I feel like it is emigration, due to the fact that mutations are random, immigration means coming in and death not really cuz climate change, flood, and landslide will not actually mean full death. In the end i feel like it is emigration but you argue about being death too.
Explanation: The answer would be b, emigration because emigration means to leave an area to go to another one, and all those factors would result in the animals leaving.
