Assertion : Mammals and birds requiring large territories are...

The assertion states that mammals and birds requiring large territories are severely affected by habitat fragmentation. This is true because these animals need extensive areas for foraging, breeding, and survival, and breaking their habitat into smaller fragments restricts their movement and reduces available resources.

The reason states that habitat loss and fragmentation is the most important cause driving animals and plants to extinction. This is also a true statement, as it is the primary factor among the 'Evil Quartet' of biodiversity loss.

However, the reason does not explain why mammals and birds requiring large territories are specifically affected by fragmentation. The correct explanation would be their intrinsic need for large, continuous areas to sustain their life processes. Therefore, both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

Answer: Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.