Overpopulation and carrying capacity
Overpopulation is a generally undesirable condition where an organism's numbers exceed the carrying capacity of its habitat. The term often refers to the relationship between the human population and its environment, the Earth, or smaller geographical areas such as countries. Overpopulation can result from an increase in births, a decline in mortality rates, an increase in immigration, or an unsustainable biome and depletion of resources. It is possible for very sparsely populated areas to be overpopulated if the area has a meager or non-existent capability to sustain life (e.g. a desert).
The population has been growing continuously since the end of the Black Death, around the year 1400, although the most significant increase has been in the last 50 years, mainly due to medical advancements and increases in agricultural productivity. Although the rate of population growth has been declining since the 1980s, the United Nations has expressed concern on continued excessive population growth in sub-Saharan Africa.As of December 5, 2012 the world human population is estimated to be 7.056 billion by the United States Census Bureau, and over 7 billion by the United Nations. Most estimates for the carrying capacity of the Earth are between 4 billion and 16 billion. Depending on which estimate is used, human overpopulation may or may not have already occurred. Nevertheless, the rapid recent increase in human population is causing some concern. The population is expected to reach between 8 and 10.5 billion between the year 2040and 2050. In May 2011, the United Nations increased the medium variant projections to 9.3 billion for 2050 and 10.1 billion for 2100.
The following definition tells us that humans have already reached a state of overpopulation in the world:
If the long-term carrying capacity of an area is clearly being depleted by its current human
Occupants, that area is overpopulated. By this Standard, the entire planet and virtually every
Nation is already vastly overpopulated.
Physical Environmental Limits:
The environmental physical limits that have
Controlled all plant and animal species over the
Billions of years since life appeared on the planet are:
Water clean air and water
Temperature adequate safe space
Food species habitat requirement
How About Other Species?
In land management, or in places where humans may have little or no effect, it is not difficult to determine if a population is healthy. If the population of a species is declining or in a continual State of under nutrition and disease, the population Numbers are above the ability of the environment to carry or support them at that level. It is thus overpopulated.
CARRYING CAPACITY: For humans, carrying capacity refers to the number who can be supported without degrading the physical, ecological, cultural, and social environments. Carrying capacity relates to the desired quality of life.
Note in this quote there are actually three types of environmental limits for humans: physical, ecological, and social. Culture is considered to be part of the social environment.
Like all living things, humans are still under the control of the basic environmental physical Limits. When these limits are reached and the population begins to decrease or people are in constant hunger and misery, physical environmental overpopulation has taken place. The results of physical overpopulation on humans can be the same as in all non-human species when they exceed their carrying capacity. The outcome may be starvation, disease, migration, and increased predation (for humans this is war). Our species lived under these physical limiting conditions for the first 200,000 years of its evolution. That is why our population remained at near zero population growth until the Agricultural Revolution.
A new form of environmental human overpopulation occurred with the development of agriculture and the destructive technology applied to natural resources. Locally, the effects can appear in a very short term, but globally some of them may take hundreds of years before they are noticed. Following is a list of environmental factors which can lower the carrying capacity of that environment if they are severe for any species.
Urban areas with at least one million inhabitants in 2006. 3% of the world's population lived in cities in 1800, rising to 47% at the end of the twentieth century.
In 1800 only 3% of the world's population lived in cities. By the 20th century's close, 47% did so. In 1950, there were 83 cities with populations exceeding one million; but by 2007, this had risen to 468 agglomerations of more than one million.If the trend continues, the world's urban population will double every 38 years, according to researchers. The UN forecasts that today's urban population of 3.2 billion will rise to nearly 5 billion by 2030, when three out of five people will live in cities.
The increase will be most dramatic in the poorest and least-urbanised continents, Asia and Africa. Projections indicate that most urban growth over the next 25 years will be in developing countries. One billion people, one-sixth of the world's population, or one-third of urban population, now live in shanty towns,which are seen as "breeding grounds" for social problems such as crime, drug addiction, alcoholism, poverty and unemployment. In many poor countries, slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care.
In 2000, there were 18 megacities—conurbations such as Tokyo, Seoul, Mexico City, Mumbai, São Paulo and New York City – that have populations in excess of 10 million inhabitants. Greater Tokyo already has 35 million, more than the entire population of Canada (at 34.1 million).
By 2025, according to the Far Eastern Economic Review, Asia alone will have at least 10 hypercities, those with more than 19 million, including Jakarta (24.9 million people), Dhaka (25 million), Karachi (26.5 million), Shanghai (27 million) and Mumbai (33 million). Lagos has grown from 300,000 in 1950 to an estimated 15 million today, and the Nigerian government estimates that city will have expanded to 25 million residents by 2015. Chinese experts forecast that Chinese cities will contain 800 million people by 2020.