E-Letter responses to:

special/viewpoint: Georgina M. Mace, John L. Gittleman, and Andy Purvis Preserving the Tree of Life Science 2003; 300: 1707-1709 [Abstract] [Full text] [PDF]

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Biodiversity conservation and the tree-of-life

Daniel P. Faith   (28 July 2003)

Biodiversity conservation and the tree-of-life 28 July 2003
Daniel P. Faith, research scientist The Australian Museum Respond to this E-Letter: Re: Biodiversity conservation and the tree-of-life	Mace et al. (1) describe how knowledge of the tree-of-life can help biodiversity conservation. They make a strong link from phylogeny to conservation in identifying the "phylogenetic diversity" ("PD") measure (2) as a "natural measure of biodiversity." They also support the largely untested conjectures (2) that PD not only may help sidestep the species problem but also may provide important new information about the biodiversity value of places. Mace et al. outline conditions, following Rodrigues et al. (3), under which PD-based valuation of places might differ from conventional species-counting. I think their arguments for PD valuation can be made even stronger, because the conditions can be made less restrictive. One reasonable stated condition implies that the species that have high PD contributions should have small geographic ranges -- that way, the PD contribution is valued because it has complementarity (2) to other places. Of course, the PD valuation will contrast with species-counting only if species counts for that place don't also yield high complementarity. A final stated condition, that "old" species are found in species-poor areas, is seen as "a particularly important one for future research." I think that this condition can be relaxed in two ways. First, the key PD value species need not be "old" ones, based on branches whose length reflects time. PD [even when called "evolutionary history" (4)] includes, but is not restricted to, branch lengths based on time. When branch lengths more generally reflect anagenesis (2), a "young" species might make high PD contributions, by nature of its rapid character evolution. So, we can replace "old" with the more general "highly divergent." Second, PD can produce different results even when such key species are found in species-rich places. For example, an approximate condition for differences in PD endemism (2, 4) versus species-endemism is that highly divergent species (or clades) are restricted to a place if and only if that place has few other endemic species. Thus, for places with many endemic species, there will be high species endemism but low PD endemism; for places with few endemic species, there will be low species endemism but high PD endemism (5). All of these places might have high overall species richness. More generally, PD will yield different results from species-counting for the same taxonomic group if PD assigns different complementarity values to places. But the presence or absence of such differences says little. PD-based complementarity values will only benefit biodiversity conservation if they are more predictive of the complementarity values obtained if we could assess all of biodiversity (6). In asking "does phylogeny make a difference?", exploring the conditions required for predicting complementarity (6) is a good focus for future research. References and Notes G. M. Mace, J. L. Gittleman, A. Purvis, Science 300, 1707 (2003). D. P. Faith, Biol. Conserv. 61, 1 (1992). A. S. L. Rodrigues, T. M. Brooks, K. J. Gaston, in Phylogeny and Conservation, A. Purvis, T. M. Brooks, J. L. Gittleman, Eds. (Cambridge Univ. Press, Cambridge, in press). D. P. Faith, in Systematics and Conservation Evaluation, P. L. Forey, C. J. Humphries, R. I. Vane-Wright, Eds. (Clarendon Press, Oxford, 1994). G. Cassis et al. (in prep.) find both kinds of differences in a comparison of species-based endemism and PD-based endemism in Australia. D. P. Faith, P. A. Walker, Biod. Lett. 3, 18 (1996).