Ecological Interactions Drive a Power-Law Relationship Between Group Size and Population Density in Social Foragers

Area of Science:

• Ecology
• Behavioral Ecology
• Theoretical Ecology

Background:

• Group formation in foraging animals offers benefits like improved resource acquisition and reduced predation risk.
• However, increased group size can also intensify within-group competition for resources.

Purpose of the Study:

• To model how individual costs and benefits of group formation influence the resulting group size.
• To predict the relationship between forager group size and population abundance under different ecological scenarios.

Main Methods:

• Developed a mathematical model to explore the dynamics of group formation.
• Analyzed the predicted scaling relationships (power-laws) between group size and population abundance.
• Validated model predictions using empirical data from group-foraging birds and ungulates.

Main Results:

• The model predicts a one-third power-law relationship between forager group size and population abundance when competition occurs both within and between groups.
• Alternative predictions include a one-half power-law or constant group size, contingent on predator-prey dynamics.
• Empirical data from birds and ungulates supported the one-third power-law, indicating hierarchical competition as a key driver.

Conclusions:

• Hierarchical competition is a significant factor determining average animal group size.
• Density-dependent group formation plays a crucial role in maintaining population stability.