Serial killers and giant hogweed would seem to have little in common. But new research by British scientists suggests an investigative tool that helps the police find criminals can also help locate the sources of invasive species.
The research, published last week in Ecography, may reverberate beyond conservation biology and criminology. In a week when National Science Foundation officials are pushing for more interdisciplinary research, the paper indirectly suggests the benefits of seeking collaborators from other disciplines. Indeed, the tool, known as geographic profiling, has also been used to find patterns in the foraging of animals and the spread of infectious disease.
Invasive species are generally regarded as the second largest cause of biodiversity loss, right after habitat destruction. In Africa, researchers have estimated 200 fish species were lost in Lake Victoria after the introduction of the Nile perch. Invasive species can have few predators to keep them in check, and can quickly establish dense populations that outcompete similar species for food.
Developing an understanding of invasive species, like much other biological research, has tended to focus on simulation models that run forward in time rather than working backward, says Steven C. Le Comber, a lecturer in biology and chemistry at Queen Mary, University of London, who led the research team that published the Ecography paper.
“There are sophisticated mathematical models on how things spread, but little work on where things come from,” said Le Comber in a telephone interview. “It’s a practical question to ask.”
In criminology, geographic profiling does not provide a magic pointer to the homes of those who have conducted multiple crimes. But it can help the police to set priorities, based on the probability of where a criminal may live. To see if geographic profiling would work on invasive species, Le Comber and colleagues used a series of computer simulations to compare it with other mathematical methods.
The researchers also applied geographic profiling to historical data on 53 species that have invaded Britain: daddy-long-legs spiders, Pacific oysters, Norway spruce trees, and giant hogweed, a noxious weed that can grow up to a dozen feet high and can cause blistering and blindness. The researchers found geographic profiling to have a strong advantage over the other methods.
In criminology, geographic profiling has two basic features: One is that the probability of a crime decreases with distance from the criminal’s “anchor point,” generally a home or office. The other feature is the existence of a “buffer zone” of lower activity around the criminal’s base. The zone is set partly by the rules of plane geometry and partly by the fact that criminals avoid activity near their homes, for fear of being discovered.
Invasive species, of course, have no such fear. But the pattern of their spread still has similar mathematical properties to criminal-activity patterns, says Le Comber. That is because the farther the invasive species are from their source, the more opportunities they have to prosper. And in some species, the buffer zone has even more specific reasons: Trees from seeds that fall in the shade of the trees’ parents are not apt to do as well as the seeds that make it out into sunnier places.
In future research, Le Comber would like to “tidy up the math” in geographic profiling. And he would like to make sure that the method is put to work, perhaps by developing a Web interface that conservationists could dump their data into to find the homes of criminal species.