 
<translate> Tasirin kwalban yana faruwa ne lokacin da yawan jama'a ya ragu sosai ba zato ba tsammani. Yawan yawan jama'a yana raguwa ta hanyar ƙaura na waje. Tasirin toshewa yana faruwa tare da ƙaura na waje. Saboda haka amsar karshe ita ce (A). <eng> Bottleneck effect occurs when a population suddenly gets much smaller. Population growth is reduced by external migration. Bottleneck effect occurs with external migration. So the final answer is (A). 