The biotic interactions hypothesis posits that biotic interactions are more important drivers of adaptation closer to the equator, evidenced by “stronger” contemporary interactions (e.g., greater interaction rates) and/or patterns of trait evolution consistent with a history of stronger interactions. Support for the hypothesis is mixed, but few studies span tropical and temperate regions while experimentally controlling for evolutionary history. Here, we integrate field observations and common garden experiments to quantify the relative importance of pollination and herbivory in a pair of tropical‐temperate congeneric perennial herbs. Phytolacca rivinoides and P. americana are pioneer species native to the Neotropics and the eastern United States, respectively. We compared plant–pollinator and plant–herbivore interactions between three tropical populations of P. rivinoides from Costa Rica and three temperate populations of P. americana from its northern range edge in Michigan and Ohio. For some metrics of interaction importance, we also included three subtropical populations of P. americana from its southern range edge in Florida. This approach confounds species and region but allows us, uniquely, to measure complementary proxies of interaction importance across a tropical‐temperate range in one system. To test the prediction that lower‐latitude plants are more reliant on insect pollinators, we quantified floral display and reward, insect visitation rates, and self‐pollination ability (autogamy). To test the prediction that lower‐latitude plants experience more herbivore pressure, we quantified herbivory rates, herbivore abundance, and leaf palatability. We found evidence supporting the biotic interactions hypothesis for most comparisons between P. rivinoides and north‐temperate P. americana (floral display, insect visitation, autogamy, herbivory, herbivore abundance, and young‐leaf palatability). Results for subtropical P. americana populations, however, were typically not intermediate between P. rivinoides and north‐temperate P. americana, as would be predicted by a linear latitudinal gradient in interaction importance. Subtropical young‐leaf palatability was intermediate, but subtropical mature leaves were the least palatable, and pollination‐related traits did not differ between temperate and subtropical regions. These nonlinear patterns of interaction importance suggest future work to link interaction importance to climatic or biotic thresholds. In sum, we found that the biotic interactions hypothesis was more consistently supported at the larger spatial scale of our study.

中文翻译：

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热带-温带同类对的昆虫授粉和草食性纬度分布模式的多个指标

生物相互作用假说认为，生物相互作用是更接近赤道的更重要的适应驱动力，这通过“更强的”当代相互作用（例如，更高的相互作用速率）和/或与更强相互作用的历史相一致的性状进化模式得到证明。对这一假设的支持是混杂的，但是很少有研究在实验控制进化史的同时跨越热带和温带地区。在这里，我们将实地观察和常见的园林实验相结合，以量化在一对热带温带同类多年生草本植物中授粉和食草的相对重要性。百草枯和美洲假单胞菌分别是新热带和美国东部的先驱物种。我们比较了来自哥斯达黎加的三个热带河豚对虾和来自北密歇根州和俄亥俄州的美洲温带河豚的三个温带种群之间的植物-授粉和植物-草食动物相互作用。对于某些交互重要性的指标，我们还包括了美洲假单胞菌的三个亚热带种群从它在佛罗里达南部的山脉边缘开始。这种方法混淆了物种和地区，但使我们能够唯一地在一个系统中测量热带温度范围内相互作用重要性的互补代理。为了检验低纬度植物更依赖昆虫传粉者的预测，我们量化了花卉展示和奖励，昆虫探视率和自花授粉能力（同性配子）。为了检验低纬度植物遭受食草动物压力的预测，我们量化了食草动物的比率，食草动物的丰度和叶片的适口性。我们发现证据支持大多数生物之间的生物相互作用假说之间的比较R. rivinoides和北温带P.美洲（花卉展示，昆虫探访，同性配偶，草食，草食动物丰富度和幼叶适口性）。但是，亚热带美洲P.美洲种群的结果通常不在里维尼亚P. rivinoides和北温带美洲P. Americana之间，这将由交互重要性中的线性纬度梯度来预测。亚热带幼叶适口性中等，但亚热带成熟叶片的可口性最低，在温带和亚热带地区，与传粉有关的性状没有差异。这些交互作用重要性的非线性模式表明了将交互作用重要性与气候或生物阈值联系起来的未来工作。总而言之，我们发现在我们研究的较大空间范围内，生物相互作用假说得到了更一致的支持。