ASSESSING CONSERVATION VALUE USING CENTERS OF POPULATION-DENSITY

We present an index of centers of density for identifying areas of hig h conservation value. This index represents the average importance of an area to species occurring there as measured by comparisons of relat ive densities of each species among avens. We evaluated the index usin g collections of stream fishes from the Clinch River system above Norr is Reservoir in Virginia and Tennessee (U.S.A.). A strong correlation between index values measured at the same sites at different times sug gested that the index could be applied to sites without replicated sam ples in the region and still allow centers of density to be distinguis hed from non-centers. Species richness showed no relationship to the i ndex, suggesting that conservation priorities based solely on species richness can be inadequate. A species-accumulation curve based on the index performed nearly as well as one based on an algorithm for identi fying the minimum number of sites in which all species in the region a re represented, This pattern reflected the tendency of the index To we ight regionally rare species more heavily than common species. But sit es with high index values were not necessarily those selected by the a lgorithm because the algorithm used only presence/absence, whereas the index used the additional information present in relative densities. Our index represents an additional tool for identifying ''hot spots'' of diversity, but conservation of biodiversity over the long term will also require that the ecological integrity of regional landscape be m aintained.