The Tasmanian devil, a unique marsupial found exclusively on the island of Tasmania, has earned its name from its fierce growls and stocky build. As the world’s largest carnivorous marsupial, this creature plays an important role in its ecosystem. Despite its robust appearance, the Tasmanian devil is currently listed as endangered. Its population has experienced a dramatic decline, with estimates indicating an 80% to 90% reduction in sightings since the mid-1990s.
Devil Facial Tumor Disease
The primary factor driving the Tasmanian devil’s decline is Devil Facial Tumor Disease (DFTD), a rare and aggressive transmissible cancer. This disease spreads through physical contact, primarily when devils bite each other during social interactions such as feeding or mating.
Once infected, devils develop visible tumors around their mouth and face. These tumors grow rapidly, hindering the animal’s ability to eat, which often leads to starvation. The disease is almost universally fatal, with infected devils typically succumbing within three to six months of the tumors appearing.
Two distinct strains of the disease have been identified: DFTD1 and DFTD2. DFTD1 is the older and more widespread strain, first described in 1996, and has impacted most of the devil population.
DFTD2, a more recently detected strain from around 2011, is currently confined to a smaller area in southern Tasmania. While both strains are contagious and fatal, they exhibit different cellular characteristics; DFTD1 avoids immune detection by not expressing certain immune system molecules, whereas DFTD2 cells do express these molecules but employ other evasion tactics.
Habitat Degradation and Fragmentation
Human activities significantly contribute to the challenges faced by Tasmanian devils through habitat degradation and fragmentation. Land clearing for agriculture, urban expansion, and forestry operations directly reduces the amount of natural habitat available to these animals. This loss makes it increasingly difficult for devils to find sufficient shelter, locate prey, and successfully breed.
Habitat fragmentation further exacerbates the issue by breaking up continuous natural areas into smaller, isolated patches. These isolated populations become more vulnerable to various threats and are less able to recover from disturbances, as gene flow and dispersal are restricted. With less interconnected habitat, devils struggle to move safely between areas, impacting their overall population health.
Bushfires, both naturally occurring and human-caused, also play a role in altering or destroying crucial devil habitats. These fires can significantly reduce the availability of food sources and suitable dens, leaving devils exposed and without resources. The aftermath of severe fires often leads to a decline in prey animals, further stressing the devil population.
A reduction in devil numbers due to habitat loss and fires can also create opportunities for invasive species, such as feral cats and foxes, to thrive. Tasmanian devils typically help suppress these introduced predators, so their absence can disrupt the ecosystem’s balance, potentially affecting other native wildlife.
Road Fatalities and Other Direct Threats
Road fatalities represent a substantial and immediate threat to individual Tasmanian devils. Devils are particularly susceptible to being hit by vehicles due to their natural behaviors. They are scavengers, frequently attracted to carrion on roads, which provides an easy meal.
Their predominantly nocturnal habits and poor night vision also increase their vulnerability to traffic collisions. Additionally, devils often use roads as convenient travel routes, especially during their nightly foraging journeys that can cover many kilometers. Their dark fur makes them difficult to see against the road surface, particularly in wet conditions, further increasing the risk of collisions.
The impact of roadkill can be significant, especially when breeding females are affected, potentially leading to the loss of several individuals, including pouch young. While road mortality is a major concern, other direct threats exist. These include accidental trapping, often in snares intended for other animals, and poisoning, which can occur from consuming poisoned baits targeting pests. Domestic dogs and foxes also pose a threat to devils in some areas.
Limited Genetic Diversity
The inherently limited genetic diversity within the Tasmanian devil population contributes to its vulnerability. Low genetic diversity means there is little variation in the genes across the devil population. This lack of genetic variation can weaken the species’ ability to adapt to new challenges, including diseases and environmental changes.
For instance, this low diversity means devils’ immune systems may struggle to recognize and fight off foreign cells, such as those of the Devil Facial Tumor Disease. The cancer cells passed from one devil to another are often genetically similar enough to the host’s own cells that the immune system does not mount a strong defense. This makes the population broadly susceptible to the disease.
The low genetic diversity is not a recent phenomenon; studies suggest it predates European settlement, likely stemming from historical population contractions and the isolation of Tasmania from mainland Australia. While historical bounty hunting further reduced their numbers in the 1800s, the species already possessed this limited genetic makeup. This inherent lack of genetic variation means there are fewer diverse traits that might naturally confer resistance to diseases or offer survival advantages in a changing environment.