DOI: 10.7291/d1q37t
title: An escape theory model for directionally moving prey and an experimental test in juvenile Chinook salmon

description: Prey evaluate risk and make decisions based on the balance between the
 costs of predation and those of engaging in antipredator behavior.
 Economic escape theory has been valuable in understanding responses of
 stationary prey under predation risk; however, current models are not
 applicable for directionally moving prey. Here we present an extension of
 existing escape theory that predicts how much predation risk is perceived
 by directionally moving prey. Perceived risk is measured by the
 extent antipredator behavior causes a change in travel speed (the distance
 to a destination divided by the total time to reach that destination).
 Cryptic or cautious antipredator behavior slows travel speed, while prey
 may also speed up to reduce predator-prey overlap. Next, we applied the
 sensitization hypothesis to our model, which predicts that prey with more
 predator experience should engage in more antipredator behavior, which
 leads to a larger change in travel speed under predation risk. We then
 compared the qualitative predictions of our model to the results of a
 behavioral assay with juvenile Chinook salmon (Oncorhynchus tshawytscha)
 that varied in their past predator experience. We timed salmon swimming
 downstream through a mesh enclosure in the river with and without predator
 cues present to measure their reaction to a predator. Hatchery salmon had
 the least predator experience, followed by wild salmon captured upstream
 (wild-upstream) and wild-salmon captured downstream (wild-downstream).
 Both wild salmon groups slowed down in response to predator cues, while
 hatchery salmon did not change travel speed. The magnitude of reaction to
 predator cues by salmon group followed the gradient of previous predator
 experience, supporting the sensitization hypothesis. Moving animals are
 conspicuous and vulnerable to predators. Here we provide a novel
 conceptual framework for understanding how directionally moving prey
 perceive risk and make antipredator decisions. Our study extends the scope
 of economic escape theory and improves general understanding of non-lethal
 effects of predators on moving prey.
description: This dataset comes from field collections of juvenile salmon,
 which were used in a behavioral assay. We timed salmon swimming downstream
 through a mesh enclosure with and without predator cues to observe their
 change in travel speed via antipredator behavior. Travel speed was
 recorded when juvenile salmon, embedded with a Passive Integrated
 Transponder (PIT) tags, passed through PIT antennae. The PIT detections
 were processed in R to summarize the values for time and speed through
 enclosure segments (antenna 1 to antenna 2, and antenna 2 to antenna
 3). The processed datafile for the behavioral assay are
 uploaded here. Also, the R files for the analyses for the
 manuscript.
description: <b>Sabal, M.C., J.E.
 Merz, S.H. Alonzo, E.P. Palkovacs. An escape theory model for
 directionally moving prey and an experimental test in juvenile Chinook
 salmon. <i>Journal of Animal Ecology.</i></b>
  
 <b>Authors</b> Megan C. Sabal University of California Santa
 Cruz, Department of Ecology and Evolutionary Biology 130 McAllister Way, Santa Cruz, CA
 95060 msabal@ucsc.edu   Joseph E. Merz University of California Santa
 Cruz, Department of Ecology and Evolutionary Biology 130 McAllister Way, Santa Cruz, CA
 95060 Cramer Fish
 Sciences 3300
 Industrial Blvd #100, West Sacramento, California 95691 jmerz@fishsciences.net
   Suzanne
 H. Alonzo University of California Santa
 Cruz, Department of Ecology and Evolutionary Biology 130 McAllister Way, Santa Cruz, CA
 95060 shalonzo@ucsc.edu   Eric P. Palkovacs University of California Santa
 Cruz, Department of Ecology and Evolutionary Biology 130 McAllister Way, Santa Cruz, CA
 95060 epalkova@ucsc.edu 
  
   <b>File
 list</b> sabal_et_al_2020_behavioral_assay_analyses_dryad.R sabal_et_al_2020_supplemental_analyses_dryad.R sabal_et_al_2020_behavioral_assay_data.txt sabal_et_al_2020_environmental_data.txt   <b>File descriptions</b> sabal_et_al_2020_behavioral_assay_analyses.R – the only R file needed to run the analyses from the main text. Must set working directory to location of sabal_et_al_2020_behavioral_assay_data.txt file.   sabal_et_al_2020_supplemental_analyses.R – this R file describes analyses for the supplemental material, including Appendices A and B. Must set working directory to location of sabal_et_al_2020_behavioral_assay_data.txt and sabal_et_al_2020_environmental_data.txt files.   sabal_et_al_2020_behavioral_assay_data.txt – the only data file you need to run the main analyses. Each line is a unique trial. Salmon data, trial data, and PIT detection data have already been combined. <b>date:</b> year-month-day format <b>fish_no:</b> unique fish number <b>salmon_group:</b> hatchery, wild-downstream, wild-upstream <b>split:</b> the split in the flume over which speed was measured. “A1_A2” is the stretch between antennas A1 and A2. “A2_A3” is the stretch between antennas A2 and A3. <b>pred_treat:</b> predator treatment. “no_pred”: predator absent, “pred”: predator present <b>order:</b> order of predator treatment for individual salmon. 1: predator treatment was run first, 2: predator treatment was run second (no predator treatment was run first). <b>time_start: </b>the general time of day the trail started as recorded by researchers, not the first detection at antenna A1. <b>time: </b>The total time from the first detection at antenna A1 until the first detection at A2 (for split A1_A2), or from the last detection at A2 until the first detection at A3 (for split A2_A3). <b>time.secs: </b>same as column “time”, but as an integer, units: seconds <b>time.cox: </b>same as column “time.secs”, but salmon that failed to reach an antenna (NAs in “time.secs” column), are recorded as the cut off time (600 seconds). This is necessary for the cox models. <b>censor:</b> 1: salmon reached the antenna in the allotted time limit. 0: salmon failed to reach the antenna in the allotted time limit (NAs in column “time.secs” and value of 600 in column “time.cox”). <b>speed.ms: </b>distance traveled (0.9144 meters per split) divided by “time.secs” <b>FL:</b> fork length, units: mm <b>WT:</b> weight, units: grams <b>Kbcond:</b> Fulton’s condition factor K, units: index <b>ATPresid:</b> ATPase activity, units: index   sabal_et_al_2020_environmental_data.txt – this data file contains environmental measurements for each day behavior trials were run. <b>date:</b> year-month-day format <b>airtempC: </b>air temperature, units: degrees Celcius <b>watertempC:</b> water temperature, units: degrees Celcius <b>turbidity:</b> turbidity, units: NTUs <b>watervelocity: </b>surface water velocity, units: m/s <b>cloudcover: </b>approximated cloud cover, units: between 0 and 100 percent