The year was 1981, and Pablo Escobar, a well-known Colombian drug trafficker, introduced four hippos, three females and one male , from an American zoo, into his Hacienda Napoles for his personal collection.
The hippopotamus is considered the second deadliest animal on the African continent, only after the mosquito , and despite this, it is classified as a vulnerable species in its natural habitat. But these four specimens were there, thousands of kilometers from their natural habitat, as the main attraction in such an outlandish exhibition, living in the pond.
The hippopotamus: ecosystem engineer
Hippos, in their natural habitat, are ecosystem engineers , meaning that through their activities they change the appearance of the landscape and thereby alter the ways in which ecosystems evolve . The most classic example of an ecosystem engineer is the beaver, which cuts down trees and creates dams, changing the course of rivers. In environments where these animals are native, these changes may be essential for ecosystem maintenance. In the case of hippopotamuses, an adult specimen that grazes on the shores and rests in aquatic environments can transport up to 750 kg of carbon and other nutrients from dry land to the wetland, through defecation .
It is true that when a new species is introduced into an ecosystem it may not survive. Or that it survives, but does not reproduce. Or even, that coming to reproduce and naturalize, it does not cause major problems. When all that is left behind, and the introduced species expands, takes over the ecosystem and alters it , that is when we have a problem and we say that, in that place, it is an invasive species . It is very common for invasive species to generate impacts such as competition with native species, disease transmission or interaction with other invasive species.
When an invasive species is also an ecosystem engineer, we can expect the worst ; The impacts that this type of species can cause are devastating for biodiversity; they alter ecosystem structure, modify food webs, and even change the way ecosystems evolve. And by extension, the social and economic impacts can be disastrous.
The story of Pablo Escobar’s hippos
But back to the hippos. We had four at Hacienda Napoles, Colombia, introduced in 1981. When the leader of the Medellin cartel is assassinated, the animals from his farm are distributed to different Colombian zoos. But the huge hippopotamuses were so difficult to transport that it was decided to leave them at the drug trafficker’s hacienda, near the Magdalena River . In 2006, the Hacienda Nápoles was converted into a tourist attraction, and the hippos were part of it. In that year, the population had already multiplied by four .
Three hippos appeared in 2009 in a swamp near Puerto Berrio, 75 km downstream from the Hacienda. And since then, they began to be sighted more and more. In 2010 one more appeared in Puerto Perales . In 2012, the known population was already 35 individuals. In 2013, three more in the Cocorná River , a tributary of the Magdalena, and several more in the Ciénaga Barbacoas, more than 100 km from Escobar’s house. This demonstrates the enormous adaptability of these animals to the wetlands of the Magdalena Valley. In 2020 it was estimated that the total population must be between 90 and 110 individuals , perhaps up to 140; a remarkably high reproductive rate. With the available data and taking into account the characteristics of the environment, it is estimated that, if nothing is done to avoid it, in 2035 the population could reach the carrying capacity of the ecosystem , that is, the maximum population that it can support; around 1500 copies .
The damage of hippos
The Magdalena river basin is the largest in Colombia. It occupies 24% of its surface. It is a region with a hot and humid climate, which is optimal for hippos. Among the fauna of the region is one of the most endangered primates, the brown spider monkey ( Ateles hybridus ) and significant populations of West Indian manatees ( Trichetus manatus ), listed as vulnerable.
In these environments, the hippopotamus can cause real ecological disasters. As stated above, a single adult specimen can transport up to 750 kg of organic matter —not counting water— from meadows, bushes and forests to lakes and rivers. As hippopotamuses tend to cluster in specific areas, this drastic increase in organic matter in the water can cause a eutrophication effect that suffocates the aquatic ecosystem. As hippos move through vegetation, they can form pathways that connect otherwise isolated ponds , thereby changing the length of time these ponds remain flooded. This also affects aquatic fauna. Finally, these hyper-polluted lagoons can end up in the main river , again due to the movements of the hippopotamuses, altering that ecosystem.
An important part of the economic development of the region depends on the river . Hippos are very territorial, and respond very aggressively; this could pose a threat to fishermen, fishermen, and boats . All crops present within 10 km of the riverbank are likely to be hippopotamus grazing, and any community living within that distance needs to be aware of the risks of encountering these animals and how to avoid encounters.
Are there solutions to this problem?
When it comes to invasive alien species, the best solution is always prevention. Conduct studies to predict which species are at risk of becoming invasive, and act accordingly, avoiding the introduction of these species. But when the damage has already been done , and prevention is not feasible, then other alternatives must be taken .
In the case of hippopotamuses in Colombia, two types of solution have been proposed: sterilization and extraction . The models indicate, however, that applying the first solution only delays the problem, but does not solve it. It is estimated that, in the best of cases, a sterilization of up to 15 individuals per year would only delay the arrival of the maximum population by about 11 years. For the measure to work, it should be sterilized at least twice, but it does not seem like a viable measure. On the other hand, even sterilized, hippos continue to cause unacceptable impacts for decades .
The second solution is simpler and less expensive, and also more efficient . An annual extraction of 20 individuals would cause a significant and gradual decline in the population until 2042, but from then on it would grow again. However, increasing to an annual removal of 30 individuals would end the invasion in the year 2033 . That extraction could be carried out in two ways: capture or sacrifice . The capture would only be recommended for those hippos that are in the vicinity of a center enabled to keep the animals in captivity and prevent them from escaping, such as Hacienda Napoles itself, if it is adapted correctly. But in the rest of the cases, and above all, taking into account the enormous volume of animals that have to be controlled, slaughter seems to be the only viable solution .
Fortunately, and having against animalists and those who want to profit from the presence of these impressive animals, this same month of February the National Technical Committee for Introduced and/or Transplanted Invasive Species of the Colombian Ministry of the Environment has included the hippopotamus as an invasive species . A first step that will allow defining concrete actions against the invasion.
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