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. 叶面觅食的蚂蚁活动可显著影响植食性昆虫对寄主植物的利用模式，同时对作为重要食叶昆虫类群的毛虫构成极高的捕食风险。由于蚂蚁会持续造访植物冠层的液态食物源——花外蜜腺（extrafloral nectaries）与昆虫蜜露（insect honeydew），蚁-植物-植食者互作（ant–plant–herbivore interactions）在塞拉多稀树草原（cerrado savanna）中尤为普遍。在植物上搜寻液态食物奖励的过程中，具有攻击性的蚂蚁常会攻击或杀死昆虫植食者，进而降低其种群数量。

由于不同蚂蚁的食性与攻击性存在差异，其对植食者的调控效应也各不相同。此外，植物与昆虫渗出物等蚂蚁引诱物（ant attractants）在植物冠层的分布差异，会导致本地植物区系（local floras）内乃至不同区域间的蚂蚁觅食强度存在显著波动。本研究旨在探究：在塞拉多稀树草原景观中，蚂蚁群落的变异以及寄主植物物种（host plant species）间的性状差异（是否具备蚂蚁引诱物），会如何改变捕食性蚂蚁（predatory ants）这类肉食类群（carnivores）对植食者群落（herbivore communities，即毛虫caterpillars）的调控效应。

我们在四个相隔70至460公里的塞拉多样地中，对毛虫与叶面觅食蚂蚁进行了取样调查。结果显示：（i）毛虫种群发生量与蚂蚁对植物的造访频次呈显著负相关；（ii）该相关关系依赖于本地蚂蚁的多度（local ant abundance）与物种组成（species composition），以及蚂蚁对带有液态引诱物的植物的本地偏好性；（iii）该相关关系与本地植物丰富度（plant richness）或植物个体大小无关；（iv）蚂蚁引诱物的存在与毛虫多度（caterpillar abundance）间的关联在不同样地间存在差异，从显著负相关转为无相关性；（v）取食带有蚂蚁引诱物的植物的毛虫，相较于取食无引诱物植物的毛虫，对蚂蚁捕食（ant predation）的抵抗力更强。

植物冠层的液态食物可通过促成广谱的蚁-毛虫拮抗作用（generalized ant–caterpillar antagonism），调控鳞翅目昆虫（lepidopterans）的寄主植物适宜性。本项在塞拉多稀树草原开展的研究表明：广食性捕食蚂蚁对植食者的负面效应可在群落水平（community level）被检测到，并会影响鳞翅目昆虫的种群多度模式与寄主植物利用策略。

在整个塞拉多稀树草原景观中，蚂蚁介导的对毛虫发生量的效应强度，可能取决于蚂蚁对本地植物的利用方式，以及它们在不同生境中对植物冠层液态食物的响应模式。本研究强化了蚁-植物与蚁-植食者互作在塞拉多生态系统中的生态学意义，并凸显了在这类蚂蚁多样性极高的环境中采用三营养级视角（tritrophic perspective）的重要性。