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Four basic ecoregional priority setting exercises were utilized for the present terrestrial ecoregions analysis. These can be classified by the two basic approaches they take. The first one includes the Biodiversity Support Program, The World Bank and WWF’s Global 200 process, are part of the same family which embraces the representative approach, guided mainly but not exclusively by the efforts of Eric Dinerstein and David Olson from World Wildlife Fund (WWF). The second approach is based on uniqueness in species richness and is represented by the hotspots, whose paradigm has been developed mainly by Norman Meyers and Russell Mittermeier for Conservation International (CI). Both approaches offer distinct perspectives that enrich ecoregional priority setting needs mainly at the global scale, but can also be utilized on exercises focused smaller territories. Other efforts to define ecological analysis units or regions for Mexico are the ones developed by the Commission for Environmental Cooperation (CEC,1997), Ecological Regions Of North America and by the Mexican Biodiversity Commission (CONABIO, 1999), Ecoregions of Mexico. Ecological regions resulting from these exercises have not yet been used for biodiversity priority setting, so they are not considered in this analysis. All freshwater and marine exercises utilized in this comparative analysis correspond to the representative approach. Some peculiarities of the two approaches and of the different exercises are detailed below, in order to facilitate their use according to their particular strengths and limits.

CI HOTSPOTS (Mittermeier et al. 1999 and Meyers et al., 2000)

Concentrating on areas where there is greatest need and where the payoff from safeguard measures would also be greatest, is the basis of the hotspots paradigm. It responds to the challenge of large-scale extinction that we are now facing and offers an objective answer to the question: of how can we protect the most species per dollar invested? The hotspots approach identifies areas featuring exceptional concentration of endemic species and experiencing exceptional loss of habitat. Hotspots focuses on species rather than populations or other taxa as the most prominent and readily recognizable form of biodiversity. (Meyers et al., 2000)

The species dimension for hotspots is based in first instance on vascular plants (90% of all plants) and to qualify as such the area must contain at least 05% of the world’s 300,000 species as endemics. Vertebrates (excluding fish) serve as a backup support and also to determine congruence and to facilitate other comparisons among the hotspots. The analysis omits invertebrates, which are largely undocumented but probably make up at least 95% of all species. A second determinant of hotspots status, applied only after an area has met the “plants” criterion is the degree of threat through habitat loss, which should represent at least 70% of its primary vegetation. Finally, the analysis is limited to the terrestrial realm, although CI is preparing an analysis of marine species and conservation priorities.. The resulting 25 hotspots contain the remaining habitat of 1333,149 plant species (44% of all plant species) and 9,645 vertebrate species (35% of all vertebrate species). These endemics are confined to an aggregate remaining expanse of 2.1 million square kilometers, or 1.4% of the earth’s land surface. (Meyers et al., 2000)

According to the authors of The Global 200 (Olson et al., 1997) the controversy between the representation approach and the hotspots approach is partly academic (Schmidt, 1996, in Olson et al. 1997). The hotspots analysis focuses on those areas that have extraordinary concentration of species and high number of endemic species. Although these areas are important conservation targets, the danger of the hotspots approach is that it is often interpreted as a triage for the remaining habitats of the world. In the process, it places in jeopardy the half of all species that occur outside certain tropical moist forests and Mediterranean shrublands. The conservation of freshwater or marine biodiversity is also not addressed. (Olson et al., 1997)


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