Selective Predation for Vertebral Number of Young Sticklebacks, Gasterosteus aculeatus

Abstract
Young laboratory-reared threespine sticklebacks, Gasterosteus aculeatus, were exposed to predation by pumpkinseed sunfish, Lepomis gibbosus, until 50–65% of the initial number were eaten; vertebral counts of survivors were compared with those of unexposed controls. Experiments were conducted on prey of two different mean sizes and at two temperatures. With smaller prey (average initial length 8.2 mm), selective predation for vertebral number was striking; survival rate was from 1.3 to 1.7 times greater for fish with 31 vertebrae than for those with 32. With larger prey (average initial length 8.9 mm), experimental and control fish did not differ significantly in vertebral number. Selection did not vary significantly with water temperature; each prey length was tested at 15 °C and 17 or 20 °C. Selectivity of predation with respect to vertebral number was not attributable to selection with respect to body size of prey.

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