Hippopotamuses are large semi-aquatic mammals native to sub-Saharan Africa, primarily found in rivers, lakes, and wetlands. They play a multifaceted role in shaping their environments, influencing both aquatic and terrestrial ecosystems and contributing to their health and diversity.
Nutrient Enrichment of Aquatic Ecosystems
Hippos engage in a unique daily cycle that fundamentally influences nutrient distribution within their ecosystems. They spend their days submerged in water for protection from the sun, but emerge at night to graze on land. This behavior creates a vital link between terrestrial and aquatic environments, as they return to the water to defecate.
Their dung acts as a natural fertilizer, transferring significant nutrients, including nitrogen, phosphorus, carbon, and silicon, from the grasslands into the waterways. This influx of organic matter stimulates the growth of algae and microorganisms, which then form the base of the aquatic food web, supporting diverse populations of fish and invertebrates. For instance, in Kenya’s Mara River, hippos transport approximately 0.4 metric tons of silicon daily, which is particularly important for diatoms. These concentrated nutrient deposits can create “nutrient hotspots” that enhance productivity, especially during dry seasons when water flow is reduced.
Shaping Waterways and Terrestrial Habitats
The sheer size and consistent movements of hippos physically alter the landscapes they inhabit, earning them the designation of ecosystem engineers. Their passage through dense vegetation and shallow waters creates and maintains distinct channels and pathways. These “hippo highways” serve as conduits for water flow, particularly during flood events, and can even influence the course of river channels over time.
These pathways also provide access routes for other animal species, allowing them to reach water sources or move through otherwise impenetrable areas. Additionally, hippos create wallows, which are depressions in riverbeds and muddy areas formed by their repetitive movements and resting. These wallows can retain water during dry periods, providing temporary habitats and water sources for aquatic organisms, including plants, invertebrates, and fish. Their activity also stirs up sediments, mixing the water column and promoting gas exchange like oxygen and carbon dioxide.
Vegetation Management through Grazing
Hippos function as substantial grazers, consuming large quantities of grass from the terrestrial areas surrounding their aquatic habitats. An adult hippo can eat between 20 to 40 kilograms of grass, or up to 100 pounds, each night. They utilize their broad lips to pluck grass tops, creating characteristic “grazing lawns” or short-grass patches.
This selective grazing influences the composition and structure of vegetation along riverbanks and in floodplains. By consistently cropping grasses, hippos prevent fast-growing plant species from dominating, which promotes structural heterogeneity and greater plant diversity. These maintained grazing lawns also benefit other herbivorous species by providing accessible, nutrient-rich forage. Their consumption of dry vegetation can contribute to reducing the accumulation of fuel, which may influence the intensity of potential wildfires in these areas.