DOES DIGESTION RATE AFFECT DIET SELECTION - A STUDY IN OCTODON-DEGUS,A GENERALIST HERBIVOROUS RODENT

Dietary chemistry and an animal digestive physiology should be conside red in any explanation of behavioral patterns of food use, as both inf luence dietary preference. In the degu Octodon degus (Molina, 1782), a generalist herbivorous rodent inhabiting central Chile, we determine the profitablity of natural food-plant items by measuring digestive ch aracteristics, such as retention time and assimilation rate while also considering the effects of food chemistry. Under our experimental con ditions, degus seem to select food based on at least two complementary factors, plant nutritional value (water content and the nitrogen:fibe r ratio) and digestive function. We found that dry-matter intake was n egatively and significantly correlated with mean retention time, that is O. degus ate more food when mean retention time was shorter and vic e versa. A higher food intake concomitant with a shorter mean retentio n time, allow degus to process more food per unit time resulting in a higher assimilation rate than alternative food sources. We conclude th at both food quality and the digestive physiology of animals should be considered in explaining the underlying processes of foraging ecology .