and the response:
Rosauer, D.F. and Mooers, A.O. 2013. Nurturing the use of evolutionary diversity in nature conservation. Trends in Ecology and Evolution. http://dx.doi.org/10.1016/j.tree.2013.01.014
The problem has been called the agony of choice – available resources for conservation are dwarfed by need. And as a result, we are forced to prioritize, to save some species and lose others. Much of the attention given to phylogenetics in ecology lately is on its use, questionable or otherwise, in ecophylogenetic metrics. However the important and useful research being done relating evolutionary information to conservation decisions deserves more attention.
This work has created a recurrent and sometimes contradictory discussion about whether evolutionary relationships contribute complementary information to traditional conservation targets (e.g. biodiversity, habitat types) and whether such information can easily be incorporated into conservation activities (e.g. Rodrigues et al. 2005; Faith 2008; Rodrigues et al. 2011; Tucker et al. 2012 etc.). A couple of papers recently in TREE are continuing this discussion and together do a nice job of summarizing the state of evolutionarily informed conservation practices. Most interesting about the article and the response is that even the opposing sides of the discussion appear to be converging on the same conclusion—that evolutionary diversity should be incorporated into conservation decisions—and differ primarily in how they justify this and the extent to which they feel it will be useful.
Phylogenetic diversity (PD) can be defined specifically as a measure of evolutionary diversity, however here it is more generally defined as the evolutionary information (e.g. phylogenetic relatedness) represented in a community and a common measure of evolutionary information. A community with high PD might include many distantly related species and hence represent many branches in a phylogenetic tree. The simplest argument for why PD might inform conservation is that maximizing PD will maximize the range of species’ ecologies and function that is conserved. In contrast, species richness targets have no relation to a community’s functionality.
Although the conservation literature includes many studies of phylogenetic diversity that are oriented towards real-world applications, in practice, conservation activities rarely incorporate PD. Winters et al. seem lukewarm about the value of phylogenetically informed approaches (one header is “A promising but yet ambiguous additional biodiversity component for conservation”). They suggest that there are a number of ways in which phylogenetic diversity can be informative: it can act as a measure of rarity and facilitate decision-making if rarity is a priority (and perhaps other measures of rarity not available) (e.g. http://www.edgeofexistence.org/). It may act as additional information to be incorporated with measures of species richness – areas with similar richness may have very different amounts of PD. However, the authors question “But what would the added value of conserving areas or communities of unexpectedly high phylogenetic diversity, or spending money on phylogenetically eroded areas, actually be?” The most common arguments, they suggest, are that phylogenetic diversity is a proxy for functional diversity and/or a measure of the evolutionary potential of a community. However, since ecological/functional similarity is not always correlated with PD, and evolutionary potential is not related to PD in a predictable manner, these are inadequate.
Winters et al. seem to suggest that PD is valuable because it can (but not always) act as a proxy for things we actually want to account for (rarity, etc). This is the point that the response from Rosauer and Mooers has the hardest time with. Why does evolutionary diversity not have intrinsic value if, say, species diversity does? Further, species richness is objectively a poor measure of diversity, since it treats all species as having equal value. In contrast, phylogenetic measures of diversity already account for one difference (evolutionary distinctiveness) between species, and hence should already be more effective in capturing total diversity in an assemblage. Rosauer and Mooers state “In an era of triage, difficult decisions are being made, and we know that inclusion of [evolutionary diversity] could make a substantial difference to the outcome for biodiversity, suggesting that it should be considered as one among many criteria”.
Regardless of differences in motivation, both authors agree that the greatest barrier is actually in bringing these ideas into practice. There are many ways of measuring evolutionary diversity (and species diversity, if we’re being fair) and choosing the correct metric can be a minefield. Calculating measures of evolutionary relationship requires specialized knowledge. On the other hand, it is easier and faster than ever to generate phylogenetic trees using DNA sequence databases and available software. Further, evolutionary information lacks the attractiveness that taxonomic-focused conservation has (it is more exciting to save the tigers than the genes). So what remains is to make the jump from theory and case studies to practice, and to find ways to explain why an echidna should receive more protection than all the other rodents. But if evolutionary information makes the agony of choice a little less, it is a worthy goal.
|The power of phylogenies?|
Faith D.P. (2008). Threatened species and the potential loss of evolutionary diversity: conservation scenarios based on estimated extinction probabilities and phylogenetic risk analysis. Conservation Biology, 22, 1461-1470.
Rodrigues A.S.L., Brooks T.M. & Gaston K.J. (2005). Integrating evolutionary diversity in the selection of priority areas for conservation: does it make a difference? In: Phylogeny and conservation (eds. Purvis A, Gittleman JL & Brooks TM). Cambridge University Press Cambridge, UK, pp. 101-199.
Rodrigues A.S.L., Grenyer R., Baillie J.E.M., Bininda-Emonds O.R.P., Gittleman J.L., Hoffmann M., Safi K. & al. e. (2011). Complete, accurate, mammalian phylogenies aid conservation planning, but not much. Philosophical Transactions of the Royal Society, London, B, 1579, 2652-2660.
Tucker C.M., Cadotte M.W., Davies T.J. & Rebelo A.G. (2012). The distribution of biodiversity: linking richness to geographical and evolutionary rarity in a biodiversity hotspot. Conservation Biology, 25:2.
Vane-Wright (1991). What to protect - systematics and the agony of choice. Biological conservation, 55, 235-254.