Non Governmental Organisations and African Wildlife Conservation ...

Appendix 5: Calculating Indices of Biodiversity.
Groombridge and Jenkins (Groombridge and Jenkins 2002) calculated an index of biodiversity by
counting the numbers of birds, mammals and plants, and endemics of the same in each country. For
each country they expressed the number of each taxon, and its endemics, as a percentage of the largest
figure found in that variable. Thus the DRC has more mammals (430) and birds (1,087) than any other
African country. Its indexes would be 1 for both measures (430/430 and 1,087/1,087). But it has less
than half the number of plants (11,007) than South Africa (23,420), giving it an index of 0.47
(11,007/23,420). Indices are similarly calculated for levels endemism in each of plants, mammals and
birds separately. To calculate the diversity index for each country they took the mean of all indices
(DI). To control for the effect of area, they modified this result by comparing it to where it could have
fallen on a species area curve (AI).
This index renders endemism equally important to numbers of species, and it makes numbers of
plants, birds and mammals equally important as each other (although there are far more plants than the
others put together). A country with the most diverse plant collection, but least diverse mammal and
bird collection would score as well as the country with most diverse birds, but least diverse mammals
and plants.
We have modified this index by using more recent data. For number of species of plants and
mammals we used the World Resources Institute figures for 2005; for birds we used Birdlife
International’s website (December 2007). We also added amphibians from the Global Amphibian
Assessment. For levels of endemism we relied on the figures contained in Groombridge and Jenkins
original work. To control for the effects of country size in accordance with the species area curve we
simply divided each country by A z , where A = area of each country and z = 0.2 for mainlands and
Madagascar and 0.25 for islands (this followed Moore and colleagues’ [2004] procedure). We found
that our indices produced a close match with Groombridge and Jenkins (Table 13).
Our index of threat used a similar method for calculating the index and controlling for area. We
obtained data on the number of plants, birds and mammals threatened in each country from the IUCN
redlist (accessed September 2007). We found that our index of threat was well correlated with our
index of diversity (Spearman’s rank coefficient 0.855, n = 47, p=0.01). This was still true when we
took country size into account (Spearman’s rank coefficient 0.725, n = 47, p=0.01).
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