For more than a century and a half, researchers interested in invasive species have looked to Charles Darwin and what has come to be called his “naturalisation conundrum.” If an invader is closely related to species in a new area, he wrote in his landmark “The Origin of Species,” it should find a more welcoming habitat. On the other hand, it could expect to compete with the related species and be vulnerable to its natural enemies. Or as Michael Renton, plant biologist at University of Western Australia, explained Darwin’s theory: “If the species is more distantly related to species within the community, it will be more likely to be invasive, because it will have different natural enemies.”
Species vs. details
But a paper that is published online on 2 December in the Proceedings of the National Academy of Sciences says the relatedness of new and established species is not as important as the details of how they go about doing their business.
Jones started pondering Darwin’s conundrum while a post-doctoral researcher in the Washington State University lab of Richard Gomulkiewicz.
Darwin’s logic doesn’t pan out
“Darwin put out a lot of interesting ideas back in the day but he didn’t have the means to check them with rigour,” says Gomulkiewicz, co-author and a professor in WSU’s School of Biological Sciences. “That’s what we did with our mathematical model, and we found that Darwin’s logic on this issue doesn’t quite pan out.”
The model Jones and her colleagues have developed in analysing Darwin’s conundrum could lead to a new way of gauging the potential of invasive species, a major ecological and economic concern as plants and animals have spread into new habitats around the planet.
Genetics alone a weak predictor
Darwin focused on phylogeny, species’ relatedness or genetic similarity. But the research team focused on species’ phenotypes, characteristics that emerge as a plant or animal’s genes interact with the environment. In the process, they found that genetic relationships alone are a weak predictor of an invaders success.
To be sure, says Jones, researchers will want to see what species an invader is related to and what interactions that species has that are important for understanding its survival. But then, she says, “you’d want to look at how those interactions depend on traits and affect births and deaths in the invading species.”
So, the new research suggests degree of relationship is not the most important factor, but the invading species’ interaction with its new environment. William Feeney, PhD candidate at Australian National University, said: “It’s suggesting that these things may be more complicated than we have given them credit for. Basically it’s showing that the evolutionary history of the interactions between species in a population could affect the likelihood of that population being successfully invaded by a new species. If there’s a lot of competition between species in a population, an invasive species could be at a disadvantage upon arrival and not do too well, compared to an ecosystem with less competition.”