Assessing the Impact of Deforestation of the Atlantic Rainforest on Ant-Fruit Interactions: A Field Experiment Using Synthetic Fruits

Ants frequently interact with fleshy fruits on the ground of tropical forests. This interaction is regarded as mutualistic because seeds benefit from enhanced germination and dispersal to nutrient-rich microsites, whereas ants benefit from consuming the nutritious pulp/aril. Considering that the process of deforestation affects many attributes of the ecosystem such as species abundance and composition, and interspecific interactions, we asked whether the interaction between ants and fallen fleshy fruits in the Brazilian Atlantic forest differs between human-created fragments and undisturbed forests. We controlled diaspore type and quantity by using synthetic fruits (a plastic ‘seed’ covered by a lipid-rich ‘pulp’), which were comparable to lipid-rich fruits. Eight independent areas (four undisturbed forests, and four disturbed forest fragments) were used in the field experiment, in which we recorded the attracted ant species, ant behaviour, and fruit removal distance. Fruits in undisturbed forest sites attracted a higher number of species than those in disturbed forests. Moreover, the occurrence of large, fruit-carrying ponerine ants (Pachycondyla, Odontomachus; 1.1 to 1.4 cm) was higher in undisturbed forests. Large species (≥3 mm) of Pheidole (Myrmicinae), also able to remove fruits, did not differ between forest types. Following these changes in species occurrence, fruit displacement was more frequent in undisturbed than in disturbed forests. Moreover, displacement distances were also greater in the undisturbed forests. Our data suggest that fallen fleshy fruits interacting with ants face different fates depending on the conservation status of the forest. Together with the severe loss of their primary dispersers in human-disturbed tropical forest sites, vertebrate-dispersed fruits may also be deprived of potential ant-derived benefits in these habitats due to shifts in the composition of interacting ant species. Our data illustrate the use of synthetic fruits to better understand the ecology of ant-fruit interactions in variable ecological settings, including human-disturbed landscapes.

热带森林地表的蚂蚁常与肉质果实发生交互作用。这种交互被视为互利共生关系：植物种子可借助该过程提升萌发率，并被传播至养分富集的微生境，而蚂蚁则通过取食果实的营养果肉/假种皮（aril）获得收益。鉴于森林砍伐过程会影响生态系统的诸多特征——包括物种丰度、群落组成以及种间交互作用，我们探究了巴西大西洋森林中，蚂蚁与落地肉质果实的交互模式在人工林片段与未受干扰原生林间是否存在差异。本研究使用合成果实（以塑料模拟"种子"，外覆富含脂质的"果肉"）来控制传播体（diaspore）的类型与数量，该合成果实可与天然富脂质果实相媲美。本野外实验共设置8个独立样区（4片未受干扰原生林与4片受干扰林片段），并记录了吸引到的蚂蚁物种、蚂蚁行为以及果实被搬运的距离。未受干扰原生林样地的果实所吸引的蚂蚁物种数量显著高于受干扰林片段。此外，体型较大、可搬运果实的猛蚁亚科（Ponerinae）物种（厚结猛蚁属*Pachycondyla*、齿猛蚁属*Odontomachus*；体长1.1~1.4 cm）在未受干扰森林中的出现频率更高。同样具备果实搬运能力的大头蚁属（切叶蚁亚科Myrmicinae）大型物种（体长≥3 mm）在两种林型中的出现频率并无显著差异。伴随物种组成的上述变化，未受干扰森林中的果实被搬运频次显著高于受干扰林片段，且果实的被搬运距离也更远。本研究数据表明，与蚂蚁发生交互的落地肉质果实，其最终命运会因森林的保护状况而异。在受人类干扰的热带森林生境中，脊椎动物传播的果实不仅会面临原有初级传播者的严重丧失，还可能因交互蚂蚁的物种组成发生改变，而无法获得蚂蚁介导的潜在收益。本研究结果证实，合成果实可用于更好地探究包括人类干扰景观在内的多变生态背景下，蚂蚁-果实交互的生态学机制。