At the peak of his cocaine-smuggling career, Colombia’s most notorious drug lord Pablo Escobar built a sweeping estate in the country’s rolling hills for his cartel friends and family, complete with a fully functional zoo filled with illegally transported exotic animals. After his death in 1993, one species was left to its own devices and has since thrived in the wet Amazonian rainforest. Now, the hippopotamus has been dubbed the “world’s largest invasive animal” and researchers at the University of California San Diego (UCSD) are evaluating the environmental impact of these massive semiaquatic mammals.
For the last two years, Jonathan Shurin, a UCSD biology professor, has been working with Colombian scientists, veterinarians, fishermen, and students under a project funded by the National Geographic Society to monitor water chemistry, study microbiome samples, and record the soundscape to paint a holistic picture of how hippos are impacting their environment across all spectrums.
Because they are dangerous, territorial, and weigh several tons, Escobar’s four hippos – three females and one male – were let loose rather than transported to nearby zoos. It’s expected that one female gives birth to a new calf every year, resulting in an annual population growth of about 6 percent that now puts Colombia’s hippo population at up to 60 animals. The massive herbivores are endemic to the rivers and swamps in Africa, where their numbers are limited by seasonal drought. However, Colombia’s hot, humid, and year-round wet climate, paired with no natural predators, has allowed their population to boom.
The team found that the big animals are leaving an equally large footprint – literally. Because of their large size, the hippos change wetland structures simply by walking through it. They are also “ecosystem engineers” that eat grass on land and poop in the water, moving nutrients from one ecosystem to the other. While their poop acts as a fertilizer, too much of it can be toxic and suffocate water systems, while a change in water chemistry can further threaten those that live in aquatic environments.
“It was not expected that the hippopotamus would be integrated into the aquatic ecosystems of Colombia so successfully,” biologist and Colombian native Aranguren-Riaño said in a statement. “The risk to native species such as manatees, turtles, and fish is high and the environmental effect is unpredictable. It is a big problem because they have migrated to the Magdalena River and could spread to other strategic regions of Colombia.”
Hippos help to manage grasslands by eating vegetation, which gives scientists a window into ecosystems 10,000 to 20,000 years ago when other giants, like mastodons and mammoths, roamed savannas and grasslands that later turned to forests after they died off.
The researchers note that Colombians and tourists often misinterpret hippos as gentle giants, which they certainly are not, and it could pose future human-animal conflicts.
Then again, hippo populations in Africa have dropped to vulnerable status, and others argue that any rebound in numbers – even on a different continent – could be a good thing.