Grasslands - Mountains and Plains: The Ecology of Wyoming Landscapes - page 86

Fig. 6.3. Most grassland biomass is in the soil. the enlargement in this drawing
shows a single root with root hairs and the hyphae of mycorrhizal fungi. A film
of water (stippled area) coats each soil particle and provides habitat for nema-
todes and numerous protozoans, including amoebae and ciliates. Air spaces
provide habitat for mites, insect larvae, and other invertebrates. Bacteria are
extremely abundant but are too small to illustrate at this scale. Magnification
about 15 times. Based on Weaver (1968) and Hunt et al. (1987).

species have fine, light-colored hairs (pubescence)
on the leaves. Small size reduces the area exposed for
heat absorption and transpiration on warm days, and
the light color reflects some solar radiation that might
otherwise cause leaf warming and increased water loss.
Most leaves of grassland plants are facultatively decidu-
ous, that is, they fall or become senescent after a period
when conditions for photosynthesis have not been
favorable.
Although grassland plants are adapted to tolerate low
water availability, some avoid drought stress by complet-
ing their growth early in the spring while water is readily
available. examples of drought-evading plants are spring
wildflowers, such as sand lily and prairie smoke. other
grassland plants store water in tissues that remain suc-
culent throughout the dry summer, for example, prickly-
pear cactus and stonecrop. Succulent plants would be

grazed heavily by thirsty herbivores were it not for spe-
cial defense mechanisms, such as sharp spines.
Animals, too, must be adapted for surviving in the
grassland environment (table 6.1). With most of the
plant biomass belowground, there are many subterra-
nean herbivores, such as nematodes, mites, insect lar-
vae, and various burrowing mammals (such as pocket
gophers). 9 Aboveground, the primary herbivores include
grasshoppers, ground squirrels, prairie dogs, jackrabbits,
and the larger mammals already mentioned. one of
the major problems for large herbivores is obtaining
enough protein from coarse grassland plants with tough
cell walls and high concentrations of lignin and silica.
chewing this kind of food causes rapid tooth abrasion.
notably, large mammals common in grasslands have
teeth that continually grow from their crown. this
adaptation began to appear in the fossil record at about