The Plains of Passage - Jean M. Auel [76]
Some specialized in eating particular plants, some in particular parts of plants; some grazed the same plants at slightly different stages of development; some fed in places that others did not go, or they followed later, or migrated differently. The diversity was maintained because eating and living habits of one species fit in between or around those of another in complementary niches.
Woolly mammoths needed great quantities of fibrous filler, rough grasses, stems, and sedges, and because they tended to bog down in deep snows, marshes or sphagnum meadows, they kept to the firm, windswept ground near the glaciers. They made long migrations along the wall of ice, moving south only in spring and summer.
Steppe horses also required bulk; like mammoths, they digested coarse stems and grasses quickly, but were somewhat more selective, preferring the mid-height varieties of grass. They could dig down through snow to find feed, but this used up more energy than they gained, and it was a struggle for them to travel when snow piled up. They could not subsist for long in deep snow and preferred the hard-surfaced, windy plains.
Unlike mammoths and horses, bison needed the leaves and sheaths of grass for the higher protein content and tended to select shortgrass, utilizing the areas of mid- and tallgrass only for new growth, usually in spring. In summer, however, an important, if inadvertent, cooperation was practiced. Horses used their teeth like clippers to bite through the tough stalks. After the horses had passed by, cutting down the stems, the densely rooted grass was stimulated to send out new leaves of re-growth. The migrations of horses were often followed, after an interval of a few days, by the gigantic bison, who welcomed the new shoots.
In winter, bison moved to southern ranges of variable weather and more snow, which kept low-growing grass leaves moist and fresher than in the dry northern plains. They were skilled at sweeping snow aside with their noses and cheeks to find their preferred close-to-the-ground feed, but the snowy steppes of the south were not without risk.
Though it kept them warm in the relatively dry cold, even of the south where more snow fell, the heavy, shaggy coats of bison and other warmly dressed animals that migrated south in winter could be hazardous or even fatal when the climate turned cold and wet, with frequent shifts between freezing and thawing. If their coats became soaking wet during a thaw, they could be vulnerable to a fatal chill during a subsequent freeze, especially if a cold snap caught them resting on the ground. Then, if their long hair froze fast, they would be unable to get up. Excessively deep snow, or icy crusts on top of snow, could also be fatal, as well as winter blizzards, or falling through the thin ice of oxbow lakes, or flooding river valleys.
Mouflon and saiga antelopes also thrived by selectively foraging on plants adapted to very dry conditions, small herbs and ground-hugging leafy shortgrass, but unlike bison, saiga did poorly on broken terrain or in deep snow, and they were not able to leap well. They were fast long-distance runners that could outdistance their predators only on the firm level surfaces of the windy steppes. Mouflon, the wild sheep, on the other hand, were expert climbers and used steep terrain to escape, but they could not dig through snow that piled up. They preferred the windblown rocky