What do scientists call regions of earth that contain an unusually large number of species that are threatened by habitat loss?

The regions of the Earth that contain unusually large number of the species experiencing threat  of the habitat loss are termed as hotspots. These biodiversity hotspots are the places containing the most amount of the species that are prone to destruction. Most of these biodiversity hotspots include the forests. The conservation of these hotspots in extremely necessary for the protection of the species living within.

Hence, the answer is 'hotspots'.

b brown mice / white sand dunes