Current population dynamics, and cause for concernDepending on which estimate is used, human overpopulation may have already occurred. Nevertheless, the rapid recent increase in human population has worried some people. The population is expected to reach between 8 and 10.5 billion between the years 2040 and 2050.
By that point, all life on the Earth will be extinct. The most probable fate of the planet is absorption by the Sun in about 7.5 billion years, after the star has entered the red giant phase and expanded beyond the planet's current orbit.
When the population is above the carrying capacity it decreases, and when it is below the carrying capacity it increases.
Anthropologist John Moore's estimate, which was published by Nasa in 2002, was modelled on small migrating groups of early humans – around 160 people. He recommends starting with young, childless couples and screening for the presence of potentially dangerous recessive genes.
1.5 billion to 2 billion people
An estimate on the "total number of people who have ever lived" as of 1995 was calculated by Haub (1995) at "about 105 billion births since the dawn of the human race" with a cut-off date at 50,000 BC (beginning of the Upper Paleolithic), and an inclusion of a high infant mortality rate throughout pre-modern history.
Earth's capacityMany scientists think Earth has a maximum carrying capacity of 9 billion to 10 billion people.
The carrying capacity of a population represents the absolute maximum number of individuals in the population, based on the amount of the limiting resource available. We can incorporate the density dependence of the growth rate by using r(1 - P/K) instead of r in our differential equation: .
As it stands now, though, the world's population is over 7.3 billion. According to United Nations predictions it could reach 9.7 billion people by 2050, and over 11 billion by 2100. Population growth has been so rapid that there is no real precedent we can turn to for clues about the possible consequences.
Reproduction rates may remain high relative to the death rate. Entire ecosystems may be severely affected and sometimes reduced to less-complex states due to prolonged overshoot. The eradication of disease can trigger overshoot when a population suddenly exceeds the land's carrying capacity.
The resources in any given habitat can support only a certain number of wildlife. As seasons change, food, water, or cover may be in short supply, causing damage to the animals or the habitat. Carrying capacity is the number of animals the habitat can support all year long.
Exponential population growth
Carrying capacity can be defined as a species' average population size in a particular habitat. The species population size is limited by environmental factors like adequate food, shelter, water, and mates.
Population growth is based on four fundamental factors: birth rate, death rate, immigration, and emigration.
Example 1: The Carrying Capacity of North American DeerAs a result of the loss of their main predator, the deer population began to boom. Deer feed on all sorts of plants, trees, shrubs, flowers, and grass, and require large quantities of such vegetation to sustain themselves.
Limiting factors determine carrying capacity. The availability of abiotic factors (such as water, oxygen, and space) and biotic factors (such as food) dictates how many organisms can live in an ecosystem. Carrying capacity is also impacted by the availability of decomposers.
