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From VOA Learning English, this is the Science Report.
The hippopotamus is an animal very important to the health of Africa’s rivers and lakes. Their dung, or solid waste, helps Africa’s water ecosystem. But researchers warn that hippopotamus populations are decreasing. They say that could damage ecosystems, everything that lives in an environment. Also called hippos, they are the third largest land mammal after the elephant and rhinoceros. Hippos spend as much as 16 hours a day in the water. They go on land at night to feed. They eat more than 40 kilograms of grasses at each feeding. They return to the water where they release their waste. Douglas McCauley is an assistant science professor at the University of California, Santa Barbara. He and his team studied the waste of hippos. He says there are a lot of nutrients, substances needed for life, that move throughout the environment through hippos’ food and their waste. He says scientists are interested in how these nutrients move across systems. Mr. McCauley says living on both the land and in water means hippos are important providers of nutrients.
Every year, hippos provide over 60,000 kilograms of dung to African lakes and rivers. The study showed that some species of river fish need the dung in their diets. Mr. McCauley says some of the nutrients in the dung are the building materials of life. But as researchers learn more about the importance of hippos, there are fewer of them. Mr. McCauley says across sub-Saharan Africa there has been a 10 to 20 percent drop in the past ten years. He says humans are responsible for most of the drop in the hippo population.
