Abstract
In the face of limited funding and widespread threats to biodiversity, conserving the widest possible variety of biological traits (functional diversity, FD) is a reasonable prioritization objective. Because species traits are often similar among closely related species (phylogenetic signal), many researchers have advocated for a “phylogenetic gambit”: maximizing phylogenetic diversity (PD) should indirectly capture FD. To our knowledge, this gambit has not been subject to a focused empirical test. Here we use data from >15,000 vertebrate species to empirically test it. We delineate >10,000 species pools and test whether prioritizing the most phylogenetically diverse set of species results in more or less FD relative to a random choice. We find that, across species pools, maximizing PD results in an average gain of 18% of FD relative to a random choice, suggesting that PD is a sound conservation prioritization strategy. However, this averaged gain hides important variability: for 10% of the species pools, maximizing PD can capture less FD than an averaged random scheme because of recent trait divergence and/or very strong trait conservatism. In addition, within a species pool, many random sets of species actually yield more FD than the PD-maximized selection – on average 36% of the time per pool. If the traits we used are representative of traits we wish to conserve, our results suggest that conservation initiatives focusing on PD will, on average, capture more FD than a random strategy, but this gain will not systematically yield more FD than random and thus can be considered risky.