Biology

Zero population growth (ZPG) occurs when the number of births is equal to the number of deaths in a population.

Let's check the data for each year to find when the number of deer born equals the number of deer that died:

1.1960: 2000 born, 600 died → Net population change = 2000 - 600 = +1400

2.1970: 1800 born, 700 died → Net population change = 1800 - 700 = +1100

3.1980: 1500 born, 800 died → Net population change = 1500 - 800 = +700