Nutrient limitation on a planktonic rotifer:: Life history consequences and starvation resistance

Nutrient content of plants is low relative to that of herbivores. Dietary nutrients can limit the growth and reproduction of herbivores. We studied life history consequences and starvation resistance for a common planktonic rotifer, Keratella cochlearis, feeding on algae grown on nutrient-limited media. A strain of Cryptomonas was grown on three types of growth medium with nitrogen (N) and phosphorus (P) adjusted to produce N-limiting, P-limiting, and nutrient-sufficient conditions. The analysis of nutrient content of Cryptomonas cells grown on nutrient-limited conditions showed that those algae exhibited higher P content than algae growing on a nutrient-sufficient medium. However, Cryptomonas reached lower densities in nutrient-limited media. The life history responses of Keratella to food quality were examined with low and high food availability. Our study showed that the interaction of food quantity and quality had a significant effect on rotifer growth rates. We observed, at low food levels, that Keratella growth rates were highest when the algae were grown under P limitation. The lowest rotifer growth rates were obtained when the rotifer fed on Cryptomonas grown in nutrient-sufficient conditions. Our study also showed that starvation resistance was higher for those rotifers fed on N-limited Cryptomonas. In natural situations, rotifers could even grow better under nutrient-limited conditions if this group of algae is dominant in the phytoplankton community. Moreover, differences in starvation resistance could be critical in determining competitive outcome and community structure in nutrient-variable environments.