An escape theory model for directionally moving prey and an experimental test in juvenile Chinook salmon
Data files
Mar 27, 2020 version files 60.72 KB
Abstract
- 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.
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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.
Methods
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.
Usage notes
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. Journal of Animal Ecology.
Authors
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
File list
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
File descriptions
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.
date: year-month-day format
fish_no: unique fish number
salmon_group: hatchery, wild-downstream, wild-upstream
split: 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.
pred_treat: predator treatment. “no_pred”: predator absent, “pred”: predator present
order: 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).
time_start: the general time of day the trail started as recorded by researchers, not the first detection at antenna A1.
time: 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).
time.secs: same as column “time”, but as an integer, units: seconds
time.cox: 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.
censor: 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”).
speed.ms: distance traveled (0.9144 meters per split) divided by “time.secs”
FL: fork length, units: mm
WT: weight, units: grams
Kbcond: Fulton’s condition factor K, units: index
ATPresid: ATPase activity, units: index
sabal_et_al_2020_environmental_data.txt – this data file contains environmental measurements for each day behavior trials were run.
date: year-month-day format
airtempC: air temperature, units: degrees Celcius
watertempC: water temperature, units: degrees Celcius
turbidity: turbidity, units: NTUs
watervelocity: surface water velocity, units: m/s
cloudcover: approximated cloud cover, units: between 0 and 100 percent