Ant’s choice: The effect of nutrients on a key ant–hemipteran mutualism

Soil fertility is understood to act in many indirect ways, in addition to directly providing nutrients to plants. Given that higher order indirect interactions frequently are key to understanding community structure, it would be natural to expect that indirect mutualisms should be as important as other interactions in generating such structure. Although mutualisms are ubiquitous in nature, exploring the myriad ways in which they interconnect with other elements of a system is less common. That soil fertility has an indirect effect on community structure is well known, suggests that soil fertility may be important in determining the effect of mutualisms on the structure of the ecological communities in which they are embedded. Here we report on a laboratory study that specifically examines the direct connection between the behavior of a mutualist and nutritional properties of the soil. We tested the effects of soil fertilization (high, medium and low levels) on the Azteca seriseasur–Coccus viridis mutualism on coffee plants in Mexico. We found that ants foraged significantly more on plants that were infected with C. viridis over control plants. Moreover, ants preferred to tend C. viridis on high fertilized over medium and low fertilized plants. This study highlights the importance of the links between soil nutrient properties and their effects on a key ant-hemipteran mutualism, illustrating the cascading effects on other interactions involving this keystone ant species.