Nectar robbing impacts pollinator behavior but not plant reproduction

Trait-mediated indirect effects (TMIEs) refer to interactions in which the effect of one species on another is mediated by the behavior of a third species. A mechanistic approach that identifies the direction and impact of TMIEs can shed light on why different net outcomes are observed in the same general phenomena across systems. Nectar robbing has variable net effects through TMIEs on animal-pollinated plants across systems, but the mechanistic steps underlying this range of outcomes are often unclear. To address this knowledge gap, we assessed linkages between nectar robbing, pollinator behavior and plant reproductive success in the Andean tree, Oreocallis grandiflora. We found that robbing in this system led to lower nectar volumes, higher nectar sucrose concentration, and higher nectar viscosity, which together negatively impact nectar quality. This drop in nectar quality was associated with decreased visitation rates by hummingbirds, which might be expected to impact plant reprodu...