Data from: How ants, birds and bats affect crop yield along shade gradients in tropical cacao agroforestry

Tropical agroforests are diverse systems where several predator groups shape animal communities and plant–arthropod interactions. Ants, birds and bats in particular can reduce herbivore numbers and thereby increase crop yield. However, the relative importance of these groups, whether they interact, and how this interaction is affected by management and landscape context, is poorly understood. We jointly manipulated access of ants, birds and bats in Indonesian smallholder cacao agroforestry across gradients of shade and distance to natural forest. We quantified arthropod abundance, pest damage and yield. In control treatments, yield was highest under 30–40% canopy cover. Ant exclusion strongly reduced yield (from 600 to 300 kg ha−1 year−1) at 15% canopy cover. Bird exclusion impaired yield (from 400 to 250 kg ha−1 year−1) at 60% and enhanced yield (from 600 to 900 kg ha−1 year−1) at 15% canopy cover, while bats had no effect. Yield increased with forest proximity, a pattern not related to predator access. No interactive effects among predator exclusions on yield, pest damage and arthropod communities were found. Ant exclusion increased numbers of herbivores below 30% canopy cover, without reducing spider abundances. Bird exclusion reduced herbivore and increased spider abundances. Synthesis and applications. Using exclusion studies, we estimated that ants and birds cause cacao yield to vary between 100 to 800 kg ha−1 year−1, depending on shade-tree management. In all but the most shaded agroforests, ants were pivotal in supporting yields. Yields under low-canopy cover were strongly dependent on access by predator groups, with birds reducing rather than increasing yield. Hence, cacao farmers should refrain from disturbing ant communities and maintain 30–40% shade-tree canopy cover not only for ecophysiological reasons but also to buffer variability in predator communities.

热带农林复合系统（tropical agroforests）是一类具有高度物种多样性的生态系统，多种捕食者类群共同塑造了当地动物群落结构与植物-节肢动物（plant–arthropod）间的互作关系。其中，蚂蚁、鸟类与蝙蝠尤为关键，它们可通过降低植食性动物种群数量，进而提升作物产量。然而，目前学界对这些捕食者类群的相对重要性、类群间是否存在互作，以及经营管理与景观背景如何调控此类互作，仍缺乏深入认知。
本研究在印度尼西亚的小农经营可可农林复合系统（smallholder cacao agroforestry）中，联合设置了针对蚂蚁、鸟类与蝙蝠的排除处理，并沿遮荫梯度与距天然林距离梯度开展实验。研究量化了节肢动物丰度、虫害程度与可可产量。
在对照组样地中，冠层覆盖度（canopy cover）为30%–40%时可可产量最高。在冠层覆盖度15%的样地中，排除蚂蚁会显著降低产量（从600千克·公顷⁻¹·年⁻¹降至300千克·公顷⁻¹·年⁻¹）；排除鸟类则在冠层覆盖度60%时损害产量（从400千克·公顷⁻¹·年⁻¹降至250千克·公顷⁻¹·年⁻¹），但在15%冠层覆盖度时反而提升产量（从600千克·公顷⁻¹·年⁻¹升至900千克·公顷⁻¹·年⁻¹）；而排除蝙蝠对产量无显著影响。可可产量随距天然林距离的减小而升高，该规律与捕食者可及性无关。各捕食者排除处理间，未发现对产量、虫害程度及节肢动物群落存在交互效应。排除蚂蚁会在冠层覆盖度低于30%时增加植食性动物数量，但未降低蜘蛛种群丰度；排除鸟类则会减少植食性动物数量，同时提升蜘蛛种群丰度。
综合与应用启示：通过排除实验，本研究估算得出，受遮荫树经营管理方式影响，蚂蚁与鸟类可导致可可产量在100至800千克·公顷⁻¹·年⁻¹间波动。除遮荫度最高的农林复合系统外，蚂蚁对维持产量均起到关键作用。低冠层覆盖度下的产量高度依赖捕食者类群的可及性，此时鸟类反而会降低而非提升产量。因此，可可种植者应避免干扰蚂蚁群落，且需维持30%–40%的遮荫树冠层覆盖度——这不仅出于生态生理层面的考量，也可缓冲捕食者群落的波动带来的影响。