THE EFFECTS OF PULSES OF PREDATION RISK ON FEEDING BEHAVIOR OF THE MARINE GASTROPOD, FASCIOLARIA LILIUM HUNTERIA (PERRY, 1811)

The importance of temporal variation in predation risk for studies of foraging behavior in the fossil record has only recently been recognized. Most ecological studies have investigated prey behavior in the presence vs absence of predation risk, which ignores the fact that predation varies greatly in space and time. The risk allocation hypothesis predicts that temporal variation in predation risk influences how organisms allocate feeding behavior among environments that differ in danger (Lima & Bednekoff 1999). We tested this hypothesis by exposing the tulip snail Fasciolaria lilium hunteria (an opportunistic predator that feeds on various invertebrates, including bivalves and gastropods) to variable predatory cues from the stone crab, Menippe mercenaria.

Tulip snails contained in 38-liter aquaria were exposed for ~ 9 weeks (7/10 – 9/13/09) to four treatments: 1, constant safety (no predatory risk); 2, constant risk (predatory cues from an adult stone crab were always present); 3, risk with a pulse of safety (tulip snails were exposed to stone crab effluent except during a 3 hr safety period once every 3 days); and 4, safety with a pulse of risk (tulips were exposed to crab effluent for a 3 hr period once every 3 days). Tulip snails were offered a constant number of oysters, Crassostrea virginica, and gastropods, Urosalpinx cinerea, as prey; consumed prey items were replaced daily.

As predicted, tulip snail activity (indexed as number of attacks on Urosalpinx prey/day) depended on the temporal pattern of risk. Tulip snails held in constant risk had lower average activity levels than snails held in constant safety (0.6 vs 1.1 Urosalpinx attacked/ day). The average activity of tulip snails did not increase substantially during a brief period of safety (0.4 vs 0.5 Urosalpinx attacked/ day for pulse vs non-pulse intervals). Surprisingly, tulip snails did not show a moderate decrease in average activity level when exposed to a pulse of danger (1.3 vs. 1.3 Urosalpinx attacked/ day). No differences between treatments were noted in activity patterns in attacks on oyster prey. Our results provide mixed support for the risk allocation hypothesis, but, if extrapolated to the fossil record, suggest that the correlation between risk and predation intensity is complicated by the pattern of temporal variation in predation risk over time.