Project U1: Nutritional Limits of Gigantism
|Title||Nutritional limits of gigantism: the allometry of diet quality and methane loss and the importance of secondary plant compounds|
|Principal Investigator||Dr. Jürgen Hummel, Prof. Dr. Karl-Heinz Südekum, Dr. Marcus Clauss|
|Researchers||Patrick Steuer, Ragna Franz|
For the development of large body sizes in terrestrial vertebrates a herbivorous feeding habit seems to be a prerequisite, due to the higher energy available for a population on the low trophic level of primary consumers. A large herbivore may also benefit from an allometric increase of the digestive capacity. However, some characteristics inherent to feeding and digestion in herbivores may also set nutritional limits to an increase in body sizei and these aspects are essential for our understanding of the digestive physiology of the largest herbivores ever, the sauropods. For example, selectivity and therefore diet quality is said to decline considerably with body size, while metabolic losses occurring during fermentative digestion become more pronounced (like e.g. methane losses). At the same time, factors such as a higher digestive capacity for fiber in larger animals are no longer relevant at a point where most dietary fiber has been completely fermented. A further factor that limits the seemingly overbundant food resources of many herbivores is the content of secondary plant compounds in food plants.
In this study, these effects will be evaluated in a quantitative way, to allow for an extrapolation to body sizes of sauropods. By exploring the chemical composition (especially nitrogen fractions and ash content) of feces of a spectrum of free-ranging herbivores (natural diet) and of captive individuals (controlled, identical diet), the allometry of diet quality (= digestibility) will be evaluated, and the allometry of the extent of fiber digestion will be evaluated via the residual fermentable fiber in these feces (using in vitro fermentation). By using controlled trials with giant tortoises and other herbivores in metabolism chambers and in vitro fermentation in a continuous system, the allometry of methane losses will be quantified. The relevance of secondary plant compounds in potential sauropod feeding plants will be evaluated in a functional (in vitro fermentation) and quantitative (chemical) way.