The "Red Data Books," published by the International Union for Conservation of Nature (IUCN), specifically focus on cataloging threatened species at risk of extinction, which encompasses endangered, vulnerable, and critically endangered plant and animal species. This classification plays a crucial role in biodiversity conservation efforts, serving as a key reference for policymakers and conservationists to prioritize actions and allocate resources effectively. Options 1 and 3, while relevant to biodiversity and conservation, do not accurately represent the primary purpose of the Red Data Books, making option 2 the correct choice.