Originally published on March 28, 2020.

New research is showing that so-called 'invasive' large herbivores are helping to restore habitat lost by the extinction of native megafauna thousands of years ago.

One of the species studied was the Colombian hippopotamus. Hippos are native to Africa, but these populations in South America are all descendants of four hippos that lived in drug kingpin Pablo Escobar's home zoo.

When Escobar was killed in Colombia in 1993, the animals in his zoo were all relocated — except for his hippos.

They made their way into the local river systems, and now, almost 30 years later, their population has grown to at least 80 animals, and they're considered a local nuisance.

Fitting into ecological niches

In the new study, published in the journal PNAS, the authors look at the effects large herbivores like these hippos have on their new homes. They found that even though these animals are considered pests, they do provide benefits that should not be overlooked.

Escobar's hippos are just one of many large herbivores around the world that are considered invasive species. From camels in Australia, to feral hogs in North America, many conservation efforts are spent trying to get rid of these animals.

The dromedary camel, also called the Arabian camel, is considered an invasive species in Australia. (Erick J. Lundgren)

Erick Lundgren, a PhD student at the University of Technology Sydney and lead author on the study, points out that the Earth used to be covered in large herbivores. These megafauna like wooly mammoths and giant sloths were all hunted to extinction by humans 10,000 years ago. With the loss of those animals, we also lost their benefits to the ecosystems on our planet.

'Introduced' — not invasive

The researchers analyzed 72 large invasive species, and compared their ecological traits to those of the native megafauna in the area.

In 64 per cent of cases, they found that the modern-day species were fitting into ecological niches that have been vacant for thousands of years.

This can affect things like nutrient dispersal, permafrost melt, wildfire causation, and wetland distribution.

A hippo feeds at a farm in Colombia. These hippos are all descendants of the animals that lived in Pablo Escobar’s private home zoo. (Raul Arboleda/AFP via Getty Images)

Pablo Escobar's hippos, for instance, are similar to two now-extinct species — giant llamas, and notoungulates, which have been gone for thousands of years. Their size, diet, and semiaquatic behaviours allow them to spread nutrients into the water column in a way that hasn't been possible for over 10,000 years.

Lundgren cautions that this doesn't necessarily mean Pablo's hippos and other invasive species should be left as-is, especially if they are causing harm to humans. But they do caution that by labelling all invasive species as inherently bad means that their benefits aren't being studied, and suggest using the term "introduced" instead.

Produced and written by Amanda Buckiewicz