Abstract
There is an increasing interest in measuring loss of phylogenetic diversity and evolutionary distinctiveness which together depict the evolutionary history of conservation interest. Those losses are assessed through the evolutionary relationships between species and species threat status or extinction probabilities. Yet, available information is not always sufficient to quantify the threat status of species that are then classified as data deficient. Data‐deficient species are a crucial issue as they cause incomplete assessments of the loss of phylogenetic diversity and evolutionary distinctiveness. We aimed to explore the potential bias caused by data‐deficient species in estimating four widely used indices: HEDGE, EDGE, PDloss, and Expected PDloss. Second, we tested four different widely applicable and multitaxa imputation methods and their potential to minimize the bias for those four indices. Two methods are based on a best‐ vs. worst‐case extinction scenarios, one is based on the frequency distribution of threat status within a taxonomic group and one is based on correlates of extinction risks. We showed that data‐deficient species led to important bias in predictions of evolutionary history loss (especially high underestimation when they were removed). This issue was particularly important when data‐deficient species tended to be clustered in the tree of life. The imputation method based on correlates of extinction risks, especially geographic range size, had the best performance and enabled us to improve risk assessments. Solving threat status of DD species can fundamentally change our understanding of loss of phylogenetic diversity. We found that this loss could be substantially higher than previously found in amphibians, squamate reptiles, and carnivores. We also identified species that are of high priority for the conservation of evolutionary distinctiveness.
Highlights
Scientists estimate that 500–36,000 species disappear each year (Monastersky 2014), which could result in a sixth mass extinction event
We found that the imputation method based on geographic range size performed the best to minimize bias in ExpPDloss, Phylogenetic Diversity loss (PDloss), Heightened Evolutionary Distinctiveness and Global Endangerment (HEDGE) and EDGE scores in amphibians and squamates independently of the parameters used (Fig. 2, Appendix S5)
We found that using both information on geographic range size and body mass generally performed best to approach the true values of HEDGE and EDGE (Fig. 2) and to correctly predict threat status (Fig. 3)
Summary
Scientists estimate that 500–36,000 species disappear each year (Monastersky 2014), which could result in a sixth mass extinction event. Species provide a wide range of benefits to ecosystems and humans most of them being still unexpected (Gascon et al 2015). Preserving phylogenetic diversity (PD) has been argued to be the best strategy to preserve those unexpected services, called option values (Gascon et al 2015; Lean and MacLaurin 2016). Conserving PD is all the more crucial as risks to lose PD may be higher than those to lose species richness due to the phylogenetic clustering of threats and to the extinctions of evolutionary distinct species (Veron et al 2016). Losing species which capture high amounts of phylogenetic diversity may have important consequences for our culture and history a 2016 The Authors.
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