ROSENTHAL and CHESS: PREDATOR-PREY RELATIONSHIP 



process involved before the sea star recognizes 

 or associates specific stimuli with food. Tin- 

 bergen (1960) proposed that learning was in- 

 volved in the feeding behavior of insect-eating 

 birds, and that initial non-acceptance of specific 

 insects by these birds was due to an unfamiliarity 

 with these forms as prey. He further related 

 initiation of feeding on a new food item with 

 chance experience and prey density. Tinbergen 

 (1960) suggested that the predator acquires a 

 "specific search image" for the prey after being 

 sufficiently impressed with it from frequent 

 chance encounters. Holling (1958 and 1965) 

 studied predation on the cocooned pupae of saw- 

 flies by shrews and mice, and suggested that as- 

 sociative learning was an important component 

 in the feeding behavior of these small mammals. 

 Unfortunately, associative learning has been 

 studied in only a relatively small number of low- 

 er animal (invertebrate) groups. Evans (1968) 

 discussed this form of learning in cephalopods, 

 insects, annelids, and flatworms. There is some 

 evidence to suggest that associative learning 

 exists in echinoderms. Landenberger (1966) 

 found that the sea star P. giganteus learned to 

 associate a light stimulus with food. The asso- 

 ciation apparently disappeared when the re- 

 sponse to the light stimulus was no longer re- 

 warded with food. If associative learning, with 

 food as a reinforcement or reward, is a compo- 

 nent in the feeding behavior of D. rmbricata, 

 then it might account for the presence of purple 

 urchins in the diets of leather stars oflF Pt. Loma. 

 This area contained a large number of highly 

 accessible S. purpuratus, and yet at the same 

 time appeared to be practically devoid of many 

 of the sessile or sedentary invertebrates that 

 these sea stars are reported to feed on. Derma- 

 sterias imbricata probably responds to a small 

 class of chemical and/or tactile stimuli; how- 

 ever, only through associative learning and ex- 

 perience can it exploit an evasive prey species 

 such as S. purpuratus. The leather star may 

 not acquire the experience necessary to capture 

 live iS. purpuratus in other subtidal areas that 

 contain alternate prey in greater abundance, 

 since these forms are more accessible and pos- 

 sibly can account for the total nutrient require- 

 ments of D. imbricata. 



ACKNOWLEDGMENTS 



We especially wish to thank W. D. Clarke, P. 

 K. Dayton, T. A. Ebert, H. M. Feder, and H. R. 

 Melchior for stimulating discussions and critical 

 evaluation of this manuscript. We also wish to 

 thank Virginia Moore who prepared Figures 1, 

 5, and 6. Westinghouse Ocean Research Labora- 

 tory assisted in financial support of this study 

 and the National Marine Fisheries Service gen- 

 erously provided laboratory facilities at the 

 Southwest Fisheries Center, La Jolla, California. 



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