The invasive species have caused havoc in Colombian waterways, but they might fill an ecological niche that benefits the ecosystem.
When infamous drug lord Pablo Escobar was shot and killed in 1993, he left behind a 9,000 pound problem at his luxurious Colombian ranch-turned-zoo, Hacienda Nápoles: Four adult hippopotamuses. There are now 80 hippos and their invasion has led to noticeable changes in the Colombian environment with recent research suggesting they're having a negative impact on waterways.
A new study, published in the journal Proceedings of the National Academy of Science on Monday, challenges that view, suggesting the hippos fill a unique ecological niche that has been lost since human occupation. The collaboration of international researchers examined how introduced herbivores, like Escobar's hippos in South America, wild boars in North America and camels in Australia, may help restore ecosystems to states last seen thousands years ago -- a concept known as "rewilding."
To uncover how foreign species might impact their new, unfamiliar environments, the team scanned through the history books and looked for big herbivores that had gone extinct over the last 100,000 to 10,000 years -- a period known as the Late Pleistocene. In that time, humans came in and messed with those ecosystems, driving some species extinct.
The team analyzed how ancient, extinct herbivores ate, the environments they lived in and their size. Then they compared those traits with introduced species to see if there was any overlap..
"We could quantify the extent to which introduced species make the world more similar or dissimilar to the pre-extinction past," said Erick Lundgren, a PhD conservation researcher at the University of Technology, Sydney, in a statement. "Amazingly they make the world more similar."
In total, the team found 64% of introduced species resembled extinct species more than living ones. This leads to a restoration of the ecosystems of the Late Pleistocene and, the authors note, could reduce instances of wildfires as the introduced species alter the landscape.
However, Escobar's hippos are a particularly notable case -- and not just because of their ties to the world's most notorious drug lord.
The four hippos he imported (dubbed the "cocaine hippos") seemed to thrive in their Colombian home and now number almost 100. They've also become an important part of Colombia's tourism industry. However, a study published in the journal Ecology in January, led by Jonathan Shurin at the University of California, San Diego, found hippo poop was helping fertilize algae and bacteria in Colombian lakes and potentially contributing to problematic algal blooms.
Shurin says the hippos in Colombia should still be removed or contained and their effects on the native biodiversity are still unknown.
"Like other plagues recently in the news, they can be controlled more cheaply, effectively and humanely early on when they're rare, rather than later when they're everywhere," he says.
Shurin says his future work will examine whether the hippos have fewer or different parasites in Colombia versus their native home of Africa and will try to understand how the lakes in Colombia have changed since the hippos arrival by analyzing sediments.
The decades-long experiment looks set to continue over the coming years, with Colombian locals keen to leave the hippo population alone and insufficient funding from the local authorities to prevent further breeding with a sterilization program. In an interview with the Los Angeles Times in February, Shurin noted that within 20 years there could be thousands of hippos in Colombia. What effect would that have on the landscape? Only time will tell.