III.16 Macroecological Perspectives on Communities and Ecosystems
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III.16 Macroecological Perspectives on Communities and Ecosystems Pablo A. Marquet OUTLINE 1. The road to macroecology 2. Macroecology: Toward a definition 3. Macroecological patterns 4. Neutral macroecology 5. Metabolic theory Macroecology is an emergent research program in ecology that examines patterns and processes in ecological systems at large spatial and temporal scales. It acknowledges the complexity of ecological systems and the limitation of reductionistic approaches, emphasizing a statistical description of patterns in ensembles of multiple species. One of its goals is the identification of regularities that might eventually unveil the general principles underlying the structure and functioning of communities and ecosystems. GLOSSARY energetic equivalence. Concept that denotes the equivalence of species in terms of the amount of energy that their populations use within natural communities metabolism. Network of chemical reactions that take place in living entities and by which energy and materials are taken up from the environment, transformed into the component of the network that sustains it, and allocated to perform specific functions metacommunity. Set of local communities that are linked by the dispersal of their components and potentially interacting species metapopulation. Set of local populations of one species linked through dispersal reductionism. Scientific approach by which understanding of complex systems can be obtained by reducing them to the interactions among their constituent parts scaling. Name given to the existence of a power–law relationship between two variables of the form y¼axy , where y is the scaling exponent and is normalization constant species–area relationship. Relationship that describes how the number of species increases with the area sampled or with the size of the system under analysis (e.g., lake, habitat fragment, or island) Theory of Insular Biogeography. Equilibrium theory proposed by MacArthur and Wilson in 1963 that proposes that the number of species in a given island results from the dynamic equilibrium of the opposite processes of immigration from a source and local extinctions 1. THE ROAD TO MACROECOLOGY As do most research programs in science, macroecology represents the crystallization of a line of inquiry that started two centuries ago with the discoveries of the German naturalist Alexander von Humboldt, published in 1807, and his remarks on the latitudinal distribution of biodiversity (the pole-to-tropic gradient ) and continued, with different intensity, in the works of Olof Arrhenius, Carrington Bonsor Williams, John Christopher Willis, Frank Preston, Leigh Van Valen, George Evelyn Hutchinson, Robert MacArthur, Eduardo Rapoport, and several others. One can ask in retrospective, What makes the work of these authors macreocological? The common theme in all of them was the usually large spatial extent (i.e., regional to continental) of the patterns they reported and the use of statistical descriptions of species ensembles with regard to attributes such as abundance, richness, geographic distribution, or body mass, with an emphasis on the emerging patterns rather than on the component species. Before macroecology, these patterns were studied in isolation and interpreted as resulting from evolutionary processes and/or ecological or biogeographic dynamics. Macroecology provided a synthetic and common framework for all of them by explicitly recognizing the importance of, and the links among, ecological, evolutionary,and biogeographical processes and scales in the understanding of ecological phenomena . Three major events contributed to the consolidation of macroecology as a research program in ecology. 1. First is the recognition of the role played by regional factors in affecting the local dynamics of populations and communities. The importance of regional effects became recognized thanks to the analysis of the degree of coupling between local and regional diversity championed by Robert Ricklefs and the development of metapopulation theory, which, although formally introduced in 1969 by Richard Levins, started to flourish in the 1980s, most notably through the work of Ilkka Hanski. 2. As we elaborate in greater detail below, macroecological work is usually concerned with patterns occurring at regional to global scales where experiments are not feasible and data are difficult to obtain. However, this changed during the last two decades with the explosive development and/or availability of data such as atlases on the distribution and abundance of different taxa (e.g., Breeding Bird Survey, Gentry Plots) and the development of new technological tools to deal with and to generate data on environmental variables at large spatial scales (e.g., satellite imagery, remote sensing, and geographic information systems). 3. Finally, one the main drivers of the macroecological approach was the growing recognition of the limitation inherent to the reductionistic, microscopic approaches that became dominant in ecology...