Ruminants
The nutrients in grasses are surrounded by difficult-to-digest cellulose fiber. Many animals adapted to eat grass belong to a family called ruminants. The multi-chambered digestive system of ruminants, as well as microbes within the rumen, are specially adapted to breaking grasses down into available nutrients. Many of the herd-dwelling animals of grasslands, including bison, deer, pronghorn, antelope and wildebeest are ruminants. The grazing herds serve an essential ecological role in grassland ecosystems. Grazing helps inhibit competing plant species and promotes new growth in grasses. The animals' manure fertilizes and reseeds grasses and the impressions from their hooves help aerate and soften soils and create pockets for water to pool.
Other Large Herbivores
Some species of large grazing animals are not equipped with a rumen but are still able to thrive on grasslands. Species in the Equus family, including horses, zebras and burrows are common to some of the world's grasslands. Zebras are one of the emblematic species of the African savanna. In some areas of the savanna, zebra herds migrate to follow the rains and help prepare the grasslands for other species of herbivores. Zebras are often the first to arrive and eat the old growth and course parts of the plants that wildebeest and gazelle cannot eat. While feral horses exist in North American grasslands, wild horses are actually native to the steppes of Eurasia. In the grasslands of Australia, large marsupials, including kangaroos and wallabies, eat grasses and shoots.
Small Mammals
While large grazing animals stand out in grassland landscapes, many types of small mammals hop and scurry through the grasses of the Earth's prairies, savannas, steppes and other grasslands. Some small grassland mammals, such as rabbits and prairie dogs, eat grass leaves, while others, including mice, eat seeds. In the high plains grasslands of South America, guinea pigs eat grasses as well as roots and shoots. Most small mammals that inhabit grasslands live in underground burrows or dens to avoid predation. The small mammals of the grasslands serve as an important food source for birds of prey and other carnivores.
Insects
Many types of insects eat grasses and plants from grasslands. Common grass-eating insects include grasshoppers and many types of caterpillars or other nymphs. Some species of swarming insects, such as locusts, consume vast amounts of plant matter in a single pass. Grassland insects provide a food source for many types of reptiles and birds.