Herbivore corridors sustain genetic footprint in plant populations: a case for Spanish drove roads

Habitat fragmentation is one of the greatest threats to biodiversity conservation and productivity, that are mediated by direct human impact. Its consequences include genetic depauperation, including phenomena such as inbreeding depression or reduction in genetic diversity. While the capacity of wild and domestic herbivores to sustain long-distance dispersal has been proven, the impact of herbivore corridors in plant population genetics remains to be observed. We conducted this study in the Conquense Drove Road in Spain, with a sustained use by livestock during centuries where transiting herds passed by twice a year en route to winter and summer pastures. We compared genetic descriptors of Plantago lagopus populations in the drove road with populations in the surrounding agricultural matrix, at varying distances from human settlements. We observed significant differences for coefficients of inbreeding between the drove road and the agricultural matrix, as well as significant trends for higher genetic diversity around human settlements. Trends for higher genetic diversity in drove roads may be present, although they were not significant with the available sample size. The resulting functional landscape has human settlements as dispersal hotspots, while the drove road act as a pollinator reservoir and possibly also as a linear structure facilitating long-distance dispersal in an agricultural matrix where local P. lagopus populations depend rather on short-distance dispersal. These results highlight the role of herbivore corridors for conserving the migration capacity of plants, and they contribute as well in understanding the role of human dispersal for the spread of invasive species.