Complex interactions in ant–plant mutualisms: The role of multiple ant food resources in mediating plant defence, pollination and fitness in a tropical shrub

Abstract Ants form mutualistic relationships with plants that offer extrafloral nectar (EFN) and with trophobiotic insects such as aphids, treehoppers or caterpillars that secrete energy‐rich honeydew. Although these insects may negatively affect plants, their presence—along with EFN—increases ant activity, which enhances herbivore predation, reduces leaf damage and indirectly improves plant growth and reproductive success. However, the same ants attracted to these resources can also interfere with pollinators—by deterring or harming them—thereby potentially reducing pollination efficiency and negatively impacting plant reproductive success. While the roles of ants in plant defence and pollination have been extensively studied, the individual and combined effects of multiple ant‐attractive resources, such as EFN and trophobionts, on these ecological services remain poorly understood. In this study, we conducted a field experiment manipulating the presence of EFN and trophobiotic insects (treehoppers or myrmecophilous caterpillars) in the tropical shrub Banisteriopsis malifolia and used a structural equation modelling approach to assess the direct and indirect effects of these ant food resources on leaf herbivory, pollinator activity and plant fitness. Our results show that ants reduced leaf herbivory on plants offering both EFN and trophobiotic insects. Although ants did not directly affect pollinator behaviour, leaf herbivory in plants hosting treehoppers indirectly influenced pollination by reducing both visit duration and frequency. Flower production in plants with EFN or treehoppers enhanced pollinator attraction, resulting in greater fruit production and fruit mass. However, neither pollinator visit duration nor visit frequency significantly influenced fruit yield across any ant resource treatments. Finally, we detected no indirect effects of ant resource availability on overall plant fitness through changes in herbivory or pollination. These findings suggest that while the presence of multiple ant food resources can enhance ant‐mediated plant defence, their effects on pollination and overall plant fitness are more nuanced, highlighting the complex and context‐dependent nature of multitrophic interactions in shaping ecological outcomes for plants.