Plant-animal interactions in fire-prone ecosystems

Resum

Understanding how plant-animal interactions respond to disturbance is one of the priorities faced by scientists. This thesis is about the responses of plant- animal interactions from environments with a long fire history (i.e. fire-prone ecosystems) to wildfires and the ultimate effects on plant reproduction. In addition, it explores how these interactions may contribute to the assembly of fire-prone communities from forest-savanna mosaics, where fire is a strong abiotic filter. In Chapter I, we assessed whether wildfires, through the postfire age and distance to the unburnt, disrupted antagonistic plant-animal interactions (i.e. seed predation and herbivory). We also evaluated whether the fire effects differed with the degree of specialization of the interactions involved (generalized vs specialized). To do that, we studied herbivory and seed predation interactions by insects in two Mediterranean plants, Ulex parviflorus and Asphodelus ramosus, with fast postfire responses. Our results showed that wildfires disrupted plant antagonistic interactions with specialist seed predators leading to temporary beneficial effects on plant reproduction. We did not reported significant differences on generalist herbivores that showed a fast recovery at recently burnt areas. In Chapter II, we studied the effects of wildfires in the specialized pollination system of the Mediterranean dwarf palm, Chamaerops humilis. We expected that wildfires disrupted the interaction between the palm and its nursery weevil pollinator, with negative consequences on plant reproduction. Our analyses, however, detected a complete recovery in the palm’s fruit set only three years after the fires. The replacement at recently burnt sites by an additional beetle pollinator, previously unnoticed, may have provided plant reproductive resilience. In Chapter III, we explored whether wildfires can change plant scents mediating pollination interactions and in turn their attractiveness to pollinators. We studied the pollination system of C. humilis by two beetle pollinators mediated by plant scents. Our study indicates that wildfires can modify plant chemical signals mediating plant pollination, which may have further effects on pollinator attraction. However, in our study system, the limited scent changes reported together with the high specificity between the signal and pollinators may have contributed to the fast postfire recovery of C. humilis pollination. Finally, in Chapter IV we evaluated the potential contribution of plant-animal mutualisms (through plant reproductive traits shaped by these interactions) into the assembly of forest-savanna mosaics from fire-prone ecosystems. Savannas exhibited overdispersed functional patterns contrasting with forests, where patterns of functional similarity emerged. Our results suggested that multiple ecological processes including fire and plant-animal mutualisms may drive species coexistence in forest-savanna mosaics by acting on different traits.