A long-standing but poorly tested hypothesis in plant ecology and evolution is that biotic interactions play a more important role in producing and maintaining species diversity in the tropics than in the temperate zone. A core prediction of this hypothesis is that tropical plants deploy a higher diversity of phytochemicals within and across communities because they experience more herbivore pressure than temperate plants. However, simultaneous comparisons of phytochemical diversity and herbivore pressure in plant communities from the tropical to the temperate zone are lacking. Here we provide clear support for this prediction by examining phytochemical diversity and herbivory in 60 tree communities ranging from species-rich tropical rainforests to species-poor subalpine forests. Using a community metabolomics approach, we show that phytochemical diversity is higher within and among tropical tree communities than within and among subtropical and subalpine communities, and that herbivore pressure and specialization are highest in the tropics. Furthermore, we show that the phytochemical similarity of trees has little phylogenetic signal, indicating rapid divergence between closely related species. In sum, we provide several lines of evidence from entire tree communities showing that biotic interactions probably play an increasingly important role in generating and maintaining tree diversity in the lower latitudes.

植物生态学和进化中一个长期存在但未经充分检验的假设是，生物相互作用在热带地区比温带地区产生和维持物种多样性方面发挥着更重要的作用。这一假设的核心预测是，热带植物在群落内部和群落之间部署了更高多样性的植物化学物质，因为它们比温带植物承受更多的食草动物压力。然而，缺乏对从热带到温带植物群落的植物化学多样性和食草动物压力的同步比较。在这里，我们通过检查 60 个树木群落（从物种丰富的热带雨林到物种贫乏的亚高山森林）的植物化学多样性和食草性，为这一预测提供了明确的支持。使用群落代谢组学方法，我们表明热带树木群落内部和之间的植物化学多样性高于亚热带和亚高山群落内部和之间的植物化学多样性，并且食草动物的压力和专业化在热带地区最高。此外，我们发现树木的植物化学相似性几乎没有系统发育信号，表明密切相关的物种之间存在快速分化。总之，我们提供了来自整个树木群落的几条证据，表明生物相互作用可能在低纬度地区产生和维持树木多样性方面发挥着越来越重要的作用。