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A biodiversity intactness index


The nations of the world have set themselves a target of reducing the rate of biodiversity loss by 2010. Here, we propose a biodiversity intactness index (BII) for assessing progress towards this target that is simple and practical—but sensitive to important factors that influence biodiversity status—and which satisfies the criteria for policy relevance set by the Convention on Biological Diversity. Application of the BII is demonstrated on a large region (4 × 106 km2) of southern Africa. The BII score in the year 2000 is about 84%: in other words, averaged across all plant and vertebrate species in the region, populations have declined to 84% of their presumed pre-modern levels. The taxonomic group with the greatest loss is mammals, at 71% of pre-modern levels, and the ecosystem type with the greatest loss is grassland, with 74% of its former populations remaining. During the 1990s, a population decline of 0.8% is estimated to have occurred.

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We thank the following experts whom we interviewed: G. Alexander, G. Bredenkamp, D. Biggs, B. Branch, V. Carruthers, A. Channing, C. Chimimba, J. du Toit, W. Haacke, J. Harrison, M. Keith, L. Minter, M. Rutherford, W. Tarboton and M. Whiting. R. Dean, C. Geldenhuys, B. Reyers, H. Simons, B. van Wilgen and M. Whiting are thanked for providing links to literature studies for validation of the expert estimates. We thank N. Burgess, J. D'Amico and the Conservation Science Programme at WWF, and G. Kier and the Biomap Working Group at the University of Bonn, Germany, for species richness data. J. Harrison is thanked for data used to derive the richness of each taxon functional type per biome. Thank you to D. van Zyl and T. Newby at the Institute for Soil, Climate and Water in Pretoria for the maximum annual normalized difference vegetation index (NDVI) data that were used to map degradation. B. Reyers at the University of Stellenbosch is thanked for the summation of the mammal distribution grids, which were provided by M. Keith. R.J.S. conceived the original idea for the index. It was then jointly developed further, and the paper was co-written by the authors. R.B. did the BII calculations, GIS application and literature validation.

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Correspondence to R. J. Scholes.

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Figure 1: Average fraction of original populations remaining under a range of land use activities.
Figure 2: Comparison of estimates of Iijk, the ratio of current populations to reference populations under various land use activities.


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