Environmental stress gradients regulate the relative importance of predator density- and trait-mediated indirect effects in oyster reef communities.

Predators affect community structure by influencing prey density and traits, but the importance of these effects often is difficult to predict. We measured the strength of blue crab predator effects on mud crab prey consumption of juvenile oysters across a flow gradient that inflicts both physical and sensory stress to determine how the relative importance of top predator density-mediated indirect effects (DMIEs) and trait-mediated indirect effects (TMIEs) change within systems. Overall, TMIEs dominated in relatively benign flow conditions where blue crab predator cues increased oyster survivorship by reducing mud crab-oyster consumption. Blue crab DMIEs became more important in high sensory stress conditions, which impaired mud crab perception of blue crab chemical cues. At high physical stress, the environment benefitted oyster survival by physically constraining mud crabs. Thus, factors that structure communities may be predicted based on an understanding of how physical and sensory performances change across environmental stress gradients.

Concept Map Assessment Reveals Short-Term Community-Engaged Fieldwork Enhances Sustainability Knowledge.

Today's rapidly changing world calls for sustainability-minded scientists who are prepared to solve complex, interconnected problems. Service learning is a pedagogical approach that allows students to engage with the needs of the community by integrating academic work with complex civic issues. Student learning was examined during a short-term service-learning experience focused on water-quality monitoring in an urban watershed to determine whether community-engaged fieldwork in an upper-level ecology lab course enhances sustainability knowledge for future biologists. We used concept map scoring methods and reflection assessments to evaluate and understand changes in the structure and content of student knowledge as a result of the experience. Students showed increases in sustainability knowledge breadth, depth, and complexity, particularly in demonstrating biological-sociological connections. Student reflections indicated most students identified at least one community-engaged serving-learning objective as a result of this experience. These results suggest that community-engaged fieldwork can illustrate ecological and sociological sustainability concepts for students and that engagement works best when we make explicit our objective of engaging communities in the learning process. Short service-learning experiences are effective, can be quickly assessed using concept maps, and can be readily incorporated in other classrooms to enhance sustainability education.

Hydrodynamics affect predator controls through physical and sensory stressors.

Predators influence communities through either consuming prey (consumptive effects, CEs) or altering prey traits (non-consumptive effects, NCEs), which has cascading effects on lower trophic levels. CEs are well known to decrease in physically stressful environments, but NCEs may be reduced at physically benign levels that affect the ability of prey to detect and respond to predators (i.e., sensory stress). We investigated the influence of physical and sensory stressors created by spatial and temporal differences in tidal flow on predator controls in a tritrophic system. We estimated mud crab reactive ranges to blue crab NCEs by evaluating mud crab CEs on juvenile oysters at different distances away from caged blue crabs across flow conditions. Mud crab reactive ranges were large at lower physical and sensory stress levels and blue crabs had a positive cascading effect on oyster survival. Blue crab NCEs were not important at higher flow conditions. Oyster survival was a complicated function of both types of stressors. Physical stress (i.e., current speed) had a positive effect on oyster survival by physically limiting mud crab CEs at high current speeds. Sensory stress (i.e., turbulence) interfered with the propagation of blue crab chemical cues used by mud crabs for predator detection, which removed blue crab NCEs. Mud crab CEs increased as a result and had a negative effect on oyster survival in turbulent conditions. Thus, environmental properties, such as fluid flow, can inflict physical and sensory stressors that have distinct effects on basal prey performance through impacts on different predator effects.