Evolutionary steps of ecophysiological adaptation and diversification of ruminants: a comparative view of their digestive system*'**

摘要: A review is made of the ruminant digestive system in its morphophysiological variations and adaptations relating to foraging behaviour, physiology, interactions between plants ruminants geographic climatic diversity ruminants' ecological niches. Evidence provided for evolutionary trends from an extreme selectivity mainly plant cell contents dependence upon a fractionated fore- hindgut fermentation, unselective intake bulk roughage subjected efficient wall forestomachs. The based on detailed comparative morphological studies all portions 65 species four continents. Their results are related physiological evidence classification extant into flexible three overlapping feeding types: concentrate selectors (40%), grass eaters (25%) intermediate, opportunistic, mixed feeders (35%). Several examples discussed how different types gaining advantage it concluded that have achieved high levels efficiency at each stage, (including well-documented seasonal system) evolution still going on. Deductions few domesticated may have, past, biased scientific evaluation free-ranging species' ecology. main threat continuous appears be man's neglect essential wild their specific habitats, which he alters or destroys.