Hippos in South America

The Washington Post has an opinion piece by Robert Gebelhoff asking the tough questions about a South American herd of African herbivores: “The great conundrum of Pablo Escobar’s hippos”:

Today, Escobar’s herd has grown to upward of 100 strong. To residents, they are a threatening menace, but among scientists their presence is the source of spirited debate. Are Escobar’s hippos “invasive”? Or are they “introduced”? Are they threatening the local ecological community? Or are they helping to “rewild” the area? The answer is far from clear, but the debate could change the way we think about preserving habitats.

He raises several interesting points, especially the fact that large notoungulates existed in South America in a hippo-like niche that is now empty, probably because of human-induced extinctions. I figure that hippos in South America are a fair exchange considering that African waterways are increasingly choked by invasive South American water hyacinths.

In the long run, of course, all large herbivores will be managed, whether they are introduced, invasive, or native. Already in large parts of the world, it is human aesthetic taste that shapes the management of large mammals of all kinds. Even the most “natural” environments are shaped by people, with conservation priorities that may look quite different from the same environments 10,000 years ago.

A recent paper in Ecology by Jonathan Shurin and coworkers looked at the way that hippos in Columbia are affecting their environment: “Ecosystem effects of the world’s largest invasive animal”.

Hippos in Africa fertilize lakes and rivers by grazing on land and excreting wastes in the water. Stable isotopes indicate that terrestrial sources contribute more carbon in Colombian lakes containing hippo populations, and daily dissolved oxygen cycles suggest that their presence stimulates ecosystem metabolism. Phytoplankton communities were more dominated by cyanobacteria in lakes with hippos, and bacteria, zooplankton, and benthic invertebrate communities were similar regardless of hippo presence. Our results suggest that hippos recapitulate their role as ecosystem engineers in Colombia, importing terrestrial organic matter and nutrients with detectable impacts on ecosystem metabolism and community structure in the early stages of invasion. Ongoing range expansion may pose a threat to water resources.

The unavoidable reality is that people will shape their understanding of nature in ways that are convenient for themselves. One day society may forget the effects of wild megafauna entirely. Or they may engineer environments using the remaining megafauna in ways that are convenient to humans.