. Animal Ecology. Animal ecology. FIG. 25-1 Grassland ani- mals. Clockwise, bison, pronghorn, coyote, badger (courtesy Forest ^j. animals that occupy similar habitats, although often quite unrelated taxonomically, is of particular interest and may best be shown in table form (Table 25-1). ANIMAL ADJUSTMENTS It is in the grasslands throughout the world that the large herbivorous ungulates reach their largest populations. Their adaptations for feeding on grasses and the high productivity of grasses, which in fact is stimulated by moderate grazing, gives an effi- cient food coaction of high
. Animal Ecology. Animal ecology. FIG. 25-1 Grassland ani- mals. Clockwise, bison, pronghorn, coyote, badger (courtesy Forest ^j. animals that occupy similar habitats, although often quite unrelated taxonomically, is of particular interest and may best be shown in table form (Table 25-1). ANIMAL ADJUSTMENTS It is in the grasslands throughout the world that the large herbivorous ungulates reach their largest populations. Their adaptations for feeding on grasses and the high productivity of grasses, which in fact is stimulated by moderate grazing, gives an effi- cient food coaction of high energy utilization. A for- est cannot support such large populations of grazing animals since the herb layer is less luxuriant, com- posed more of the broad-leaved herbs, and shrub and tree foliage cannot tolerate continued browsing. The evolutionary development of these large ungulate populations had to await the evolution of these ex- tensive grasslands in mid-Tertiary time (Stirton 1947). Previous to the formation of the grasslands in North America, we may suppose that the ancestral forerunners of bison and pronghorn were largely lim- ited to serai grassy stages in the Arcto-tertiary and perhaps Madro-tertiary floras. It is common for these large ungulates to feed in large herds. The primitive population of bison in-. North America is estimated at 50-60 million animals, perhaps an average of 6 per sq km (15 per sq mi). Few occurred west of the Rockies even in colonial times, but to the east and north the species penetrated far into forested areas. Herds containing 20,000 indi- viduals were common and an occasional herd reached. a pupulaliuii as liigli as 4 million animals ( Seton 1909). When attacked by wolves or other predators the bulls formed a circle facing outward with the cows and calves inside. The animals shed their fur in the sum- mer and were greatly annoyed by flies, mosquitoes, and the penetrating seeds of the needle grass. They relieved their miseries by rolling
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