444: Many-eyes or Sentinels? How Cost Curvature Shapes Collective Vigilance

Pilgrim C et al., PNAS - A minimal analytical model shows that whether animal groups adopt distributed low-level vigilance (many-eyes) or concentrated high-vigilance roles (sentinels) depends on how individual vigilance costs scale with effort. The same dichotomy appears in selfish and cooperative groups and explains switching, edge effects, and turn-taking. Key terms: collective vigilance, many-eyes, sentinel behavior, vigilance costs, behavioral ecology.

Study Highlights:
The authors derive a minimal model where collective vigilance benefit is a function of summed individual vigilance and costs depend on individual effort. When vigilance costs are convex (steepening) many-eyes strategies with equal low vigilance across individuals are optimal; when costs are concave (flattening) sentinel strategies with vigilance concentrated in one or a few individuals are optimal. This outcome holds in both selfish (game-dynamic) and cooperative (group-optimal) contexts and is supported by simulations. Extensions reproduce behavioral switching with S-shaped costs, edge effects from heterogeneous costs, and turn-taking when energy state dynamics are included.

Conclusion:
The curvature of individual vigilance costs determines whether groups distribute vigilance across many members or concentrate it in sentinels; habitat structure that creates flattening costs (vantage points) favors sentinels, while uniform habitats with steepening costs favor many-eyes.

Music:
Enjoy the music based on this article at the end of the episode.

Article title:
Many-eyes and sentinels in selﬁsh and cooperative groups

First author:
Pilgrim C

Journal:
PNAS

DOI:
10.1073/pnas.2536017123

Reference:
Pilgrim C, Bate AM, Sigalou A, Aellen M, Morford J, Warren E, Krupenye C, Biro D, Mann RP. Many-eyes and sentinels in selfish and cooperative groups. PNAS. 2026;123(33):e2536017123. doi:10.1073/pnas.2536017123

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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Episode link: https://basebybase.com/episodes/many-eyes-or-sentinels-cost-curvature-vigilance

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-08-19.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Audited the transcript sections describing the minimal model fi = b(S) − c(vi); S = ∑vi; cost-curvature (convex vs concave); environmental structure; selfish vs cooperative results; behavioral switching (sigmoidal costs); edge effects; turn-taking; energy-state dynamics; and discussed limitations.
- transcript topics: Model of collective vigilance (fi = b(S) − c(vi)); Cost curvature and environmental structure (convex vs concave); Selfish vs cooperative group outcomes; Behavioral switching with sigmoidal costs; Edge effects and spatial positioning; Energy-state dynamics and turn-taking

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 6
- claims flagged for review: 0
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited:
- article_doi
- article_title

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