Underlying the diversity of life and the complexity of ecology is order that re ects the operation of fundamental physical and biological processes. Power laws describe empirical scaling relationships that are emergent quantitative features of biodiversity. These features are patterns of structure or dynamics that are self-similar or fractal-like over many orders of magnitude. Power laws allow extrapolation and prediction over a wide range of scales. Some appear to be universal, occurring in virtually all taxa of organisms and types of environments. They offer clues to underlying mechanisms that powerfully constrain biodiversity. We describe recent progress and future prospects for understanding the mechanisms that generate these power laws, and for explaining the diversity of species and complexity of ecosystems in terms of fundamental principles of physical and biological science.Keywords: biodiversity; ecology; fractal; power law; scaling; self-similarity BACKGROUNDThe Earth's surface and the living things that inhabit it are incredibly diverse. The Earth presents an abiotic template of geology, physical oceanography and limnology, and climate that varies on a scale from the largest oceans, continents, lakes and rivers to the tiniest microsites. Billions of individual organisms belonging to millions of species are distributed over the Earth. They interact with each other and the abiotic environment on time-scales from microseconds to millennia and on spatial scales from a few micrometres to the entire globe. Underlying this enormous physical and biological diversity, however, are emergent patterns of ecological organization that are precise, quantitative, and universal or nearly so. Examples include the latitudinal, elevational and other gradients of species diversity, the way that species are aggregated into genera and higher taxonomic categories, the body sizes and relative abundances of coexisting species in ecological communities, the way that species diversity changes with sample area, and the successional changes in productivity, biomass and species composition and diversity following disturbance (Williams 1964;MacArthur 1972;Brown 1995).These emergent general features of ecological systems provide powerful clues about the underlying mechanisms that constrain ecological complexity and regulate biodiversity. On the one hand, the emergent patterns represent the * Author for correspondence (jhbrown@unm.edu).One contribution of 11 to a special Theme Issue 'The biosphere as a complex adaptive system'. outcome of the fundamental law-like processes of physics, chemistry and biology. Many of these mechanisms are well understood. They include thermodynamics, conservation of mass and energy, atomic particles and chemical elements, chemical stoicheiometry, geological tectonics and erosion, laws of biological inheritance, evolution by natural selection, and many others. It is obvious that they must play a role in regulating biodiversity. On the other hand, it is far from clear how these fundamental processes act an...

Understanding how animals interact with their environment is critical for evaluating, mitigating and coping with anthropogenic alteration of Earth's biosphere. Researchers have attempted to understand some aspects of these interactions by examining patterns in animal body mass distributions. Energetic, phylogenetic, biogeographical, textural discontinuity and community interaction hypotheses have been advanced to explain observed patterns. Energetic and textural discontinuity hypotheses focus upon the allometry of resource use. The community interaction hypothesis contends that biotic interactions within assemblages of species are of primary importance. Biogeographical and phylogenetic hypotheses focus on the role of constraints on the organization of communities. This paper examines and organizes these various propositions about species body mass distributions and discusses the multiple competing hypotheses, how their predictions vary, and possible methods by which the hypotheses can be distinguished and tested. Each of the hypotheses is partial, and explains some elements of pattern in body mass distributions. The scale of appropriate application, relevance and interpretation varies among the hypotheses, and the mechanisms underlying observed patterns are likely to be multicausal and vary with scale.

Landsliding is a complex process that modifies mountainscapes worldwide. Its severe and sometimes long-lasting negative effects contrast with the less-documented positive effects on ecosystems, raising numerous questions about the dual role of landsliding, the feedbacks between biotic and geomorphic processes, and, ultimately, the ecological and evolutionary responses of organisms. We present a conceptual model in which feedbacks between biotic and geomorphic processes, landslides, and ecosystem attributes are hypothesized to drive the dynamics of mountain ecosystems at multiple scales. This model is used to integrate and synthesize a rich, but fragmented, body of literature generated in different disciplines, and to highlight the need for profitable collaborations between biologists and geoscientists. Such efforts should help identify attributes that contribute to the resilience of mountain ecosystems, and also should help in conservation, restoration, and hazard assessment. Given the sensitivity of mountains to land-use and global climate change, these endeavors are both relevant and timely.

