Adrastic short-term reduction of population size caused by natural disasters, disease, or predators is called:

A drastic short-term reduction of population size caused by natural disasters, disease or predators is called a bottleneck event. A bottleneck event or also known as genetic bottleneck results in the reduction of the gene pool of the population, making the current population have a low genetic diversity and high genetic deviation. Because of low genetic variation, the new population will become distinct from the original.

The arrangements of lipids in the membrane makes the cell semi permeable .