The Tasmanian devil (Sarcophilus harrisii) is a species of mammal whose only wild population is native to the isolated island of Tasmania, off the coast of Australia. Tasmanian devils have a very low level of genetic diversity across the entire species. Researchers hypothesize this lack of diversity is the result of several genetic bottlenecks in the species’ history. In 1996 a new disease called devil facial tumor disease (DFTDDFTD) appeared in the wild Tasmanian devil population. DFTDDFTD can spread from one animal to another and causes the death of most affected animals. The impact of DFTDDFTD on the Tasmanian devil population has resulted in a decrease in the total population of more than 85% over the last two decades. (a) Describe the process that maintained a stable Tasmanian devil population size before the appearance of DFTDDFTD in 1996. (b) Explain how the huge reduction of the Tasmanian devil population since 1996 affects the susceptibility of the current population to new diseases in comparison with the susceptibility of the population before 1996. (c) Tasmanian devils are top predators and are considered a keystone species in their community. Predict the effect of the rapid reduction of the Tasmanian devil population on the rest of the community. (d) Justify the prediction of Part c

The Tasmanian devil (Sarcophilus harrisii) is a carnivorous marsupial of the family Dasyuridae. Until recently, it was only found on the island state of Tasmania, but it has now been reintroduced to New South Wales in mainland Australia, with a small breeding population.[3] The size of a small dog, the Tasmanian devil became the largest carnivorous marsupial in the world, following the extinction of the thylacine in 1936. It is related to quolls, and distantly related to the thylacine. It is characterised by its stocky and muscular build, black fur, pungent odour, extremely loud and disturbing screech, keen sense of smell, and ferocity when feeding. The Tasmanian devil's large head and neck allow it to generate among the strongest bites per unit body mass of any extant predatory land mammal. It hunts prey and scavenges on carrion.

Although devils are usually solitary, they sometimes eat and defecate together in a communal location. Unlike most other dasyurids, the devil thermoregulates effectively, and is active during the middle of the day without overheating. Despite its rotund appearance, it is capable of surprising speed and endurance, and can climb trees and swim across rivers. Devils are not monogamous. Males fight one another for females, and guard their partners to prevent female infidelity. Females can ovulate three times in as many weeks during the mating season, and 80% of two-year-old females are seen to be pregnant during the annual mating season.

Females average four breeding seasons in their life, and give birth to 20 to 30 live young after three weeks' gestation. The newborn are pink, lack fur, have indistinct facial features, and weigh around 0.20 g (0.0071 oz) at birth. As there are only four nipples in the pouch, competition is fierce, and few newborns survive. The young grow rapidly, and are ejected from the pouch after around 100 days, weighing roughly 200 g (7.1 oz). The young become independent after around nine months.

It is believed that ancient marsupials migrated across Gondwana tens of millions of years ago, and that they evolved as Australia became more arid. Fossils of species similar to modern devils have been found, but it is not known whether devils are descended from these species or co-existed with them. It is unclear when Tasmanian devils became locally extinct from the Australian mainland; most evidence suggests they had contracted to three relict populations around 3000 years ago. A tooth found in Augusta, Western Australia, has been dated to 430 years ago, but archaeologist Oliver Brown disputes this and considers the devil's mainland extinction to have occurred around 3000 years ago.[4] This disappearance is blamed on climate change, a population increase in humans and the introduction of the dingo, the latter of which is absent from Tasmania.[5][6]

In 1941, devils became officially protected, and since then, scientists have contended that earlier concerns over the threat to livestock were overestimated and misplaced. Since the late 1990s, the devil facial tumour disease (DFTD) has drastically reduced the population and now threatens the survival of the species, which in 2008 was declared to be endangered. Programs undertaken by the Government of Tasmania to reduce the impact of the disease include an initiative to build up a group of healthy devils in captivity, isolated from the disease. Localised populations of devils have also been severely reduced by collisions with motor vehicles, particularly when they are eating roadkill.

The devil is an iconic symbol of Tasmania and many organisations, groups and products associated with the state use the animal in their logos. It is seen as an important attractor of tourists to Tasmania and has come to worldwide attention through the Looney Tunes character of the same name. Starting in 2013, Tasmanian devils are again being sent to zoos around the world as part of the Australian government's Save the Tasmanian Devil Program.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).