BioEd Online

When the 188 parties to the Convention on Biological Diversity met in South Africa nearly three years ago, they agreed to significantly reduce biodiversity loss by 2010. But it was not clear how this would be measured.

Now, scientists have proposed a way to calculate the overall impact that different countries are having on species richness.

Over the past year, several groups have been looking at ways of following trends in the abundance and distribution of species. But the methods developed so far have focused on counting quite narrow lists of species to see which ones are present.

"We have bits and pieces of information, but generally lack the comprehensive picture because biodiversity is so complex," says Robert Höft, an environmental affairs officer at the secretariat of the biodiversity convention in Montreal.

Looking for the presence of particular species also tends to focus on extinction rates. "The basic problem with using extinction as an indicator is that by the time you get the information, it is too late to take any action," explains Bob Scholes, a systems ecologist at the Council for Scientific and Industrial Research in Pretoria, South Africa.

So Scholes and his colleague Oonsie Biggs, also at the council, have come up with a different approach, which they call the Biodiversity Intactness Index. They suggest grouping similar species together, and then estimating the effect that changes in land use will have on each of the groups, to give a broader picture of how ecosystems are faring.

When an area of land gets converted for crop agriculture, for example, it affects species differently. Large mammals are likely to suffer. "You can't have elephants walking around in your maize field," says Scholes. Rodents, on the other hand, are likely to thrive in such an environment thanks to an abundance of food.

Field work

Scholes and Biggs suggest using information from field trials and other studies to make estimate for each group of animals or plants about which are likely to fare better, and which worse. Those numbers are then combined to give a final number on a scale of 100.

The top figure of 100 indicates that the species richness on the land is not affected. Any number lower than 100 flags up a decline in the number of species, usually as a result of human development.

The scores for different areas of land can be added up to give an indication of whether a country is conserving biodiversity effectively. The researchers detail their proposed index in this week's Nature¹.

"There's room and need for improvement and so this document is a very important contribution to the discussion," says Höft. "It's the first index that really includes plants, which is very important."

Scholes and Biggs have already used their method to find out how the number and range of plant and vertebrate species in southern Africa looks in 2000, compared with pre-modern levels (inferred from untouched areas of land).

Although 99% of the original species are still present across the whole region, they awarded the region a score of 84, which flags up the fact that, in many areas, biodiversity has declined.