Some observations on the diet of the backswimmer, Anisops wakefieldi (Hemiptera: Notonectidae)

Abstract

In a series of laboratory experiments, A. wakefieldi was presented with a variety of prey from different systems to investigate its potential for cannibalism and for eating cladocerans, copepods and rotifers. Large (ca. 7 mm) Anisops decreased the survivorship of small (ca. 3 mm) Anisops, but ate only 0.1 individual predator-1 d-1. Ingestion rates of small Anisops on small (<0.5 mm) and large (0.5–0.9 mm) Ceriodaphnia dubia were 53 and 28 individuals predator-1 d-1, while those of large Anisops on these prey were about twice as high. Clearance rates showed that small Anisops ate small and large C. dubia with similar efficiencies, while large Anisops ate large C. dubia much more efficiently. Anisops ate C. dubia much more efficiently than the calanoid copepod Boeckella hamata. Only the large Anisops ate adult B. hamata. Large Anisops had a very low ingestion rate (0.6 individuals predator-1 d-1) on the larger congener, B. triarticulata. Small, but not large, Anisops ate the rotifer Synchaeta pectinata and small Anisops presented with a natural assemblage of rotifers ate S. pectinata and Polyarthra dolichoptera, but not four other species with a more well-developed lorica – Anuraeopsis fissa, Brachionus angularis, Keratella cochlearis and K. slacki. Ingestion rates on Synchaeta and Polyarthra were 14–20 individuals Anisops -1 d-1.