Bottleneck effect can occur with 
external migration direct damage to the lungs Movement of an air mass competition if humans disturb bears competing for resources Plant growth is reduced Temperature changing
A B C D E F G H
Population growth is reduced by external migration.
Bottleneck effect occurs with external migration.
Bottleneck effect can occur with  (A) external migration (B) direct damage to the lungs (C) Movement of an air mass (D) competition (E) if humans disturb bears (F) competing for resources (G) Plant growth is reduced (H) Temperature changing