Data from: Conserving phylogenetic diversity can be a poor strategy for conserving functional diversity

For decades, academic biologists have advocated for making conservation decisions in light of evolutionary history. Specifically, they suggest that policy makers should prioritize conserving phylogenetically diverse assemblages. The most prominent argument is that conserving phylogenetic diversity (PD) will also conserve diversity in traits and features (functional diversity [FD]), which may be valuable for a number of reasons. The claim that PD-maximized (“maxPD”) sets of taxa will also have high FD is often taken at face value and in cases where researchers have actually tested it, they have done so by measuring the phylogenetic signal in ecologically important functional traits. The rationale is that if traits closely mirror phylogeny, then saving the maxPD set of taxa will tend to maximize FD and if traits do not have phylogenetic structure, then saving the maxPD set of taxa will be no better at capturing FD than criteria that ignore PD. Here, we suggest that measuring the phylogenetic signal in traits is uninformative for evaluating the effectiveness of using PD in conservation. We evolve traits under several different models and, for the first time, directly compare the FD of a set of taxa that maximize PD to the FD of a random set of the same size. Under many common models of trait evolution and tree shapes, conserving the maxPD set of taxa will conserve more FD than conserving a random set of the same size. However, this result cannot be generalized to other classes of models. We find that under biologically plausible scenarios, using PD to select species can actually lead to less FD compared with a random set. Critically, this can occur even when there is phylogenetic signal in the traits. Predicting exactly when we expect using PD to be a good strategy for conserving FD is challenging, as it depends on complex interactions between tree shape and the assumptions of the evolutionary model. Nonetheless, if our goal is to maintain trait diversity, the fact that conserving taxa based on PD will not reliably conserve at least as much FD as choosing randomly raises serious concerns about the general utility of PD in conservation.

数十年来，学术生物学家一直倡导基于演化历史制定保护决策。具体而言，他们建议政策制定者应优先保护系统发育多样的类群组合。最具影响力的论点指出，保护系统发育多样性（phylogenetic diversity, PD），亦可同时保护性状与特征的多样性——即功能多样性（functional diversity, FD），而这类多样性的价值可源自多方面原因。“最大化系统发育多样性（maxPD）的类群集合，其功能多样性亦会较高”这一主张，常被直接采信；在实际开展相关检验的研究中，学者们均通过测量生态重要功能性状中的系统发育信号（phylogenetic signal）来验证该主张。其背后的逻辑为：若性状紧密反映系统发育关系，那么选择maxPD类群集合往往能最大化功能多样性；若性状不存在系统发育结构，那么选择maxPD类群集合在捕获功能多样性方面，并不优于忽略系统发育多样性的选择标准。本文中，我们提出，通过测量性状中的系统发育信号来评估PD在保护中的有效性，并无参考价值。我们基于多种不同的演化模型生成性状，并首次直接对比了maxPD类群集合与同等规模随机类群集合的功能多样性。在诸多常见的性状演化与系统发育树结构模型下，选择maxPD类群集合所保留的功能多样性，要高于选择同等规模随机类群集合的结果。然而，这一结论无法推广至其他类别演化模型。我们发现，在生物学上合理的场景中，基于PD选择物种，反而可能比随机选择保留更少的功能多样性。尤为关键的是，即便性状中存在系统发育信号，这一情况仍可能发生。准确预判何时采用PD作为保护策略以保留功能多样性颇具挑战，因为这取决于系统发育树结构与演化模型假设之间的复杂相互作用。尽管如此，若我们的目标是维持性状多样性，那么“基于PD选择类群，无法可靠地至少保留与随机选择同等规模的功能多样性”这一事实，无疑对PD在保护领域的通用实用性提出了严峻质疑。