Over the years, the world has witnessed a sustained growth in human populations. UN-DESA (United Nations-Department of Economics and Social Affairs) (2013, 2014) projects that the 2014 population of 7.244 billion people will, most likely, increase to 9.6 billion by 2050 and to 10.9 billion by 2100. With regard to current fertility patterns, it is envisaged that much of the increase in population will be in countries with high fertility levels, mainly in Africa and in countries such as Pakistan, India, the Philippines and the United States which have large population sizes. In spite of global population growth, UN-DESA (2014) projections indicate that fertility rates across the world have consistently declined from 4.5 children in the 1970s to 2.5 children per woman in 2014. These populations depend on the ecosystem for sustenance and the provision of other services such as carbon sequestration and defence against natural disasters (Black et al., 2008).