Imagine a healthy forest, home to a variety of species: Birds are flitting between tree branches, salamanders are sliding through leaf litter, and wolves are tracking the scent of deer through the understory. Each of these animals has a role in the forest, and most ecologists would argue that losing any one of these species would be bad for the ecosystem as a whole.

Unfortunately – whether due to habitat loss, overhunting or introduced species – humans have made some species disappear. At the same time, other species have adapted to us and spread more widely.

As an ecologist, I’m curious about what these changes mean for ecosystems – can these newly arrived species functionally replace the species that used to be there? I studied this process in eastern North America, where some top predators have disappeared and a new predator has arrived.

Wolves used to roam across every state east of the Mississippi River. But as the land was developed, many people viewed wolves as threats and wiped most of them out. These days, a mix of gray wolves and

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