Prairies have been described as oceans of grass; if that's true, then, like the oceans, prairies possess a remarkable degree of biodiversity and are, in their own distinctive way, important contributors to our way of life.
Geology and Soils
One cannot understand biodiversity without understanding the natural history of the area in question. In the case of the Great Plains, that history consists of repeated marine incursions as well as glaciation of the northern portion of North America. The marine incursions contributed sedimentary rock in the form of limestone, sandstone, and the like, while the repeated glaciations ground rock into till- this till eventually became the basis for many of the fertile soils this region is known for.
Plants
The next building block of the plains ecosystem is plants, and the plants in this region are adapted for drier environments than you might find on either coast, since the region is in the rain shadow of the Rocky Mountains. This dryness is (along with wildfires) the reason why prairie regions lack trees but have no shortage of sunlight. The flora and fauna that flourish here are well adapted to deal with (and indeed rely on) direct sunlight as well as fire. One amazing adaptation is the root system of prairie plants; for every foot of biomass aboveground, there is two belowground. This concentration helps prairie plants to survive the winter and fires, as well, and creates a mat of roots that is very efficient at pulling moisture and nutrients from the soil. The tendency of dead plant matter to stay in place contributes to a thick layer of topsoil with a high organic content, a condition ideal for the planting of crops; this is the main reason that, out of the original prairies that covered this region, less than 1% remains.
Animals
Animals that live on the prairie have to be adapted for these conditions and thus tend to be drought- and heat-tolerant as well as able to dwell on or under the ground (in case of animals larger than insects). A bias towards nocturnal activity is another common adaptation. Prairie dogs are perhaps the classic example of an organism well-adapted to this environment- others include snakes, mice, butterflies, bees, and coyotes.
Conclusion
Though most of North America’s prairies were destroyed during settlement in order to clear land for agriculture, prairies have recently started to attract attention as a less resource-intensive means of generating biomass for ethanol as well as an extremely efficient means of CO2 sequestration. Combined with the natural beauty and diversity of grasses and wildflowers, prairies play a distinctive role in our planetary biosphere.