Overshoot (population)

This article duplicates the scope of other articles, specifically Human overpopulation. Please discuss this issue and help introduce a summary style to the article. (October 2021)

In environmental science, a population "overshoots" its local carrying capacity — the capacity of the biome to feed and sustain that population — when that population has not only begun to outstrip its food supply in excess of regeneration, but actually shot past that point, setting up a potentially catastrophic crash of that feeder population once its food populations have been consumed completely. Overshoot can apply to human overpopulation as well as other animal populations: any life-form that consumes others to sustain itself.

Environmental science studies to what extent human populations through their resource consumption have risen above the sustainable use of resources. For people, "overshoot" is that portion of their demand or ecological footprint which must be eliminated to be sustainable, or the delta between a sustainable population and what we currently have.^[1][2] Excessive demand leading to overshoot is driven by both consumption and population.^[3]

Population decline due to overshoot is known as 'collapse'. The path taken by such a population is referred to as 'overshoot-and-collapse'. Collapse, like overshoot, can occur due to various factors, with the Malthusian catastrophe being a specific but not identical case.^{[citation needed]}

Overshoot can happen as a result of delayed impacts, where reproduction rates persistently surpass the death rate.^[4] This can lead to significant consequences, with entire ecosystems being profoundly impacted and sometimes simplified due to prolonged overshoot.^[5] An instance of this phenomenon took place in the Horn of Africa when smallpox was eradicated, causing a sudden increase in the population that exceeded the region's carrying capacity. For centuries, the land had sustained approximately 1 million pastoralists, but with the elimination of the disease, the population suddenly grew to 14 million people. Consequently, overgrazing occurred, leading to soil erosion.^[6]

The most famous example of an overshoot-and-crash may be from St. Matthew Island. In 1944, 29 reindeer were introduced to the island, which by 1963 had grown to a peak population of roughly 6000 individuals — well past the estimated carrying capacity. At next count, in 1965, the population had plummeted and only 42 reindeer were left alive.

Thomas Malthus (1766-1864) is perhaps the most well-known writer to have articulated the roots of the modern concept of human overshoot, with The Population Bomb (1967) by Paul Ehrlich reigniting the hotly-debated topic in more recent history. Daniel Quinn claims to have modernized the concept of human overpopulation in what are likely the most well-read volumes to have given it extensive treatment as a subject of ecology: The Story of B (1996) and My Ishmael (1997).