Differential pollinator response underlies plant reproductive resilience after fires.

Abstract

Assessing the resilience of plant-animal interactions is critical to understanding how plant communities respond to habitat disturbances. Most ecosystems experience some level of natural disturbance (e.g. wildfires) to which many organisms are adapted. Wildfires have structured biotic communities for millennia; however, the effects of fire on interactions such as pollination have only recently received attention. A few studies have shown that generalist plants can buffer the impact of fires by pollinator replacement, suggesting that the resilience to disturbance could depend on the level of specialization of the interactions. Here, we hypothesize that (1) fires could impose negative effects on plants with specialized pollination systems, and (2) in large wildfires, these negative effects will be stronger with increasing distance inside the burnt area because pollinators will need more time to recolonize. These questions were tested in the specialized pollination system of a widespread Mediterranean palm, Chamaerops humilis. The post-fire pollination resilience was assessed in replicated wildfires representing three post-fire ages by measuring the abundance of beetle pollinators and by estimating fruit set (i.e. the proportion of flowers setting fruits) in burnt and unburnt areas. To test for distance effects, plants were sampled along transects inside the burnt area. Despite a marked post-fire decline in the specialist pollinator, exacerbated by the distance from the fire's edge, the palm's fruit set was barely affected. The temporary replacement by a sap beetle at burnt sites - an effective pollinator that had not been previously recognized - provided post-fire reproductive resilience. Differential pollinator responses to disturbance can ensure plant success even in plants with only two functionally similar pollinators. This highlights the importance of pollinator replacement and dynamics for the resilience of interactions and ultimately of plant reproduction in disturbance-prone ecosystems.