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 campanula te morphs of Asplanchna intermedia fed five species of rotifer (Brachi onus rubens, B. patulus, B. calyciflorus, Hexarthra mira and Filinia l ongiseta). The vulnerability of the prey varied with their morphology and mode of swimming. 2. To test the numerical and functional response s, prey species differing in their morphology and mode of swimming wer e provided. Responses were also tested with mixtures of evasive and no n-evasive prey provided in three different ratios. 3. A. intermedia sh owed a type II functional response to all the prey species provided. 4 . The population growth rate of A. intermedia on the various prey spec ies provided ranged from a minimum of -0.24 to a maximum of 0.68. Ther e was a significant correlation between the capturability of a prey sp ecies and the population growth rate of the predator feeding on it. Th e 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 corroborate d by the laboratory findings.