On how risk and group size interact to influence vigilance

Area of Science:

• Ethology
• Behavioral Ecology
• Evolutionary Biology

Background:

• Vigilance is crucial for animals to detect predators and rivals, but it incurs costs.
• Models predict vigilance increases with risk and decreases with group size.
• The interaction between risk and group size on vigilance is not well understood.

Purpose of the Study:

• To review the literature on vigilance in birds and mammals.
• To assess the commonality of interactive effects between risk and group size on vigilance.
• To determine the patterns of these interactions when present.

Main Methods:

• Literature review of studies on animal vigilance.
• Analysis of studies considering predation risk.
• Analysis of studies considering social risk (rivals).

Main Results:

• Most studies on predation risk found no significant interaction between risk and group size.
• In studies with social risk, vigilance decreased more rapidly with group size at low risk.
• Low statistical power may hinder detection of interactive effects.

Conclusions:

• Interactive effects between risk and group size on vigilance are not consistently observed, especially concerning predation risk.
• The pattern of interaction in social risk suggests increased rival monitoring in larger groups.
• Further research is needed to understand the constraints and implications of vigilance adjustments for sociality and defense evolution.