According to Demeny (1990), a significant change in the demographic parameters is found to cause shifts in relationships between population, income and resource-use intensity, sometimes compensating and sometimes reinforcing the environmental impact. To quote:

In particular, over time non-linearties to scale may appear. Quantitative increases can generate qualitative changes; thresholds separating, for example, tolerable levels of pollution from levels that generate unacceptable risks for human health may be crossed. Up to a certain level, damage to a renewable resource such as a forest ecosystem, may be corrected by a spontaneous and relatively rapid biological process; beyond that level the damage may be irreparable, or the natural recovery or the human-engineered repair of the ecosystem in question may require a very long time or entail exorbitant cost.

In simple language, the relationship between population and environment is not amenable to one simple formulation. Population dynamics may offset or catalyze the effect of population size on environment. It depends on a number of socio-economic, political, cultural, technological and environmental factors. It also depends on whether we are focusing at micro level or macro level. Imagine that due to increase in family size in moderate fertility context there is a division of land, and in per capita terms the family becomes poorer. The family may respond by increasing fertility with the aim of diversification of economic activities and benefiting from division of labour and offset the negative effect of population growth on development. The family may increase fertility without having the possibility of raising income and the negative impact of population may be reinforced. In the same way there are different possibilities for societies and nations. In the absence of capital they may decide to substitute capital by labour and thus ignore or encourage high fertility. They may benefit from this strategy. They may simply increase fertility due to religious, cultural or political reasons. Then they suffer more. Ironically, some of the poorest countries of the world have high fertility levels though it would be rational if they controlled it.