Invasive species undergoes mysterious change as it dominates Australia
The difference was noted in new research led by the University of Adelaide's Associate Professor Emma Sherratt, which studied the body sizes of 912 rabbits from around the world.
'We found Australian feral rabbits are quite a lot larger than European rabbits. We intend to find out why,' she said.
It's hypothesised the changes could be due to "relaxed functional demands" on rabbits in Australia, because they face fewer threats from large predators.
Physical developments have been observed in other feral animals released in Australia which give them an ecological advantage over native wildlife.
In 2023, the Invasive Species Council noted that cane toads are changing in size and appearance as they adapt to different regions in Australia.
As they expand west through Kakadu and into the Kimberly, cane toads at the edge of the "invasion front" have longer legs than those following them, allowing them to conquer new territory quickly.
When you exclude the direct impact of humans, feral animals are responsible for more extinctions than anything else in Australia. Researchers are desperately working to give native species an edge by either genetically engineering them to avoid disease, or protecting them within dedicated sanctuaries.
Native marsupials like the greater bilby once occupied up to 80 per cent of Australia's mainland. For thousands of years, throughout the night people would have seen the land teeming with the tiny creatures.
Since European settlement, small marsupial numbers have dwindled, and conservationists have turned to protecting them inside fenced reserves. At the same time, feral rabbit numbers have exploded from an estimated 13 in 1859, to 200 million today, and scars from their warrens can be seen across the landscape.
Meanwhile fewer than 10,000 greater bilbies survive.
The researchers also examined rabbit skull shapes because changes in appearance indicate how they interact with their environment and what they feed on.
'Understanding how animals change when they become feral and invade new habitats helps us to predict what effect other invasive animals will have on our environment, and how we may mitigate their success,' Sherratt said.
The work also included comparing the physical differences between rabbits that were raised for meat and fur, with wild animals. They found domesticated rabbit populations often didn't revert to their wild form after they were released into the environment.
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'While you might expect that a feral animal would revert to body types seen in wild populations, we found that feral rabbits' body size and skull-shape range is somewhere between wild and domestic rabbits, but also overlaps with them in large parts,' Sherratt said.
'Because the range is so variable and sometimes like neither wild nor domestic, feralisation in rabbits is not morphologically predictable if extrapolated from the wild or the domestic stock.'
The research was published in the journal Proceedings of the Royal Society.
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