Sunday, December 24, 2006
An open access/free article from the Proceedings of the National Academy of Sciences (PNAS):
Global mammal distributions, biodiversity hotspots, and conservation
by Gerardo Ceballos (homepage) and Paul R. Ehrlich*
Abstract and Introduction
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 degree latitude x 1 degree 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.
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 x 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.
*Info on Paul Ehrlich:
...Dr. Ehrlich's main area of research is Population Biology, which includes ecology, evolutionary biology, behavior, and human ecology. Ehrlich has carried out field, laboratory, and theoretical research on a wide array of problems ranging from the dynamics and genetics of insect populations, studies of the ecological and evolutionary interactions of plants and herbivores, and the behavioral ecology of birds and reef fishes, to experimental studies of the effects of crowding on human beings. His fieldwork has carried him to all continents, from the arctic and the antarctic to the tropics, and from high mountains to the ocean floor. He collaborates with colleagues in biology and in the disciplines of economics, psychology, political science, and the law, in policy research on human ecology...