The ability of prey to detect and respond appropriately to predator risk is important to overall prey fitness. Many aquatic organisms assess risk through the use of chemical cues that can change with predator diet. Two variable characteristics of diet are: 1. prey type and 2. prey mass. To assess the effect of these two characteristics on the assessment of risk by the mud crab Panopeus herbstii, I exposed mud crabs to the urine of the blue crab Callinectes sapidus fed one of 5 diet treatments: 10g of oyster shell free wet mass, 5g of oyster shell free wet mass, 10g crushed mud crabs, 5g crushed mud crabs, and a mix of 5g of oyster shell free wet mass and 5g crushed mud crab. Effects on P. herbstii foraging were tested in a previously developed bioassay by measuring shrimp consumption over a 4 hour period. I hypothesized that P. herbstii would have a larger magnitude response to urine from C. sapidus fed a diet of crushed mud crabs than to urine from C. sapidus fed a diet of oysters. I further hypothesized that P. herbstii would have a larger magnitude response to urine from C. sapidus fed a high mass diet relative to a lower mass diet. Contrary to expectations there was no observed effect of urine on P. herbstii foraging in any of the treatments. Results suggest that bioassay protocol may be unreliable suggesting further replication to determine the difference between this study and previous results. Future studies examining how P. herbstii varies with urine concentration will aid in understanding the ecological scale of this predator cue system. Determining the role of other potential cue sources will improve the predictive abilities of these studies.

Predators can have large effects on prey populations and on the structure and function of communities. In addition to direct consumption of prey, predators often cause prey to alter their foraging behavior, habitat selection, and morphology. These non-lethal effects of predators can propagate to multiple trophic levels and often exert equal or larger effects upon communities than those of direct consumption. For non-lethal predatory effects to occur, prey must detect and respond to predation risk. While the importance of information transfer in this process has been realized, few studies explore how prey responses are influenced by predator characteristics and environmental conditions that influence the transmission of cues indicative of predation risk. In this dissertation I investigate factors that influence how a single prey species evaluates and responds to predation risk. Here, I examined: 1) the type and nature of cues prey use to evaluate predator risk; 2) how predator identity, predator diet, and the relative risk of predators influence prey response to predation risk; 3) how hydrodynamic conditions influence the delivery of predator cues; 4) how biogeographic trends in predator distribution influence prey response to predation risk; and 5) how genetic structure might vary according to prey geographic location and habitat. To address these questions, I used a common intertidal model system consisting of the rocky intertidal whelk Nucella lapillus (Linnaeus, 1758) and a suite of its predators, the native rock crab Cancer irroratus (Say, 1817), Jonah crab Cancer borealis (Stimpson, 1859), and the invasive green crab Carcinus maenas (Linnaeus, 1758). Nucella use chemical cues emanating from their most common predator (Carcinus maenas) and crushed conspecifics to evaluate predation risk. Nucella from different habitats experience different levels of predation risk, and Nucella from habitats with high levels of predation had larger antipredatory responses to predator risk cues than Nucella that experienced less predation. These chemical cues indicative of predation risk are influenced by hydrodynamic conditions, and Nucella have the strongest anti-predatory response in flow velocities of u= ~4- 8 cm s^-1. Furthermore, Nucella from geographic regions where green crabs are historically absent did not elicit anti-predatory responses, while Nucella from regions where green crabs are common frequently responded. Findings from my dissertation research demonstrate that prey detection and response to predation risk is highly dependent upon predator identity, predator diet, environmental forces, and biogeographic patterns in predator and prey distributions.