Data from: Preference for mammalian urine is higher in the canopy than on the ground in a tropical rainforest ant community in Yunnan, China

Ants are among the most abundant groups of arthropods, and approximately half of all ant species are associated with forest canopies. The forest canopy environment is distinct from the understory and forest floor, and vertical stratification in environmental conditions shapes species assembly and organismal traits and behaviors across taxa in forest communities. Canopy ants are faced with a more nitrogen-limited environment compared with ground ants because of their reliance on nitrogen-poor plant and insect exudates. Despite prior work suggesting that some ant species consume mammalian urine and use symbiotic bacteria to extract nitrogen, we have little knowledge about the consumption of urine in canopy ants or the relative preference for urine between ground and canopy ants. We conducted an observational field experiment in a lowland tropical rainforest in southern China to test for vertical stratification in ant preference for sugar and urine, setting ground and canopy baited pitfall traps with the use of a canopy crane. We found distinct vertical stratification in the use of urine, with higher richness and abundance in sugar baits on the ground, and a higher abundance in urine baits in the canopy. Furthermore, the composition of captured ants differentiated according to both vertical stratum and bait type. This distinct vertical stratification of niche preference may represent an important case of niche partitioning that contributes to high ant species diversity in tropical rainforests as well as high species turnover between ground and canopy strata. The preference of canopy ants for mammalian urine also highlights the importance of interspecific interactions across highly unrelated animal taxa and emphasizes the need for a holistic understanding of biological networks to effectively conserve threatened tropical forest communities.

蚂蚁是节肢动物（arthropods）中物种丰度最高的类群之一，全世界约半数蚂蚁物种与林冠层（forest canopy）相关联。林冠层环境与林下层（understory）及林地表层（forest floor）差异显著，环境条件的垂直分层（vertical stratification）塑造了森林群落中各生物类群的物种组装模式、生物体性状与行为特征。相较于地表蚂蚁，林冠层蚂蚁所处环境的氮素更为匮乏，这是因为它们依赖氮含量较低的植物与昆虫分泌物（exudates）。尽管已有研究表明部分蚂蚁物种会取食哺乳动物尿液，并借助共生细菌（symbiotic bacteria）获取氮素，但目前学界对林冠层蚂蚁的尿液取食行为，以及地表与林冠层蚂蚁对尿液的相对偏好仍知之甚少。本研究在中国南部的一处低地热带雨林（lowland tropical rainforest）中开展野外观测实验，以探究蚂蚁对糖类与尿液的偏好是否存在垂直分层现象。实验借助林冠起重机（canopy crane）布设了地表与林冠层的带诱饵陷阱罐（baited pitfall traps）。实验结果显示，蚂蚁对尿液的利用存在显著的垂直分层：地表糖类诱饵诱集到的蚂蚁物种丰富度（richness）与个体丰度（abundance）均更高，而林冠层尿液诱饵的蚂蚁个体丰度则显著更高。此外，诱集得到的蚂蚁群落组成同时受垂直分层与诱饵类型的影响而发生分化。这种显著的生态位偏好（niche preference）垂直分层现象，或代表了一类重要的生态位分化（niche partitioning）案例，其既有助于提升热带雨林的蚂蚁物种多样性，也驱动了地表与林冠层之间的物种更替（species turnover）。林冠层蚂蚁对哺乳动物尿液的偏好，亦凸显了亲缘关系甚远的动物类群之间种间互作（interspecific interactions）的重要性，同时强调，若要有效保护受威胁的热带雨林群落，需对生物网络（biological networks）形成整体性认知。