1974, the public gоt а grаphic illustrаtiоn оf the "tragedy of the commons" in satellite photos of the earth. Pictures of northern Africa showed an irregular dark patch 390 square miles in area. Ground-level investigation revealed a fenced area inside of which there was plenty of grass. Outside, the ground cover was devastated by overgrazing. Consider the two dimensions of product characteristics: i) rival versus non-rival and ii) excludable versus non-excludable. Which dimension would explain the difference in results for the fenced area and the non-fenced (common) area? Be sure to explain why.