Emerging conflict between conservation programmes: when a threatened vertebrate facilitates the dispersal of exotic species in a rare plant community

As an ever-increasing variety of conservation programmes are applied in human-altered environments, there is a growing risk that different conservation actions with conflicting objectives may impede one another. Preventing and resolving the negative impacts of such conflicting conservation programmes could become a key challenge for conservationists. To date, however, the issue of conflicting conservation programmes has been largely overlooked. We explored a potential conflict between the preservation of threatened free-ranging plains bison Bison bison bison and the conservation in a National Park of a rare plant community - native rough fescue Festuca hallii grasslands. We investigated the dispersal of exotic seeds by examining 283 samples of bison faeces and the spatial distribution of exotic plant species in relation to bison behaviour. We showed that bison facilitated the long-distance dispersal of exotic plant species into the park by transporting seeds. Our analysis indicated there was a high probability (>75%) of occurrence of clover Trifolium spp. and timothy Phleum pratense on bison trails across 38% and 27%, respectively, of fescue grassland area. There was also a high probability of occurrence of timothy on bison wallows across 20% of fescue grasslands area. Furthermore, we demonstrated that exotic plant species were most likely to occur within 3 km of potential introduction points, and identified specific grassland patches most at risk of exotic plant species introduction by bison. By revealing the ecological mechanism underlying the emergence of a potential conflict, we were able to delineate spatial variation in the relative threat that bison might pose to the integrity of native fescue plant communities, allowing managers to optimize the allocation of conservation effort. Our study highlights the value of understanding the ecological mechanisms driving conflict between conservation programmes in order to set evidence-based priorities for guiding future conservation decision-making.