Rumen physiology constrains diet niche: linking digestive physiology and food selection across wild ruminant species

Abstract

Rumen physiology constrains diet niche: linking digestive physiology and food selection across wild ruminant species Codron, D; Clauss, M Codron, D; Clauss, M (2010). Rumen physiology constrains diet niche: linking digestive physiology and food selection across wild ruminant species. Canadian Journal of Zoology, 88:1129Zoology, 88: -1138 We propose a hypothesis for digestive constraints on the browsing and grazing options 22 available to ruminants: that the diet niche range (maximum and minimum grass intake) of a 23 species is dependent upon its predisposition to a stratified rumen contents, based on 24 observations that this characteristic is a critical step towards enhanced fibre digestion and 25 greater fluid throughput. We compare a physiological (heterogeneity of ingesta fluid content) 26and an anatomical (the intraruminal papillation pattern) measure with dietary evidence for a 27 range of African and temperate species. Both measures are strongly related to the mean % 28 grass in species' natural diets, as well as to the maximum and minimum levels of grass 29 intake, respectively. The nature of these effects implies a stratification level threshold, below 30 which a species will not use a grass-based diet, but above which grass consumption can 31 increase exponentially. However, above this threshold, a minimum % grass in the diet is a 32 prerequisite for optimal performance. We argue that this second constraint is crucial, as it 33 depicts how a greater fluid throughput reduces potential for detoxification of plant secondary 34 compounds, and therefore limits the maximum amount of browse a stratifying species will 35 consume. 36 37

Gross anatomy of the stomach of the pampas deer, Ozotoceros bezoarticus (Artiodactyla: Cervidae)

“…Comparison of data from Pampas deer from this study with data on (5) reticulorumen wet contents (in percentage of body mass) and (6) rumen pillar thickness (both from CLAUSS et al 2003(both from CLAUSS et al , 2006a(both from CLAUSS et al , 2009a), (7) reticular crest height (CLAUSS et al 2010), and (8) the curvature of the omasum (CLAUSS et al 2006ab, 2009a. Regression lines for browsing ruminants in inferior line and for grazing ruminants in superior line.…”

“…Pampas deer most likely evolved a certain degree of RR fluid throughput and RR contents stratification typical for many intermediate feeder and grazing species. The correlation with various physiological measures (CLAUSS et al 2009b, CODRON & CLAUSS 2010 implies that the intraruminal papillation pattern may be the most important comparative anatomical indicator between ruminant feeding types.…”

Old World Ruminant Morphophysiology, Life History, and Fossil Record: Exploring Key Innovations of a Diversification Sequence

“…Notably, a 'moose-type' strategy does not prevent animals from ingesting grass or mixed grass/browse diets in an experimental setting (Lechner et al 2010) or when no other competitors are present. For example, the reindeer is an outlier to a general pattern, because its natural diet includes much more grass than one would expect based on its 'moose-type' rumen physiology (the major outlier in the dataset of Codron & Clauss 2010); this species hardly faces competition from sympatric grazers. In most real ecological settings, 'moosetype' ruminants are limited to browse-dominated diets, whereas 'cattle-type' ruminants dominate grass or mixed grass/browse diet niches (Codron & Clauss 2010).…”

“…For example, the reindeer is an outlier to a general pattern, because its natural diet includes much more grass than one would expect based on its 'moose-type' rumen physiology (the major outlier in the dataset of Codron & Clauss 2010); this species hardly faces competition from sympatric grazers. In most real ecological settings, 'moosetype' ruminants are limited to browse-dominated diets, whereas 'cattle-type' ruminants dominate grass or mixed grass/browse diet niches (Codron & Clauss 2010). This difference matches the observed reduction of the tragulid niche to that of 'moose-type' ruminants.…”

“…A typical feature of such innovations is that the clade that diversified (due to that innovation) does not necessarily occupy a new or specialised niche but covers a similar broad niche spectrum as its predecessors, or an even broader one. Examples for such innovations are the mammalian molar hypocone (Hunter & Jernvall 1995), ungulate hypsodonty (Feranec 2007), the evolution of a 'cattle-type' rumen physiology with a high fluid throughput through the rumen (Codron & Clauss 2010), and maybe also short gestation periods . One characteristic of these increased fitness key innovations yet to be proven is that they are not costly during ontogeny or life.…”