In 1859 an Australian farmer named Thomas Austin released 24 grey rabbits from Europe into the wild because it "could do little harm and might provide a touch of home, in addition to a spot of hunting."
By the end of the century, the rabbits had begun to overrun native ecosystems, reaching nationwide numbers of 600 million by 1950. They were propagating under a principle known as the Allee effect - the observation that larger groups of animals do better at establishing populations in a new environment. Had Austin instead spread the rabbits into many smaller groups across the landscape, things might have turned out differently.
With the help of E. coli and some clever synthetic biology techniques, engineers at Duke University have now tested the limits of the Allee effect. The results have implications for both ecologists dealing with invasive species and medical practitioners fighting infections.
Organisms exhibiting a very strong Allee effect need a certain number of individuals to survive, below which the group will collapse. And while intuition suggests that the more places a species spreads, the more it will thrive, scattering a population too thin by forming too many new colonies could result in the ruin of them all.
The paper appears online in the Proceedings of the National Academy of Sciences the week of Jan. 20.
"From the perspective of an invasive species, it appears to be a good idea to spread out to many different habitats simultaneously," said Lingchong You, associate professor of biomedical engineering at Duke. "If they all survive, the overall growth is much more efficient. But there's a catch because of the Allee effect; there is also a greater chance each population will fall below the critical threshold and every location will fail."
"This can offer insights for people managing invasive species," continued You. "If you limit the number of targets that an invasive species can travel into, you might inadvertently help them thrive."