loss of diversity in a reduced population is called
population bottleneck
title: Population bottleneck text: Population bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events (such as famines, earthquakes, floods, fires, disease, or droughts) or human activities (such as genocide). Such events can reduce the variation in the gene pool of a population; thereafter, a smaller population, with a smaller genetic diversity, remains to pass on genes to future generations of offspring through sexual reproduction. Genetic diversity remains lower, increasing only when gene flow with another population occurs or very slowly increasing with time as random mutations occur. As a consequence of such title: Genetic diversity text: human-caused population effects. A genetic bottleneck can occur when a population goes through a period of low number of individuals, resulting in a rapid decrease in genetic diversity. Even with an increase in population size, the genetic diversity often continues to be low if the entire species began with a small population, since beneficial mutations (see below) are rare, and the gene pool is limited by the small starting population. This is an important consideration in the area of conservation genetics, when working toward a rescued population or species that is genetically-healthy. Random mutations consistently generate genetic variation. A mutation title: Population decline text: Population decline A population decline (or depopulation) in humans is any great reduction in a human population caused by events such as long-term demographic trends, as in sub-replacement fertility, urban decay, white flight or rural flight, or due to violence, disease, or other catastrophes. A reduction over time in a region's population can be caused by several factors including sub-replacement fertility (along with limited immigration), heavy emigration, disease, famine, and war. History is replete with examples of large-scale depopulations. Many wars, for example, have been accompanied by significant depopulations. Before the 20th century, population decline was mostly observed due to title: Crop diversity text: Crop diversity Crop diversity is the variance in genetic and phenotypic characteristics of plants used in agriculture. Over the past 50 years, there has been a major decline in two components of crop diversity; genetic diversity within each crop and the number of species commonly grown. Crop diversity loss threatens global food security, as the world's human population depends on a diminishing number of varieties of a diminishing number of crop species. Crops are increasingly grown in monoculture, meaning that if, as in the historic Irish Potato Famine, a single disease overcomes a variety's resistance, it may destroy an entire title: Genetic erosion text: Genetic erosion Genetic erosion (also known as genetic depletion) is a process where the limited gene pool of an endangered species diminishes even more when reproductive individuals die off before reproducing low population. The term is sometimes used in a narrow sense, such as when describing the loss of particular alleles or genes, as well as being used more broadly, as when referring to the loss of a phenotype or whole species. Genetic erosion occurs because each individual organism has many unique genes which get lost when it dies without getting a chance to breed. Low genetic diversity in a