Does body mass convey a digestive advantage for large herbivores?

Abstract

Summary 1.A key concept of body mass (BM) in niche separation of large herbivores assumes that the decrease in diet quality inherent to increasing BM (due to less selective feeding behaviour) is balanced by a simultaneous increase in digestive ability (due to longer retention times), resulting in no or less-than-expected reduction in digestibility (as measured in the animal as a result of diet quality and digestive ability). However, the second part of this concept has been challenged recently due to theoretical problems and mismatch with empirical data. 2. A proxy for digestibility, such as metabolic faecal nitrogen (MFN), will comprise both information on diet quality and digestive ability in free-ranging animals. In captive animals, if diet is kept constant, such a proxy can exclusively indicate digestive ability. Comparing freeranging and captive animals under such conditions, one would expect an increase in MFN with BM in captive animals and no relationship between these measures in free-ranging animals if BM was related to digestive ability. 3. We compared captive ungulates on a consistent grass hay diet (17 species; 30-4000 kg BM) to a sample of free-ranging East African ungulates (19 species; 12-4000 kg BM). MFN was used as the major proxy for digestibility. 4. In captive animals, there was no influence of BM on MFN (P = 0Á466); for free-ranging animals, a significant decreasing effect of body mass on MFN (P = 0Á002) and therefore diet quality was found at a scaling of BM À0Á15 . 5.In conclusion, scenarios that assume a compensation of the evident decrease in diet quality with BM via an increased digestive ability are not supported by this study. This does not rule out other feeding-related factors in facilitating large BM, such as compensation by an increased diet intake.

The Stoichiometry of Nutrient Release by Terrestrial Herbivores and Its Ecosystem Consequences

“…Furthermore, urinary N (excretion) of large ungulates increases with plant N concentration (Hobbs, 1996). These relationships seem so reliable that fecal N and P contents are used to predict food N and P contents (Wrench et al, 1997;Verheyden et al, 2011;Gil-Jimenez et al, 2015), although corrections for the presence of indigestible forms of N, e.g., tannins, are needed (Verheyden et al, 2011;Steuer et al, 2014).…”

Effect of pelleted cereal-based feed used in the diet on feed intake, eating behaviour, rumination and nutrient digestibility in antelope sitatunga (<i>Tragelaphus spekii</i>)

“…The sitatunga ( ) is a medium sized, semi-aquatic, tropical antelope with many specific adaptations to wetland areas (Estes, 1991;Tweheyo et al, 2010) for which many different diets in the wild have been reported, ranging from grazing to intermediate feeding (Gagnon and Chew, 2000;Cerling et al, 2003;Sponheimer et al, 2003;Steuer et al, 2014). Most likely, the sitatunga is an intermediate feeder consuming the substantial proportion of grass and herbs in the natural diet (Gagnon and Chew, 2000;Sponheimer et al, 2003).…”

Chemical composition and fermentation characteristics of feedstuffs for giraffes (<i>Giraffa camelopardalis</i>) in German zoos

“…In accordance with their classification as purely browsing, but comparatively little selective ruminants (Van Soest, 1988;Steuer et al, 2014), giraffes ( ) forage efficiently for sp. under natural conditions (Pellew, 1984).…”