Macroecology is concerned with the statistical distributions of variables among large numbers of comparable ecological "particles." Usually these particles are either many individual organisms within species populations, or many species within local, regional or continental biotas. The individuals and species are not exactly identical; they vary in their characteristics. Macroecology seeks to discover, describe and explain the patterns of variation.
Much of the emphasis is on the shapes and boundaries of statistical distribution because these appear to reflect intrinsic, evolutionary or extrinsic environmental constraints on the variation. In order to characterize and compare these distributions, it is desirable - but not always possible - to have samples of hundreds or thousands of particles.
The variables of macroecological study are ecologically relevant characteristics of organisms. The kinds of attributes that can be used are necessarily limited by the requirement for samples of large numbers of individuals, populations, or species. Most of my research has focused on variables, such as body mass, population density, and area of geographic range that affect the use of space and nutritional resources. Body mass is correlated with the energetic, nutrient and space requirements of individual organisms.
Local population density indicates the number of individuals that coexist in and are supported by a small area. The size and configuration of the geographic range shows the area of space and range of environmental conditions within which all populations of a species occur. Note that each of the above variables characterizes a different level of organization: individual, population, and species, respectively. Note also that this is by no means an exhaustive list; these are just examples of the variables I have most frequently used in my macroecological studies.
Macroecology tends to focus on phenomena at regional to global spatial scales and decadal to millennial temporal scales. This is a practical limitation imposed by the need for large samples, but it means macroecology is often concerned with patterns and processes at much larger scales that in the small study plots and short field seasons of most experimental ecologists. Studies must often consider regional and global envrionmental variation, earth history, species dynamics (speciation, extinction and geographic range shifts), and phylogenetic relationships. Macroecology explores the domain where ecology, biogeography, paleobiology, and macroevolution come together, and thus has the potential to forge synthetic links among these disciplines.
The macroecology research program is both empirical and theoretical, both inductive and deductive. It is concerned with the relationship between pattern and process. It is based on the assumption that some of the general processes regulating abundance, distribution and diversity of organisms are reflected in emergent patterns in the statistical distributions of individuals, populations and species.
Macroecological research seeks to discover and describe these patterns and to develop and test hypotheses to account for them. While much of the initial inspiration comes inductively, from the discovery of patterns in data, the validity of the ideas ultimately must be evaluated deductively, by casting them as hypotheses that make testable predictions.
Macroecology has not only discovered some intriguing patterns, but has also begun to develop and test mechanistic hypotheses.
Information contained in this document is © copyright James H. Brown, 2009. All rights reserved.