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 (Sarracen ia purpurea I,.) inquiline, Habrotocha rosa Donner (Rotifera: Bdelloidea), its consumption by other pitcher-plant inqulines, and its excretion of phos phorus (PO4-P) and nitrogen (NO3-N and NH4-N), were investigated in laborat ory 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 inqulin es Wyeomyia smithii (Coq.) and Blaesoxipha fletcheri (Aldrich) that co-occu r with H. rosa in S. purpurea pitchers. Abundance of H, rosa within a pitch er is negatively associated with abundance of dipteran larvae, and these la rvae consume rotifers in direct proportion to rotifer density (Type I funct ional 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 le af, and excretion rate is independent of water pH. Over the six-month growi ng season of pitcher-plants in Massachusetts, U.S.A., we estimate that roti fers could supply 8.8-43 mg of N and 18.2-88 mg of P. These values far exce ed the amount of N and P previously estimated to be supplied annually to th e plants through insect capture or rainfall.