Balancing phylogenetic diversity and species numbers in conservation prioritization, using a case study of threatened species in New Zealand

Funding for managing threatened species is currently insufficient to assist recovery of all species, so management projects must be prioritized. In attempts to maximize phylogenetic diversity conserved, prioritization protocols for threatened species are increasingly weighting species using metrics that incorporate their evolutionary distinctiveness. In a case study using 700 of the most threatened species in New Zealand, we examined trade-offs between emphasis on species’ evolutionary distinctiveness weights, and the numbers of species prioritized, as well as costs and probabilities of success for recovery projects. Increasing emphasis on species’ evolutionary distinctiveness weights in the prioritization protocol led to greater per-species costs and higher risk of project failure. In a realistic, limited-budget scenario, this resulted in fewer species prioritized, which imposed limits on the total phylogenetic diversity that could be conserved. However, by systematically varying the emphasis on evolutionary distinctiveness weight in the prioritization protocol we were able to minimize trade-offs, and obtain species groups that were near-optimal for both species numbers and phylogenetic diversity conserved. Phylogenetic diversity may not equate perfectly with functional diversity or evolutionary potential, and conservation agencies may be reluctant to sacrifice species numbers. Thus, we recommend prioritizing species groups that achieve an effective balance between maximizing phylogenetic diversity and number of species conserved.