2.2.2 FRESHWATER ECOREGIONAL EXERCISES COMPARATIVE ANALYSIS
BIODIVERSITY SUPPORT PROGRAM (Olson et al., 1997 and 1999)
Forty-two freshwater ecoregion complexes were identified for Latin America and the Caribbean, within which 117 ecoregions were delineated. Ecoregions were classified according to their major habitat type, ranging from large rivers to closed basins in dry regions. Ecoregions were assessed using two principal discriminators. (Olson et al., 1999)
Biological distinctiveness was assessed through the analysis of species richness, endemism, ecosystem diversity and special considerations (rarity of major habitat type and unusual ecological or evolutionary phenomena) and point scores were assigned for each characteristic to define ecoregional priorities. (Olson et al., 1999)
Conservation status is an estimate of current and future ability of an ecoregion to maintain viable species populations, sustain ecological processes and be responsive to short and long term change. Determinants of an ecoregion’s conservation status include: habitat loss, water quality and hydrographic integrity, with which they were classified. Globally outstanding ecoregions that are relatively intact were not identified as highest priority because of the urgency of more threatened ecoregions. Globally and regionally outstanding ecoregions whose final conservation status was critical were ranked as second and third priority respectively for conservation action. This due in part, for the extreme difficulty of restoring critical freshwater ecosystems, in contrast to the selection methods for terrestrial ecoregions which give highest priority to this combined set of criteria. (Olson et al., 1999)
WWF GLOBAL 200 (Olson and Dinerstein, 1997)
The Global 200 freshwater ecoregions are composite ecoregions based on the BSP ecoregions. These have been mapped for Mexico in different forms in Olson and Dinerstein, 1997 and in WWF, 2000, and thus are not used in the composite comparative analysis.
WWF - FRESHWATER ECOREGIONS OF NORTH AMERICA (Abell et al., 2000)
In contrast with the BSP freshwater priority setting exercise which was carried out within the Neotropical Realm of which southern Mexico is part of, this exercise is developed within the framework of the Neartic Realm which constitutes a more appropriate biogeographical comparison field for northern Mexico. In contrast to the BSP exercise, this one is based on best available quantitative data sets for: fish, crayfish and herpentofauna for Mexico.
The assignment of freshwater priorities differs substantially from that proposed for North American terrestrial Ecoregions (Ricketts et al. 1999 in Abell et al., 2000) but is similar to that offered for freshwater ecoregions of Latin America and the Caribbean (Olson et al. 1997 in Abell et al., 2000). Freshwater ecoregions differ from their terrestrial counterparts in two important and related ways. First, because the connectedness of freshwater habitats, spatial and functional linkages across large distances are strong, with upstream activities manifested in downstream effects. Second, conservation of a given freshwater site must nearly always occur at the watershed scale. Considering that entire ecoregions must be the focus of any ambitious conservation action, North American freshwater experts agreed that critically imperiled ecoregions are likely beyond repair, and that the greatest biodiversity conservation may be achieved by focusing on endangered and vulnerable ecoregions with globally outstanding biodiversity. (Abell et al., 2000)