Variability in the diet specialization of Enteroctopus dofleini (Cephalopoda: Octopodidae) in the eastern Pacific examined from midden contents

摘要

We examined variation in dietary specialization of Enteroctopus dofleini (Wülker, 1910), the giant Pacific octopus, from Puget Sound to the Aleutian Islands, as represented in midden remains. Dietary specialization was measured from midden contents as: species richness (R) and Cardona's niche breadth (regional indices), and proportional similarity of a midden to the regional sample (an individual index). We found an influence of items per midden and prey species maximum size on these indices. In Puget Sound, middens and common prey species were large, richness, R = 21 species, and individuals specialized more often than in other areas, typically on large prey species. In Saanich Inlet, British Columbia, middens were smaller, R = 9 species, and the large crab Cancer productus was common in nearly all middens, such that the population specialized rather than the individual. In Prince William Sound, Alaska, middens contained fewer individuals of smaller prey species, R = 52 species, and diet was generalized at both the population and the individual levels. Cardona's niche breadth ranged from. 11 to. 14 except in the Aleutian Islands, Alaska where it was higher (.30). Most individual E. dofleini were generalists, and dietary species richness was very high (R = 69 species overall). Specialists within a generalist population were common only where middens and dominant prey were both large.