The Balance of nature refers to the theory that biological systems are usually in a stable equilibrium, which is to say that a small change in some particular parameter (the size of a particular population, for example) will be corrected by some negative feedback that will bring the parameter back to its original "point of balance" with the rest of the system. It may apply where populations depend on each other, for example in predator/prey systems, or relationships between herbivores and their food source. It is also sometimes applied to the relationship between the Earth's ecosystem, the composition of the atmosphere, and the world's climate.
The concept is very old; Herodotus described the relationship between predator and prey species, and commented on how they were in an essentially static balance, with predators never excessively consuming their prey populations. The "balance of nature" concept once ruled ecological research, as well as once governing the management of, natural resources. This lead to a doctrine popular among some conservationists that nature was best left to its own devices, and that human intervention into it was by definition unacceptable.
The concept has been criticised in recent times as being a pseudoscientific fallacy. It was first put into question when a substantial number of studies showed that predator/prey populations display a continuing state of disturbance and fluctuation rather than constancy and balance. It has been proposed by some scientists that ecological communities of plants and animals are inherently unstable, due to substantial idiosyncratic differences in behavior among communities and individuals in them. An aggressive, dominant wolf for example can greatly increase the chances of a pack in securing food, just as the death of a pack leader can lead to the pack's mass starvation. It is reasoned that any apparent equilibrium is illusory because external factors (such as variations in weather patterns, fires, hurricanes or disease) seldom allow ecological communities to stabilise. Dr. George L. Jacobson Jr., a paleoecologist at the University of Maine stated that according to ancient rock sediments; "[regarding natural systems] there is almost no circumstance one can find where something isn't changing the system.. it's never allowed to [stabilise], so we might as well not expect [balance] to exist."
Although some conservationist organisations argue that human activity is incompatible with a balanced ecosystem, there are numerous examples in history showing that several modern day habitats originate from human activity: some of Latin America's rain forests owe their existence to humans planting and transplanting them, while the abundance of grazing animals in the Serengeti plain of Africa is thought by some ecologists to be partly due to human-set fires that created savanna habitats.
Despite being discredited among ecologists, the theory is widely held to be true in the wider population: a report written by psychologist Corinne Zimmerman of Illinois State University and ecologist Kim Cuddington of Ohio University demonstrated that at least in Midwestern America, the "balance of nature" idea is widely held among both science majors and the general student population.
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