A biologist studied the population of rats in a barn. He found that the average natality was $250$, average mortality $240$, immigration $20$ and emigration $30$. The net increase in population is

Two opposite forces operate in the growth and development of every population. One of them related to the ability to reproduce at a given rate. The force opposite to it is called

Verhulst – pearl logistic growth equation

Sigmoid growth curve is represented by

Natality refers to.