Avoidance or escape? Discriminating between two hypotheses for the function of schooling in threespine sticklebacks.

Area of Science:

• Ethology
• Behavioral Ecology
• Animal Behavior

Background:

• Grouping with conspecifics offers antipredator benefits in many species.
• Two main hypotheses explain aggregation: the avoidance hypothesis (prior predation risk experience) and the escape hypothesis (immediate predation risk).

Purpose of the Study:

• To simultaneously test the avoidance and escape hypotheses in threespine sticklebacks.
• To investigate how past and immediate predation risk influence schooling behavior.

Main Methods:

• Quantified schooling behavior (time schooling, latency, position) using a mobile model school.
• Exposed fish to either a past predation risk treatment (chased by a model predator) or an immediate risk treatment (model pike vs. control stick).
• Assessed fish perception of stimuli in a second experiment.

Main Results:

• Fish with prior predation experience exhibited increased schooling, faster initiation, and more central positioning.
• Immediate exposure to a model predator or control stimulus did not significantly alter schooling behavior.
• Fish differentiated between predator and control stimuli, showing distinct behavioral responses.

Conclusions:

• Results strongly support the avoidance hypothesis, indicating that past predation risk is a key driver of threespine stickleback aggregation.
• Immediate predation risk does not appear to be the primary factor driving schooling behavior in this species.
• Learned predator avoidance through prior experience is crucial for group defense strategies.