Data from: Ant–caterpillar antagonism at the community level: interhabitat variation of tritrophic interactions in a neotropical savanna

1. Ant foraging on foliage can substantially affect how phytophagous insects use host plants and represents a high predation risk for caterpillars, which are important folivores. Ant–plant–herbivore interactions are especially pervasive in cerrado savanna due to continuous ant visitation to liquid food sources on foliage (extrafloral nectaries, insect honeydew). While searching for liquid rewards on plants, aggressive ants frequently attack or kill insect herbivores, decreasing their numbers. Because ants vary in diet and aggressiveness, their effect on herbivores also varies. Additionally, the differential occurrence of ant attractants (plant and insect exudates) on foliage produces variable levels of ant foraging within local floras and among localities. Here, we investigate how variation of ant communities and of traits among host plant species (presence or absence of ant attractants) can change the effect of carnivores (predatory ants) on herbivore communities (caterpillars) in a cerrado savanna landscape. We sampled caterpillars and foliage-foraging ants in four cerrado localities (70–460 km apart). We found that: (i) caterpillar infestation was negatively related with ant visitation to plants; (ii) this relationship depended on local ant abundance and species composition, and on local preference by ants for plants with liquid attractants; (iii) this was not related to local plant richness or plant size; (iv) the relationship between the presence of ant attractants and caterpillar abundance varied among sites from negative to neutral; and (v) caterpillars feeding on plants with ant attractants are more resistant to ant predation than those feeding on plants lacking attractants. Liquid food on foliage mediates host plant quality for lepidopterans by promoting generalized ant–caterpillar antagonism. Our study in cerrado shows that the negative effects of generalist predatory ants on herbivores are detectable at a community level, affecting patterns of abundance and host plant use by lepidopterans. The magnitude of ant-induced effects on caterpillar occurrence across the cerrado landscape may depend on how ants use plants locally and how they respond to liquid food on plants at different habitats. This study enhances the relevance of plant–ant and ant–herbivore interactions in cerrado and highlights the importance of a tritrophic perspective in this ant-rich environment.

1. 蚁类在植被上觅食可显著影响植食性昆虫（phytophagous insects）对寄主植物的利用方式，同时对毛虫（caterpillars）——这类重要的食叶类群（folivores）——构成极高的捕食风险。由于蚁类会持续造访植被上的液态食物源——花外蜜腺（extrafloral nectaries）与昆虫蜜露（insect honeydew），因此蚁-植-植食者互作（ant–plant–herbivore interactions）在塞拉多稀树草原（cerrado savanna）中尤为普遍。在植物上搜寻液态奖励物时，具有攻击性的蚁类常会攻击或杀死昆虫植食者，从而降低其种群数量。由于蚁类的食性与攻击性存在差异，其对植食者的影响也各不相同。此外，植被上蚁类引诱物（植物与昆虫渗出液）的分布差异，使得本地植物区系间以及不同研究地点之间的蚁类觅食水平存在波动。本研究以塞拉多稀树草原景观为研究对象，探究蚁类群落的变异以及寄主植物物种的性状差异（是否含有蚁类引诱物）如何改变肉食性类群（捕食性蚁类）对植食者群落（毛虫）的调控效应。我们在4个相距70至460千米的塞拉多研究区域内，对毛虫以及在植被上觅食的蚁类开展了采样工作。研究发现：（i）毛虫侵染率与蚁类造访植物的频率呈负相关关系；（ii）该相关关系取决于本地蚁类的丰度与物种组成，以及蚁类对带有液态引诱物植物的本地偏好；（iii）该相关关系与本地植物丰富度及植物个体大小均无关联；（iv）蚁类引诱物的存在与否与毛虫丰度之间的相关关系在不同样地间存在差异，从负相关转为无显著关联；（v）取食带有蚁类引诱物植物的毛虫，相较于取食无引诱物植物的毛虫，对蚁类捕食的抵抗力更强。植被上的液态食物通过引发广谱的蚁-毛虫拮抗作用，调控了鳞翅目（lepidopterans）昆虫的寄主植物适宜性。我们在塞拉多开展的研究表明，广食性捕食性蚁类对植食者的负面影响可在群落尺度上被检测到，进而影响鳞翅目昆虫的种群丰度模式与寄主植物利用策略。在塞拉多整个景观中，蚁类诱导的效应对毛虫发生的影响强度，可能取决于蚁类在本地对植物的利用方式，以及它们对不同生境中植物液态食物的响应模式。本研究提升了塞拉多生态系统中蚁-植、蚁-植食者互作的研究价值，并强调了在这一蚁类多样性极高的环境中，采用三重营养级研究视角（tritrophic perspective）的重要性。