Gardners and biologists often grumble about the ways non-native animals and plants have invaded a region, spoiling things for all the locals. Sometimes a non-native species can destroy an ecosystem — a common example is the introduction of rabbits to Australia, where they have no native predators. Sometimes, however, they are far more beneficial than local creatures like the mountain pine beetle, a native species that kills more trees than any other insect in North America.
Now scientists are calling for a dramatic change in the way we understand ecosystems. Whether a species is native shouldn't matter, they say. Instead, we should worry more about how a species interacts with its environment.
Governments and preservation groups have spent a great deal of money and time trying to rid environments of nonnative species on the presumption that these invaders will destroy the delicate balance of local ecosystems. But Macalester College biologist Mark Davis and an international group of 18 other environmental scientists argue in Nature this week that it is misguided to focus on eliminating invasive species. There has been so much intermixing of species between regions, and so many changes brought about by climate change, that dividing species into native and non-native is meaningless — and fruitless.
It's true that some nonnative species, like the zebra mussel, can be a nuisance. Yet most nonnative species are neutral, like the Devil's Claw plant (pictured above) and the beautiful flowering tamarisk. Others can actually be beneficial.
So if we don't work to eliminate non-native species, what will happen to nature? It will do what it does best: grow and change.
Write Davis and colleagues:
Most human and natural communities now consist both of long-term residents and of new arrivals, and ecosystems are emerging that never existed before. It is impractical to try to restore ecosystems to some ‘rightful' historical state. For example, of the 30 planned plant eradication efforts undertaken in the Galapagos Islands since 1996, only 4 have been successful. We must embrace the fact of ‘novel ecosystems' and incorporate many alien species into management plans, rather than try to achieve the often impossible goal of eradicating them or drastically reducing their abundance. Indeed, many of the species that people think of as native are actually alien. For instance, in the United States, the ring-necked pheasant, the state bird of South Dakota, is not native to the great plains of North America but was introduced from Asia as a game bird in the latter half of the nineteenth century.
Specifically, policy and management decisions must take into account the positive effects of many invaders. During the 1990s, the US Department of Agriculture (USDA) declared several species of introduced honeysuckles to be alien (harmful), and banned their sale in more than 25 states. Ironically, from the 1960s to the 1980s, the USDA had introduced many of these same species in land reclamation projects, and to improve bird habitats. Recent data suggest that the agency's initial instincts may have been appropriate. In Pennsylvania, more non-native honeysuckles mean more native bird species. Also the seed dispersal of native berry-producing plants is higher in places where non-native honeysuckles are most abundant.
There is something genuinely moving and beautiful about this statement. I love the idea of biologists welcoming "novel ecosystems" and incorporating alien species into their land management plans. The point is that we need to stop fetishizing the idea that nature is a single, static entity. It is always changing, mixing in new ways, and transforming what it means to be a native in the first place.
Bunny photo by Eric Isselée/Shutterstock; Devil's Claw photo by Mike Connealy