The prairie grasses or native grasslands evolved with major grazers. They co-evolved and one relies on the other. A major ruminant, which most grazers are—that is, bison, cattle, and sheep—are effectively nutrient cyclers. They take grass, which is non-usable to a lot of the other species that occupy the grassland ecosystem, and they convert it to manure, which insects feed on. Then songbirds feed on the insects. It's a whole dynamic process. If you take one element, namely, the major grazer out of it, you simplify the ecosystem and you don't have a highly functioning biological ecosystem.
Bison, and a bunch of other factors, filled that role naturally on the North American great plains. We domesticated livestock in Europe and brought them over here. They provide the revenue stream currently that we get off the grasslands. The other byproducts, which are some of the ecological goods and services that some of the other people mentioned, don't provide some of that same revenue stream.
Grasslands National Park found out that you can't have a functioning grassland ecosystem without a major grazer. They have bison on one part of it, and they have cattle on the other part. Cattle are more controllable than bison. We have to evolve our science to evolve that. We have had very little science on major ecosystems, and that is my emphasis on research, which is that it's government's role to assist in providing that research capability for everybody's benefit .