“Biodiversity” is a popular notion. The intent is good but just counting species, often only charismatic ones, leads to dangerous conclusions. Just counting species is like just collecting any old stamps and then judging your collection simply by the number of different stamps you have.

A fundamental hazard in such thinking is illustrated by the repeated proposal that most of our attention and resources should be devoted to the few places on earth that have the most species. To test that thinking, ask: is one species in an arctic ecosystem equal in ecological value to one species in a tropical ecosystem. Both are irreplaceable but removal of one arctic species will cause more disruption of that ecosystem than removing one tropical species. Extinction of the polar bear would cause a major change in the coastal tundra ecosystem.

The same differential in ecological value exists between “keystone” species and other ecologically less influential species in the same ecosystems. The boreal system would be changed more by the removal of black spruce or beaver than by the removal of some other species.

Further, the lists of species substituted for a measure of biodiversity are commonly just presence or absence information. Yet some of those listed species are exceedingly rare while others are very abundant. The number of species derived from listing does not account for differences in commonness or rarity.

Our deficiency in specifying measures of biodiversity is due to lack of field data not lack of theory on the subject. As far back as 1949, Simpson published a measure of diversity – the Simpson Index. Information-based measures also have been available since 1949 (Shannon and Weaver). Pielou reviewed the theory of diversity indices in 1969 and separate measures of both diversity and “evenness” or the variation in commonness and rarity, have been available since then.

It is unfortunate that we have slipped back into trying to draw conclusions based on biodiversity from species lists without being given insightful measures of diversity.