinostomes247 Resistance248 Fasciola249 Schistosomes252 Echinostomes259 Population regulation262 Aspidogastrids268 Unionicolids269 Summary270 7Predation273 The malefactors274 Mammals274 Birds277 Turtles279 Salamanders281 Fish282 Crustaceans293 Insects295 Molluscs300 Leeches301 x · Contents Triclads304 Defences305 Behaviour305 Shell309 Life history314 Consequences316 Community composition316 Distribution318 Summary322 8Biogeography326 Environmental calcium327 Laboratory studies328 Field studies332 Area338 Isolation349 Other environmental factors352 Community composition354 Summary364 9Communities367 Terms and conditions368 Interspecific ecological overlap371 Gut content371 Feeding strategy377 Depth, temperature, and oxygen378 Substrate386 Current390 Models ofspecies distribution391 Models ofspecies similarity407 Models ofspecies abundance421 The assembly ofcommunities428 Summary431 Literature cited434 Index499 Preface In the twentieth century we have witnessed a general movement away from the study of organisms and toward the study of processes. The old faculties of zoology, botany, and microbiology have reorganized them- selves into departments of genetics, physiology, molecular biology, and ecology. Without question, there have been some benefits. For example, early in my career I remember my attention being called to a work by Brown and Davidson (1977) showing competition between such dis- parate groups as ants and rodents for seeds in ‘desert systems’. The impli- cation seems to have been that organismal biologists (entomologists, mammalogists, and botanists in this case) might each have missed impor- tant aspects of a phenomenon central to the composition of the desert biota. A biologist more broadly trained in ecological processes would seem to be required. But I feel certain that the authors of that particular work on desert ecology would join ecologists generally in acknowledging the founda- tion of entomology, mammalogy, and botany upon which their insight stood. Thus the declines we have witnessed in the fortunes of organismal biology in the last decades are ultimately quite troubling. This work is an unabashed advertisement for the study of organisms. In particular, here I offer the great diversity of freshwater molluscs as an untapped resource for the study of ecological questions of considerable generality and importance. It is my hope that this work will serve to open freshwater malacology to the larger community of ecologists worldwide, reviewing the known, and suggesting some directions for the future. Perhaps I can recruit a few collaborators. The following dear friends and insightful colleagues have, in some cases without their direct knowledge, exerted special in fluence upon me in this endeavour: Fred Benfield, Ken Brown, George Davis, Sally Dennis, Bob McMahon, Bob Ricklefs, and Amy Wethington. Others xii · Preface contributing time and intellect have included B. Dennis, P. Dustan, A. S. Harold, A. D. McCallum, B. Stiglitz, and G. T. Watters. David S. Brown read an early version of the manuscript to excellent effect. Many friends have been most forthcoming with data and access to their works both published and otherwise. Among these are K. Baba, A. G. Eversole, M. E. Havlik, D. M. Lodge, P. Jarne, J-G. Je, E. H. Jokinen, J. Monge-Najera, G. L. Mackie, G. Majoros, B. McKillop, R. W. Neck, T. D. Richardson, S. Szabo, C. R. Villalobos and S-K. Wu. D. J. Eernisse was a gracious host while I visited The University of Michigan libraries. I am especially indebted to S. A. Ahlstedt and I. J. Holopainen for fur- nishing large and valuable data sets, and to T. Roop for his computer skills. This work would not have been conceived without the love and support of my father, R. T. Dillon (Sr), for 20 years the best field assis- tant a boy could have. It has come to fruition only through even larger measures of the same two commodities from my wife, Shary, and my children, Ginny and Bryan. I’ll be home soon. 1 · Introduction The invasion launched by elements of the molluscan army upon fresh water has aptly been characterized as ‘desultory’ (Deaton and Greenberg 1991). Dozens of offensives seem to have taken place, sporadically timed over hundreds of millions of years, some ultimately carrying the works, others now witnessed only in the fossil record. The diversity of fresh- water molluscs is vast. Yet it is my thesis here that in their interactions with the environment and with each other, freshwater molluscs share enough similarities that some intellectual profit may be gained by exam- ining their ecology together. We might begin with a brief overview of the forces (Tables 1.1 and 1.2). The larger freshwater bivalves belong to the order Unionoidea, an ancient group of six families whose fossil record extends to the Devonian period. They are distinguished by a parasitic larval stage that is unique among the Bivalvia. The best-known families are the Margaritiferidae and the highly diverse Unionidae, both worldwide. The hyriids of Neotropical and Australian regions are less studied, while the Neotrop- ical mycetopodids, and the Ethiopian mutelids and etheriids, remain rather obscure. The smaller infaunal freshwater bivalves belong to the superfamily Corbiculoidea. This is a somewhat younger group, generally hermaph- roditic, with a fossil record beginning in the Jurassic and Cretaceous periods. The two corbiculoid families may represent separate invasions of fresh water (Park and O’Foighil 1998). Bivalves of the worldwide family Pisidiidae hold developing embryos for extended periods, ultimately releasing juveniles quite large in relation to their own bodies. The family Corbiculidae (restricted to old world tropics and subtropics until recently) release juveniles as smaller ‘pediveligers’. The Dreissenoidea is much less diverse than the Unionoidea or Corbiculoidea, the freshwater Dreissena being restricted to the Ponto-Caspian basins until recently. 2 · Introduction Table 1.1. A