Which of the following best explains why the Sahara Desert is unable to support large populations of grazing herbivores?

• A. Excessive rainfall leads to frequent flooding
• B. Low primary productivity due to limited water availability
• C. Dense forest cover limits grazing opportunities
• D. High levels of soil nutrients support only small plants

Answer: (B)

Verified step by step guidance

1. Understand the concept of primary productivity: Primary productivity refers to the rate at which plants and other photosynthetic organisms produce organic compounds (biomass) from inorganic substances like carbon dioxide and water. It is a key factor in determining the amount of energy available to support higher trophic levels, such as herbivores.
2. Analyze the role of water availability: Water is a critical resource for photosynthesis and plant growth. In arid environments like the Sahara Desert, limited water availability restricts the growth of plants, leading to low primary productivity.
3. Connect primary productivity to herbivore populations: Grazing herbivores depend on plants for food. If primary productivity is low due to limited water, there will be insufficient plant biomass to support large populations of herbivores.
4. Evaluate the other options: Excessive rainfall and flooding are not characteristic of the Sahara Desert, so this option can be eliminated. Dense forest cover is also not applicable, as the Sahara is a desert environment. High levels of soil nutrients supporting only small plants is incorrect because the primary limiting factor in the Sahara is water, not soil nutrients.
5. Conclude that the correct explanation is 'Low primary productivity due to limited water availability,' as this directly addresses the relationship between water scarcity, plant growth, and the inability to support large populations of grazing herbivores.