Undergraduate Research Accomplishments Accomplishments: OUR Grantee: The Influence of Lethality on the Magnitude of Prey Response to Predation Risk

Predators can influence prey via both consumptive, i.e., killing, and non-consumptive predation risk effects (Sih et al. 1985; Peacor et al. 2020). Predation risk effects can alter prey behavior, physiology and morphology, which can scale up to alter individual fitness. These prey risk-responses are dependent upon the environment or context in which the predator-prey interaction occur (Schmitz 2017; Sheriff et al. 2020b), e.g., refuge availability, prey state, and predator hunting mode all influence risk responses. While predator lethality, defined as the probability that an encounter with the predator proves fatal for prey (Cooper and Frederick 2010), has been theorized to alter prey risk responses (Brown 1999; Cooper and Frederick 2010) there is little evidence to support this assumption. In marine systems the idea of predator lethality driving prey responses to predation risk is particularly of interest given that predator-prey relationships and predator identity is largely influence by individual body size; i.e., an individual’s body size relative to another dictates whether that individual is predator or prey (Barnes et al. 2010). By using a rocky intertidal system, Haleigh Nogueira examined the effect of predator lethality on prey response. To determine the lethality of predators, Nogueira first used an experimental mesocosm manipulation to measure the consumption rates of different predator species at different sizes. A single crab of each species was placed into a mesocosm with 5 snails and their consumption was measured over 24 h. Snails were separated into two size classes (and each size placed into separate mesocosms). The mesocosms were small enough to eliminate spatial refuge for the snails. The predator, and the size of the predator, with the higher rate of consumption will be considered to have greater lethality. Nogueira tested the hypothesis that the lethality of a predator will alter the magnitude of prey risk responses. Specifically, she predicted that when exposed to the more lethal predator snails will have reduced tissue and shell growth, increased shell: tissue ratio, reduced foraging, and increased refuge use. This was tested using two size classes of Hemigrapsus sanguineus and Carcinus maenas and two size classes of Nucella lapillus (prey); thus, Nogueira had a fully crossed design with large and small crabs and large and small snails. Animals were placed into a mesocosm with a single crab (rendered non-lethal) and snails of a single size class. The mesocosms had a tile-refuge added. Snail tissue and shell weight was measured at the start and end of experiment using the Palmer (1982) buoyancy technique that provides non-destructive estimates; foraging and refuge use of snails was measured by behavioral observations every 3 days. The experiment ran over 20 days. This study is still in progress, but will be one of the first to provide empirical evidence testing the long-held assumption that predator lethality influences prey risk responses. The results of this work will provide a better understanding of and insights into predator-prey interactions and how predation risk may alter prey phenotype and scale up to alter populations and communities. Nogueira is grateful to the Office of Undergraduate Research (OUR) and the College of Arts & Sciences (CAS) for providing her with the funds to pursue this project in 2022. She also credits her advisor, Dr. Michael Sheriff and her lab mates, for the guidance and support they have given her throughout.