Abstract
Ecosystem engineers modify habitats through processes other than trophic interactions, such as by regulating soil nutrients, and can influence resource availability and quality for other organisms. Predator-mediated elemental cycling may be especially important in determining plant diversity and growth in ecosystems where soil fertility and primary productivity are low. Red foxes (Vulpes vulpes L.), top predators in the Subarctic, could engineer local ecosystems through denning, which could create biogeochemical hotspots of nutrients due to continual input of feces, urine and prey remains. We examined soil and vegetation characteristics on red fox dens and paired control sites in woodland habitats near the Arctic treeline in Manitoba, Canada. The organic soil layer on den sites had 81% more inorganic nitrogen and 250% more extractable phosphorus than in control areas. Denning also increased soil respiration and pH in the organic layer, suggesting improved soil quality and nutrient availability for plants. By enriching nutrients and disturbing soils through digging, den sites had a higher plant species ß-diversity and a greater cover of erect woody shrubs (Salix spp.), grasses (Leymus mollis (Trinius) Pilger) and weedy ephemerals compared to control sites, resulting in a regional increase in plant species richness. Our research highlights the importance of considering impacts of predators other than through their consumption of prey, and provides insight into the role of red foxes in modifying plant diversity and productivity in the Subarctic.
Highlights
The harsh climate previously limited red foxes in the Arctic and Subarctic, warmer temperatures in these regions over the last century may have facilitated the range expansion and increasing densities of red foxes in the North[18,19]. Vegetation in both Subarctic and Arctic ecosystems could be sensitive to red fox denning, given that vegetation may be responding to climate warming, which has resulted in increased plant productivity and shrub growth on the tundra, as well as decreased productivity in many regions of the boreal forest[20,21,22,23]
Vegetation growth in the region is influenced by Hudson Bay, which remains frozen for 7 months each year, and includes erect shrubs, such as willows (Salix L. spp.) and dwarf birch (Betula glanudulosa Michaud), prostrate shrubs, such as black crowberry (Empetrum nigrum L.) and bog bilberry (Vaccinium uliginosum L.), as well as various forbs and lichens[33,34,35]
Dens had higher soil respiration compared to controls in the organic layer (t7 = − 3.351, P = 0.012), but soil respiration did not differ between dens and controls in the mineral layer (Fig. 2c; t7 = − 0.890, P = 0.401)
Summary
The harsh climate previously limited red foxes in the Arctic and Subarctic, warmer temperatures in these regions over the last century may have facilitated the range expansion and increasing densities of red foxes in the North[18,19] Vegetation in both Subarctic and Arctic ecosystems could be sensitive to red fox denning, given that vegetation may be responding to climate warming, which has resulted in increased plant productivity and shrub growth on the tundra, as well as decreased productivity in many regions of the boreal forest[20,21,22,23]. We predicted that soils on red fox dens would have higher concentrations of inorganic nitrogen and extractable phosphorus and higher rates of soil respiration, and that dens would host nutrient-demanding plant species and enhance the growth of weedy ephemerals where soil is frequently disturbed, such as around burrows. Examining the role of red foxes as ecosystem engineers can provide insight into the broad ecological importance of predators in shaping the spatial distribution and diversity of resources across the landscape, which can influence a variety of other organisms
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