DIGESTIVE EFFICIENCIES IN HERBIVOROUS AND OMNIVOROUS FRESH-WATER TURTLES ON PLANT DIETS - DO HERBIVORES HAVE A NUTRITIONAL ADVANTAGE

Digestive performances of two freshwater turtles-a herbivore and an om nivore-were compared on two diets of aquatic plants to test the predic tion that the digestive efficiency (nutrient or energy gain per unit t ime) of herbivores is greater than that of omnivores on plant diets. O n a diet of hydrilla, Hydrilla verticillata, the herbivore gained sign ificantly more nutrition from the diet on a daily basis, as a result o f higher intake and more rapid digestive processing. When fed duckweed , Spirodela polyrhiza, the two turtle species bad equivalent digestive performances. Thus, the herbivore did not consistently outperform the omnivore. The herbivore had greater digestive efficiency on a diet th at was extensively fermented (hydrilla), but, on a diet that underwent limited microbial degradation (duckweed), the herbivore bad no nutrit ional advantage over the omnivore.