Trade-off in plant-ant interactions: seasonal variations

Abstract This work evaluated the effect of seasonality on ant-plant interaction in a Seasonally Dry Tropical Forests, using as an ecological model the species Ipomoea carnea subs. fistulosa (Convolvulaceae). We performed systematic collection of ants, herbivores and leaves in marked plants, evaluated the efficiency of herbivorous capture by ants, and the effects of ant presence over the pollinator behavior and plant fitness in dry and rainy seasons. The presence of ants in the plants reduced the number of herbivores (dry season: F2.27=4.7617, p=0.0166; rainy season: F2.27=5.8655, p=0.0078). However, the capture efficiency was negatively affected by the presence of myrmecophilous larvae, so that the average of ants recruited on termite leaves was 2.06 ants per termite, the average recruitment of ants on larval leaves was 22.4 larva ants. In addition, the presence of ants reduced pollinator visits and promoted fruit reduction during the dry season (ANOVA: F = 3.44; p = 0.0653). In conclusion, the association with ants can result in a balance not always favorable to the host plant, and this result actually depends on abiotic (e.g. precipitation) and biotic factors (e.g. ant species composition and abundance, influence of other trophic levels and identity of associated herbivores).

摘要 本研究以季节性热带干燥林（Seasonally Dry Tropical Forests）为研究场景，以番薯属物种Ipomoea carnea subs. fistulosa（旋花科Convolvulaceae）为生态模型，评估了季节动态对蚁植相互作用的影响。研究人员对标记植株上的蚂蚁、植食性昆虫与叶片开展系统性采集，分析了蚂蚁捕获植食性昆虫的效率，并探究了旱季与雨季中蚂蚁存在对传粉者行为及植物适合度的作用。结果表明，植株上的蚂蚁可显著降低植食性昆虫的种群数量（旱季：F₂.₂₇=4.7617，p=0.0166；雨季：F₂.₂₇=5.8655，p=0.0078）。但嗜蚁幼虫（myrmecophilous larvae）的存在会对蚂蚁的捕获效率产生负面影响：白蚁叶片上招募的蚂蚁平均数量为2.06只/白蚁，而幼虫叶片上招募的蚂蚁平均数量为22.4只/幼虫。此外，旱季中蚂蚁的存在会减少传粉者的访花频次，并导致果实结实量下降（方差分析：F = 3.44；p = 0.0653）。综上，与蚂蚁的共生关联并不总是对宿主植物有利，其最终效果取决于非生物因子（如降水量）与生物因子（如蚂蚁的物种组成与种群多度、其他营养级的影响以及关联植食性昆虫的种类）。