1201
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1202
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Berlow EL, Neutel AM, Cohen JE, de Ruiter PC, Ebenman B, Emmerson M, Fox JW, Jansen VAA, Iwan Jones J, Kokkoris GD, Logofet DO, McKane AJ, Montoya JM, Petchey O. Interaction strengths in food webs: issues and opportunities. J Anim Ecol 2004. [DOI: 10.1111/j.0021-8790.2004.00833.x] [Citation(s) in RCA: 479] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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1203
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Emmerson MC, Raffaelli D. Predator-prey body size, interaction strength and the stability of a real food web. J Anim Ecol 2004. [DOI: 10.1111/j.0021-8790.2004.00818.x] [Citation(s) in RCA: 289] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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1204
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Madritch MD, Hunter MD. Phenotypic diversity and litter chemistry affect nutrient dynamics during litter decomposition in a two species mix. OIKOS 2004. [DOI: 10.1111/j.0030-1299.2004.12760.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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1205
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Jessup CM, Kassen R, Forde SE, Kerr B, Buckling A, Rainey PB, Bohannan BJM. Big questions, small worlds: microbial model systems in ecology. Trends Ecol Evol 2004; 19:189-97. [PMID: 16701253 DOI: 10.1016/j.tree.2004.01.008] [Citation(s) in RCA: 258] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Although many biologists have embraced microbial model systems as tools to address genetic and physiological questions, the explicit use of microbial communities as model systems in ecology has traditionally been more restricted. Here, we highlight recent studies that use laboratory-based microbial model systems to address ecological questions. Such studies have significantly advanced our understanding of processes that have proven difficult to study in field systems, including the genetic and biochemical underpinnings of traits involved in ecological interactions, and the ecological differences driving evolutionary change. It is the simplicity of microbial model systems that makes them such powerful tools for the study of ecology. Such simplicity enables the high degrees of experimental control and replication that are necessary to address many questions that are inaccessible through field observation or experimentation.
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Affiliation(s)
- Christine M Jessup
- Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA.
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1206
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Loladze I, Kuang Y, Elser JJ, Fagan WF. Competition and stoichiometry: coexistence of two predators on one prey. Theor Popul Biol 2004; 65:1-15. [PMID: 14642340 DOI: 10.1016/s0040-5809(03)00105-9] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The competitive exclusion principle (CEP) states that no equilibrium is possible if n species exploit fewer than n resources. This principle does not appear to hold in nature, where high biodiversity is commonly observed, even in seemingly homogenous habitats. Although various mechanisms, such as spatial heterogeneity or chaotic fluctuations, have been proposed to explain this coexistence, none of them invalidates this principle. Here we evaluate whether principles of ecological stoichiometry can contribute to the stable maintenance of biodiverse communities. Stoichiometric analysis recognizes that each organism is a mixture of multiple chemical elements such as carbon (C), nitrogen (N), and phosphorus (P) that are present in various proportions in organisms. We incorporate these principles into a standard predator-prey model to analyze competition between two predators on one autotrophic prey. The model tracks two essential elements, C and P, in each species. We show that a stable equilibrium is possible with two predators on this single prey. At this equilibrium both predators can be limited by the P content of the prey. The analysis suggests that chemical heterogeneity within and among species provides new mechanisms that can support species coexistence and that may be important in maintaining biodiversity.
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Affiliation(s)
- Irakli Loladze
- Department of Ecology & Evolutionary Biology, Princeton University, Princeton, NJ 08544-1003, USA.
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1207
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J. Morin P, McGrady-Steed J. Biodiversity and ecosystem functioning in aquatic microbial systems: a new analysis of temporal variation and species richness-predictability relations. OIKOS 2004. [DOI: 10.1111/j.0030-1299.2004.13256.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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1208
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HilleRisLambers R, Dieckmann U. Competition and predation in simple food webs: intermediately strong trade-offs maximize coexistence. Proc Biol Sci 2004; 270:2591-8. [PMID: 14728782 PMCID: PMC1691548 DOI: 10.1098/rspb.2003.2532] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Competition and predation are fundamental interactions structuring food webs. However, rather than always following these neat theoretical categories, mixed interactions are ubiquitous in nature. Of particular importance are omnivorous species, such as intra-guild predators that can both compete with and predate on their prey. Here, we examine trade-offs between competitive and predatory capacities by analysing the entire continuum of food web configurations existing between purely predator-prey and purely competitive interactions of two consumers subsisting on a single resource. Our results show that the range of conditions allowing for coexistence of the consumers is maximized at intermediately strong trade-offs. Even though coexistence under weak trade-offs and under very strong trade-offs is also possible, it occurs under much more restrictive conditions. We explain these findings by an intricate interplay between energy acquisition and interaction strength.
