Ecological Studies, Vol. 161

Transcription

1 Ecological Studies, Vol. 161 Analysis and Synthesis Edited by I.T. Baldwin, Jena, Germany M.M. Caldwell, Logan, USA G. Heldmaier, Marburg, Germany O.L. Lange, Wiirzburg, Germany H.A. Mooney, Stanford, USA E.-D. Schulze, Jena, Germany U. Sommer, Kiel, Germany

2 Ecological Studies Volumes published since 1996 are listed at the end ofthis book. Springer-Verlag Berlin Heidelberg GmbH

3 U. Sommer and B. Worm (Eds.) Competition and Coexistence With 69 Figures, 5 in Color, and 2 Tables, Springer

4 Prof. Dr. Ulrich Sommer Universităt Kiel Institut fiir Meereskunde Diisternbrooker Weg Kiel Germany Dr. Boris Worm Universităt Kiel Institut fiir Meereskunde Diisternbrooker Weg Kiel Germany and Dalhousie University Biology Department Halifax, NS, B3H 4Jl Canada Cover illustration: Left photo (by B. Worm): Coexistence of numerous species at a relatively pristine rocky shore community in the Western Baltic Sea. Right photo (by C. Bostrom): Competitive exclusion of other species by the fast -growing filamentous alga Pilayella littoralis at a heavily eutrophied site in the Eastern Baltic. ISSN ISBN library of Congress Cataloging-in-Publication Data Competition and coexistence I U. Sommer and B. Worm (eds.). p. cm. -- (Ecological studies, ; v. 161) Includes bibliographical references (p. ). ISBN ISBN (ebook) DOI / Competition (Biology) 2. Spatial ecology. I. Sommer, illrich, II. Worm, B. (Boris), III. Series. QH546.3.C '3--dc This work is subject to copyright. AlI rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permissions for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. Springer-Verlag Berlin Heidelberg 2002 Originally published by Springer-Verlag Berlin Heide1berg New York in 2002 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover design: design & production GmbH, Heidelberg Typesetting: Kroner, Heidelberg SPIN /

5 Preface The question "Why are there so many species?" has puzzled ecologist for a long time. Initially, an academic question, it has gained practical interest by the recent awareness of global biodiversity loss. Species diversity in local ecosystems has always been discussed in relation to the problem of competitive exclusion and the apparent contradiction between the competitive exclusion principle and the overwhelming richness of species found in nature. Competition as a mechanism structuring ecological communities has never been uncontroversial. Not only its importance but even its existence have been debated. On the one extreme, some ecologists have taken competition for granted and have used it as an explanation by default if the distribution of a species was more restricted than could be explained by physiology and dispersal history. For decades, competition has been a core mechanism behind popular concepts like ecological niche, succession, limiting similarity, and character displacement, among others. For some, competition has almost become synonymous with the Darwinian "struggle for existence", although simple plausibility should tell us that organisms have to struggle against much more than competitors, e.g. predators, parasites, pathogens, and environmental harshness. In contrast to this obvious overestimation, other ecologists have denied competition almost completely and considered it as an artifact of overly simplified models and experimental systems. This view was fueled by field studies indicating that competitive exclusion occurs less frequently in nature than predicted by models. Similar to the "competitionists", the "non-competitionists" have grossly overstated their case by ignoring simple plausibility. For example, why should anybody care for weeding a garden, if weeds have no competitive impact on garden plants? The real question that has emerged from decades of competition research is not whether or not competition was important, but which factors may prevent exclusion and loss of diversity despite intense competition. Like most of the major conceptual debates in ecology, also this debate could not be resolved as long as competition was simply inferred from patterns without directly analyzing the process of competitive displacements, and it was usually not too difficult to demonstrate that these patterns could have

6 VI Preface been caused by other processes as well. However, about three decades ago, more mechanistic experimental approaches to study competition were developed. The focus shifted from the search for patterns to the direct study of mechanisms that drive competitive interactions. Competitive success has been related to physiological, morphological, and life-form traits. For experimental systems, it has become possible to predict the winner of competition at the species level, and for natural systems this has become possible at least at the functional-type level. At the same time, these mechanistic approaches have led to answers to critical questions such as: - When is competition likely to occur? - When will competition lead to exclusion? - When will species coexist in spite of competition? We think that mechanistic research on competition-coexistence relationships has now reached a level of maturity, which calls for a summary and for an outlook to future challenges. For this summary, we have tried to bring together scientists active in modeling and experimental research who have provided major contributions to the enigma of coexistence in spite of competition. We would like to thank the authors and numerous reviewers of this volume as well as Springer-Verlag for their good cooperation, which was greatly appreciated. B.W. would like to thank Heike K. Lotze for her support, comments, and constructive criticism during the writing of this book. Kiel and Halifax, June 2002 Ulrich Sommer, Boris Worm

