Should we conserve phylogenetic diversity?
Analysis from data on ecologically-relevant traits from >15,000 vertebrate species show that maximizing phylogenetic diversity results in an average gain of 18% of functional diversity relative to random choice, but this gain is not significant
The full paper is here
Phylogenetic diversity and conservation biology
There is clearly academic interest in phylogenetic diversity (PD) as a metric of conservation prioritization: Dan Faith’s seminal 1992 paper has been cited more than 2329 times as of June 2018 (data: Google Scholar). Adoption by conservationists, however, has been delayed in the extreme, in part due to the lack of strong conceptual and empirical links between phylogenetic diversity and more traditionally valued aspects of biodiversity. Beginning in 2016, Arne O. Mooers and Caroline Tucker organized a diverse set of young scientists to focus on the links between PD and values relevant to conservation. With support from the Synthesis Centre of the German Centre for Integrative Biodiversity Research and the Canadian Institute for Ecology and Evolution, the working group met three times over two years. I started my first post-doc with the objective to lead some of this necessary synthesis work.
Why should we conserve phylogenetic diversity?
During our first meeting in Ottawa (Fig. 1), the working group identified that a key (but often unstated) argument for conserving PD is that by protecting more PD, we should also protect a greater amount of total trait (or functional) diversity (FD). Protecting greater trait diversity in turn might lead to the maintenance of more biological goods and ecosystem services for direct use, increased ‘option value’ (i.e. biological goods useful in the future), and the raw material for future biodiversity production via evolution. This central hypothesis, which we named the ‘phylogenetic gambit,’ has been widely embraced by some academic biologists but had, surprisingly, never been tested. The aim of my post-doc became to test just that. The question was simple: if we chose a subset of species to maximizing the phylogenetic diversity contained in that group, do we also capture more functional diversity (FD) compared to if we just selected a random subset of the same number of species?
Troubling theoretical results…
I started exploring this question using simulations. We had strong expectations that the PD-maximization strategy should be better at capturing FD than random choice. But we were wrong, and that was pretty exciting: in some plausible evolutionary scenarios, maximizing PD could actually lead to lower FD than a random choice. This somewhat troubling finding had the potential to invalidate the PD-based conservation program (Mazel et al. 2017).
I took these simulations results to the additional meetings were held in Leipzig (Figure 2). The real question in all of our minds was, 'what does the phylogenetic gambit look like in the real world?' We identified global datasets of the distribution, traits and phylogenies for >15,000 mammals, birds and fish species. When I applied the same question (does selecting species to maximize PD better capture PD compared to a random set?) to this data, I found that prioritizing the most phylogenetically diverse set of species did lead to an average gain of 18% more trait diversity compared to applying the same conservation effort without considering phylogeny (Figure 4). The phylogenetic gambit seemed to pay off in the real world. However, this average gain masked an important caveat: the PD prioritization scheme on our data was quite unreliable - in fully 36% of all our runs, it captured less FD than a scheme that ignores phylogeny. The troubling feeling remained.
So, what’s next? Shall we abandon or pursue the PD-based conservation program? Our empirical test suggests that, while global conservation initiatives focusing on PD will, on average, capture more FD than a random strategy, it might be considered fairly risky. However, we are not ready to say more: our test needs to be repeated in other taxa and at other spatial scale, and, critically, with other and more trait data. Given how important plants are to ecosystems, they should be the next target. There seems no other way to narrow the uncertainties of our results.
Faith, D. P. (1992). Conservation evaluation and phylogenetic diversity. Biological conservation, 61(1), 1-10.
Mazel, F. et al. 2017. Conserving Phylogenetic Diversity Can Be a Poor Strategy for Conserving Functional Diversity. - Syst. Biol. 66: 1019–1027.