Nutrient deposition on Arctic fox dens creates atypical tundra plant assemblages at the edge of the Arctic

Questions: In most ecosystems, some organisms can be considered ecosystem engineers because they modify their physical environment in a way that can affect many other organisms. Nutrient deposition may be extremely important as an ecosystem engineering activity in nutrient-limited environments, but this mechanism remains understudied. In low-Arctic tundra, a region characterized by continuous permafrost, low-nutrient soils, and slow nutrient turnover, Arctic foxes (Vulpes lagopus) concentrate nutrients on their dens through fecal deposition and feeding their young. This nutrient concentration enhances productivity in patches on the landscape, likely creating a unique habitat for a variety of plants, and could have cascading effects on the distribution and diversity of vegetation on the tundra. 

Location: Low-Arctic tundra in Wapusk National Park, Manitoba, Canada

Methods: We quantified differences in vegetation composition between 20 fox dens and adjacent control sites. 

Results: Plant growth form differed greatly between dens, which were dominated by deciduous grasses near the coast and erect shrubs farther from the coast, and control sites, which were dominated by evergreen prostrate shrubs. Dens also had more forb cover and less cover of lichens, mosses, and sedges. Species composition also varied greatly between control and den areas, with 17 of the 20 species found in at least 10% of the sampled sites being indicator species for dens or control sites. 

Conclusions: By providing habitat for plants reliant on higher nutrient availability not typical of tundra heath, Arctic foxes enhance the biodiversity of the region. These erect plants may also help create new habitat by retaining snow on normally windswept beach ridges. Overall, this study illustrates the broader impacts of predators on diversity and community composition through mechanisms other than predation.