The Influence of Lethality on the Magnitude of Prey Response to Predation Risk 

By Haleigh Nogueira 

 

This past summer I worked on a project to examine the effect of predator lethality on prey response using a rocky intertidal system. I carried out this experiment at UMass Dartmouth’s School for Marine Science & Technology (SMAST) and collected the animals from nearby sites. The summer research award from the Office of Undergraduate Research (OUR) allowed me to obtain all the needed supplies for my project and ensured I was able to solely focus on my work.

Portrait of Haleigh Nogueira at work in Buzzards Bay

 

Introduction

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, I can examine the effect of predator lethality on prey response.

Methods

To determine the lethality of predators, I 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.

I tested the hypothesis that the lethality of a predator will alter the magnitude of prey risk responses. Specifically, I predicted that when exposed to the more lethal predator (expected that larger crabs are more lethal) 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 (predators tested in part 1) and two size classes of Nucella lapillus (prey); thus, I 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.

Discussion

This study 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. At this time I do not have any results to share, but plan to spend the rest of the semester working on my data analysis. I want to thank the Office of Undergraduate Research (OUR) and the College of Arts & Sciences (CAS) for providing me with the funds to pursue this project. I also would like to thank Dr. Michael Sheriff and my lab mates for the guidance and support they have given me throughout.

 

 

References

Barnes C, Maxwell D, Reuman DC, Jennings S. (2010). Global patterns in predator-prey    size relationships reveal size dependency of trophic transfer efficiency. Ecology.        91 (1): 222 232. https://doi.org/10.1890/08-2061.1

Brown JS. (1999). Vigilance, patch use and habitat selection: Foraging under predation     risk. Evolutionary Ecology Research. 1: 49-71.

Cooper WE, Frederick WG. (2010). Predator lethality, optimal escape behavior, and         autotomy. Behavioral Ecology. 21(1): 91–96.      https://doi.org/10.1093/beheco/arp151

Palmer AR. (1982) Growth in Marine Gastropods: A Non-Destructive Technique for          Independently Measuring Shell and Body Weight. Malacologia.23(1): 63-73

Peacor SD, Barton BT, Kimbro DL, Sih A, Sheriff MJ. (2020). A framework and        standardized   terminology to facilitate the study of predation-risk effects.         Ecology. 101(12). https://doi.org/10.1002/ecy.3152

Schmitz O. (2017). Predator and prey functional traits: Understanding the adaptive          machinery driving predator-prey interactions. F1000Research. 6: 1767 https://doi.org/10.12688/f1000research.11813.1

Sheriff MJ, Orrock JL, Ferrari MCO, Karban R, Preisser EL, Sih A, Thaler JS. (2020b).            Proportional fitness loss and the timing of defensive investment: a cohesive       framework across animals and plants. Oecologia. 193(2):273–283.          https://doi.org/10.1007/s0044202004681-1

Sheriff MJ, Peacor SD, Hawlena D, Thaker M. (2020a). Non-consumptive predator effects on prey population size: A dearth of evidence. Journal of Animal Ecology. 89 (6):1302-1316. https://doi.org/10.1111/1365-2656.13213

Sih A, Crowley P, Mcpeek M, Petranka J, Strohmeier K. (1985). Predation,

Competition, and Prey Communities: A Review of Field Experiments. Annual Review Ecological Systems.16:269311. https://doi.org/10.1146/annurev.es.16.110185.001413