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The diversity of currently extant species is the result of many different evolutionary lineages. While life on Earth started several thousand million years ago, life on Earth, in terms of the total number of years of evolution, represents many times this figure. Extinction, of course, permanently erases evolutionary lineages. Therefore, conservation scientists, often implicitly but increasingly explicitly, rank which species to save in these phylogenetic diversity terms. The more evolutionary distinct a species is, the more important it is to conserve it.

One of the good news about evolutionary lineages is that the vast majority of species are recently diverged. Nee and May in 1997 showed that for most real phylogenies, a random extinction of species would result in a relatively low amount of lost evolutionary history, as most species are closely related. So it is relatively straight-forward to save phylogenetic diversity? Unfortunately no. Purvis et al. 2000 showed that mammal and bird species that tend to be at risk tend to be in small taxa. So losing species that are currently at risk will result in more lost evolutionary history than under random extinction.

Nobody, however, has done a similar analysis on plants. Interestingly, rarity in plants at local scales is clustered in speciose taxa. Note that rarity is separate from extinction risk: some species are adapted to living at low numbers and/or density, whereas some species with large populations (and so not considered ‘rare’) may be very sensitive to sudden environmental changes.

In collaboration with a researcher from Canada, a C·I·B post-doc investigated phylogenetic patterns in the IUCN global red list for angiosperms (a list of those species that are of conservation concern). As with mammals and birds, species-poor (especially monotypic) angiosperm families are more often at risk of extinction than expected. This means that the amount of evolutionary history plausibly lost in the next 100 years exceeds that predicted from random extinction by up to 1165 million years!

And the good news? These high-risk species-poor families are as evolutionarily distinct as other families. Therefore extinction risk is not concentrated in basal lineages at the family level. Perhaps small comfort, but it pays to take it where you can.

Nee, S. & May, R. M. (1997) Extinction and the loss of evolutionary history. Science, 278, 692-694.

Purvis, A., Agapow, P. M., Gittleman, J. L. & Mace, G. M. (2000) Nonrandom extinction and the loss of evolutionary history. Science, 288, 328-330.

Vamosi, J. C. & Wilson, J. R. U. (2008) Nonrandom extinction leads to elevated loss of angiosperm evolutionary history. Ecology Letters, 11, 1047–1053.

The expected loss of evolutionary history due to predicted family extinction (black) compared to random (red) simulations (10 000 randomizations at 0.01 intervals of P (with a standard background extinction rate of 0.01)). The species predicted to go extinct are those that are categorised as 'at risk' by the IUCN.