Global mammal distributions, biodiversity hotspots, and conservation

Abstract

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 degrees latitude x 1 degrees 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.

Fig. 1.

Patterns of species distribution of mammals throughout the world, showing species richness (A), restricted-range species (B), and threatened species (C). All scales are in terms of number of species per 10,000-km² grid cell. (See Materials and Methods for further details.)

Fig. 2.

Hotspots of species richness (A), restricted-range species (B), and threatened species (C). The 2.5% hotspots are shown in red, and the 5% hotspots are shown in yellow and red.

Fig. 3.

Congruence of mammalian species richness, restricted-range species, and threatened species in the 2.5% (A) and 5% (B) hotspot grid cells. Note the relatively high number of species shared by all grid cells in the 5% hotspots. Percentages are of total number of mammal species represented in three types of hotspots (see Table 2).

Fig. 4.

Comparison of the percentage of species represented in the three types of hotspots of diversity between mammals (blue bars) and birds (red bars, data from ref. 4).

Fig. 5.

Congruence of mammalian species richness, restricted-range species, and threatened species clearly increases as a function of both the number of cells considered as hotspots (A) and the area covered by the hotspots (B). In A, the percentages of cells considered hotspots, 2.5%, 5%, 20%, and 40%, are represented as 1, 2, 3, and 4, respectively, on the x axis. In B, the areas covered by the hotspots, 10,000, 20,000, 40,000, and 90,000 km², are represented as 1, 2, 3, and 4, respectively, on the x axis. The blue line indicates the percentage of species shared by the three types of hotspots; the red line indicates the percentage of species found in only one of the three types of hotspots.