Panbiogeographical analysis of passion vines at their southern limit of distribution in the Neotropics

Abstract

The origin of the extant flora of the state of Rio Grande do Sul (RS) in Brazil has long been debated. Spatial distributions of passion vines (Passifloraceae) have been used to support the corresponding hypotheses, subsequent to the pioneer studies of Balduino Rambo. Using a panbiogeographical analysis based on literature data and herbarium material, we mapped the spatial distributions of the 15 species of passion vine that occur naturally in RS, taking into account a broader geographical range (southern South America). None of these passion-vine species has its distribution entirely within the RS political borders. The escarpments of the Serra do Mar  (circa -30oS latitude), which coincides with the southern limit of the Paraná biogeographic subregion, was identified as the southern limit for the existence of important diversity of passion vines in the Neotropics. The generalized tracks obtained were associated with different panbiogeographic provinces, indicating a mixed history for the RS passion-vine flora. Two main biotic components were identified: first, species with a northern occurrence, from east of the Andes to the Brazilian Atlantic Forest; second, species typically found in the Brazilian Atlantic Forest. A continuous, U-shaped curve formed by the generalized tracks suggested that the RS area is an extant, southern transition zone, which in conjunction with the Chaco province maintains Amazonian and Atlantic populations of these plants in contact. A node located in the northeast region, roughly on the border between the Pampa province and Paraná subregion, and where three provinces of the latter converge, indicated the existence of greater diversity and endemism of passion-vine species in that part of the state. On a preliminary basis, the consequences of the variation in passion-vine spatial distributions for the herbivores, specifically heliconian butterflies, associated with these plants are also discussed.