Natural fire does not affect the structure and beta diversity of plant-pollinator networks, but diminishes floral-visitor specialization in Cerrado

Abstract

Fire acts as an ecological filter determining species diversity and composition of communities. In tropical savannas in Central Brazil, natural fire happens through lightning, but anthropogenic fire is also common, either controlled fire prescribed for management of vegetation and to promote grass growth or accidental and intentional fires related to deforestation and land use changes. Frequent fire events can have a negative effect on biodiversity by causing deaths of susceptible organisms, as well as through the homogenization of vegetation. Besides the composition of plant and animal species, fire also modifies biotic interactions, such as pollination, which impact ecosystem functioning. Here, we evaluated how time since the last fire event (hereafter postfire time interval) affects the structure, beta diversity of interactions and specialization of plants and floral visitors in a naturally burned Cerrado area. Postfire time interval had no effect on the structure of interaction networks and community diversity metrics, including beta-diversity of interactions. We did, however, find a positive relationship between flower abundance and postfire time intervals, and a negative effect of postfire time intervals on floral visitor species-level specialization. Thus, the negative effect of postfire time intervals on floral visitor specialization may be explained by the lower resource availability in areas recently burnt. The lack of strong and consistent effect of time interval since the last fire on plant-pollinator interactions from the Cerrado probably results from the resilience of these interactions to natural fires, which is a common element in this ecosystem. Increased frequency of more intense anthropogenic fires, however, may have stronger effects on biodiversity, and deserves further investigation in this biodiversity hotspot.