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）是一类兼具高度多样性的生态系统，多种捕食者类群共同塑造了其中的动物群落以及植物-节肢动物（Arthropods）间的互作关系。其中尤以蚂蚁、鸟类与蝙蝠最为突出，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、它们之间是否存在互作，以及管理措施与景观背景如何调控这类互作，仍知之甚少。本研究在印度尼西亚的小农户可可农林复合系统中，设置了针对蚂蚁、鸟类与蝙蝠的准入限制操控实验，并覆盖了遮阴梯度与距天然林距离梯度两个变量。研究人员量化了节肢动物种群丰度、害虫为害程度与作物产量三项指标。在对照组处理中，当林冠覆盖率为30%~40%时，可可产量达到峰值。当林冠覆盖率为15%时，排除蚂蚁的处理组产量大幅下降（从600 kg·ha⁻¹·年⁻¹降至300 kg·ha⁻¹·年⁻¹）。当林冠覆盖率为60%时，排除鸟类的处理组产量受损（从400 kg·ha⁻¹·年⁻¹降至250 kg·ha⁻¹·年⁻¹）；而当林冠覆盖率为15%时，排除鸟类反而提升了产量（从600 kg·ha⁻¹·年⁻¹升至900 kg·ha⁻¹·年⁻¹）；蝙蝠排除处理则未对产量产生显著影响。产量随距天然林距离的缩短而提升，这一规律与捕食者类群的准入情况无关。各捕食者排除处理之间，未对产量、害虫为害程度以及节肢动物群落产生交互效应。当林冠覆盖率低于30%时，排除蚂蚁会导致植食性动物种群数量上升，但并未降低蜘蛛的种群丰度。排除鸟类则会降低植食性动物种群丰度，同时提升蜘蛛种群丰度。综合分析与实践应用：本研究通过排除实验估算得出，遮阴树管理措施不同时，蚂蚁与鸟类可导致可可产量在100~800 kg·ha⁻¹·年⁻¹区间内波动。除遮阴程度最高的农林复合系统外，其余生境中蚂蚁均为维持产量的关键类群。低林冠覆盖率生境下的产量高度依赖捕食者类群的准入情况，此时鸟类反而会降低而非提升产量。因此，可可种植者不仅应从生态生理层面出发，避免干扰蚂蚁群落，同时需维持30%~40%的遮阴树林冠覆盖率，以缓冲捕食者类群群落的波动性。