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  Population in Animal Ecology, Biology tutorial

Introduction:

A population is all the organisms that both belong to the same species and live in the same geographical area. The area that is used to define the population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals from other areas. Normally breeding is substantially more common within the area than across the border.

In sociology, population refers to a collection of human beings. Demography is a sociological discipline which entails the statistical study of human populations. This article refers mainly to human population.

Population genetics:         

In population genetics a population is a set of organisms in which any pair of members can breed together. This implies that all members belong to the same species and live near each other.

World human population:

As of 16 March 2011, world population is evaluated by the United States Census Bureau to be 6.906 billion. According to papers published by United States Census Bureau, the world population hit 6.5 billion (6,500,000,000) on 24 February 2006. The United Nations Population Fund designated 12 October 1999 as the approximate day on which world population reached 6 billion. This was about 12 years after world population reached 5 billion in 1987, and 6 years after world population reached 5.5 billion in 1993. The population of some countries, such as Nigeria and China is not even known to the nearest million, so there is a considerable margin of error in such estimates.

i) Population growth:

Population growth increased significantly as the Industrial Revolution gathered pace from 1700 onwards. The last 50 years have seen a yet more rapid increase in the rate of population growth due to medical advances and substantial increases in agricultural productivity, particularly beginning in the 1960s, made by the Green Revolution. In 2007 the United Nations Population Division projected that the world's population will likely surpass 10 billion in 2055. In the future, world population has been expected to reach a peak of growth, from there it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. There is around an 85% chance that the world's population will stop growing before the end of the century. There is a 60% probability that the world's population will not exceed 10 billion people before 2100, and around a 15% probability that the world's population at the end of the century will be lower than it is today. For different regions, the date and size of the peak population will vary considerably.

The population pattern of less-developed regions of the world in recent years has been marked by gradually declining birth rates following an earlier sharp reduction in death rates. This transition from high birth and death rates to low birth and death rates is often referred to as the demographic transition.

ii) Control:

Human population control:

Human population control is the practice of artificially altering the rate of growth of a human population. Historically, human population control has been implemented by limiting the population's birth rate, usually by government mandate, and has been undertaken as a response to factors including high or increasing levels of poverty, environmental concerns, religious reasons, and overpopulation. While population control can involve measures that improve people's lives by giving them greater control of their reproduction, some programs have exposed them to exploitation.

Worldwide, the population control movement was active throughout the 1960s and 1970s, driving many reproductive health and family planning programs. In the 1980s, tension grew between population control advocates and women's health activists who advanced women's reproductive rights as part of a human rights-based approach. Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1990s.

Introduction to Population cycle:

The population cycle in zoology is phenomenon where populations rise and fall over expected period of time. There are some species where population numbers have sensibly predictable patterns of change though full reasons for population cycles is one of the main unsolved ecological problems. There are number of factors that influence population change like availability of predators, food, diseases and climate.

Occurrence in mammal populations:

Olaus Magnus, the Archbishop of Uppsala in central Sweden, recognized that species of northern rodents had periodic peaks in population and published two reports on subject in middle of 16th century.

In North America, the event was recognized in populations of snowshoe hare. In 1865, trappers with Hudson's Bay Company were catching plenty of animals. By 1870, they were catching very few. It was lastly recognized that cycle of high and low catches ran over about a ten year period.

Other species:

While phenomenon is frequently related with rodents, it does occur in other species like ruffed grouse. There are other species that have irregular population explosions like grasshoppers where overpopulation results in locust swarms in Africa and Australia.

Relationships between predators and prey:        

There is also interaction between prey with periodic cycles and predators. As population expands, there is more food available for predators. As it contracts, there is less food available for predators, putting pressure on the population numbers.

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