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Affiliation(s)
- Reinier HilleRisLambers
- Section of Population Biology, University of Amsterdam, Kruislaan 320, 1098SM Amsterdam, The Netherlands.
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1209
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Kolasa J, Li BL. Removing the confounding effect of habitat specialization reveals the stabilizing contribution of diversity to species variability. Proc Biol Sci 2004; 270 Suppl 2:S198-201. [PMID: 14667382 PMCID: PMC1809961 DOI: 10.1098/rsbl.2003.0059] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Earlier studies have found that diversity, S, stabilizes the relative variability of combined biomass or abundance of species making up a community. However, the effect of S on variability of constituent species has been elusive. We hypothesize that the proportion of specialists increases with S and, because specialists are more variable, this shift in composition will mask the stabilizing effect of S on populations of species making up a community. The test uses data on variability and ecological specialization of species in 49 natural rock pool invertebrate communities. Initial analyses produced inconclusive results similar to earlier studies. However, when variability owing to species' specialization was factored out, S reduced species' abundance variability, although not in all communities. Our study explains why the stabilizing effect of diversity on populations has not been found earlier.
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Affiliation(s)
- Jurek Kolasa
- Department of Biology, McMaster University, Hamilton, Ontario L8S 4K, Canada.
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1210
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1211
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Lefeuvre JC, Laffaille P, Feunteun E, Bouchard V, Radureau A. Biodiversity in salt marshes: from patrimonial value to ecosystem functioning. The case study of the Mont-Saint-Michel bay. C R Biol 2003; 326 Suppl 1:S125-31. [PMID: 14558461 DOI: 10.1016/s1631-0691(03)00049-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Until 1979, European salt marshes were known only through the inventories of fauna and especially of flora. On such criteria, the salt marshes of the Mont-Saint-Michel bay (France) were regarded as most significant of the French coasts. However, it took 20 years of research on the role of these wetlands of the estuaries-salt marsh systems to highlight the ecological, social and economic interest of this ecotone, between continental and marine systems, a long time considered as territory "without value", except for stock breeders or hunters.
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Affiliation(s)
- Jean-Claude Lefeuvre
- UMR 6653 EcoBio, Equipe d'animation de la zone atelier La Baie du Mont-Saint-Michel et ses bassins versants, Université de Rennes 1, Campus Beaulieu, 35042 Rennes, France
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1212
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Abstract
Pursuit of sustainable development requires a systems approach to the design of industrial product and service systems. Although many business enterprises have adopted sustainability goals, the actual development of sustainable systems remains challenging because of the broad range of economic, environmental and social factors that need to be considered across the system life cycle. Traditional systems engineering practices try to anticipate and resist disruptions but may be vulnerable to unforeseen factors. An alternative is to design systems with inherent "resilience" bytaking advantage of fundamental properties such as diversity, efficiency, adaptability, and cohesion. Previous work on sustainable design has focused largely upon ecological efficiency improvements. For example, companies have found that reducing material and energy intensity and converting wastes into valuable secondary products creates value for shareholders as well as for society at large. To encourage broader systems thinking, a design protocol is presented that involves the following steps: identifying system function and boundaries, establishing requirements, selecting appropriate technologies, developing a system design, evaluating anticipated performance, and devising a practical means for system deployment. The approach encourages explicit consideration of resilience in both engineered systems and the larger systems in which they are embedded.
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Affiliation(s)
- Joseph Fiksel
- Eco-Nomics LLC, 2351 Kensington Drive, Columbus, Ohio 43221, USA.
