There’s nothing more iconic than a moose standing in a pond munching on a pondweed. But the real magic is happening below the belt. By pooping and peeing, this giant deer is helping keep its habitat thriving, animal ecologists have now shown.
In the northern, cooler climates that moose live in, there’s barely enough nitrogen to fuel plant growth. Plants get this critical nutrient from soil and air, and animals depend on the plant’s supply to help meet their own nitrogen needs.
Watching moose dive underwater and come up dribbling mud and green stuff from their mouths (see video), researchers in Minnesota wondered how that activity might affect nutrient availability. During its 45-minute feeding bout, a diving moose can disturb 100 square meters of a lake bottom. Foraging for underwater plants almost tripled the amount of nitrogen in the water, where tiny organisms had easy access to it, the team reported in 2017.
Now, these researchers have discovered that moose also move significant amounts of nitrogen back onto land as well. They studied moose from northeastern Minnesota, whose moose population has declined, and on Isle Royale in Lake Superior. In both places, the moose chow down on aquatic plants, which are especially rich in nitrogen. Each moose passes about 78 grams of nitrogen through urination or defecation each day. That’s the equivalent of two 20-kilogram bags of fertilizer a year, the scientists report today in the Philosophical Transactions of the Royal Society B.
Moose aren’t the only animals that move nutrients from the water to the land. Hippos, too, help reverse the leaching of nutrients from the savanna in Africa. But given the fast-rising temperatures in Minnesota, and the fact that moose have already disappeared from another part of the state possibly because of heat stress, there are concerns about how the loss of these iconic beasts will affect those ecosystems. Deer may move north to “replace” moose, but because they don’t really eat aquatic plants, they likely won’t replace the moose’s key nutrient-carrying function, the researchers note.