Biodiversity – All Listed Species are not Equal

“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.

2 comments to Biodiversity – All Listed Species are not Equal

  • What about the argument that is often presented that conservationists are attempting to maintain what is naturally a system in flux? I might argue that the rate of extinction is dramatic and in the most part human induced, therefore we have an ethical obligation to mitigate those impacts. But when you’re looking at impacts in the arctic of a 5 degree C increase in annual temperatures… how do you turn back that clock? And are resources wasted on the polar bear?

    To your point about a lack in field data, the feds really need to invest in research and development in more areas than carbon capture and storage. To that end I will do all I can. And if anyone needs a research assistant in the arctic, please ask me first!!

    Love the blog
    ps. if you can please add e-mail, facebook or twitter sharing and this will help us spread the word.

  • Bardi Vorster

    Hi There Gray and Aileen,
    This is great! I usually don’t ‘blog’ but this subject is near an dear to my heart. I would like to build a new reference library of ecosystems information and I’m happy to find a full bibliography to start me on my journey. There is always something to learn, re-discover re-think and change.


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