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. In a montane tropical forest in southwestern Colombia, we investigated how anthropogenic edges may alter bird-mediated seed dispersal from edge to forest interior as a function of edge age and presence of treefall gaps. We estimated fruit abundance and mist-netted birds at four distances from edge to forest interior (0-10, 30-40, 60-70, and 190-200 m) in three young (<12 yr) and three old (>40 yr) edges. Fruit-sampling plots (50-M2 plots) at each of the four distances were classified into gap and intact forest.Fruit abundance and frugivore capture rates varied from edge to forest interior, but such changes depended on edge age. At new edges, the total number of fruits was higher at the forest edge than at the forest interior, whereas bird captures showed the opposite trend. At old edges, the total number of fruits and bird capture rates did not vary among the four distances. In a first group of 12 plant and four bird species, the distribution of individuals in fruit (7 species) and captures (3 species) from edge to forest interior differed between old and new edges. In a second group of 18 plant and five bird species, which included those that were not amenable for a comparison between old and new edges and those that were not influenced by edge age, the distribution of individuals in fruit (12 species) and captures (3 species) was not uniform from forest edge to forest interior. Lastly, 124 plant and 19 bird species with <20 individuals in fruit and captures, respectively, were classified into very sparse and sparse species. We found that all but the sparse frugivores were more abundant at the forest edge than in the forest interior. Because very sparse and sparse plant species showed such a clear trend, we used seeds retrieved from mist-netted birds to assess potential seed movement of these species from edge to forest interior. Seeds of very sparse and sparse plant species were found both at forest "edge" (0-10 m) and at forest "interior" (the three other distances combined).Our results suggest that birds are not responding to changes in fruit abundance (resourcebase-driven mechanism). Instead, they indicate that frugivore capture rates reflect either a direct edge effect or a non-edge induced effect on birds. The apparent uncoupling of processes generating the observed patterns in fruit and frugivore abundance may affect seed dispersal in important ways. Furthermore, our results indicate that, as edges age, "edge effects" (i.e., maximum distance at which changes induced by edge creation are apparent within forest stands) change.

In a montane tropical forest in southwestern Colombia, we investigated how anthropogenic edges may alter bird‐mediated seed dispersal from edge to forest interior as a function of edge age and presence of treefall gaps. We estimated fruit abundance and mist‐netted birds at four distances from edge to forest interior (0–10, 30–40, 60–70, and 190–200 m) in three young (<12 yr) and three old (>40 yr) edges. Fruit‐sampling plots (50‐m2 plots) at each of the four distances were classified into gap and intact forest. Fruit abundance and frugivore capture rates varied from edge to forest interior, but such changes depended on edge age. At new edges, the total number of fruits was higher at the forest edge than at the forest interior, whereas bird captures showed the opposite trend. At old edges, the total number of fruits and bird capture rates did not vary among the four distances. In a first group of 12 plant and four bird species, the distribution of individuals in fruit (7 species) and captures (3 species) from edge to forest interior differed between old and new edges. In a second group of 18 plant and five bird species, which included those that were not amenable for a comparison between old and new edges and those that were not influenced by edge age, the distribution of individuals in fruit (12 species) and captures (3 species) was not uniform from forest edge to forest interior. Lastly, 124 plant and 19 bird species with <20 individuals in fruit and captures, respectively, were classified into very sparse and sparse species. We found that all but the sparse frugivores were more abundant at the forest edge than in the forest interior. Because very sparse and sparse plant species showed such a clear trend, we used seeds retrieved from mist‐netted birds to assess potential seed movement of these species from edge to forest interior. Seeds of very sparse and sparse plant species were found both at forest “edge” (0–10 m) and at forest “interior” (the three other distances combined). Our results suggest that birds are not responding to changes in fruit abundance (resource‐base‐driven mechanism). Instead, they indicate that frugivore capture rates reflect either a direct edge effect or a non‐edge induced effect on birds. The apparent uncoupling of processes generating the observed patterns in fruit and frugivore abundance may affect seed dispersal in important ways. Furthermore, our results indicate that, as edges age, “edge effects” (i.e., maximum distance at which changes induced by edge creation are apparent within forest stands) change.