Beaver

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

A keystone, in an arch, is the single wedge shaped block at the top that holds the whole structure together. Pull it out and the arch collapses. The National Park Service uses that image deliberately for the beaver, a keystone species that affects habitat structure and dynamics through the damming and diverting of streams, and the felling of trees and other woody vegetation, whose removal can contribute to an ecosystem collapse the same way pulling the actual keystone drops the arch. The Park Service goes further, calling the beaver more industrious than any other mammal besides humans, and larger than any other rodent in the United States. What makes a beaver different from most animals called ecosystem engineers is that it does not merely use a habitat, it manufactures one. Damming a stream floods the surrounding land, raising the water table, reconnecting and expanding floodplains, and creating the still, shallow ponds that other fish and wildlife then move into. Many species come to rely partly or entirely on beaver ponds for their own survival, some of them already threatened or endangered in their own right, which means the beaver is not just adapted to wetlands. In a real sense, across most of North America, it is the reason wetlands as habitat exist in the first place.

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

Yellowstone National Park has been counting its own beaver colonies for over a century, and the National Park Service's own numbers trace a full boom, bust and recovery arc rather than a steady line. The first survey, in 1921, found twenty five colonies on the park's northern range. By 1953 that had collapsed to just eight, and none of them were even at the same sites the 1921 survey had recorded. Aerial surveys in 1996 counted the population back up to forty nine colonies, and by 2007 it had climbed further still, to one hundred twenty seven, before settling to an estimated one hundred twenty one by 2024. NPS credits the resurgence in willow since the late 1990s and the presence of suitable habitat for the recovery, while noting plainly that natural fluctuations in beaver population dynamics and the practical difficulty of surveying them at all complicate any exact count. The mechanism behind the numbers is the same one the colonies themselves depend on: beaver ponds and the flooding they cause create conditions favorable to willow and aspen, the beavers' preferred winter food and building material, so a healthy willow stand and a healthy beaver colony count tend to rise and fall together, each one feeding the other. An old dam is still visible today at Beaver Lake, between Norris and Mammoth, evidence that some of this engineering long outlasts the animals who built it.