Paper-Lecture2 - Oecologia (2000) 125:8284 Springer-Verlag...

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Abstract In his landmark 1989 paper, R.R. Hofmann classified ruminants into three categories based upon di- gestive anatomy and preferred forages, and proposed that divergence of feeding strategies among ruminants is a re- sult of morphological evolution of the digestive tract. Be- cause of the hypothetical nature of these views and the in- grained beliefs that they challenged, several papers were published that reported tests of Hofmann’s predictions. The consensus among these papers was that Hofmann’s predictions were inadequate. I describe the experimental evidence that has been put forth in opposition to the rumi- nant diversification hypothesis and contend that we have failed to adequately test Hofmann’s predictions. Key words Concentrate selectors · Intermediate feeders · Roughage eaters · Rumen bypass · Ruminant diversification Early attempts to explain variation found in feeding strate- gies of free-ranging ruminants classified individual species as “browsers” or “grazers” based upon types of forage con- sumed. Though an important step in understanding the complexities of ruminant nutrition, Hofmann and Stewart (1972) recognized that feeding strategies of ruminants could not simply be classified into two categories, and pro- posed three categories (i.e., bulk and roughage eaters, se- lectors of concentrate forages, and intermediate feeders) based upon stomach structure and feeding ecology. Hof- mann (1984) later documented variation in all portions of the digestive anatomy among the three categories of his system of ruminant classification. The dynamic interac- tions among body size, fermentation and passage rates, and energetic requirements, and their influence on dietary strat- egy formed the basis for these early classifications. In a landmark paper, Hofmann (1989) expanded upon the concepts proposed by Hofmann and Stewart (1972) and Hofmann (1984) by providing a working hypothesis of the functional and morphological basis for diversity in ruminant feeding strategies. Hofmann (1989) proposed that feeding strategies ranged from nonselective intake of bulk roughage and efficient fermentation in the fore- stomach, to selectivity for concentrate forages (high in plant cell content) with increased post-ruminal digestion. This hypothesis challenged many beliefs regarding di- gestion in free-ranging ruminants and proposed that we reexamine the manner in which ruminant herbivores ob- tain nutrients from the environment. Because of the magnitude of Hofmann’s hypothesis, several papers (Gordon and Illius 1994, 1996; Robbins et al. 1995) were published describing tests of his predic- tions. These researchers examined components of Hof- mann’s hypothesis and concluded that they did not find support for morpho-physiological adaptations to diet type within classes of ruminants. They attributed differ- ences in digestive function to body mass or food charac- teristics. As a result, the consensus has been that Hof- mann’s hypothesis regarding gut morphology and func-
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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Paper-Lecture2 - Oecologia (2000) 125:8284 Springer-Verlag...

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