Human-mediated species invasion and climate change are leading to global extinctions and are predicted to result in the loss of important axes of phylogenetic and functional diversity. However, the long-term robustness of modern communities to invasion is unknown, given the limited timescales over which they can be studied. Using the fossil record of the Paleocene-Eocene thermal maximum (PETM; ∼56 Ma) in North America, we evaluate mammalian community-level response to a rapid global warming event (5°–8°C) and invasion by three Eurasian mammalian orders and by species undergoing northward range shifts. We assembled a database of 144 species body sizes and created a time-scaled composite phylogeny. We calculated the phylogenetic and functional diversity of all communities before, during, and after the PETM. Despite increases in the phylogenetic diversity of the regional species pool, phylogenetic diversity of mammalian communities remained relatively unchanged, a pattern that is invariant to the tree dating method, uncertainty in tree topology, and resolution. Similarly, body size dispersion and the degree of spatial taxonomic turnover of communities remained similar across the PETM. We suggest that invasion by new taxa had little impact on Paleocene-Eocene mammal communities because niches were not saturated. Our findings are consistent with the numerous studies of modern communities that record little change in community-scale richness despite turnover in taxonomic composition during invasion. What remains unknown is whether long-term robustness to biotic and abiotic perturbation are retained by modern communities given global anthropogenic landscape modification.

中文翻译：

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通过新世-始新世热最大值的哺乳动物群落结构。

人类介导的物种入侵和气候变化正在导致全球灭绝，并预计将导致系统发育和功能多样性重要轴的丧失。但是，由于研究它们的时间范围有限，现代社区对入侵的长期稳定性尚不明确。利用北美古新世-始新世热最大值（PETM；〜56 Ma）的化石记录，我们评估了哺乳动物对快速全球变暖事件（5°-8°C）和三个欧亚哺乳动物入侵的社区响应和经历北移的物种。我们组装了一个144种物种的体型数据库，并创建了一个按时标的复合系统发育史。我们计算了PETM之前，之中和之后所有社区的系统发育和功能多样性。尽管区域物种库的系统进化多样性有所增加，但哺乳动物群落的系统进化多样性仍然相对不变，这种模式与树木定年方法，树木拓扑结构的不确定性和分辨率无关。同样，在整个PETM中，人体的大小分布和社区的空间生物分类学变化程度仍然相似。我们建议新生物群的入侵对古新世-始新世哺乳动物群落几乎没有影响，因为生态位并未饱和。我们的发现与现代社区的大量研究一致，尽管入侵期间生物分类的组成发生了变化，但社区规模的丰富程度几乎没有变化。