Decision of the asteroid Leptasterias polaris to abandon its prey when confronted with its predator, the asteroid Asterias vulgaris

We examined the decision of the asteroid Leptasterias polaris to abandon it s bivalve prey Spisula polynyma when confronted with the predatory asteroid Asterias vulgaris. The frequency of abandonment decreased as the proportio n of prey ingested increased from 10 to 40%, and increased with further inc reases in proportion of prey ingested. The escape response of L. point-is a ppears to be a compromise between risk of predation and benefits of feeding . This increase in the frequency of abandonment as the prey became further consumed beyond 30-40% likely represented decreasing benefits in the face o f continued risk of predation. Wie propose that the initial decrease in fle eing as the proportion of prey eaten increased from 10 to 40% was because o f a decreasing costs in subduing the prey, as there was a coincident decrea se in the proportion of prey which were still capable of holding their valv es closed. (C) 2000 Elsevier Science B.V. All rights reserved.