Harsh environments: Multi-player cooperation with excludability and congestion.

Area of Science:

• Evolutionary Biology
• Game Theory
• Behavioral Ecology

Background:

• The common-enemy hypothesis suggests harsher environments promote cooperation.
• Previous models focused on pure public goods, yielding ambiguous environmental effects on cooperation.
• Real-world collective goods are often excludable or congestible, necessitating a refined model.

Purpose of the Study:

• To investigate how excludability and congestibility of collective goods influence cooperation under harsh environmental conditions.
• To resolve the ambiguity in the common-enemy hypothesis for pure public goods.
• To generate testable hypotheses for by-product mutualism.

Main Methods:

• Theoretical modeling of cooperation dynamics.
• Analysis of collective goods categorized by excludability and congestibility (public, club, charity goods).
• Examination of environmental effects on cooperation probabilities.

Main Results:

• Unambiguous environmental effects on cooperation emerge with excludable and/or congestible goods.
• Club goods (excluding defectors) predict a competing effect (reduced cooperation in harsher environments).
• Charity goods (excluding cooperators) predict a common-enemy effect (increased cooperation in harsher environments).

Conclusions:

• The nature of the collective good (excludable/congestible) systematically predicts cooperation responses to environmental harshness.
• Contrasting predictions for public, club, and charity goods offer testable avenues for the common-enemy hypothesis.
• Findings refine our understanding of cooperation's evolutionary underpinnings in by-product mutualism.