Biodiversity Gradients

by

Bradford A. Hawkins

• LAST REVIEWED: 26 February 2013
• LAST MODIFIED: 26 February 2013
• DOI: 10.1093/obo/9780199874002-0074

Introduction

The study of spatial variation in the numbers of species across the Earth represents a core research area of several scientific disciplines, including ecology, evolutionary biology, paleontology, biogeography, and conservation biology. It encompasses all groups of organisms, extant and extinct, all geographic areas from small islands to the globe, all time frames, including the future, and all biomes and habitats both wet and dry. Although broad-scale diversity patterns have been known since the late 18th century, until relatively recently most quantitative research focused on mountains, islands, coarsely defined regions, or small-scale community gradients, because of the limited availability of broad-scale distributional data. Data remain limited for many groups of organisms, especially in the hyperdiverse tropics, but many biologists sense that time may be running out for diversity as we move into a new mass extinction episode resulting from invasive species, global climate change, and habitat destruction. This has greatly stimulated the generation and distribution of the geographic data on which diversity gradient analyses are based. The increasing availability of phylogenies for ever larger and more inclusive groups is also revolutionizing how diversity analyses are conducted and interpreted.

Reference Works

Gradients in taxon richness get some attention in virtually all general ecology and biogeography textbooks, but there are few authored books focused entirely on this topic, with Huston 1994 and Rosenzweig 1995 being the primary examples. Among books covering multiple topics, three stand out. Robert H. MacArthur effectively defined the discipline to which the study of diversity gradients belongs when he opened his book by writing, “To do science is to search for repeated patterns, not simply to accumulate facts, and to do the science of geographical ecology is to search for patterns of plant and animal life that can be put on a map” (MacArthur 1972). Two decades later, Ricklefs and Schuter 1993 argued forcefully for the need to bring geological and historical perspectives to ecology, particularly to the study of diversity patterns, as part of the still developing integration of biogeography and ecology. An update of some of the approaches for studying broad-scale patterns can be found in the “Diversity Gradients” section of Lomolino and Heany 2004.

• Huston, Michael A. Biological Diversity: The Coexistence of Species on Changing Landscapes. Cambridge, UK: Cambridge University Press, 1994.

  At 681 pages (99 of which are references), this sweeping survey of diversity gradients remains an excellent source for the literature up to the early 1990s.

• Lomolino, Mark V., and Lawrence R. Heaney, eds. Frontiers of Biogeography: New Directions in the Geography of Nature. Sunderland, MA: Sinauer, 2004.

  This collection of chapters covering emerging trends in biogeography includes a section with four chapters devoted to diversity gradients.

• MacArthur, Robert H. Geographical Ecology: Patterns in the Distribution of Species. New York: Harper & Row, 1972.

  Although outdated from a research perspective, this treatise drawn from MacArthur’s course lectures at Princeton offers discussion of influences on a wide range of diversity patterns and mixes simple ecological theory with his knowledge of natural history.

• Ricklefs, Robert E., and Dolph Schluter. Species Diversity in Ecological Communities: Historical and Geographical Perspectives. Chicago: University of Chicago Press, 1993.

  This edited volume contains a number of chapters that were influential at the time and remain relevant today.

• Rosenzweig, Michael L. Species Diversity in Space and Time. Cambridge, UK: Cambridge University Press, 1995.

  DOI: 10.1017/CBO9780511623387

  A highly personal account of species diversity that champions area as the primary regulator of spatial and temporal patterns.