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 predationrisk on snail habitat use and resource dynamics. Pulmonate snails(Physella gyrina) were placed into experimental pools and exposedto four levels of predation risk while holding their densityconstant. Periphyton resources were made available in two habitats:open and covered. I hypothesized that a behavioral responseby snails to predation risk would influence periphyton standingcrop in the open and covered habitats. Snails responded to increasingpredation risk by moving into safer (covered) habitats, andthe magnitude of their response was sensitive to the actuallevel of risk: intermediate levels of risk resulted in intermediatehabitat use. However, use of the risky (open) habitat by snailswas time dependent Snails initially responded strongly to predationrisk, but they exhibited similar patterns of habitat use atall risk levels by the end of the experiment Periphyton standingcrop was positively related to predation risk. In contrast tosnail habitat use, this response was initially weak and becamestronger as the experiment progressed. Thus, the short-and long-termresponses of snail habitat use and periphyton standing cropcontrasted sharply. I suggest that the changing patterns ofsnail habitat use over time are consistent with the idea thatsnails balance predation risk against foraging gains when selectinghabitats and that the manner in which they balance foraginggains and predation risk determines the pattern of periphytonstanding crops across habitats