Wealth as a source of density dependence in human population growth

Abstract

In modern industrialized countries, human birth rates have been declining persistently for decades, and have now fallen below the replacement threshold in many countries. However, unlike in natural populations where population growth is constrained by limited resources, lower birth rates in modern industrialized countries are positively correlated with resource availability. Here, we show that declining birth rates in human populations are actually a manifestation of density-regulated population growth brought on by socioeconomic development. This is demonstrated by combining empirical power law relations between population size, GDP per capita, and fertility in a simple theoretical model describing population dynamics in developed countries. For a closed population, the model exhibits growth to a globally-stable equilibrium population size, for both national and city populations. The model exhibits a good fit to long-term time series data on population size, GDP per capita, and birth rates for the United States, France, and Japan.