The two-toed amphiuma, Amphiuma means, is a large aquatic salamander and a potentially important predator of crayfish. However, little is known about the effects of predation by A. means on crayfish communities. This study was carried out to determine if there is a size preference in A. means predation on crayfish. A. means was expected to prefer medium sized crayfish in accordance with the optimal foraging theory because they were more energetically rewarding than smaller crayfish but easier to capture than larger crayfish. Seven similarly-sized A. means were placed in individual aquatic mesocosms. Six crayfish of the subgenus Scapulicambarus, two from each of three size categories, were also placed in each tub. The percent mortality and location of the crayfish in the tub were observed for 11 days. A. means had a significant preference for medium-sized crayfish on day four, but there were no significant differences among predation rates by the final day. Small crayfish had the lowest predation rates. Surviving crayfish were found most often on the edges of the tubs. Medium-sized crayfish may have experienced the highest amount of predation because they have weaker defenses than large crayfish and are unable to hide as well as small crayfish. However, crayfish may be unable to outgrow predation because even some of the largest crayfish were preyed upon during the experiment.
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Vol. 84 • No. 1