Global mammal distributions, biodiversity hotspots, and conservation
Gerardo Ceballos*† and Paul R. Ehrlich†‡
*Departamento de Ecologia de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Apdo Postal 70-245, 04510 México D.F., México; and
‡Center for Conservation Biology, Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020
Contributed by Paul R. Ehrlich, October 24, 2006
Author contributions: G.C. and P.R.E. designed research, performed research, analyzed data, and wrote the paper.
Hotspots, which have played a central role in the selection of sites for reserves, require careful rethinking. We carried out a global examination of distributions of all nonmarine mammals to determine patterns of species richness, endemism, and endangerment, and to evaluate the degree of congruence among hotspots of these three measures of diversity in mammals. We then compare congruence of hotspots in two animal groups (mammals and birds) to assess the generality of these patterns. We defined hotspots as the richest 2.5% of cells in a global equal-area grid comparable to 1° latitude × 1° longitude. Hotspots of species richness, “endemism,” and extinction threat were noncongruent. Only 1% of cells and 16% of species were common to the three types of mammalian hotspots. Congruence increased with increases in both the geographic scope of the analysis and the percentage of cells defined as being hotspots. The within-mammal hotspot noncongruence was similar to the pattern recently found for birds. Thus, assigning global conservation priorities based on hotspots is at best a limited strategy.
Keywords: hotspot congruence, birds, patterns of species distribution, endemism, threatened species
Proc Natl Acad Sci U S A. 2006 December 19; 103(51): 19374–19379. OPEN ACCESS ARTICLE.
Few topics in conservation biology have received as much attention as hotspots of species diversity. Hotspots have been widely used to determine priority areas for conservation at different geographic scales, and in recommending concentrating resources in those regions to maximize the number of protected species (1, 2). Hotspots are defined as either the top sites in terms of species diversity or as the most threatened and most diverse sites (1, 3, 4). In these definitions, identifying hotspots requires a measure of species diversity, which often is species richness, number of restricted-range (e.g., endemic) species, or number of species at risk, and a measure of threat, which often is human population density or land converted to agriculture (5, 6). A critical assumption of the use of hotspots for conservation that has not been widely tested at a global level is how much congruence or overlap there is among hotspots of species richness, endemic species, or species at risk. Wide overlap among these three types of hotspots implies the selection of fewer sites to represent all species and the possibility of using one of them as a surrogate for the others.
In this paper we assessed the distribution of 4,818 nonmarine mammal species (excluding cetaceans, sirenians, and pinnipeds; list available from G.C. on request) to make a general evaluation of the utility of hotspots for determining conservation priorities for the mammals of the World. Global patterns of species distribution were assessed by comparing the distribution of all mammal species in 17,800 equal-area terrestrial cells of 100 × 100 km (5, 7). Using this database, we evaluated (i) mammalian species richness, endemism (hereafter, more accurately, restricted–range species or “narrow-ranging” species (8), and threatened species: (ii) hotspots for those three aspects of mammal diversity, defined as the top 2.5% of cells in each category: (iii) congruence among the three kinds of hotspots and comparisons with published data on bird hotspots; (iv) sensitivity of results to hotspot definitions (i.e., geographic area covered by the hotspot and the percentage of cells considered as hotspot cells); and (v) efficiency of hotspots for conservation of mammalian species diversity.