Overpopulation is the condition where an organism's numbers exceed the carrying capacity of its habitat. In common parlance, the term usually refers to the relationship between the human population and its environment, the Earth.
Overpopulation is not a function of the size or density of the population only. Overpopulation is determined using the ratio of population to available sustainable resources. If a given environment has a population of ten, but there is food or drinking water enough for only nine, then in a closed system where no trade is possible, that environment is overpopulated; if the population is 100 individuals but there is enough food, shelter, and water for 200 for the indefinite future, then it is not. Overpopulation can result from an increase in births, a decline in mortality rates due to medical advances, from an increase in immigration, or from an unsustainable biome and depletion of resources. It is possible for very sparsely-populated areas to be overpopulated, as the area in question may have a meager or non-existent capability to sustain human life (e.g. the middle of the Sahara Desert or Antarctica).
The resources to be considered when evaluating whether an ecological niche is overpopulated include clean water, clean air, food, shelter, warmth, and other resources necessary to sustain life. If the quality of human life is addressed, there may be additional resources considered, such as medical care, employment, education, electricity, proper sewage treatment and waste disposal. Overpopulation places competitive stress on these basic life sustaining resources, leading to a diminished quality of life.
Some countries have managed to increase their carrying capacity by using technologies such as modern agriculture, desalination and nuclear power. Some economists such as Thomas Sowell and Walter E. Williams have argued that poverty and famine are caused by bad government and economic policies, not necessarily by overpopulation. In his book The Ultimate Resource, economist Julian Simon argued that higher population density leads to more specialization and technological innovation, producing a higher standard of living. Others argue that overpopulation is an important cause of these problems.
Over-consumption is a concept related to overpopulation, referring to situations where per capita consumption is so high that even in spite of a moderate population density, sustainability is not achieved. The concept was coined to augment the discussion of overpopulation, which reflects issues of carrying capacity without taking into account per capita consumption, by which developing nations are evaluated to consume more than their land can support. Green parties and the ecology movement often argue that consumption per person, or ecological footprint, is typically lower in poor than in rich nations.
For More Information:
Overpopulation - Wikipedia
Overconsumption - Wikipedia
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)