EDGE2: advancing the prioritisation of threatened evolutionary history for conservation action

Abstract

The global biodiversity crisis threatens the natural world and its capacity to provide benefits to humans into the future. The conservation of evolutionary history, captured by the measure phylogenetic diversity (PD), is linked to the maintenance of these benefits and future options. The Evolutionarily Distinct and Globally Endangered (EDGE) metric has, since 2007, been used to identify species for conservation action that embody large amounts of threatened evolutionary history. In 2017, we convened a workshop to update the EDGE metric to incorporate advances in the field of phylogenetically-informed conservation. Building on that workshop, we devised the metric ‘EDGE2’, which we present here. EDGE2 uses a modular, tiered approach to provide priority rankings—and associated measures of uncertainty in both phylogenetic and extinction risk data—for all species in a clade. EDGE2 takes into account the extinction risk of closely-related species to better reflect the contribution a species is expected to make to overall PD in the future. We applied EDGE2 to the world’s mammals to identify an updated list of priority EDGE species and compare the results with the original EDGE approach. Despite similarity in the priority lists produced between EDGE and EDGE2, EDGE2 places greater priority on species with fewer close relatives on the Tree of Life. As we approach a crossroads for global biodiversity policy, EDGE2 exemplifies how academic and applied conservation biologists can collaborate to guide effective priority-setting to conserve the most irreplaceable components of biodiversity upon which humanity depends.

Conserving evolutionary history to safeguard our future: incorporating the Tree of Life into biodiversity policy

“…The EDGE scores of species can be calculated as species-specific contributions to expected PD loss (Steel et al 2007;Faith et al 2018;Gumbs et al 2022), and can be derived for birds, cycads and mammals from the phylogenetic trees with branches weighted by extinction risk for the calculation of the expected PD loss indicator outlined above. The expected PD loss contribution of a species can be calculated from a phylogenetic tree whose branch lengths have been multiplied by the overall probability of extinction of descendant species, such as those trees used to calculate the PD indicator outlined above.…”

“…We used the median EDGE score for each species to represent its EDGE score at that point in time. Priority EDGE Species were identified as those species with above median expected PD contributions and in Red List threatened categories at that RLI time point (Isaac et al 2007;Gumbs et al 2022). The whole process was repeated for each RLI time point and we calculated several components as follows (also see Appendix S2): a. i.…”

“…Our updated approach to estimate the PD indicator explicitly incorporates the concept of PD complementarity to directly estimate the expected loss of branches of the Tree of Life. This approach is widely recommended for accurate calculation of expected PD loss (Steel et al 2007; Faith 2008; Nunes et al 2015; Faith et al 2018; Gumbs et al 2022) but was not used for the initial IPBES PD indicator formulation (for detailed methods, see Appendix S2). Our updated PD indicator utilises probabilities of extinction—converted from IUCN Red List categories (Mooers et al 2008)—to calculate the amount of PD expected to be lost from each branch of the Tree of Life, based on the probability that the set of species responsible for the survival of that branch are lost in the future.…”

Comparing species and evolutionary diversity metrics to inform conservation

“…However, environmental changes are causing losses that go unnoticed by traditional species‐based metrics. Conservation can be much more effective when based on phylogenetic diversity (Gumbs et al, 2022; Laity et al, 2015; Voskamp et al, 2022). Colombia contains great richness of landraces and CWR species which are highly valuable genetic resources for food and agriculture (Eastwood et al, 2022; González‐Orozco, Sosa, et al, 2021; Maxted & Vincent, 2021), but PD measurements have not been widely applied to identify centres of diversity of CWR due to lack of genetic data.…”

“…Phylogenetic diversity metrics can capture both the evolution of species over time and the relationship between species in the Tree of Life (González‐Orozco et al, 2016). The Evolutionarily Distinct and Globally Endangered (EDGE) approach is a PD‐derived metric that has been used to identify threatened evolutionary history and hence, improve conservation actions (Faith, 2019; Gumbs et al, 2022). Evolutionarily Distinct and Globally Endangered has proven to be helpful in identifying endangered species with fewer close relatives (Gumbs et al, 2022).…”