Prey selectivity, functional response, and population growth of Asplanchna girodi de Guerne (Rotifera) fed four different brachionid prey

Abstract

ABSTRACTWe determined numerical response, functional response, and prey selection by the predator Asplanchna girodi using 4 brachionid rotifer species, varying in size and lorica spines. We hypothesized that the consumption by the predators and thus population growth rates would be highest on prey with small spines compared with those with long spines. Data on the numerical response study showed that the population growth patterns of A. girodi were significantly influenced by prey species and density. With greater prey availability, the populations of the predator reached higher densities. At any given prey density, population densities of A. girodi were higher when feeding on Plationus patulus and Brachionus angularis than on B. rubens and B. havanaensis. The highest numbers of males were produced on diets of B. havanaensis and P. patulus. The rate of population increase ranged between 0.2 and 0.4 d−1 and was highest when feeding on a diet of P. patulus. A. girodi showed type II functional response for all the tested prey species. Among the 4 prey taxa tested, A. girodi showed the highest preference for B. angularis, regardless of its density. By contrast, it avoided B. rubens and P. patulus completely. These observations corroborate our hypothesis and suggest that prey morphology is an important determinant in prey selection by nonvisual predators such as Asplanchna.