THE FEEDING RESPONSE OF HYDRA VIRIDIS: EFFECTS OF PREY DENSITY ON CAPTURE RATES

¹ Department of Biological Sciences, State University of New York at Buffalo, Buffalo, N.Y. 14260

A model of the feeding processes of Hydra viridis was developed and used to predict the environmental parameters which maximize feeding.

Feeding was measured by exposing individual hydra to Artemia salina nauplii and recording the number ingested. When fed to repletion H. viridis resumed feeding after 4.8 hours and ingested significantly fewer Artemia during the second feeding. At low prey densities, increasing the exposure time from 15 to 60 minutes increased the number of Artemia ingested. However, at higher densities exposure time did not affect the number of Artemia ingested. There was a strong correlation between the number of Artemia captured and the number ingested. Increased prey capture did not alter the duration of the feeding response but did reduce the time interval between ingestions. Exposure to Artemia extract reduced the number of Artemia ingested and the duration of the feeding response.

These data indicate that feeding success under conditions of low prey density is limited by the availability of prey. At high prey density the feeding process is itself saturated and prey availability has limited effects on ingestion. H. viridis is well suited to high density feeding and ingests more prey when prey density is high even if the total exposure to prey is maintained at a constant level.