able grass forage, 47 per cent of forbs, and 30 per 

 cent of browse. Browse and forbs are used more 

 than grasses by pronghorn antelope and deer (Stod- 

 dart and Smith 1943). Because of difference in food 

 preferences, competition between the latter big-game 

 species and cattle, although significant, is not as great 

 as is sometimes supposed. Furthermore, deer and 

 wapiti are able to graze steep slopes and other areas 

 which cattle ordinarily do not (Stoddart and Ras- 

 mussen 1945). Competition between deer and wapiti, 

 sheep and goats is more direct, however, because 

 sheep and goats also feed largely on forbs rather 

 than on grass. 



Overgrazing produces a change both in the kinds 

 and numbers of animals present (Table 9-6). This 

 is correlated with the change from mid-grasses to 

 short grasses to weedy perennials. The short-horned 

 grasshoppers increase in variety of species with this 

 change, but in other orders of insects, the number of 

 species present in overgrazed pastures either remains 

 the same or declines. There is generally an increase 

 in population level of all groups of arthropods, except 

 beetles, with overgrazing until the pasture deterio- 

 rates to such an extent that erosion becomes severe, 

 then there is a decline in abundance of all groups ex- 

 cept the Hymenoptera and Lepidoptera. 



Meadow voles, cotton rats, and cottontails are 

 less numerous in overgrazed than in undisturbed 

 grassland, but other rodents and lagomorphs increase 

 in abundance. Tall grass in ungrazed pastures 

 hinders the vision of jack rabbits, kangaroo rats, 



prairie dogs, and ground squirrels. Some rodents are 

 benefited by the larger and more numerous seeds 

 of the annual weedy species, and pocket gophers find 

 more tap- and bulbous-rooted plants in deteriorated 

 range (Bond 1945). Increased populations of insects 

 and rodents are a result, not a cause, of overgrazing. 

 If grazing by larger mammals is eliminated, suc- 

 cession back to thick grassland will occur in spite of 

 the smaller animals, and prairie dogs and ground 

 squirrels may actually be eliminated from the area 

 (Osborn and Allan 1949). 



In the luxuriant native prairie of early days, there 

 was seldom overgrazing by such large mammals as 

 bison, antelope, and wapiti, although this sometimes 

 occurred in the more arid Great Plains. Insects and 

 rodents occurred in populations that were in equi- 

 librium with their food supply, and overpopulations 

 of the species were held in check partly by the vege- 

 tation itself and partly by predatory birds, mammals, 

 and reptiles. The most important of the larger preda- 

 tors were the hawks and owls, coyotes, foxes, 

 badgers, black-footed ferrets, bullsnakes, and rattle- 

 snakes (Shelford 1942). In California, it has been 

 estimated that these predators eliminate about half 

 of the annual increase of ground squirrels (Fitch 

 1948). Because coyotes and wolves occasionally took 

 calves and lambs, they were systematically killed by 

 ranchers ; many other predators suffered with them. 

 With the elimination of these predators, one of the 

 checks on the rodent population was removed at a 

 time when increased grazing by livestock rendered 



128 Habitats, communities, succession 