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1213
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Krause AE, Frank KA, Mason DM, Ulanowicz RE, Taylor WW. Compartments revealed in food-web structure. Nature 2003; 426:282-5. [PMID: 14628050 DOI: 10.1038/nature02115] [Citation(s) in RCA: 308] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2003] [Accepted: 10/10/2003] [Indexed: 11/08/2022]
Abstract
Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs. Compartments have been difficult to detect in empirical food webs because of incompatible approaches or insufficient methodological rigour. Here we show that a method for detecting compartments from the social networking science identified significant compartments in three of five complex, empirical food webs. Detection of compartments was influenced by food web resolution, such as interactions with weights. Because the method identifies compartmental boundaries in which interactions are concentrated, it is compatible with the definition of compartments. The method is rigorous because it maximizes an explicit function, identifies the number of non-overlapping compartments, assigns membership to compartments, and tests the statistical significance of the results. A graphical presentation reveals systemic relationships and taxa-specific positions as structured by compartments. From this graphic, we explore two scenarios of disturbance to develop a hypothesis for testing how compartmentalized interactions increase stability in food webs.
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Affiliation(s)
- Ann E Krause
- Department of Fisheries and Wildlife, Educational Psychology, and Special Education, Michigan State University, East Lansing, Michigan 48824, USA.
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1214
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Valone TJ, Hoffman CD. A mechanistic examination of diversity-stability relationships in annual plant communities. OIKOS 2003. [DOI: 10.1034/j.1600-0706.2003.12279.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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1215
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Stevens MHH, Petchey OL, Smouse PE. Stochastic relations between species richness and the variability of species composition. OIKOS 2003. [DOI: 10.1034/j.1600-0706.2003.12215.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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1216
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Wilson WG, Lundberg P, Vazquez DP, Shurin JB, Smith MD, Langford W, Gross KL, Mittelbach GG. Biodiversity and species interactions: extending Lotka-Volterra community theory. Ecol Lett 2003. [DOI: 10.1046/j.1461-0248.2003.00521.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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1217
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DeWoody YD, Swihart RK, Craig BA, Goheen JR. Diversity and Stability in Communities Structured by Asymmetric Resource Allocation. Am Nat 2003; 162:514-27. [PMID: 14582012 DOI: 10.1086/378049] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2002] [Accepted: 04/11/2003] [Indexed: 11/03/2022]
Affiliation(s)
- Yssa D DeWoody
- Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana 47907, USA.
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1218
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Abstract
Most textbook treatments imply, and almost all theoretical analyses assume, that mutualistic interactions take place between a single pair of interacting partner species. A major goal of this symposium is to broaden and shift this pairwise perspective and make it concordant with the emerging view that locally exclusive mutualisms between just two species are the exception and that many communities include guilds of mutualistic species on one or both sides of the interaction. Many pollination and seed-dispersal mutualisms have long been recognized as diffuse, but recent molecular analyses are revealing unrecognized partner diversity in mutualistic interactions previously thought to be locally species specific. Co-occurring species within a mutualist guild are unlikely to be ecologically equivalent in the way they locate, compete for, and/or reward partners, and so intraguild interactions have the potential to influence population dynamics and patterns of selection in species on both sides of the mutualistic interaction. To illustrate some of these potential complexities for population dynamics, I use simple path analytic models to show that positive pairwise interactions between mutualists do not necessarily translate into positive net interactions within a mutualism involving more than two species. For example, when there is intraguild competition for partners, or even for resources external to the mutualism, the presence of a lower-quality mutualist can negatively affect the partner population by reducing associations it can form with better mutualists. Variation in quality among potential partners is likely to place a premium on traits or behaviors that enhance association with better mutualists. More investigations are needed to determine how variation among interacting mutualists, with respect to characteristics such as longevity, dispersal capability, and competitive ability, influence population dynamics and selection in multispecies mutualisms.
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Affiliation(s)
- Maureen L Stanton
- Section of Evolution and Ecology and Center for Population Biology, University of California, Davis, California 95616, USA.
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1219
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1220
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1221
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Brose U, Williams RJ, Martinez ND. Comment on "Foraging adaptation and the relationship between food-web complexity and stability". Science 2003; 301:918; author reply 918. [PMID: 12920282 DOI: 10.1126/science.1085902] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Ulrich Brose
- Romberg Tiburon Center, Department of Biology, San Francisco State University, 3152 Paradise Drive, Tiburon, CA 94920, USA.
