The world’s grasslands, encompassing the vast savannas of Africa, the steppes of Eurasia, and the prairies of North America, represent one of the planet’s largest biomes. These ecosystems are defined by their dominant vegetation, which belongs to the plant family Poaceae, or true grasses. Grass serves as the foundational primary producer, capturing solar energy and forming the base of the food web. The unique challenge of grass is its tough cell wall, which is high in cellulose, a complex carbohydrate that most animals cannot digest without specialized adaptations. The consumption of this abundant, yet difficult-to-process, resource supports an incredible diversity of animal life, from the largest mammals to the smallest insects.
Large Mammalian Grazers
Large mammalian grazers, often moving in massive migratory herds, are the most recognizable consumers in the grassland biome. These herbivores are characterized by their size and enormous daily intake, which collectively shapes the physical structure of the landscape. An adult zebra, for instance, can consume approximately 20 to 30 pounds of forage daily.
In the African savanna, species like the blue wildebeest and the plains zebra demonstrate resource partitioning, allowing them to coexist by eating different parts of the grass sward. Wildebeest prefer the shorter, greener grasses of new growth areas, which offer higher nutritional content. The less selective zebra follows behind, processing the taller, tougher, and more fibrous parts of the grass stem. This continuous grazing pressure also reduces the buildup of dry, flammable biomass, which historically helped suppress large wildfires across the plains.
In North America, the plains bison fulfills a similar role, with its diet consisting of 90 to 100 percent grasses and sedges. These large animals use their hooves to break up the soil surface and their grazing to create a mosaic of different grass heights. This selective consumption and physical disturbance maintain the health and diversity of the grassland ecosystem.
Smaller Mammalian Consumers
The grasslands support a specialized community of smaller mammals that consume grass, hay, and grass seeds. While they consume less individually than large herds, these animals often exist in high population densities, making their collective impact significant. Species like the North American prairie dog and various ground squirrels are known for consuming fresh grass and for their burrowing activities.
Many of these smaller consumers, such as deer mice and voles, act as granivores, preying heavily on grass seeds. Seed predation by these mammals can strongly influence the composition and regeneration of the plant community by limiting the recruitment of new seedlings. Rabbits and hares, which are lagomorphs, are also common grazers that clip grass close to the ground. These animals must re-ingest their own soft fecal pellets, a process called coprophagy, to gain maximum nutrition from the fibrous grasses they consume.
Invertebrates and Other Grass Eaters
Beyond mammals, the grassland biome is home to an immense population of invertebrates that consume grass. Insects, often overlooked due to their size, can have a substantial localized impact on grass biomass. Grasshoppers and locusts are classic examples, capable of consuming vast quantities of foliage, especially during periodic outbreaks when they strip entire fields bare.
Termites are another major group of invertebrate grass consumers, particularly in tropical savannas where they feed on dead plant matter and roots. Their feeding and nest-building activities play a role in breaking down tough cellulose fibers and cycling nutrients back into the soil. Other non-mammalian consumers include birds, such as sparrows, finches, and larks, that rely on the seasonal abundance of grass seeds for a significant part of their diet.
Digestive Strategies for Processing Grass
The greatest challenge for all grass-eating animals is breaking down the cellulose and hemicellulose that form the plant’s cell walls. The solution lies in a symbiotic relationship with microorganisms, which produce the necessary enzyme, cellulase. Herbivorous mammals have evolved two primary digestive strategies to house microbial fermentation.
The first strategy is foregut fermentation, employed by ruminants like bison and wildebeest, which possess a multi-chambered stomach. In the first chamber, the rumen, a dense population of bacteria and protozoa ferment the partially chewed grass. The animal regurgitates and chews the material, known as cud, multiple times to physically break down the tough fibers, increasing the surface area for microbial action. This process is highly efficient, allowing the animal to absorb the volatile fatty acids produced by the microbes as its main energy source.
The second strategy is hindgut fermentation, seen in animals like horses, zebras, and rabbits. These non-ruminants use an enlarged cecum and large intestine as their fermentation vat, located after the main stomach and small intestine. While they can process large volumes of lower-quality forage quickly, this method is generally less efficient because the nutrients released by the microbes are absorbed later in the digestive tract. Grazers using both strategies also rely on specialized dental adaptations, specifically high-crowned molars known as hypsodont teeth. These teeth are resistant to the abrasive wear caused by grinding the silica-rich grass fibers and the grit ingested with food, ensuring they can process their tough diet throughout their lifespan.