Assessing conservation value using centers of population density

We present an index of centers of density for identifying areas of high conservation value. This index represents the average importance of an area to species occurring there as measured by comparisons of relative densities of each species among areas. We evaluated the index using collections of stream fishes from the Clinch River system above Norris Reservoir in Virginia and Tennessee (U.S.A.). A strong correlation between index values measured at the same sites at different times suggested that the index could be applied to sites without replicated samples in the region and still allow centers of density to be distinguished from noncenters. Species richness showed no relationship to the index, 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 identifying the minimum number of sites in which all species in the region are represented. This pattern reflected the tendency of the index to weight regionally rare species more heavily than common species. But sites with high index values were not necessarily those selected by the algorithm 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 maintained. Presentamos un indice de Centros de Densidad para identificar areas de alto valor para la conservacion de diversidad biologica. Este indice indica la importancio promedia de un area para las especies quen habitan en ella, usando ta distribucion relativa de las densidades de esas especies entre todas las areas estudiadas. El indice fue evaluado usando datos recolectados en peces de la cuenca del Rio Clinch en Virginia y Tennessee. Encontramos una alta correlacion entre el indice calculado en diferentes anos; esto sugiere que el indice puede ser aplicado en areas donde no haya duplicacion de muestras y, sin embargo, permite la identificacion de los centros de densidad. No encontramos relacion entre la abundancia de especies en un area y el indice, lo que sugiere que el primero puede ser inadecuado para establecer prioridades para la conservacion de especies. La curva acumulativa de especies basada en el indice fue similar a la curva basada en un algoritmo para identificar el numero minima de areas en los cuales todas las especies de una region estan representadas. Este patron reckja que el indice tiene la tendencia de darle mas peso a las especies regionales raras que a las especies comunes. Sin embargo, las areas con altos a indices no fueron necesariamente las mismas seleccionadas por el algoritmo. Esto es debido a que el algoritmo se basa en la presencia o ausencia de especies mientras que el indice usa la informacion adicional contenida en la densidade relativa de las especies. Es importante resaltar que, para la conservacion de la diversidad biologica, el uso de estos indices tiene poca probabilidad de exito a largo plazo si no se mantiene la integridad biologica de la region.

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