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1222
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1223
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DeVault TL, Rhodes Jr. OE, Shivik JA. Scavenging by vertebrates: behavioral, ecological, and evolutionary perspectives on an important energy transfer pathway in terrestrial ecosystems. OIKOS 2003. [DOI: 10.1034/j.1600-0706.2003.12378.x] [Citation(s) in RCA: 464] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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1224
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Fath BD, Cabezas H, Pawlowski CW. Regime changes in ecological systems: an information theory approach. J Theor Biol 2003; 222:517-30. [PMID: 12781750 DOI: 10.1016/s0022-5193(03)00067-5] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present our efforts at developing an ecological system index using information theory. Specifically, we derive an expression for Fisher Information based on sampling of the system trajectory as it evolves in the space defined by the state variables of the system, i.e. its state space. The Fisher Information index, as we have derived it, is a measure of system order, and captures the characteristic variation in speed and acceleration along the system's periodic steady-state trajectories. When calculated repeatedly over the system period, this index tracks steady states and transient behavior. We believe that such an index could be useful in detecting system 'flips' associated with a regime change, i.e. determining when systems are in a transient between one steady state and another. We illustrate the concepts using model ecosystems.
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Affiliation(s)
- Brian D Fath
- Biology Department, Towson University, Towson, MD 21252, USA
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1225
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1226
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Briones A, Raskin L. Diversity and dynamics of microbial communities in engineered environments and their implications for process stability. Curr Opin Biotechnol 2003; 14:270-6. [PMID: 12849779 DOI: 10.1016/s0958-1669(03)00065-x] [Citation(s) in RCA: 269] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The availability of molecular biological tools for studying microbial communities in bioreactors and other engineered systems has resulted in remarkable insights linking diversity and dynamics to process stability. As engineered systems are often more manageable than large-scale ecosystems, and because parallels between engineered environments and other ecosystems exist, the former can be used to elucidate some unresolved ecological issues. For example, the process stability of methanogenic bioreactors containing well-defined trophic groups appears to depend on the diversity of the functional groups within each trophic level as well as on how these functional groups complement each other. In addition to using engineered systems to study general ecological questions, microbial ecologists and environmental engineers need to investigate conditions, processes, and interactions in engineered environments in order to make the ecological engineering of bioreactor design and operation more practicable.
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Affiliation(s)
- Aurelio Briones
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, IL 61801, USA.
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1227
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Dambacher JM, Luh HK, Li HW, Rossignol PA. Qualitative stability and ambiguity in model ecosystems. Am Nat 2003; 161:876-88. [PMID: 12858273 DOI: 10.1086/367590] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2002] [Accepted: 09/04/2002] [Indexed: 11/03/2022]
Abstract
Qualitative analysis of stability in model ecosystems has previously been limited to determining whether a community matrix is sign stable or not with little analytical means to assess the impact of complexity on system stability. Systems are seen as either unconditionally or conditionally stable with little distinction and therefore much ambiguity in the likelihood of stability. First, we reexamine Hurwitz's principal theorem for stability and propose two "Hurwitz criteria" that address different aspects of instability: positive feedback and insufficient lower-level feedback. Second, we derive two qualitative metrics based on these criteria: weighted feedback (wF(n)) and weighted determinants (wDelta(n)). Third, we test the utility of these qualitative metrics through quantitative simulations in a random and evenly distributed parameter space in models of various sizes and complexities. Taken together they provide a practical means to assess the relative degree to which ambiguity has entered into calculations of stability as a result of system structure and complexity. From these metrics we identify two classes of models that may have significant relevance to system research and management. This work helps to resolve some of the impasse between theoretical and empirical discussions on the complexity and stability of natural communities.
