Since wolves' reintroduction, studies have shown they've had a mostly positive impact on the ecosystem: “Preliminary data from studies indicate that wolf recovery will likely lead to greater biodiversity throughout the Greater Yellowstone Ecosystem,” according to the National Parks Service page. The experiment has also led to their proliferation, as wolves are now found throughout Colorado, Washington and Oregon. Biologists keep track of wolf populations with radio collars, and they gather DNA (usually in the form of scat, or feces) to trace wolves’ lineages. Each state has created a unique management plan to keep the wolf population at a level where both wolves and their human competitors can thrive. Many states have decided to list the wolf as an endangered species, which gives it a unique level of protection.