Comprehension of the benefits involved in mutualisms is crucial to disentangle the role of interactions in the structure and functioning of populations, communities and ecosystems. The understanding of positive interactions is becoming more important as the planet earth is experiencing a new era – the Anthropocene – where the expansion of human societies is promoting unprecedented biodiversity loss. In ant-plant mutualisms, benefits provided by plants to ants are immediately recognizable, but reverse benefits are less obvious, conditional and accumulate over longer time spans. Here we tested the hypothesis that the ant Azteca muelleri simultaneously provides multiple benefits to its host plant (Cecropia glaziovii), ultimately increasing plant performance. We planted seedlings and experimentally prevented ant colonization for half of them. Over 4.5 years we quantified the effects of ant presence or absence on plant growth, herbivory levels, fungal infection, fertilization via ant debris and changes in defense strategies. Ant colonization increased plant height by 125% compared to ant-free plants. Such an improvement in plant performance can be explained because plants with ants faced less herbivory, lower prevalence of pathogenic fungi, invested less in foliar trichomes and had more foliar nitrogen. We thus confirmed that ant mutualists provide cumulative benefits including nutritional benefits, effective defense and lower investment into other defenses – which result in increased plant growth. We highlight the importance of long-term experiments that simultaneously evaluate a multiplicity of potential ant effects to better understand their relative contribution to the performance of the mutualistic partner. We recommend that future studies on the association between Cecropia and Azteca should focus on whether the observed increase in plant growth might translate to an increase in plant reproductive success.
defensive mutualism, herbivory, myrmecophytes, myrmecotrophy, trade-off, trichomes