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1228
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1229
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1230
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Alados C, Pueyo Y, Giner M, Navarro T, Escos J, Barroso F, Cabezudo B, Emlen J. Quantitative characterization of the regressive ecological succession by fractal analysis of plant spatial patterns. Ecol Modell 2003. [DOI: 10.1016/s0304-3800(02)00294-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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1231
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1232
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Dicke M, De Boer JG, Höfte M, Rocha-Granados MC. Mixed blends of herbivore-induced plant volatiles and foraging success of carnivorous arthropods. OIKOS 2003. [DOI: 10.1034/j.1600-0706.2003.12571.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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1233
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Bellwood DR, Hoey AS, Choat JH. Limited functional redundancy in high diversity systems: resilience and ecosystem function on coral reefs. Ecol Lett 2003. [DOI: 10.1046/j.1461-0248.2003.00432.x] [Citation(s) in RCA: 368] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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1234
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Sommer U, Sommer F, Santer B, Zöllner E, Jürgens K, Jamieson C, Boersma M, Gocke K. Daphnia versus copepod impact on summer phytoplankton: functional compensation at both trophic levels. Oecologia 2003; 135:639-47. [PMID: 16228259 DOI: 10.1007/s00442-003-1214-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2002] [Accepted: 02/10/2003] [Indexed: 11/26/2022]
Abstract
Here we report on a mesocom study performed to compare the top-down impact of microphagous and macrophagous zooplankton on phytoplankton. We exposed a species-rich, summer phytoplankton assemblage from the mesotrophic Lake Schöhsee (Germany) to logarithmically scaled abundance gradients of the microphagous cladoceran Daphnia hyalinaxgaleata and of a macrophagous copepod assemblage. Total phytoplankton biomass, chlorophyll a and primary production showed only a weak or even insignificant response to zooplankton density in both gradients. In contrast to the weak responses of bulk parameters, both zooplankton groups exerted a strong and contrasting influence on the phytoplankton species composition. The copepods suppressed large phytoplankton, while nanoplanktonic algae increased with increasing copepod density. Daphnia suppressed small algae, while larger species compensated in terms of biomass for the losses. Autotrophic picoplankton declined with zooplankton density in both gradients. Gelatinous, colonial algae were fostered by both zooplankton functional groups, while medium-sized (ca. 3,000 microm3), non-gelatinous algae were suppressed by both. The impact of a functionally mixed zooplankton assemblage became evident when Daphnia began to invade and grow in copepod mesocosms after ca. 10 days. Contrary to the impact of a single functional group, the combined impact of both zooplankton groups led to a substantial decline in total phytoplankton biomass.
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Affiliation(s)
- Ulrich Sommer
- Institut für Meereskunde, Düsternbrooker Weg 20, 24105, Kiel, Germany.
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1235
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Woodward G, Hildrew AG. The impact of a sit-and-wait predator: separating consumption and prey emigration. OIKOS 2003. [DOI: 10.1034/j.1600-0706.2002.11210.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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1236
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Kilpatrick AM, Ives AR. Species interactions can explain Taylor's power law for ecological time series. Nature 2003; 422:65-8. [PMID: 12621433 DOI: 10.1038/nature01471] [Citation(s) in RCA: 152] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2002] [Accepted: 01/28/2003] [Indexed: 11/10/2022]
Abstract
One of the few generalities in ecology, Taylor's power law, describes the species-specific relationship between the temporal or spatial variance of populations and their mean abundances. For populations experiencing constant per capita environmental variability, the regression of log variance versus log mean abundance gives a line with a slope of 2. Despite this expectation, most species have slopes of less than 2 (refs 2, 3-4), indicating that more abundant populations of a species are relatively less variable than expected on the basis of simple statistical grounds. What causes abundant populations to be less variable has received considerable attention, but an explanation for the generality of this pattern is still lacking. Here we suggest a novel explanation for the scaling of temporal variability in population abundances. Using stochastic simulation and analytical models, we demonstrate how negative interactions among species in a community can produce slopes of Taylor's power law of less than 2, like those observed in real data sets. This result provides an example in which the population dynamics of single species can be understood only in the context of interactions within an ecological community.
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Affiliation(s)
- A M Kilpatrick
- Department of Zoology, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
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1237
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Wilmers CC, Sinha S, Brede M. Examining the effects of species richness on community stability: an assembly model approach. OIKOS 2002. [DOI: 10.1034/j.1600-0706.2002.990218.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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1238
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Woodward G, Hildrew AG. Body-size determinants of niche overlap and intraguild predation within a complex food web. J Anim Ecol 2002. [DOI: 10.1046/j.1365-2656.2002.00669.x] [Citation(s) in RCA: 306] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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1239
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Lhomme JP, Winkel T. Diversity-stability relationships in community ecology: re-examination of the portfolio effect. Theor Popul Biol 2002; 62:271-9. [PMID: 12408946 DOI: 10.1006/tpbi.2002.1612] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In plant communities, the portfolio effect, also called "statistical averaging effect", expresses the fact that stability in aggregate community properties such as biomass productivity generally rises with species diversity, simply because of the statistical averaging of the fluctuations in species' properties. This paper essentially upgrades the previous formulations of the portfolio effect, first developed by Doak and collaborators and then by Tilman. It uses a theoretical approach based on simple statistical relationships and some simplifying assumptions proposed by these authors. The new formulation presented extends and improves the previous relationships in the sense that it takes into account simultaneously a varying scaling power of the variance, the interaction effect between species, the heterogeneity in species productivity and interspecies correlated responses to the environment. It appears that the simple statistical averaging, as inferred from this formulation, does not necessarily lead to a positive correlation between species diversity and community stability.
