Constrating short-term and long-term effects of predation risk on consumer habitat use and resources

I contrasted the short-term and long-term effects of predation risk on snail habitat use and resource dynamics. Pulmonate snails (Physella gyrina) were placed into experimental pools and exposed to four levels of predation risk while holding their density constant. Periphyton resources were made available in two habitats: open and covered. I hypothesized that a behavioral response by snails to predation risk would influence periphyton standing crop in the open and covered habitats. Snails responded to increasing predation risk by moving into safer (covered) habitats, and the magnitude of their response was sensitive to the actual level of risk: intermediate levels of risk resulted in intermediate habitat use. However, use of the risky (open) habitat by snails was time dependent Snails initially responded strongly to predation risk, but they exhibited similar patterns of habitat use at all risk levels by the end of the experiment Periphyton standing crop was positively related to predation risk. In contrast to snail habitat use, this response was initially weak and became stronger as the experiment progressed. Thus, the short-and long-term responses of snail habitat use and periphyton standing crop contrasted sharply. I suggest that the changing patterns of snail habitat use over time are consistent with the idea that snails balance predation risk against foraging gains when selecting habitats and that the manner in which they balance foraging gains and predation risk determines the pattern of periphyton standing crops across habitats