Temporal patterns of resource limitation in natural populations of rotifers

The availability of resources may limit consumer populations, and temporal variation in resources may facilitate the coexistence of competitors. Accur ate estimates of resource availability often cannot be obtained by counting potential food items, because of difficulties in determining resource qual ity. Instead, resource supplementation experiments must be conducted, but f ew experimental studies have examined the temporal patterns of resource lim itation. To determine the occurrence, intensity, and temporal variation of resource limitation in natural populations of planktonic rotifers, experime nts were conducted using two species of herbivorous rotifers from a eutroph ic pond, Keratella cochlearis and Synchaeta sp. The difference in populatio n growth rates in food-supplemented treatments relative to controls (Delta r) was used as a measure of the intensity of food limitation. Rotifers were usually food limited, with Keratella and Synchaeta showing significant foo d limitation (Delta r > 0) in 63% and 87% of the experiments, respectively. There was temporal variability in Delta r on time scales of one to a few w eeks, indicating rapid changes in resource availability. Synchaeta populati on dynamics were more closely controlled by resources than was the case for Keratella, and the intensity of food limitation was higher for Synchaeta t han for Keratella, possibly due to the more specialized feeding habits of S ynchaeta.