European rabbits, Oryctolagus cuniculus, are a plague on the inland deserts of southern Australia. Settlers brought them over back in the 1800s, and the rabbits multiplied (as they’re wont to do) until they numbered in the billions. They ate up young plants, destroyed ecosystems, and contributed to the extinction of small native mammals. That is, until 1995, when the Rabbit Haemorrhagic Disease Virus (RHDV) was unintentionally released, and their numbers plummeted by as much as 95 percent in arid regions. This also reduced the populations of feral cats and red foxes, two predators that were also introduced. And that’s when threatened native mammals finally began to recover. The findings are published in Conservation Biology this month.
Due to a combination of factors ranging from introduced non-native species to land-use, Australia now has the planet’s worst modern record of mammal extinctions: Ten percent of species have been lost, and 43 percent of all terrestrial species are at least “near threatened.” RHDV, a naturally occurring pathogen of rabbits, was identified as a potential biological control agent, and pre-release trials were conducted offshore on an island in South Australia. But the virus escaped containment in September of 1995 and spread throughout the southern Australian mainland.
To study the response of four native species to the spread of RHDV, a team led by Reece Pedler from South Australia’s Department of Environment, Water and Natural Resources compiled decades’ worth of small mammal and rainfall records from various reports and databases for a 615,000-square-kilometer (237,000-square-mile) study site in northeastern arid inland South Australia. This included three rodents – the dusky hopping-mouse (Notomys fuscus), spinifex hopping-mouse (Notomys alexis), and plains mouse (Pseudomys australis) – and a marsupial micro-predator called the crest-tailed mulgara (Dasycercus cristicauda).
They found that all four small mammals – three of which were listed as “vulnerable” – substantially increased the extent of their occurrences and the area of their occupancy following the RHDV outbreak. And that’s despite low rainfall during the first 14 years after RHDV spread and rabbit numbers crashed.
The dusky hopping-mouse and plains mouse increased their extent of occurrence by 241 to 365 percent, and the crest-tailed mulgara saw a 70-fold increase in its extent of occurrence and a 20-fold increase in its area of occupancy. The small rodents likely benefited from the reduced competition for plants and seeds and also from the protection provided by increased vegetation cover. Additionally, the drop in cats and foxes (which preyed mostly on the rabbits) helped the recovery of not just the small rodents, but also the marsupial micro-predator.