The effect of herbivory on pollinators: a revisited meta-analysis

Plant-herbivore and plant-pollinator interactions are closely interconnected through their combined influence on plant reproduction, involving both direct and indirect (plant-mediated) effects between these consumer groups. Although these dynamics have been investigated for nearly three decades and were previously synthesized in a meta-analysis, rapid growth in the field in recent years warrants an updated quantitative assessment.

We extend the most recent synthesis by incorporating primary studies published between 2018 and 2023, nearly doubling the dataset from 88 to 171 studies and increasing the number of independent observations from 568 to 1348. We reanalysed the effects of both natural and simulated herbivory on floral traits, pollinator visitation and plant reproductive output, expanding previous damage categories to include stem damage and mixed-tissue damage - defined here as damage affecting multiple plant tissues simultaneously (e.g. grazing that impacts both leaves and flowers).

Plant damage significantly reduced floral traits, pollinator attraction and reproductive success. These effects varied with both the type of damage and the tissue affected, with their interaction strongly moderating plant responses. Natural damage to leaves and flowers in most cases reduced floral traits, pollinator visitation and reproduction (except floral traits in the case of flower damage). By contrast, root and mixed damage had no significant effects. Simulated damage, on the other hand, also influenced responses: damage to flowers and stems only reduced floral traits, while damage to leaves reduced pollinator attraction. Importantly, our updated analysis corroborates some trends but also overturns earlier findings: whereas previous work suggested no impact of simulated herbivory, we now detect significant negative effects, and natural floral damage, once considered neutral or in some cases positive for reproduction, is revealed to be detrimental.

These findings demonstrate that herbivory alters plant-pollinator interactions in trait- and tissue-specific ways, providing new insights into the ecological and evolutionary consequences of plant-herbivore-pollinator linkages.