Elevational gradients affect the production of plant secondary metabolites through changes in both biotic and abiotic conditions. Previous studies have suggested both elevational increases and decreases in host-plant chemical defences. We analysed the correlation of alkaloids and polyphenols with elevation in a community of nine Ficus species along a continuously forested elevational gradient in Papua New Guinea. We sampled 204 insect species feeding on the leaves of these hosts and correlated their community structure to the focal compounds. Additionally, we explored species richness of folivorous mammals along the gradient. When we accounted for Ficus species identity, we found a general elevational increase in flavonoids and alkaloids. Elevational trends in non-flavonol polyphenols were less pronounced or showed non-linear correlations with elevation. Polyphenols responded more strongly to changes in temperature and humidity than alkaloids. The abundance of insect herbivores decreased with elevation, while the species richness of folivorous mammals showed an elevational increase. Insect community structure was affected mainly by alkaloid concentration and diversity. Although our results show an elevational increase in several groups of metabolites, the drivers behind these trends likely differ. Flavonoids may provide figs with protection against abiotic stressors. In contrast, alkaloids affect insect herbivores and may provide protection against mammalian herbivores and pathogens. Concurrent analysis of multiple compound groups alongside ecological data is an important approach for understanding the selective landscape that shapes plant defences.

中文翻译：

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沿上升梯度的榕树化学防御的复合特定趋势反映了复杂的选择性环境。

上升梯度通过生物和非生物条件的变化影响植物次生代谢产物的产生。先前的研究表明，寄主植物化学防御力的升高和降低均会增加。我们分析了巴布亚新几内亚沿连续森林海拔梯度的9个榕属物种群落中生物碱和多酚与海拔的相关性。我们采样了以这些寄主的叶子为食的204种昆虫，并将它们的群落结构与主要化合物相关联。此外，我们探索了沿梯度食性哺乳动物的物种丰富度。当我们占榕物种同一性，我们发现类黄酮和生物碱的总海拔升高。非黄酮醇多酚的上升趋势不太明显，或与海拔呈非线性关系。与生物碱相比，多酚对温度和湿度的变化反应更强烈。昆虫食草动物的丰度随海拔升高而降低，而食性哺乳动物的物种丰富度则呈升高趋势。昆虫群落结构主要受生物碱浓度和多样性的影响。尽管我们的结果显示几类代谢物的升高，但这些趋势背后的驱动因素可能有所不同。类黄酮可以为无花果提供保护，使其免受非生物胁迫的侵害。相反，生物碱会影响昆虫的食草动物，并可能针对哺乳动物的食草动物和病原体提供保护。