A challenge for nature conservation is to know why many species are absent from suitable habitats and whether they might be able to disperse and to establish. Here, we used 272 dry grassland patches within a fragmented landscape to investigate the role of local abiotic conditions and dispersal filtering in determining the likelihood of vascular plants to belong to the dark diversity (i.e. absent portion of the species pool). First, we quantified the species (SD), functional (FD) and phylogenetic (PD) diversity of both observed and dark communities. Second, we determined the roles of abiotic, present‐day and historical landscape configuration variables in shaping their patterns. Third, we evaluated the importance of each variable in determining their species. Environmental filtering was assessed as effects of local abiotic conditions and dispersal filtering as the effects of present‐day and historical landscape configuration. Dispersal filtering was also estimated by comparing dispersal traits of observed and dark diversity. Finally, we assessed community completeness to determine how much of the species pool was realized within a local community. We found higher SD in the observed compared to the dark communities, but PD did not differ. Contrary to expectations, dark communities resembled higher FD compared to the observed communities. Species with low dispersal capacity, low competitive abilities and high stress‐tolerance were more often absent. Observed and dark diversities were mostly affected by local abiotic variables. In the observed communities, present‐day landscape configuration variables affected SD while historical landscape configuration variables explained FD and PD. In the dark communities, we found the opposite pattern. Completeness was affected by present‐day and historical patch size. Our results explain why dry grassland species may belong to the dark diversity and highlight the importance of local abiotic and dispersal traits of the species to conserve dry grasslands in changing landscapes.

中文翻译：

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功能性状决定了为什么物种属于干旱草地破碎景观中的黑暗多样性

自然保护的挑战是要知道为什么合适的生境中缺少许多物种，以及它们是否能够传播和建立。在这里，我们在一个零散的景观中使用了272个干燥的草原斑块，以调查当地非生物条件和分散过滤在确定维管植物属于黑暗多样性（即物种库中缺少的部分）的可能性中的作用。首先，我们对观察到的社区和黑暗社区的物种（SD），功能（FD）和系统发生（PD）多样性进行了量化。其次，我们确定了非生物，当今和历史景观配置变量在塑造其模式中的作用。第三，我们评估了每个变量在确定其种类方面的重要性。环境过滤被评估为当地非生物条件的影响，而分散过滤被评估为当前和历史景观配置的影响。分散过滤也通过比较观察到的和黑暗多样性的分散特性来估计。最后，我们评估了社区的完整性，以确定在本地社区内实现了多少物种库。与黑暗社区相比，我们发现观察到的SD较高，但PD并无差异。与预期相反，与观察到的社区相比，黑暗社区的FD更高。低散布能力，低竞争能力和高耐压性的物种更为常见。观察到的和黑暗的多样性主要受当地非生物变量的影响。在观察到的社区中，今天的景观配置变量影响了SD，而历史景观配置变量则解释了FD和PD。在黑暗的社区中，我们发现了相反的模式。完整性受当今和历史补丁大小的影响。我们的结果解释了为什么干旱草原物种可能属于黑暗多样性，并突出了该物种的当地非生物和分散性对于在不断变化的景观中保护干旱草原的重要性。