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This is scientific Americans 60 Second Science. I'm Jason Goldman.

Around 115 miles east of Mediene in Colombia sits the enormous hacienda built by the

drug lord Pablo Escobar, who had his own personal zoo, which included hippos. When Escobar's empire fell, most of the exotic animals were safely

relocated, except for the hippos who eventually escaped.

He brought four from a zoo in the U.S. to Columbia and they lived at his ranch and they've grown slowly but steadily.

Jonathan Shurin, ecologist from the University of California and San Diego.

The original population of 4 in 1981 is estimated to be at least 80 now.

Hippos have a tremendous influence on their native ecosystems in Africa.

So Sherin wanted to see how they might be affecting their new ecosystem in Colombia.

You know, shouldn't be a surprise to anybody that Hippos poop in the water in South America just as they do in Africa.

Hippos on both continents wallow in ponds and lakes, where their droppings release a tremendous amount of nutrients into the water.

That imported material stimulates photosynthesis of algae and aquatic plants and also microbial

bacterial production of bacteria that are living off of the organic matter that's imported.

And that's where the hippos can cause ecological trouble.

If there is too much photosynthesis occurring,

then the water becomes full of oxygen during the daytime.

But at night, when the sun goes down and the plants and algae stop releasing oxygen into the water,

a phenomenon called eutrophication occurs.

All the creatures that consume oxygen keep consuming it,

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