State-dependent foraging among social fish in a risky environment
In the presence of a predator, foraging is a dangerous task. Social individuals can respond to risk by forming groups, benefiting from enhanced collective anti-predator behavior but suffering from increased conspicuousness to predators. Within groups, individuals exhibit variable foraging behavior. One important factor influencing risky foraging behaviour is current energetic state, and individuals must trade off food and safety by deciding when to leave a protected refuge in order to find food. We generated mixed groups of goldfish (Carassius auratus) containing equal numbers of underfed and well-fed individuals and examined individual refuge use and willingness to take risks venturing into risky foraging areas in the presence of an avian predator (little egret—Egretta garzetta). Underfed fish exhibited higher levels of risky behaviour by participating in more foraging outings and emerging from the refuge in frontal group positions, compared with well-fed individuals. As expected, underfed fish benefitted by consuming more food, but surprisingly did not experience higher rates of mortality. This may be due to the fact that the egret predator rarely captured the first fish to emerge from the refuge, preferentially attacked groups of three or more fish, and often captured fish in the chaotic period following a failed initial strike. We demonstrate how differences in energetic condition can influence risk-taking behaviours among social individuals that subsequently influence relative levels of foraging success and group fission–fusion dynamics. Moreover, our results illustrate the risk associated with foraging in larger groups.
KeywordsCosts and benefits Predator–prey Hunger Trade-off Group size
This study was supported by Israel Science Foundation (Grant 05/14 to ZA). SV is grateful to the Azrieli Foundation for the award of a Postdoctoral Fellowship at Ben-Gurion University.
Author contribution statement
JBF conceived the experiment and wrote the manuscript; WAM contributed to statistical analyses; BPK, SV, LTTE, and ZA contributed to experimental design, video analyses, and edited early drafts of the manuscript.
Compliance with ethical standards
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. The experiments were conducted in full accordance with the animal care and ethical guidelines of Ben-Gurion University of the Negev, and the Abramsky lab was granted permission to use egrets and goldfish in this study by the committee for the ethical care and use of animals in experiments (authorization number: IL-37-07-2017).
Conflict of interest
The authors declare that they have no conflict of interest.
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