Other anti-social species have an effect, though rather small, on the relationship between wolves and moose on Isle Royale. Before wolves hunted them to extinction, coyotes used to inhabit the island. Beavers and snowshoe hares also have an effect on both populations, because beavers and snowshoe hares are the only two animals that wolves prey on excluding moose, constituting a tenth of an Isle Royale wolf's diet. The beaver population has sharply declined since the arrival of wolves, but they still are present, and though they are not a prime food source for typical wolves, they are the second to moose as the most consumed animal by the wolves on the island. Beavers benefit both species. They are as easy prey for wolves and they create aquatic macrophytes, very nutritional plants for moose, although the macrophytes are also consumed by the beavers. Though wolves are thought to contribute to the decline in beaver, researchers believe that the decline of aspen, the primary food source of beavers, which used to be plentiful, could have led to their decrease. Beavers have been exposed to predation by having to travel long distances to find only parts of the island where aspen remains.