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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Explanation of the patterns of species abundances is important because it may help in understanding mechanisms structuring communities. A general conceptual model is proposed and examined as an alternative to previous propositions, which focused too narrowly on specific mechanisms. According to this model, viewing the structure of an environment as a nested hierarchy of habitat units provides a general mechanism sufficient to account for empirically established regularities in species abundances. Various biotic and abiotic factors can be considered as specific mechanisms sorting biological components into respective levels and compartments of the hierarchical structure of the environment. Because "sizes" of these compartments vary in a predictable way as a function of their position in the hierarchy, so should the abundances. The model may provide a conceptual framework that allows evaluation of the relative contributions of competition, predation, and other biological interactions. The operational and highly simplified version of the model uses spatial or temporal measures of ecological ranges of species to facilitate testing of the general model. The operational model makes three qualitative and quantitative predictions: (1) although the species display a continuous gradation of properties, the nested hierarchy of habitat units should lead to clustering of species at distinct levels;(2) generalists should be relatively more successful than specialists; (3) relative abundances of species should be predictable from their position in the hierarchical structure. An analysis of eight communities, including flatworms, aquatic insects, foraminiferans, rodents, and birds, supports these predictions. The clusters, or "breaks" in community structure, appear to be a new and possibly general property. Moreover, quantitative predictions of relative abundances for these communities are in surprisingly good agreement with the actual abundances. A hierarchical structure of the environment appears promising in accounting for some poorly explained community-level phenomena, such as correlation between the species range and abundance, and differences between abundance structures of communities in rigorous and less severe environments. The model is compatible with commonly observed as well as irregular patterns of distribution of species abundances, with high local abundance of some species, with differentiation of extinction probabilities, and with scale dependence of ecological phenomena.

An axiomatic system is proposed to improve identification, description, and analysis of complex ecological systems. Such systems are assumed to be organized and have structure. Organization is the complex of interactions and properties of structure that make the perpetuation of structure possible. An entity of structure is assumed to be composed of other entities. The term entity is adopted as a "primitive term." The concept of minimum interactive structure is imposed as an epistemological constraint on the structural infinity of real systems. Other terms are defined as either relations between entities of structure, derived properties resulting from combining such entities into entities of higher order, or conditions necessary for this assembly. Organization is a composite term and consists of complementarity, coordination, integration, and hierarchy. Evaluation of overall organization of an ecological entity appears theoretically possible through parametrization and quantification of these components of organization.Although ecology studies various entities, there is no general theory that might aid in the study of organization and principles by which ecological entities might be maintained (1). Here, we present a system of concepts for identifying ecological entities, analyzing their basic properties, and determining relations between entities. We propose a set of definitions that are necessary to build a precise conceptual framework. Addressing the problem of ecological units requires a theory of self-maintaining units, or a theory of organization.Our system differs from the current thrust in hierarchy theory. Our method uses axioms and our approach gives priority to ontology of ecological entities over epistemological concerns. Hierarchy theory identifies adequate scales for studying operationally defined ecological units. Such operationally defined units may be underlaid by hierarchically organized structures. The axiomatic approach may help to study this underlying structure. Thus, rather than searching for adequate scales to study operational ecological units driven by specific questions (2-5), we focus on the broader problem of organization of ecological systems.The objectives of this paper are to define organization, determine its component phenomena, and ultimately permit ecologists to abandon imprecise and unusable notions of "emergence." This exercise offers a basis for a general theory of organization of ecological systems and provides prerequisites for operational measurements of the components of organization. Such a theory will require much more development than a single paper can present. The system of notions will help identify ecological entities throughout all scales of organization; clarify distinctions between structure, function, and process; and indicate new research directions.We assume that basic ecological units are organized. Researchers may use other units, which may not be organized (sensu stricto), as a matter of convenience or to address specific questions. As a result of...

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