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1240
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Turgeon J, McPeek MA. Phylogeographic analysis of a recent radiation of Enallagma damselflies (Odonata: Coenagrionidae). Mol Ecol 2002; 11:1989-2001. [PMID: 12296943 DOI: 10.1046/j.1365-294x.2002.01580.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A phylogenetic hypothesis revealed two recent radiations among species of Enallagma damselflies, and extensive ecological work suggests that both adaptive and nonadaptive processes are involved in these radiations. We analysed the geographical pattern of genetic variability at 868 bp of mitochondrial DNA (mtDNA) among 283 individuals of 5 species displaying little ecological differentiation to identify the ancestral lineage, support their independent evolutionary trajectories and identify historical events and the underlying mechanism for one of these radiations. Nested clade analysis results clearly support a past event of range fragmentation in E. hageni. These Atlantic and Continental hageni races experienced distinct dispersal histories and still maintain nearly nonoverlapping ranges All four other species derive from the Continental hageni. Whereas three species endemic to the Atlantic coastal plain show little genetic variation, E. ebrium shared several haplotypes with the Continental hageni. Contrasting levels of genetic differentiation between E. hageni and E. ebrium in geographical areas associated with distinct events of E. hageni's recent history support the recent origin of this species. Altogether, our results are compatible with a process of radiation via divergence in mate recognition systems within the Continental hageni race following secondary contacts between putative refugial races.
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Affiliation(s)
- J Turgeon
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03755 USA.
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Williams RJ, Berlow EL, Dunne JA, Barabási AL, Martinez ND. Two degrees of separation in complex food webs. Proc Natl Acad Sci U S A 2002; 99:12913-6. [PMID: 12235367 PMCID: PMC130559 DOI: 10.1073/pnas.192448799] [Citation(s) in RCA: 256] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2002] [Accepted: 07/26/2002] [Indexed: 11/18/2022] Open
Abstract
Feeding relationships can cause invasions, extirpations, and population fluctuations of a species to dramatically affect other species within a variety of natural habitats. Empirical evidence suggests that such strong effects rarely propagate through food webs more than three links away from the initial perturbation. However, the size of these spheres of potential influence within complex communities is generally unknown. Here, we show for that species within large communities from a variety of aquatic and terrestrial ecosystems are on average two links apart, with >95% of species typically within three links of each other. Species are drawn even closer as network complexity and, more unexpectedly, species richness increase. Our findings are based on seven of the largest and most complex food webs available as well as a food-web model that extends the generality of the empirical results. These results indicate that the dynamics of species within ecosystems may be more highly interconnected and that biodiversity loss and species invasions may affect more species than previously thought.
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Affiliation(s)
- Richard J Williams
- Romberg Tiburon Center and Department of Biology, San Francisco State University, 3150 Paradise Drive, Tiburon, CA 94920, USA
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Troumbis AY, Galanidis A, Kokkoris GD. Components of short-term invasibility in experimental Mediterranean grasslands. OIKOS 2002. [DOI: 10.1034/j.1600-0706.2002.980206.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Carr MH, Anderson TW, Hixon MA. Biodiversity, population regulation, and the stability of coral-reef fish communities. Proc Natl Acad Sci U S A 2002; 99:11241-5. [PMID: 12177430 PMCID: PMC123240 DOI: 10.1073/pnas.162653499] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Unprecedented population declines and extinctions because of human activities, combined with a growing recognition that such losses affect the stability of ecosystems, underscore the need to better understand how populations persist naturally. We provide field experimental evidence that high biodiversity-in particular, the combined effects of predators and competitors-acts in a way that regulates the size of local fish populations within their coral-reef community. These results indicate that complex interactions among multiple species are necessary for the stability of a highly diverse community, and so forewarn that overexploiting such species may have cascading negative consequences for the entire system.
