Tropics: latitudinal biodiversity gradient

Article By:

Valentine, James W. Department of Integrative Biology, University of California, Berkeley, California.

Last reviewed:2008

DOI:https://doi.org/10.1036/1097-8542.YB081740

The latitudinal diversity gradient (LDG) is the most pervasive pattern exhibited by the living biota on a global scale. Tropical latitudes are rich in species and in groups of organisms on higher levels of the tree of life, a richness that declines nearly monotonically toward polar latitudes, where the biota is most species-poor. This gradient of diversity is found in all major groups or organisms, such as fungi, land plants, vertebrates, and invertebrate groups, and characterizes both the terrestrial and marine realms. In the oceans, the gradient is recorded for organisms living on the sea floor of the continental shelves, in the deep sea, in the water column over the shelves, and in the open ocean. The LDG was well known in Darwin's day, and in 1878 Alfred Wallace, the coauthor of natural selection, suggested that the tropics were diverse because they were climatically more stable than higher latitudes, permitting evolution to accumulate species there. The diversity gradient has spawned many studies—some supporting Wallace's notion, others offering alternative explanations. A number of explanations center around temperature, which of course varies with latitude. The higher tropical temperatures have been held to support more rapid evolutionary activity, which is then progressively damped in colder climates. However, mechanisms that might underlie this relationship have never been satisfactorily demonstrated.

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