Illustration of an African river ecosystem, showing the impact of the herbivorous mammal the hippopotamus (Hippopotamus amphibius). Until recently, our knowledge of hippos effect on ecosystems has been remarkably slim due to the danger they pose to scientists. New research has shed light on their huge ecological impact: from increased grazing due to the shortened grass lawn they create, to water ecosystems impacted by their defecation. Their grazing creates areas that allow other animals to graze such as antelopes. The waterways and rivers they inhabit also benefit from the faces they deposit (lower right). The nutrients from the plant material in their feces support various food chains (circular insets at lower left), including microbes, plankton and aquatic insects and crustaceans. These are eaten by birds (one at upper left) and by fish, which are in turn caught by birds of prey, humans, and predatory reptiles.