杏吧原创

Satellite images of plants growing around the dens of Arctic foxes add to the evidence that the foxes are 鈥渆cosystem engineers鈥� whose activities create habitat for other organisms.

Against the harsh tundra, the dens of Arctic foxes (Vulpes lagopus) stand out like islands of green. Called 鈥済ardens of the tundra鈥�, they are covered in distinctive, lush vegetation, often attributed to nutrients in the soil concentrated there from the foxes excrement and prey. The foxes also perturb soil in ways that might benefit certain plants.

However, researchers studying the dens at small scales weren鈥檛 able to rule out the possibility that the foxes were merely selecting the greenest sites, rather than contributing to the greening of the sites themselves.

鈥淐hanges on the tundra are slow,鈥� says at the University of Manitoba in Canada, and the foxes can inhabit dens for many decades. 鈥淭rying to get at that cause and effect is not something that鈥檚 easily done.鈥�

Johnson-Bice and his colleagues used high-resolution satellite images to measure the plants around 84 Arctic fox dens in Wapusk National Park in Canada. They compared plants at these sites with those at sites that had no foxes but would be suitable for dens. They also compared them with random sites.

They found plant productivity 鈥�听measured by the greenness in the satellite images 鈥撎�was greater at the sites with active fox dens than at similar sites without fox dens. There was no difference between sites with fox dens and random sites, which the researchers say suggests the foxes tend to choose sites with relatively low productivity. However, Johnson-Bice says they have yet to show the foxes directly cause the increase in productivity.

at the Voyageurs Wolf Project in Minnesota says the study is 鈥渃onvincing鈥� given the challenges of studying long-term changes. 鈥淵ou can鈥檛 go back 400 years ago and look at how those sites looked before those foxes showed up,鈥� he says.

Unlike other ecosystem engineers like beavers, however, it is unclear if the foxes benefit from any changes they cause, says at the University of Copenhagen in Denmark. It is possible the vegetation provides protection for foxes or helps them identify dens, says Johnson-Bice. Or it may just be a lovely side effect of foxes on the land.