Ant mutualism increases long-term growth and survival of a common Amazonian tree

How ecological context shapes mutualistic relationships remains poorly understood. We combined long-term tree census data with ant censuses in a permanent 25-ha Amazonian forest dynamics plot to evaluate the effect of the mutualistic ant Myrmelachista schumanni (Formicinae) on the growth and survival of the common Amazonian tree Duroia hirsuta (Rubiaceae), considering its interactions with tree growth, population structure, and habitat. We found that the mutualist ant more than doubled tree relative growth rates and increased odds of survival. However, host tree size and density of conspecific neighbors modified the effect of the ant. Smaller trees hosting the mutualist ant consistently grew faster when surrounded by higher densities of conspecifics, suggesting that the benefit to the tree outweighs any negative effects of high conspecific densities. Moreover, our findings suggest that the benefit afforded by the ant diminishes with plant age and also depends on the density of conspecif...生态背景如何塑造互利共生关系，目前仍是学界尚未充分阐释的科学问题。本研究结合长期树木普查数据与蚂蚁普查数据，在一处面积为25公顷的永久性亚马逊森林动态样地中，评估互利共生蚁Myrmelachista schumanni（蚁亚科Formicinae）对亚马逊常见树木Duroia hirsuta（茜草科Rubiaceae）生长与存活的影响，同时考量其与树木生长、种群结构及生境的相互作用。研究结果显示，该互利共生蚁可使树木相对生长速率提升一倍以上，并显著提高树木存活概率。不过，宿主树木的个体大小以及同种邻株密度会调控该蚂蚁的作用效果。当被较高密度同种个体环绕时，携带有该互利共生蚁的幼树始终生长更快，这表明树木获得的益处超过了高同种密度所带来的负面影响。此外，本研究结果还表明，该蚂蚁提供的益处会随植物年龄增长而减弱，且同样取决于同种个体的密度……