When Pablo Escobar died in 1993, the Colombian drug kingpin’s four adult African hippopotamuses were forgotten. But the fields and ponds along the Magdalena River suited them. One estimate puts their current population at 50 to 80 animals: By 2050 there may be anywhere from 800 to 5,000 in a landscape that never before knew hippos.

They aren’t the only herbivores showing up in unexpected places. In Australia, feral camels roam the outback. Antelope are a common sight in rangelands from Texas to Patagonia. And feral hogs are everywhere. Conventional wisdom holds that these animals are causing new, and potentially damaging, impacts to beleaguered ecosystems. But a study published Monday in the Proceedings of the National Academy of Sciences argues that the lifestyles of these and other exotic fauna may be restoring the ecological functions of species lost to extinction during the last ice age.

“We found that, amazingly, the world is more similar to the pre-extinction past when introduced species are included,” said Erick Lundgren, an ecologist at the University of Technology in Sydney, Australia, and the study’s lead author.