Latitudinal Gradients of Biodiversity: Pattern, Process, Scale, and Synthesis

TLDR

The latitudinal gradient of decreasing species richness from tropical to extratropical regions is ecology's longest recognized pattern, though exceptions exist and patterns depend on spatial scale and taxonomic hierarchy. The study seeks to synthesize how scale and taxon characteristics influence variations in latitudinal biodiversity patterns. The authors surveyed the literature, assessing pattern variations across generic and familial richness, species evenness, and diversity to determine the role of scale and taxon. They classified over 30 hypotheses for the gradient, highlighted seven most promising, and proposed future research directions.

Abstract

▪ Abstract The latitudinal gradient of decreasing richness from tropical to extratropical areas is ecology's longest recognized pattern. Nonetheless, notable exceptions to the general pattern exist, and it is well recognized that patterns may be dependent on characteristics of spatial scale and taxonomic hierarchy. We conducted an extensive survey of the literature and provide a synthetic assessment of the degree to which variation in patterns (positive linear, negative linear, modal, or nonsignificant) is a consequence of characteristics of scale (extent or focus) or taxon. In addition, we considered latitudinal gradients with respect to generic and familial richness, as well as species evenness and diversity. We provide a classification of the over 30 hypotheses advanced to account for the latitudinal gradient, and we discuss seven hypotheses with most promise for advancing ecological, biogeographic, and evolutionary understanding. We conclude with a forward-looking synthesis and list of fertile areas for future research.