Grasslands - Mountains and Plains: The Ecology of Wyoming Landscapes - page 87

Fig. 6.4. Grassland plants are toler-
ant of grazing by large herbivores,
especially if most of the forage is con-
sumed later in the growing season.
nearly all the plants are perennials,
and most biomass is belowground.
this rangeland in the Laramie Basin
is in excellent condition. Problems
are inevitable near water sources and
where too many animals are con-
fined by fences for too long in areas
that are too small.

the same time that grasslands became widespread, some
20 million years ago (during the Miocene).
Another adaptation of some large grassland mam-
mals is the ruminant digestive system of bison, deer,
elk, and pronghorn (also shared by cattle and sheep).
the four chambers of their stomachs contain bacteria
and protozoans that facilitate digestion and the extrac-
tion of protein from coarse plant material. Regurgita-
tion and additional chewing is an important feature of
this digestive system. nonruminants, such as horses,
can also survive in grasslands, but they must consume
considerably more food, because it passes through their
digestive systems more quickly and with less energy and
nutrients extracted. to facilitate the digestion of plant
tissues in general, all mammalian herbivores, regardless
of their habitats or digestive systems, have longer intes-
tines per unit of body weight than do carnivores.

Partitioning Grassland Resources

Many species of plants coexist in grasslands and occupy
nearly the same space, and many grassland animals
seem to share the same habitat. However, careful study
has demonstrated that there are subtle differences in
the ways that different species obtain what they need
to survive. Some plants, for example, complete their
growth at a different time of year than their neighbors.
Plants and animals that use different resources in the
same community or at different times of the year are
viewed as occupying different ecological niches. there
is a tendency during evolution for the niches of coexist-
ing species to become less similar, reducing the inten-
sity of competition.
in the 1950s, John Weaver at the University of
nebraska conducted one of the first studies that sug-
gested resource partitioning among grassland plants. He