RESULTS AND DISCUSSION Vertebrate Census Species composition, relative abundance, and seasonal status of vertebrates in NAEG study areas have been presented in earlier reports (Moor and Bradley, 1974; Bradley and Moor, agree with other investigations at NTS 1975) and in general (Hayward et al., and Jorgensen, 1963; Jorgensen and Hayward, 1963; Tanner 1965). Probably there have been major changes in the rodent fauna in two study areas of NTS since the last formal report. Table 1 presents population estimates of rodents in Area 5 and Area 11 in the springs of 1973, 1974, and 1975. The rodent fauna in Area 5 appears to have increased dramatically from 1973 animals/hectare). (0.38 animals/hectare) to 1975 (3.39 There is an apparent increase in two important granivores, Dipodomys merriamt and D. mtcrops, which now comprise over 90% of the rodent fauna in Area 5. This increase is attributed to the more abundant precipitation and production of green plants during and following 1973. The dependence of the desert fauna in southern Nevada upon green vegetation for successful reproduction has been reported previously (Beatley, 1971; Bradley and Mauer, 1971). Conversely, Area 13 had undergone an apparent drastic reduction in rodent species in richness and numbers. During the springs of 1973 and 1974, numbers of rodents were estimated at 3.5 animals/hectare. During spring of 1975, however, estimates were 0.52 animals/hectare. This reduction of rodents is probably due to the activities of large herbivores (cattle and goats) in summer, 1973. introduced as part of the grazing study Whereas more data need to be gathered before the extent of the impact of herbivores on the rodent fauna can be properly evaluated, definite destructive alteration of certain rodent habitats within the enclosure of Area 13 is evident. Radioanalysis One hundred resident vertebrates from NAEG intensive study areas and 20 control animals from off-site have been collected, 56 autopsied, and