Population growth and production of Habrotrocha rosa Donner (Rotifera: Bdelloidea) and its contribution to the nutrient supply of its host, the northern pitcher plant, Sarracenia purpurea L. (Sarraceniaceae)

The population growth and biomass production of the pitcher-plant (Sarracenia purpurea I,.) inquiline, Habrotocha rosa Donner (Rotifera: Bdelloidea), its consumption by other pitcher-plant inqulines, and its excretion of phosphorus (PO4-P) and nitrogen (NO3-N and NH4-N), were investigated in laboratory experiments. Observed population growth and production rate of H. rosa were higher at pH 4 (2.3 rotifers d(-1)) than at pH 3 (1.3 rotifers d(-1)), 5 (1.9 rotifers d(-1)), or 6 (0.8 rotifers d(-1)). Populations of H. rosa are an abundant and reliable food source for larvae of the dipteran inqulines Wyeomyia smithii (Coq.) and Blaesoxipha fletcheri (Aldrich) that co-occur with H. rosa in S. purpurea pitchers. Abundance of H, rosa within a pitcher is negatively associated with abundance of dipteran larvae, and these larvae consume rotifers in direct proportion to rotifer density (Type I functional response). Habrotrocha rosa may also account for the majority of the plant's supply of N and P. An average population of rotifers in the field (similar to 400 per pitcher) can excrete similar to 5.2 mu g NO3-N, similar to 3.91 mu g NH4-N, and similar to 18.4 mu g PO4-P per day into a single leaf, and excretion rate is independent of water pH. Over the six-month growing season of pitcher-plants in Massachusetts, U.S.A., we estimate that rotifers could supply 8.8-43 mg of N and 18.2-88 mg of P. These values far exceed the amount of N and P previously estimated to be supplied annually to the plants through insect capture or rainfall.