Survivors of "King of Cocaine" Pablo Escobar's exotic menagerie are floating, reproducing, pooping, and just plain thriving in Colombian lakes, where they are literally reshaping the ecosystem with every new hippo and each new bowel movement.
This motley crew are the descendants of four hippos which were once a part of the drug kingpin's private exotic-animal collection, housed at his former estate, Hacienda Nápoles. When Escobar's empire dissolved, his creatures were re-homed – all save the four hippopotamuses who proved too big a challenge to relocate.
The unexpectedly liberated hippos have made the most of their freedom. Now, there are 80 of them — and the population boom is showing now signs of slowing down, Jonathan Shurin, professor at the University of California San Diego, tells Inverse.
"It is apparently a very happy environment for them, they seem to be living and reproducing quite well," he says.
As happy as the hippos are, they are also causing some significant damage to the surrounding ecosystem, which was not built equipped for herds of hippo. In fact, the hippos are proving so destructive they have altered the chemical composition of 14 small lakes — their preferred hangout.
That's the upshot of a paper co-authored by Shurin and published Tuesday in the journal Ecology. It offers the first scientific look at the ramifications of unleashing a band of a wild hippos on the Colombian ecosystem.
"There's a real dilemma about what to do about them in Colombia," Shurin says. "On one hand, they're a local tourist attraction and curiosity. On the other, they pose a real risk to the public and the environment."
Small lakes, big hippos
Shurin's analysis focuses on 14 small lakes located near Antioquia in Colombia. Each lake contained significant hippo populations — one had between 20 and 30 of the creatures bathing in its waters. The scientists sampled lake water from the shore "due to the hazard presented by hippos." That hazard is very real: hippos typically weigh over 3,000 pounds and they are not benign. In African countries, hippos kill an estimated 500 people each year.
The samples revealed that hippos are efficient carbon dumpers. During the night, the hippos roam on land, eating plants. During the day, they take shelter in the lakes, where they then poop out those plants.
That excrement triggers a set of chemical changes in the lake, Shurin says. The team saw changes in the algae and bacteria populations that may be early earning signs of nutrient pollution — that's when there are so many nutrients in the water that it sets the stage for harmful algal blooms. Blooms create "dead zones," where there is no longer enough oxygen in the water to support life.
"Hippo lakes have bigger daily changes in dissolved oxygen, and oxygen may drop low enough at night to kill fish and other aquatic animals that breathe oxygen in water," Shurin says.
Thing is, that is just what hippos do. They are environmental engineers par excellence.
In East Africa, some estimates suggest there are about 70,000 hippopotami, which together dump some 52,800 metric tons of poo into bodies of water every year. As one 2018 Nature Communications paper notes, that discharge led to 9 mass fish die-off events over 5 years.
But the hippos in Colombia are particularly special: They are also the world's largest invasive mammal.
What do we actually do about them?
It's not the hippos' fault that their ancestors were brought to South America to please a cash-flush cartel boss. And now they are free, they are still a public curiosity and attraction — which leaves scientists scratching their heads as to what to do about them.
As things stand, authorities are taking the laissez-faire approach — sitting by and watching the hippos multiply, poop, and generally go about their business, Shurin says. But that isn't a great strategy and has "problems for public safety and the environment," he says.
Unfortunately, the other options aren't great, either.
Two other options for hippo control include catching and sterilizing them, or shooting them, Shurin says. Of the two options the latter is unpopular. The former option, however, is dangerous, given the sheer size of a hippo and the increasing size of the population.
Still the pressure is on: Every day they are left to their devices, the hippos are likely to continue to multiply.
"Whatever solution will be cheaper and more humane when there are 100, than when there are thousands," he says.
In lieu of a good solution, the cycle of life continues. They fornicate, they eat, and excrete — basically they live their best life. Meanwhile, the lakes bear the burden of these huge invasive herbivores.
Abstract: The keystone roles of mega‐fauna in many terrestrial ecosystems have been lost to defaunation. Large predators and herbivores often play keystone roles in their native ranges, and some have established invasive populations in new biogeographic regions. However, few empirical examples are available to guide expectations about how mega‐fauna affect ecosystems in novel environmental and evolutionary contexts. We examined the impacts on aquatic ecosystems of an emerging population of hippopotamus (Hippopotamus amphibus) that has been growing in Colombia over the last 25 years. Hippos in Africa fertilize lakes and rivers by grazing on land and excreting wastes in the water. Stable isotopes indicate that terrestrial sources contribute more carbon in Colombian lakes containing hippo populations, and daily dissolved oxygen cycles suggest that their presence stimulates ecosystem metabolism. Phytoplankton communities were more dominated by cyanobacteria in lakes with hippos, while bacteria, zooplankton and benthic invertebrate communities were similar regardless of hippo presence. Our results suggest that hippos recapitulate their role as ecosystem engineers in Colombia, importing terrestrial organic matter and nutrients with detectable impacts on ecosystem metabolism and community structure in the early stages of invasion. Ongoing range expansion may pose a threat to water resources.