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The processes that influence the distribution and diversity of species throughout the world has long fascinated biologists. In a Perspective, Storch, Marquet and Gaston discuss a recent meeting that explored ways to quantitate and analyze the processes that drive patterns of biodiversity.

Interspecific comparisons of animal population density to body size has been the subject of active research in the last decade, especially for terrestrial animals when considering particular taxa or taxonomic assemblages. Studies of rocky intertidal communities showed that animal population density scales with body size to the -0.77 power. This relation held within local communities representing a broad array of animal taxa and was not affected by a dramatic alteration in the network of between-species interactions, as revealed by two long-term human exclusion experiments.

Power laws are used by biologists to express how physiological, ecological, and life-history attributes relate to body size in animals (scaling or allometric relationships). In his Perspective, Marquet discusses new data (Carbone and Gittleman) that explain the anomalous nature of the power law for carnivore population density and body size.

There has been much debate about scaling laws in nature. It is believed that as body size increases the number of individuals in the population decreases. As Marquet explains in his Perspective, an elegant new study in two totally separate stream communities ( Schmid et al.) confirms that this scaling law holds across more than 400 species of invertebrates.