The Atlantic Forest as a barrier to invasive rodents: study of a seaport in southern Brazil

Invasive rats and mice typically arrive in novel regions through unintentional transportation aboard ocean-going vessels, which makes seaports the principal point of entry of these species. In this innovative study, we modeled the spatial distribution and abundance of two invasive rodent species (Rattus norvegicus and Mus musculus) in Paranaguá, a port city, in southern Brazil whose original vegetation cover was Atlantic Forest. Occupancy and abundance were estimated using live and pitfall traps during nine field campaigns (4,214 trap.nights) at 18 sampling sites distributed along a gradient of habitat between the port and the forest. The abundance and occupancy of both species were affected negatively by the percentage of forest cover within a radius of 1,000 m. The occupancy of M. musculus was also affected by the abundance of buildings within a radius of 100 m and by the distance to the nearest forest edge. The occupancy of R. norvegicus was related positively to the proximity of the access roads that link the port of Paranaguá with the rest of the state of Paraná. We conclude that, while the port is the point of entry for invasive rodents, neither study species was associated strongly with this area. The study identified the principal elements associated with rat and mouse occupancy, which provides the local authorities with important insights for the implementation of an effective invasive species management program in the municipality of Paranaguá. Overall, the Atlantic Forest reveals a remarkable ecosystem service and appears to act as a natural barrier to the dispersal of both rats and mice, being associated with a reduced abundance of these species and low occupancy probabilities.