Opposing Responses to Scarcity Emerge from Functionally Unique Sociality Drivers

Area of Science:

• Ecology
• Evolutionary Biology
• Behavioral Ecology

Background:

• Organisms across taxa form groups, gaining benefits like resource acquisition and predator defense.
• However, group living incurs costs, primarily increased competition for resources.
• Responses in group size to resource scarcity vary, with some species decreasing, while others maintain or increase group size.

Purpose of the Study:

• To explain the divergent responses of group sizes to resource scarcity across species.
• To investigate the role of different sociality benefits in mediating group size adjustments under resource limitation.

Main Methods:

• Developed a conceptual framework and theoretical model based on a literature review.
• Categorized resource-related benefits of sociality into six distinct classes.
• Modeled the impact of these benefits on individual survival in groups under varying resource conditions.

Main Results:

• The dominant benefit of sociality significantly influences whether optimal group size increases, decreases, or remains constant with declining resource abundance.
• Model predictions align with existing, albeit limited, empirical data across diverse taxa.
• Resource competition is a key factor, but the specific benefits of sociality dictate the adaptive response.

Conclusions:

• Differences in how group size responds to resource declines are driven by the primary benefits of sociality for a given species.
• Understanding the dominant sociality mechanism is crucial for predicting group dynamics under environmental change.
• This framework provides a unified explanation for varied group size responses to resource scarcity.