No description available.

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.

Biological invasions are one of the main factors responsible for the imperiled status of freshwater ecosystems, but much remains to be learned about their indirect effects on native communities. The first part of this dissertation examines community effects of long-term efforts to selectively control invasive Eurasian watermilfoil. Results of the first study show that native plants immediately recolonized treated areas and habitat complexity was unaffected. Fish community was not influenced by invasive plant control. Macroinvertebrate communities were highly variable and part of their variability could be explained by plant community attributes. Both fish and macroinvertebrates used invasive watermilfoil, which emphasizes the need for timely restoration of native macrophytes to mitigate for lost habitat. Because fish and macroinvertebrates were more affected by complexity than other attributes of plant assemblage, reestablishment of habitat complexity appears to be a promising restoration strategy. The second study, which examined species interactions after watermilfoil control, found that fish feeding activity was not correlated with invasive plants or habitat complexity and that invasive macrophyte control did not affect characteristics of fish feeding investigated. The relationship between fish and macrophytes was further explored in the context of interactions between an invasive piscivore and its native prey. First, I examined the prey naiveté hypothesis with non-native peacock bass in Paraná River, Brazil. Prey responded to visual and chemical cues of peacock bass and displayed avoidance behaviors similar to those observed with a native predator, meaning that lack of recognition was not responsible for the observed vulnerability of native species to this introduced predator. After confirming lack of naiveté, I assessed direct and indirect effects of this non-native predator on native prey. Peacock bass had no indirect effects on its prey feeding activity. Macrophyte type did not affect indirect predator-prey interactions, whereas direct predator effects slightly decreased in the presence of aquatic vegetation. I discuss implications of these findings for native biodiversity and convene other potential explanations for the observed effects of peacock bass. Both projects contribute to our understanding of the relationship between aquatic plants and their animal communities and effects of invasive species in freshwater habitats.