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Affiliation(s)
- Mark H Carr
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064, USA.
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Abstract
Biodiversity has acquired such a general meaning that people now find it difficult to pin down a precise sense for planning and policy-making aimed at biodiversity conservation. Because biodiversity is rooted in place, the task of conserving biodiversity should target places for conservation action; and because all places contain biodiversity, but not all places can be targeted for action, places have to be prioritized. What is needed for this is a measure of the extent to which biodiversity varies from place to place. We do not need a precise measure of biodiversity to prioritize places. Relative estimates of similarity or difference can be derived using partial measures, or what have come to be called biodiversity surrogates. Biodiversity surrogates are supposed to stand in for general biodiversity in planning applications. We distinguish between true surrogates, those that might truly stand in for general biodiversity, and estimator surrogates, which have true surrogates as their target variable. For example, species richness has traditionally been the estimator surrogate for the true surrogate, species diversity. But species richness does not capture the differences in composition between places; the essence of biodiversity. Another measure, called complementarity, explicitly captures the differences between places as we iterate the process of place prioritization, starting with an initial place. The relative concept of biodiversity built into the definition of complementarity has the level of precision needed to undertake conservation planning.
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Affiliation(s)
- Sahotra Sarkar
- Biodiversity and Biocultural Conservation Laboratory, Program in the History and Philosophy of Science, University of Texas at Austin, Austin, TX 78701, USA.
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Dunne JA, Williams RJ, Martinez ND. Network structure and biodiversity loss in food webs: robustness increases with connectance. Ecol Lett 2002. [DOI: 10.1046/j.1461-0248.2002.00354.x] [Citation(s) in RCA: 1096] [Impact Index Per Article: 49.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Solé RV, Alonso D, McKane A. Self-organized instability in complex ecosystems. Philos Trans R Soc Lond B Biol Sci 2002; 357:667-71. [PMID: 12079528 PMCID: PMC1692980 DOI: 10.1098/rstb.2001.0992] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Why are some ecosystems so rich, yet contain so many rare species? High species diversity, together with rarity, is a general trend in neotropical forests and coral reefs. However, the origin of such diversity and the consequences of food web complexity in both species abundances and temporal fluctuations are not well understood. Several regularities are observed in complex, multispecies ecosystems that suggest that these ecologies might be organized close to points of instability. We explore, in greater depth, a recent stochastic model of population dynamics that is shown to reproduce: (i) the scaling law linking species number and connectivity; (ii) the observed distributions of species abundance reported from field studies (showing long tails and thus a predominance of rare species); (iii) the complex fluctuations displayed by natural communities (including chaotic dynamics); and (iv) the species-area relations displayed by rainforest plots. It is conjectured that the conflict between the natural tendency towards higher diversity due to immigration, and the ecosystem level constraints derived from an increasing number of links, leaves the system poised at a critical boundary separating stable from unstable communities, where large fluctuations are expected to occur. We suggest that the patterns displayed by species-rich communities, including rarity, would result from such a spontaneous tendency towards instability.
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Affiliation(s)
- Ricard V Solé
- Complex Systems Research Group, Department of Physics, FEN-UPC Campus Nord B4, 08034 Barcelona, Spain.
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Solé RV, Montoya JM, Erwin DH. Recovery after mass extinction: evolutionary assembly in large-scale biosphere dynamics. Philos Trans R Soc Lond B Biol Sci 2002; 357:697-707. [PMID: 12079530 PMCID: PMC1692978 DOI: 10.1098/rstb.2001.0987] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Biotic recoveries following mass extinctions are characterized by a process in which whole ecologies are reconstructed from low-diversity systems, often characterized by opportunistic groups. The recovery process provides an unexpected window to ecosystem dynamics. In many aspects, recovery is very similar to ecological succession, but important differences are also apparently linked to the innovative patterns of niche construction observed in the fossil record. In this paper, we analyse the similarities and differences between ecological succession and evolutionary recovery to provide a preliminary ecological theory of recoveries. A simple evolutionary model with three trophic levels is presented, and its properties (closely resembling those observed in the fossil record) are compared with characteristic patterns of ecological response to disturbances in continuous models of three-level ecosystems.
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Affiliation(s)
- Ricard V Solé
- Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA.
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