Grazing networks promote plant functional connectivity among isolated grassland communities

Abstract

Aim: Habitat loss threatens plant diversity globally. Lack of plant functional connectivity between isolated populations is often pinpointed as one of the major underlying mechanisms driving subsequent species extinctions. Therefore, landscape-scale conservation management promoting functional connectivity needs to be implemented urgently. Supporting the movement of seed dispersal vectors such as grazing animals may help safeguard local and regional plant diversity in fragmented landscapes. However, the efficacy of such management remains to be thoroughly assessed. Location: Stockholm archipelago, Sweden. Methods: We test how grazing animals may serve as mobile corridors within rotational grazing networks promoting plant functional connectivity via directed seed dispersal. Using landscape genetics, we compare isolated populations of the grassland perennial Campanula rotundifolia located in either active or abandoned grazing networks, to test if spatial patterns in their genetic diversity, differentiation and allele frequencies relate to the presence or absence of connectivity via rotational grazing management. Results: Grazing networks imprinted strong landscape-scale spatial patterning in pairwise population genetic differentiation and within-population genetic diversity. Isolated C. rotundifolia populations functionally connected by grazing animals held higher genetic diversity compared to populations no longer connected by grazing livestock. Gene flow linked to the directed seed dispersal was higher between populations within grazing networks, confirmed by their increased allele richness. We found a predictable, nested loss of genetic diversity among C. rotundifolia populations in abandoned grazing networks. Main conclusions: Grazing animals were important seed dispersal vectors, functionally connecting isolated grassland communities, so being vital to the successful long-term persistence and conservation of not only species but also genetic diversity. Crucially, the study underlines the possibilities of using domestic livestock as mobile corridors within rotational grazing networks as an effective tool to manage, conserve and restore both genetic and species diversity among isolated plant communities in fragmented landscapes.