Deaths per Costa Rica United States Hungary population 13 1100 1090 1088 1080 1070 1070 1052 1050 1040 1034 1030 1030 1024 1020H017 1018 1012 1010 Year 1000 997 Total population increase Total population increase Total population decrease 8.8% Births per thousand ulation +15 Effect of Birthrate and Death Rate on Population Size For a population to grow, the birthrate must exceed the death rate for a period of time. These three human populations illustrate how the combined effects of births and deaths would change population size if birthrates and death rates were maintained for a five-year periodEffect of Birthrate and Death Rate on Population Size Effect of Birthrate and Death Rate on Population Size For a population to grow, the birthrate must exceed the death rate for a period of time. These three human populations illustrate how the combined effects of births and deaths would change population size if birthrates and death rates were maintained for a five-year period