Responses of the predatory rotifer Asplanchna intermedia to prey species differing in vulnerability: laboratory and field studies

1. We have studied the numerical and functional responses of campanulate morphs of Asplanchna intermedia fed five species of rotifer (Brachionus rubens, B. patulus, B. calyciflorus, Hexarthra mira and Filinia longiseta). The vulnerability of the prey varied with their morphology and mode of swimming. 2. To test the numerical and functional responses, prey species differing in their morphology and mode of swimming were provided. Responses were also tested with mixtures of evasive and non‐evasive prey provided in three different ratios. 3. A. intermedia showed a type II functional response to all the prey species provided. 4. The population growth rate of A. intermedia on the various prey species provided ranged from a minimum of –0.24 to a maximum of 0.68. There was a significant correlation between the capturability of a prey species and the population growth rate of the predator feeding on it. The capturability of a prey species also has a significant influence on the maximal predator density but not on the time taken to reach it. 5. Observations from a field study undertaken over a 10‐month period to study the prey preferences of A. intermedia in nature were corroborated by the laboratory findings.