Pablo Escobar Brought Hippos to Colombia. Now They're Taking the Place of Animals Wiped Out by Humans Thousands of Years Ago

The introduction of non-native herbivores by humans to countries around the world may—in some instances—counteract a legacy of extinctions by replacing traits which have long been lost in ecosystems.

Scientists tend to view invasive species like these in a negative light, given the potentially harmful impacts that they can have on their local environment.

Among the most famous examples of introduced animals are the hippos brought to Colombia in the 1990s by drug lord Pablo Escobar, who housed them at his luxurious country estate east of Medellin, which featured a private zoo.

After Escobar's death in 1993, the hippos multiplied and spread out over the local area to the point where there are thought to be between 80 and 100 of the animals living in the country today. This can lead to ecological problems. One recent study, for example, found that the invasive hippos may be having a negative impact on the water quality of lakes in the area around the ranch.

However, a study published in in the journal Proceedings of the National Academy of Sciences—led by Erick Lundgren, a Ph.D. student at the University of Technology Sydney Centre for Compassionate Conservation in Australia—has challenged the view that the introduction of non-native herbivores, like Escobar's hippos, always has negative outcomes given that the animals may restore beneficial traits to an ecosystem that may have been lost for thousands of years.

Large mammalian herbivores dominated the Earth's land ecosystems for several million years before suffering significant extinctions and declines over the past 100,000 years or so, largely as a result of human pressures, such as hunting.

The decline in these animals led to significant ecological changes due to the loss of their unique combination of traits. However, humans have recently introduced large numbers of herbivore species to parts of the world where they are not native.

According to the researchers, one of the most significant outcomes of this trend is that key ecological functions have been reintroduced, reflecting environmental conditions before the widespread extinction of large herbivores. These introduced herbivores can affect various aspects of their new ecosystems, ranging from the frequency of wildfires to the dispersal of nutrients.

"While we found that some introduced herbivores are perfect ecological matches for extinct ones, in other cases the introduced species represents a mix of traits seen in extinct species," John Rowan, a co-author of the study from the University of Massachusetts Amherst, said in a statement.

Pablo Escobar hippos
Hippopotamus swim in one of the lakes near by Hacienda Napoles on September 24, 2018 in Doradal, Colombia. Juancho Torres/Getty Images

"For example, the feral hippos in South America are similar in diet and body size to extinct giant llamas, while a bizarre type of extinct mammal—a notoungulate—shares with hippos large size and semiaquatic habitats. So, while hippos don't perfectly replace any one extinct species, they restore parts of important ecologies across several species," he said.

According to Rowan, the study came about when he and Lundgren realized that the introduced donkeys the lead author was studying in Death Valley National Park were not so different from the wild horses that roamed North America thousands of years ago.

"We thought this might also be the case in other areas of the world, where introduced herbivores are labelled as pests only by definition that 'they shouldn't be here,'" Rowan told Newsweek. "But, we knew such views were based on narrow time perspectives—often the last few hundred years—and ignored the far more relevant evolutionary past. For example, the fact that horses had roamed North America for over 50 million years, and only disappeared very recently—the last 12,000 years—due to human impacts. While 12,000 years may not seem like a long time in human eyes, it is an evolutionary blink of an eye. With the loss of large herbivore species, we have also lost their influences on ecosystems."

"So we decided to team up on this project and see how many of these supposedly 'exotic' introduced species actually had extinct counterparts, in terms of their ecology, in the regions of the world they've been introduced," he said.

introduced herbivores, extinct species
Introduced herbivores share many key ecological traits with extinct species across the world. University of Kansas/Oscar Sanisidro

For the study, the Lundgren, Rowan and colleagues conducted an analysis comparing the ecological traits —for example, body size, diet and habitat—of introduced herbivores like Escobar's hippos to those of the large fauna which once roamed the Earth before the widespread human-driven extinctions.

"This allowed us to compare species that are not necessarily closely related to each other, but are similar in terms of how they affect ecosystems," Lundgren said in the statement. "By doing this, we could quantify the extent to which introduced species make the world more similar or dissimilar to the pre-extinction past. Amazingly they make the world more similar."

Specifically, the authors found that 64 percent of introduced herbivores have more similarities to extinct species than native animals, bringing a range of ecological benefits, they argue.

"Many people are concerned about feral horses and donkeys in the American southwest, because they aren't known from the continent in historic times," Rowan said in a statement. "But this view overlooks the fact that horses had been present in North America for over 50 million years—all major milestones of their evolution, including their origin, takes place here. They only disappeared a few thousand years ago because of humans, meaning the North American ecosystems they have since been reintroduced to had coevolved with horses for millions of years."

According to the authors, the latest study could have implications for how we view introduced herbivores and their impact on ecosystems.

"This paper is likely to stir the pot, but that's a good thing—hopefully it ignites a debate on entrenched views in conservation biology and encourages folks to 'take the long view' when thinking about biodiversity's past, present, and future. All we need is an open mind and a little creativity," Rowan told Newsweek.