Population bottleneck in the context of "Inbreeding depression"

In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, using existing theoretical work by those such as Sewall Wright. As a result of the loss of genetic variation, the new population may be distinctively different, both genotypically and phenotypically, from the parent population from which it is derived. In extreme cases, the founder effect is thought to lead to the speciation and subsequent evolution of new species.

In the figure shown, the original population has nearly equal numbers of blue and red individuals. The three smaller founder populations show that one or the other color may predominate (founder effect), due to random sampling of the original population. A population bottleneck may also cause a founder effect, though it is not strictly a new population.

Cladogenesis is an evolutionary splitting of a parent species into two distinct species, forming a clade.

This event usually occurs when a few organisms end up in new, often distant areas or when environmental changes cause several extinctions, opening up ecological niches for the survivors and causing population bottlenecks and founder effects changing allele frequencies of diverging populations compared to their ancestral population. The events that cause these species to originally separate from each other over distant areas may still allow both of the species to have equal chances of surviving, reproducing, and even evolving to better suit their environments while still being two distinct species due to subsequent natural selection, mutations and genetic drift.

The conservation of bison in North America is an ongoing, diverse effort to bring American bison (Bison bison) back from the brink of extinction. Plains bison, a subspecies (Bison bison bison), are a keystone species in the North American Great Plains. Bison are a species of conservation concern in part because they suffered a severe population bottleneck at the end of the 19th century. The near extinction of the species during the 19th century unraveled fundamental ties between bison, grassland ecosystems, and indigenous peoples’ cultures and livelihoods. English speakers used the word buffalo for this animal when they arrived. Bison was used as the scientific term to distinguish them from the true buffalo. Buffalo is commonly used as it continues to hold cultural significance, particularly for Indigenous people.

Recovery began in the late 19th century with a handful of individuals independently saving the last surviving bison and the government efforts to protect the remnant herd in Yellowstone National Park. Dedicated restoration efforts in the 20th century bolstered bison numbers though they still exist in mostly small and isolated populations. Expansion of the understanding of bison ecology and management is ongoing. The contemporary widespread, collaborative effort includes attention to heritage genetics and minimal cattle introgression.

Lake Toba (Indonesian: Danau Toba, Toba Batak: ᯖᯀᯬ ᯖᯬᯅ; romanized: Tao Toba) is a large natural lake in North Sumatra, Indonesia, occupying the caldera of the Toba supervolcano. The lake is located in the middle of the northern part of the island of Sumatra, with a surface elevation of about 900 metres (2,953 ft), the lake stretches from 2°53′N 98°31′E / 2.88°N 98.52°E / 2.88; 98.52 to 2°21′N 99°06′E / 2.35°N 99.1°E / 2.35; 99.1. The lake is about 100 kilometres (62 miles) long, 30 kilometres (19 mi) wide, and up to 505 metres (1,657 ft) deep. It is the largest lake in Indonesia and the largest volcanic lake in the world. Toba Caldera is one of twenty geoparks in Indonesia, and was recognised in July 2020 as one of the UNESCO Global Geoparks.

Lake Toba is the site of a supervolcanic eruption estimated at VEI 8 that occurred 69,000 to 77,000 years ago, representing a climate-changing event. Recent advances in dating methods suggest a more accurate eruption date of 74,000 years ago. It is the largest-known explosive eruption on Earth in the last 25 million years. According to the Toba catastrophe theory, the eruption had global consequences for human populations as it killed most humans living at that time and is believed to have created a population bottleneck in central east Africa and India, which affects the genetic make-up of the human worldwide population to the present. A recent study has cast doubt on this theory and found no evidence of substantial changes in global population.

It is widely agreed that the evolutionary lineage of the grey wolf can be traced back 2 million years to the Early Pleistocene species Canis etruscus, and its successor the Middle Pleistocene Canis mosbachensis. The grey wolf Canis lupus is a highly adaptable species that is able to exist in a range of environments and which possesses a wide distribution across the Holarctic. Studies of modern grey wolves have identified distinct sub-populations that live in close proximity to each other. This variation in sub-populations is closely linked to differences in habitat – precipitation, temperature, vegetation, and prey specialization – which affect cranio-dental plasticity.

The earliest specimens of the modern grey wolf date to around 400,000 years ago, or possibly earlier to 1 million years ago. Most modern wolves share most of their common ancestry within the last 25-23,000 years from earlier Siberian wolf populations. While some sources have suggested that this is the result of a population bottleneck, others suggest that this is a normal consequence of gene flow homogenising wolf genomes across their range.