Tuesday, March 5, 2013

Evolution of conservation – what counts?

Winter, M., Devictor, V. and Schweiger, O.. 2013. Evolutionary diversity and nature conservation: where are we? Trends in Ecology and Evolution. http://dx.doi.org/10.1016/j.tree.2012.10.015

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?
(Lanna Jin)
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.


Marc Cadotte said...

One of the things that Caroline and I discussed is the incongruent use of terminology. The Winter et al paper refers to phylogenetic diversity (PD) and the Rosauer and Mooers paper to evolutionary diversity (ED). This is confusing since both PD and ED also refer to specific metrics that quantify phylogenetic information.

There needs to be a consensus about terminology for this growing research area.

George Benson said...

What I'm missing from the Rosauer and Mooers piece is an argument about why I shouldn't consider all species equal from a priority perspective. Why are ancestral relationships instrinsically good?

Caroline Tucker said...

Hi George - I think the R & M response is more or less focused on the fact that if we intrinsically value species, we should intrinsically value all forms of diversity, including PD. So from this most pure perspective, why not incorporate PD into conservation?

Completely separate from this argument is the question of why PD over species richness. If we conceptually believe there is value in biodiversity, which has many forms and measures. In a perfect world we would seek to conserve all differences in nature that we could. Taxonomic species do not all equally contribute to the many forms of biodiversity we are interested in and the utility we might hope to preserve - some species, for example, are quite similar. Making choices using "species" as the unit is essentially a random way to capture different forms of biodiversity.

If nothing else, using evolutionary information as the unit of focus means that you capture some component of biodiversity. It's not that ancestral relationships are intrinsically valuable (although some would argue that they are), it's just that if you select based on evolutionary diversity you are now explicitly capturing a part of the biodiversity we want to capture. Obviously there are weaknesses in this argument, and unlike the first argument about intrinsic value, I think it requires that we have some a priori ideas about what we want to value and how species richness vs evolutionary diversity relates to them.

So the first argument is - they both have equal value, hence evolutionary info should be incorporated into conservation. The second is - evolutionary info should be incorporated because it has useful or desirable properties above its intrinsic value.

Marten Winter said...

Thanks for picking this up.
We actually used not PD in the beginning but called it Evolutionary Diversity (EvDiv) but the reviewers wanted to see PD and we explained it in the very 1st paragraph that it shouldn't get confused with the metric PD.
Anyway...I agree that the main two things are:
1. the barrier between our research and existing knowledge and the people on the implementation side, and
2. The still unclear question, what is the value of EvDiv? This is the question we get always asked form conservationsists. And hence your work Marc & team is highly valuable, since you show that EvDiv seems to be important for ecosystem functions.

Thanks and cheers
Marten Winter

Caroline Tucker said...

Hi Marten - the fact that these two papers use different terms to refer to the same conceptual idea definitely muddied the water a bit. And worse, the fact that conceptual ideas (phylogenetic diversity, evolutionary diversity) share names or acronyms with precisely defined metrics definitely makes this area of research a bit confusing to read and write about.

Arne Mooers said...

Hi all,

Vert fun to see this discussion here. To clarify: like Marten, we also used "Evolutionary Diversity" in our letter to match Winter et al.'s terminology (we thought) and to be more general than PD. The term got edited down to ED during production (which most people read as Evolutionary Distinct(ive)ness, as used in the EDGE programme) and we didn't catch it. We apologize for letting that slip through. We agree that we need a common terminology and PD might be the correct general term. Wrt. the value of PD: having it be a surrogate for biodiversity effects on ecosystem function is very exciting and important. However, if this surrogacy does not end up being general, would that mean it is not a meaningful measure of biodiversity? Dan's and my intuition is that it is a meaningful biodiversity value, but more hard thinking is needed.

Caroline Tucker said...

Hi Arne, definitely lots to still be done. Marc and I have been talking a bit about future directions for this kind of research and there are a few I can think of off the top of my head: the obvious need is for more work on making non-species based metrics easily available for use in conservation and planning, something the EDGE program is doing a good job with. Mike Steele (University of Canterbury, NZ) has looked at creating reserve selection algorithms that maximize evolutionary diversity, which is also a good step forward. Secondly, we're far from establishing what the extrinsic value of evolutionary diversity is (I.e. does it relate predictably to ecosystem services? What are the evolutionary dynamics that produce communities with correlated versus uncorrelated evolutionary and functional diversity). And no doubt there are many other things I'm missing...