7 Contents 1 Introduction..... U. SOMMER, B. WORM 1.1 The Intellectual Debate Until Progress During the Last Decade Consequences for the Structure of the Book References Competition in Well-Mixed Habitats: From Competitive Exclusion to Competitive Chaos J. PAS SARGE, J. HUISMAN Introduction Competition for a Single Abiotic Resource Growth of a Single Species Competitive Interactions Competition for Light... Resource Storage... A Competition Model Based on Storage Storage in a Constant Environment.. Storage in a Variable Environment... Competition for a Single Biotic Resource Competition for Two Resources... Essential vs. Substitutable Resources Abiotic Resources Biotic Resources Competition for Three Resources Competitive Oscillations Competitive Chaos 2.7 Discussion References

8 VIII 3 Spatial Models of Competition C.A. KLAUSMEIER, D. TILMAN Contents Introduction Implicitly Spatial Models Single Species Model Two Species Models Conclusions Explicitly Spatial Models Interacting Particle Systems Point Process Models Pair Approximation and Moment Methods Reaction-Diffusion Models Comparing and Connecting Methods Underlying Spatial Heterogeneity Reaction-Diffusion Models Neighborhood Models Patch Models Conclusions Competition and Coexistence Future Directions More Work on Environmental Heterogeneity Combining Population and Ecosystem Perspectives Competition for Light Among Terrestrial Plants Evolution and Community Assembly References Competition and Coexistence in Plankton Communities 79 U.SOMMER 4.1 Introduction What Makes Plankton Competition Special? The Chemostat as an Experimental System Competition Experiments in Laboratory Microcosms Competition Experiments Under Constant Conditions Competition Experiments Under Temporally Variable Conditions Experiments in Field Mesocosms Tests of the Intermediate Disturbance Hypothesis by Field Data Herbivory and Diversity

9 Contents 4.6 The Role of Abundance and of Seasonality 4.7 Conclusions References IX Competition and Coexistence in Mobile Animals M.RITCHIE 5.1 Introduction Competition Among Mobile Animals Heterogeneity, Trade-Offs, and Competition 5.4 Scale and Heterogeneity 5.5 New Challenges References Competition, Coexistence and Diversity on Rocky Shores B. WORM, R. KAREZ Introduction What Distinguishes Rocky Shores from Other Communities? Evolution of Competition Theory Disruption of Competitive Exclusion: The Non-Equilibrium View Keystone Predation and Herbivory Strong vs. Weak Interactions The Effects of Physical Disturbance Coexistence Through Trade-Offs: The Equilibrium View The Resource-Ratio Hypothesis The Competitive Hierarchy Hypothesis Intransitive Competitive Networks Synthesis: Integrating the Effects of Competition, Consumption and Disturbance Consumer vs. Resource Control of Species Diversity An Integrated Competition Model Conclusion Unifying Competition Theory Competition, Coexistence and the Human Impact 157 References

10 x 7 Competition and Coexistence in Terrestrial Plants J. FARGIONE, D. TILMAN Contents Introduction Competition Resource Competition.... For Which Resources Do Species Compete? Physiological and Morphological Mechanisms of Competition.... Competition Summary Coexistence.... Neutral Theory of Biodiversity... Spatial Heterogeneity Competition-Colonization Trade-Off.... Temporal Variability.... Additional Trophic Levels.... Multiple Mechanisms of Coexistence and Limits to Diversity Coexistence Summary Conclusion References Synthesis: Back to Santa Rosalia, or No Wonder There Are So Many Species U. SOMMER, B. WORM Trade-Offs.... Disturbance, Predation and Competition.. The Spatial Dimension.... Self-Generated Heterogeneity.... Exclusive Resources Slow Exclusion Equilibrium vs. Non-Equilibrium Concepts The Semantic Problem The Scale Problem Future Challenges References Subject Index

11 Contributors JOSEPH FARGIONE Department of Ecology, Evolution and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul, Minnesota 55108, USA JEF HUISMAN Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Nieuwe Achtergracht 127,1018 WS Amsterdam, The Netherlands ROLF KAREZ Institut fur Meereskunde, Dusternbrooker Weg 20,24105 Kiel, Germany CHRISTOPHER A. KLAUSMEIER Department of Ecology and Evolutionary Biology, Guyot Hall, Princeton University, Princeton, New Jersey , USA JUTTA PASSARGE Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Nieuwe Achtergracht 127,1018 WS Amsterdam, The Netherlands MARK E. RITCHIE Department of Biology, Syracuse University, 130 College Place, Syracuse, New York , USA ULRICH SOMMER Institut fur Meereskunde, Dusternbrooker Weg 20, Kiel, Germany G. DAVID TILMAN McKnight Presidential University Chair in Ecology, Department of Ecology, Evolution and Behavior, University of Minnesota, 1987 Upper Buford Circle, st. Paul, Minnesota 55108, USA BORIS WORM Institut fur Meereskunde, Dusternbrooker Weg 20,24105 Kiel, Germany and Biology Department, Dalhousie University, Halifax, Nova Scotia, B3H 4Jl, Canada