Just off the mouth of the Mississippi, a rare breed of Chinese deer has found a new home--and new hope--for its embattled species. Further east, the gopher tortoise, one of nature's expert diggers, recovers from catastrophic population decline brought on by human encroachment and habitat loss. Track the exciting efforts to revive some of the lesser-known animal empires.

Sometimes, a species' survival hinges on inhabiting an area that isn't theirs. From the ubiquitous brown rat to the seals of Pier 39 in San Francisco and the flying foxes of South Eastern Australia, meet nature's unwelcome guests who've found a way to impose themselves onto new and unlikely environments.