Impacts of Anthropogenic Barriers and Road Networks on Large Mammal Migration Corridors and Gene Flow

Abstract

Man-made obstacles, especially road systems and other related infrastructure, essentially change the trends of migration and genetic connectivity of large mammals over a landscape. The study focused on effects of road- networks, types of barriers and landscape fragmentation on the migratory patterns with regard to genetic flow of three large mammal species (Elephas maximus, Panthera leo and Syncerus caffer), in a habitat of 12,500 km 2 in sub-Saharan Africa. The population structure and movement patterns were described using genetic sampling (n=384 individuals), and GPS telemetry (n=67 individuals followed 24 months). Barrier density, road network structure, and habitat connectivity were measure using land-scape analysis. Microsatellite genotyping showed high genetic differentiation among populations that were separated by major road networks (FST=0.187, p<0.001). The 14 critical pathways identified by migration corridor analysis experienced a restriction under barriers that decreased functionality of a corridor by 34-68 percent based on the configuration of barriers. Road networks lowered the migratory connectivity to 0.42 in comparison to the normal connectivity of 0.89 without the existence of barriers. There was a substantial loss of genetic diversity in barrier-isolated populations (Ar 3.8-4.2 vs. 5.6-6.1 alleles between isolated and connected populations). The permeability analysis revealed that the high roads (more than 3 meters) and fenced barriers had an almost complete impediment to large mammal crossing, whereas single-lane non-fenced roads could still be partly crossed. Each of the two suggested that the connectivity could be restored to 0.71-0.78 by modeling the effects of maintenance of the corridor permeability with the aid of wildlife overpasses and unfenced road sections. Findings reveal that the current anthropogenic obstacles are a major barrier to the genetic flow and migration of large mammals, and that has serious conservation implications of the preservation of viable populations.