Ref ID : 1643
Marianne V. Moore and John J. Gilbert; Age-specific Chaoborus predation on rotifer prey. Freshwater Biology 17:223-236, 1987
Reprint
In File
Notes
1. This is the first study to examine predator-prey interactions between Chaoborus instars and rotifer prey. The predatory behaviour of instars I-III of Chaoborus punctipennis and the diet selectivity of instars I-IV feeding on rotifers were examined in the laboratory. Prey used in direct observations of predatory behaviour included a variety of rotifers (Synchaeta pectinata, S. oblonga, Polyarthra remata, Asplanchna girodi, Keratella crassa, spined and unspined forms of Keratella cochlearis) and two crustaceans (Bosmina lonirostris, Mesocyclops edax nauplii). 2. In general, strike efficiencies (percentage of strikes resulting in ingestion) increased in successive instars I-III. Early instar (I and II) strike efficiencies were low when compared with other invertebrate predators. For a given instar, mean prey handling times varied among prey species more than strike efficiencies. Mean handling times for small, soft-bodied rotifers were lowest and those for wide, hard-bodied prey were highest. 3. Instar I exhibited significantly greater selectivity for the small, soft-bodied S. oblonga than for the larger S. pectinata, hard-bodied K. crassa, and spined and unspined forms of K. cochlearis. Instars II-IV positively selected both the large and small Synchaeta species over all Keratella species. The relationship between Chaoborus selectivity and prey value (weight of prey per unit handling time) can be described by a power function. Ingestion rates of rotifers by older instars (III and IV) are among the highest reported for invertebrate predators. 4. Rotifer vulnerability to Chaoborus predation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected from Chaoborus predation because Chaoborus can manipulate and swallow them. Giguere et al.'s (1982) encounter rate model must be modified to predict encounter rates of slow-moving rotifer prey with Chaoborus.