Effective dispersal and genetic structure of a small mammal in an intensively managed agricultural landscape: is there any barrier to movement?

Dispersal and gene flow are key processes for the persistence of populations, because they enable the maintenance of large effective population sizes and the recolonization of empty patches. Therefore, assessing how these processes are modulated by landscape characteristics is crucial in a context of anthropogenic landscape change and habitat fragmentation. We used several spatial genetics approaches to study the genetic structure of populations of the rodent Calomys venustus in an intensively managed agroecosystem in central Argentina. The landscape consists of crop fields separated by a network of “borders” (narrow strips of vegetation along fence lines, roads and water streams) providing habitat and structural connectivity for species, crossed by dirt roads and a few paved roads and water streams. We tested the hypothesis that this species, despite showing a strong preference for borders, perceives the matrix as a lower-quality habitat that does not impede dispersal. Our results showed that functional connectivity was not limited to borders, gene flow was not restricted by any of the landscape elements considered in this study, and suggested that long distance movements would not be uncommon. The genetic structure of C. venustus consisted of groups of genetically similar individuals that were remarkably variable in spatial extent, were genetically differentiated, followed an isolation by distance pattern, but were not delimited by any apparent landscape features that may restrict dispersal and explain their boundaries. Cluster boundaries could result from the interaction between the grain of resource patches and the spatial scale of the range of perception of individuals, determining that habitat-matrix boundaries would be crossed in some places but not in others. Our results add to the growing list of cases of higher-than-expected dispersal ability in species with strong habitat preferences.