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Colombia’s hippo population is a fascinating ecological conundrum

emblematic of our mixed-up 21st-century Earth
January 15, 2020

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With origins in the private zoo of cartel kingpin Pablo Escobar, Colombia’s growing hippopotamus population is easily dismissed as an anomalous footnote of natural history. Yet they’re also an provocative ecological case study.

Originally native to sub-Saharan Africa, hippos are considered ecosystem engineers in their homeland—but they’ve never before lived in South America. How will their impacts translate? This “novel introduction of a megaherbivore onto a new continent,” write researchers in the journal Oryx, “raises questions about the future dynamics of the socio-ecological system into which it has been introduced.”

Led by Amanda Subalusky, an ecologist at Yale University, the researchers review what’s known about hippos in their native range, with an eye to how the enormous creatures—full-grown females weigh around 3,000 pounds, and males several times that—may fit into the vast wetland plains of Colombia’s Magdalena River, into which they wandered following Escobar’s 1993 death and their subsequent abandonment.

An estimated 50 hippos live there now. Subalusky and colleagues draw on demographic data from Africa to predict a population of 800 by 2050. Depending on reproductive rates that figure could come closer to 5,000, more than enough to have significant consequences.

In just one year, a single hippo’s feeding and defecation can transfer more than one ton of carbon and other nutrients from terrestrial to aquatic systems. This fertilizer pulse causes life to bloom, nourishing plants and insects and fish—although, at very high quantities, it can have the opposite effect, feeding so many oxygen-hungry bacteria that the water becomes anoxic, leading to mass fish kills.

Yet these kills can in turn provide a surge of nourishment for scavengers; and as hippos wallow, their bodies scour pools and carve channels through vegetation, forming new ponds and connecting old ones. All this “alters the habitat and resource availability for a range of other species,” write Subalusky’s team, and in Africa that’s generally regarded as positive.

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But what of the Magdalena River basin, where many local species evolved without such disturbance? The researchers describe how some creatures need to spend part of their lives in isolated seasonal pools; connecting them would be disruptive. The hippos’ feeding habits could also destabilize riverbanks, accelerating erosion and destroying riparian areas.

On the other hand, sedimentation caused by human activity and land development is a problem in the Magdalena; hippos could help keep the floodplains from filling in. And until about 10,000 years ago, South America was home to giant sloths and truck-sized relatives of elephants; perhaps hippos actually perform ecological duties lost when those animals went extinct.

In short, it’s complicated. The same is certain to be true of their impacts on human economies and societies. Some people may benefit from them, while others may be inconvenienced and even harmed. Some people will like them, but others won’t. Ultimately these attitudes will determine the hippos’ future.

Subalusky and colleagues don’t themselves take a position on what this should be. As of now, the Colombian government says it will try to halt their population growth—using surgical sterilization, as attempts at shooting them were met by public outrage—and eventually relocate them from the wild.

This may well prove impractical, though, particularly if it’s not done soon and their numbers swell. As with so many situations on a planet suddenly and dramatically changed by human activity, time is short and the uncertainties are great.

Source: Subalusky et al. “Potential ecological and socio-economic effects of a novel megaherbivore introduction: the hippopotamus in Colombia.” Oryx, 2019.



About the author: Brandon Keim is a freelance journalist specializing in animals, nature and science. He is now writing Meet the Neighbors, a book about what animal personhood means for our relationships to animals and to nature. Connect with him on Twitter, Instagram and Facebook.

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