The Earth's evolutionary history is threatened by species loss in the current sixth mass extinction event in Earth's history. Such extinction events not only eliminate species but also their unique evolutionary histories. Here we review the expected loss of Earth's evolutionary history quantified by phylogenetic diversity (PD) and evolutionary distinctiveness (ED) at risk.
I came across this interesting publication recently and I find the idea intriguing. A number of colleagues is arguing for a while already that it is important to in quantify the loss not only of species but also of evolutionary history because it might capture the diversity of life better than simple measures of taxonomic richness.
The paper reviews the state of current knowledge on the loss of evolutionary history. The authors review and assess common indices used to quantify evolutionary history and its loss. They also have a closer look at evolutionary history at risk from human impacts and how well it is protected by current conservation practices.
Due to the general paucity of data, global evolutionary history losses have been predicted for only a few groups, such as mammals, birds, amphibians, plants, corals and fishes. Among these groups, there is now empirical support that extinction threats are clustered on the phylogeny; however this is not always a sufficient condition to cause higher loss of phylogenetic diversity in comparison to a scenario of random extinctions. Extinctions of the most evolutionarily distinct species and the shape of phylogenetic trees are additional factors that can elevate losses of evolutionary history. Consequently, impacts of species extinctions differ among groups and regions, and even if global losses are low within large groups, losses can be high among subgroups or within some regions.
The study also shows that evolutionary history is poorly protected by current conservation practices. Although there is a chance that it is indirectly protected by current conservation schemes, it needs optimization by integrating phylogenetic indices with those that capture rarity and extinction risk. The paper shows a potential approach to this by using both PD and ED and ways to quantify loss for both utilizing a species' IUCN threat status.
The authors repeatedly argue that data availability and quality, in particular, on species phylogenetic relationships and extinction probabilities are key to proper predictions of PD and ED loss. I agree with them that important progress has been made and I think that the large amount of DNA barcode data could be much more utilized. PD of barcode sequences for example has been used a few times calculate accumulation curves to determine completeness of sampling.
Of course, there is no such thing as enough data but some of the remaining challenges actually lie in the evaluation of a threat status for data-deficient species. Such improvements could provide more complete and accurate predictions paving a way for phylogenetic diversity and evolutionary distinctiveness to become part of routine conservation practices.