4. IMPORTANT AREAS FOR FRESHWATER DIVERSITY

If sites or areas of high diversity, often termed 'hotspots', can be identified, there

is an opportunity to implement measures to conserve biodiversity and manage land use in a concerted and cost-effective manner. In the context of biological diversity, the word 'hotspots' was originally applied during the late 1980s to areas in tropical forest regions that each supported high concentrations of plant species found nowhere else, and which in most cases were also suffering higher than average rates of deforestation (Myers, 1988, 1990). The central point was that, although not necessarily small in absolute terms (the hotspots included entire islands, such as New Caledonia and Madagascar, and large sections of countries, such as all of Peninsular Malaysia) they included so many endemics that they collectively supported a large proportion of the world's total flora on a relatively small proportion of the world's surface. The term 'hotspots' is now widely applied to any area that appears to be of especially high biodiversity value.

Considerable interest remains in identifying hotspots. This is partly because of the scientific interest attached to the search for natural patterns in the distribution of species, but primarily because conservation measures undertaken in 'hotspot' areas can in theory be extremely cost-effective because of the amount of biodiversity that can be maintained per unit cost.

Large and long-lived lakes have long been known to support high diversity in fishes, molluscs, crustaceans and others, sometimes in several groups (see Table 15). As sources of unique lineages, these lakes are indeed 'hotspots', and are the aquatic equivalents of islands such as Hawaii or the Galápagos.

However, lake sites are relatively easy to assess and compare, simply because lakes typically have clear and permanent boundaries. It is a much greater challenge similarly to identify, delimit and compare other areas important for freshwater biodiversity. This is in part because geographic boundaries are diffuse or otherwise difficult to determine, and in part because available diversity data are very sparse and have not been collected in a manner that allows standardised comparisons to be made.

For the present study, we have collated the preliminary views of a number of leading systematists and aquatic biologists (see Acknowledgements) on the identity of areas of special importance for a selection of key animal groups (freshwater fishes, molluscs, crayfish, crabs, and fairy shrimps). This 'expert opinion' approach is

Notes: 1) A few other lakes have notable endemism among fishes, molluscs, crustaceans or other groups - among these are lakes Inle (Myanmar), Lanao (Phillippines); Malili (Indonesia) and the Cuatro Cienegas basin (Mexico) - but their ages are not yet firmly established. 2) Qualitative remarks (eg. "very high", "low") in the 'biodiversity' column are related to long-lived lakes, not to lake systems in general.

Source: collated from data in Martens et al., 1994.

valuable in making effective use of readily available information, and although preliminary, has yielded the first global overview of freshwater biodiversity hotspots. Kottelat and Whitten (1996) have reviewed many aspects of freshwater biodiversity in Asia, including discussion of taxonomy, hotspots and policy. Regional assessments for Latin America (Olson et al., 1997) and North America (Abell, et al., 1998) are now available.

Although this indicative synthesis has a real heuristic value, it has not yet been possible to evaluate candidate areas against a globally consistent set of spatial and diversity criteria. A more comprehensive global analysis will require development of such criteria, and a prolonged phase of research and international consultation; we believe this is well justified by the results of the present study.

Table 16 lists in summary form some of the sites and areas that have been identified as of special importance for more than one of the groups (fishes, molluscs, crabs, crayfish, fairy shrimp). It is not intended to be a comprehensive global listing: it omits the large but imprecisely defined areas of known high diversity as listed more fully in Table 17; it omits diverse taxa not covered in this assessment (eg. amphipods, copepods, etc); and it does not mention sites of key importance mainly for one group of animals. See Maps 2-5; Map 2 shows the general location of areas noted in Table 16.

The fact that only two regions in South America are listed reflects the continuing lack of detailed information for taxa other than fishes. On the evidence of fishes alone the Amazon basin is likely to be exceptionally rich in other freshwater groups, but although known to be rich in freshwater crabs, for example, it is not possible to delimit special areas within the basin. However, this table is a valid reflection of current information and begins to meet the need for global information on the relative importance of hotspots of freshwater biodiversity.

This summary should be consulted in conjunction with Table 17, which outlines biodiversity and geographic information distilled from the material provided by contributors.

Notes: this table includes sites and areas noted in Table 17 (important areas...) that are identified as of particular importance for more than one of the groups discussed; see relevant entries in Table 17 for description; # - key to area code number in Table 17; the table is not intended to include all areas of global importance for freshwater diversity

Sources: See sources cited at end of Table 17.