A meta‐analysis of herbivore effects on plant attractiveness to pollinators

Herbivores may directly or indirectly affect plant attractiveness to pollinators. Although several studies have reported on these effects, there is yet no general consensus on the strength and sign of such interactions or their contingency on herbivory features such as the plant tissue attacked. We performed a meta‐analysis of studies testing for effects of herbivores on floral traits, plant attractiveness to pollinators, and plant reproductive success. We also assessed whether herbivore effects depended on the plant tissue attacked by herbivores and if real or simulated herbivory was used. We found an overall significant negative effect of herbivores on floral traits, plant attractiveness to pollinators, and plant reproductive success. These effects were, however, contingent on the plant tissue attacked and on whether real or simulated damage was used. Real floral and leaf, but not root, herbivores showed detrimental effects on floral traits and plant attractiveness to pollinators. In addition, real leaf, but not floral or root herbivory, lowered plant reproductive success. Contrastingly, simulated leaf and floral herbivory showed no effect on any of the response variables. These findings help move forward our understanding of the strength and directionality of herbivore effects on plant attractiveness to pollinators and their underlying mechanisms. Herbivores can directly or indirectly affect plant attractiveness to pollinators, and such effects may ultimately influence plant reproductive success (reviewed by Bronstein et al. 2007, Jones and Agrawal 2017). The outcome of these interactions between herbivores and pollinators is variable and ranges from studies showing the expected negative effects of herbivores (Karban and Strauss 1993, Strauss et al. 1996, Lehtil？ and Strauss 1997, Barber et al. 2011, 2015), to studies showing positive effects (Ivey and Carr 2005, Zhu et al. 2017), no effect (Gómez 2005, Pareja et al. 2012), or mixed patterns depending on the identity of the herbivore and pollinator species or guild (Poveda et al. 2003, 2005, Rusman et al. 2018). Thus, although herbivore–pollinator interactions are presumably widespread, there is yet no consensus on the nature (i.e., directionality) and strength of these effects. Herbivores can influence plant attractiveness to pollinators in multiple and interdependent ways, and these frequently imply negative effects on pollinator attraction and plant reproduction. First, herbivores can directly alter plant attractiveness to pollinators when the latter avoid contact with herbivore‐infested flowers