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Brood size matching: a novel perspective on predator dilution.
1Aronia Coastal Zone Research Team, Åbo Akademi University and Novia University of Applied Sciences, Raseborgsvägen 9, FI-10600 Ekenäs, Finland. kim.jaatinen@gmail.com
The American Naturalist
|January 26, 2013
Summary
Subgroups merge to reduce predator risk, with smaller subgroups more eager to join larger ones. This study reveals that partners negotiate contributions to predator dilution, favoring mergers between similarly sized groups.
Area of Science:
- Behavioral Ecology
- Evolutionary Biology
- Animal Behavior
Background:
- Predator avoidance is a key driver of animal sociality, with group living offering benefits like predator dilution.
- The role of subgroups (e.g., families) within larger groups and their specific contributions to risk dilution have been understudied.
- Subgroup size relative to the total group influences individual risk and willingness to merge.
Purpose of the Study:
- To investigate how subgroup proportional contribution to predator dilution impacts group formation dynamics.
- To test predictions regarding subgroup size matching, predation pressure, and bargaining power in coalition formation.
- To understand the negotiation process and criteria used by subgroups when forming partnerships.
Main Methods:
- Developed a "bidding game" model to predict subgroup merger preferences based on parental care and risk dilution.
- Collected and analyzed data on common eiders (Somateria mollissima) forming brood-rearing coalitions.
- Tested specific hypotheses regarding subgroup size, predation influence, and female body condition (as a proxy for bargaining power).
Main Results:
- Confirmed that size-matched subgroups exhibit a higher propensity to merge.
- Found that increased predation risk positively correlates with group formation propensity.
- Demonstrated that greater bargaining power (indicated by female body condition) leads to longer partnership establishment times.
- Observed that partners actively negotiate and evaluate contributions to predator dilution before forming coalitions.
Conclusions:
- Subgroup size and its proportional contribution to predator dilution are critical factors in understanding group formation.
- Negotiation over risk dilution is a significant component of partnership formation in social groups.
- Predation threat and individual bargaining power shape the dynamics of cooperative group living.
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