it's hippo to be square

DATE

When a person thinks of hippos, they usually think of two things: 1) hippos are the most dangerous animal in Africa (true), and 2) Moo Deng (the baby pygmy hippo internet sensation). This is kind of hilarious considering these two concepts are in opposition to each other.  But this article is instead going to argue that you should think of a more important third thing: hippos are the beavers of Africa.

What is an ecosystem engineer? It's when a species physically modifies the environment in a way that is both long-term and affects other species. Beavers are the quintessential example of engineers, creating dams which in turn create wetland habitats. Hippos should also be considered ecosystem engineers, because they make a lot of changes to their habitats.

Hippopotamuses (Hippopotamus amphibius), also called hippos, belong to a group termed megaherbivores, which are so called because they are plant eating and because they are very large (at least 1000kg!), tend to not be predated on, and travel large distances. They seem to especially have an impact on the environment for these reasons. Unsurprisingly, most megaherbivores today reside in Africa, and include elephants and rhinos.

Required listening for today: It's hip to be square - Huey Lewis & The News.

The nutrient cycle:

Hippos are pretty unique in that they are amphibious, and live on both the land and the water. They are herbivores and consume massive amounts of grasses, up to 40 kg in one day. They seem to poop almost exclusively in water for some reason, so they are essentially nutrient moving machines from land to water. Hippos transport nutrients including nitrogen and phosphorus, allowing algae and plant growth, which in turn provides foods for other animals like fish and insects. Truly, the Lion King's Circle of Life should have included hippo poop.

They also eat fruits sometimes and will distribute the seeds around - the sausage tree fruit is one they especially go for.

This movement is considered a type of nutrient cycling, by the flow of organic matter from terrestrial to aquatic ecosystems. There is some evidence that hippos are even changing the availability of nutrients and other chemicals, especially nitrogen and phosphorous, which are especially important for plants. Hippo presence is also known to promote plant and algal growth. Hippos are pretty tough because they can process the silica in grasses, which is a really tough component. They contribute to silica cycling because they can process it.

Get off my lawn:

Because hippos have to go onto land to eat grass, they create small patches of habitat called 'hippo lawns', which is a region of short-cropped grass that looks as if you mowed it. These are specific grassland communities that host specific grass species. This basically alters the habitat and opens up some areas, because they eat so much. The lawns are then used by other herbivores around.

Hippopotamasus are social animals and live in large herds, mainly staying in tightly associated family groups. As a result, hippos are highly concentrated on the landscape, which increases their impact on the local habitat. So many hippos in one area, eating grass, clipping lawns, and transporting nutrients can cause a large nutrient cycling effect. Individuals are also surprisingly long-lived, reaching about 30-35 years old, so they can really cause long-term impacts.

The diversity of habitats across the landscape is altered by this lawn formation also. By creating hippo laws, the landscape becomes 'patchy', with interrupted regions of lawns and dense habitat. Some patches have untouched woody plants, some patches consist of the grassy lawn. It's thought that this patchiness basically acts as a firewall to stop wildfire from moving across the landscape. When a wildfire hits a hippo lawn, its usually stopped. Overall you end up with a mosaic of habitats across the landscape.

As hippos travel between their grassy feeding grounds and their safe water grounds, they take the same path over time and create trails in the landscape. Trails can be up to 5 meters wide and 1 meter deep. Their traveling and wallowing also affects river channels, creating new streamflows and keeping channels open. Hippo activity can partly determine the fluvial characteristics of wetlands overall. But to note, there is little concrete evidence of this because its admittedly hard to study.

People think of hippos in water with birds riding on their backs (the Lion King again...), and this is mostly a true association. Hippo presence tends to attract fish like mudfish, catfish, and tilapia, which come out to feed on the parasites and dung. In turn, birds like herons and kingfishers are looking for the fish, so they tend to hang out where hippos are.

Hippo troubles:

The problem with determining hippo ecosystem impacts is because they are especially difficult to study. We already know they can be dangerous and aggressive, so getting close to them is difficult. It also makes it difficult to put trackers on them - you can tranquilize one hippo, but what about all the other hippos around? Because hippos are almost never on their own, it's difficult to isolate one to immobilize it.

Relevant to that, hippos apparently don't tranquilize well anyway because they are very sensitive to opioid-containing drugs, so it's especially risky. They just don't survive well. It's also hard because hippos are always close to water, which is never a safe situation when tranquilizing an animal - they could enter the water and drown.

In terms of tracking hippos, they can't be collared because their necks are just too thick! Researchers usually use ankle collars instead.

Basically, hippos are beavers. Really big, dangerous beavers.