Ecological footprint and biocapacity concepts are used to assess sustainability. Sustainability exists when:

• A. Biocapacity is always larger than footprint regardless.
• B. Ecological footprint measures land used for recreation.
• C. Sustainability exists when the ecological footprint equals or is less than biocapacity.
• D. Sustainability exists when the ecological footprint is greater than biocapacity.

Answer: (C)

The main idea here is demand versus Earth's capacity. The ecological footprint measures how much productive land and sea area a population needs to supply its resources and absorb its wastes. Biocapacity is how much productive land and sea area is available to generate those resources and absorb wastes. Sustainability exists when the demand on nature does not exceed this available capacity, meaning the ecological footprint is equal to or less than biocapacity. If the footprint surpasses biocapacity, we’re overusing resources and depleting natural capital, which is unsustainable.

So the best statement is that the ecological footprint equals or is less than biocapacity. The other ideas don’t fit: ecological footprint isn’t just land used for recreation, it covers all resource use and waste absorption; biocapacity isn’t guaranteed to always exceed footprint in all scenarios; and if the footprint were greater than biocapacity, that would indicate unsustainable overshoot rather than sustainability.