Demography and population growth of Asplanchna girodi (Rotifera) as a function of prey (Anuraeopsis fissa) density

Abstract

Laboratory studies on population growth and life table demography of Asplanchna girodi were conducted at 25±1 °c using Anuraeopsis fissa as prey at four (250, 500, 1000 and 2000 ind ml−1) densities. A prey density of 100 ind ml−1 per predator per day did not support A. girodi, while at the highest prey concentration, A. girodi reached a peak of 115±7 ind ml−1. The age distribution of A. girodi indicated that non-adults constituted about 2/3rd of the population at all prey concentrations. A decrease in prey availability resulted in increased mortality of non-adults. At the highest prey density, the rate of population increase (r) was 1.51 d−1. The significance of estimating mortality in population growth studies is discussed. Life table demography of A. girodi was also studied using the same prey at the same concentrations. None of the survivorship parameters (e.g. mean lifespan and mean survivorship) showed a significant relation to prey density. Net reproductive rate and generation time (but not rate of population increase) were affected by prey abundance.