Arctic Foxes: The Unintentional Gardeners

Predators are an integral component of any healthy ecosystem. Their influence can even be felt at the botanical level via what are called top-down controls. Either through direct predation or through altering their behavior, predators influence the herbivores in any system, which usually results in healthier plant communities. This method is rather indirect but new evidence shows that in the Arctic tundra, a top predator is having quite a direct influence on plant communities.

What's not to love about Arctic foxes? All anthropomorphic views aside, Arctic foxes are important predators in this ecosystem. Although the food web complexity on the tundra is largely driven by limits to plant productivity, a paper published in 2016 shows that these little canids can have profound effects on vegetation. This doesn't have to do with predation directly but rather their reproductive behavior. 

Arctic foxes live, give birth, and raise their young in underground dens. Without these subterranean homes, the foxes would be much more vulnerable to other predators as well as the harsh Arctic climate. Dens don't happen overnight either. Suitable sites are tended for generations and some dens may well be more than a century old. All this equates to a lot of activity in and around a good den site. 

With an average litter size of 8 - 10 pups per female, one can imagine the food and waste buildup must be considerable. Like all predators, Arctic fox food and waste are rich in nitrogen and phosphorus compounds, the necessary building blocks of life. Many an onlooker has noticed that, unsurprisingly, plant growth around Arctic fox dens is much more lush than on the surrounding landscape. Until recently though, such differences have hardly been quantified.

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By examining the soil and plant characteristics around Artic fox dens in Canada and comparing these data to surrounding sites without Arctic fox dens, a team of researchers put the first comprehensive numbers to the effects of Arctic foxes on tundra plant communities. They found that soils from in and around Arctic fox dens contained significantly higher levels of nitrogen and phosphorus than did the surrounding control plots. What's more, these levels varied throughout the year. In June, for instance, soil nitrogen and phosphorus levels were 71% and 1195% higher than non-den soils. These levels seemed to switch later in the summer. In August, soil nitrogen from fox dens were 242% higher and soil phosphorus levels were 191% higher.

As you can probably imagine, all of these extra nutrients caused a change in vegetation around the dens. Den sites were far more productive in terms of vegetation. The team found that, on average, Arctic fox dens supported 2.8 times more plant biomass than did the surrounding area. The authors note that these were conservative estimates and that the true values are much higher. Taken together, these results demonstrate that far from simply being top predators, Arctic foxes are true ecosystem engineers, at least on local scales. This is especially important in such a demanding ecosystem as the Arctic tundra.

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