Native species or invasive? The distinction blurs as the world warms
With species on the move as the climate changes, a growing number of scientists say that efforts must be made to help migrating species adapt to their new habitats.
This article was originally published on Yale e360.
Across the warming globe, a mass exodus of tens of thousands of species is transforming the distribution of biodiversity — and challenging fundamental tenets in conservation policy and science. Are policymakers, land managers and conservationists prepared?
In recent years, scientists have documented countless species shifting their ranges toward the poles, higher into the mountains and deeper into the seas in response to the changing climate. Deciduous shrubs of willow, birch and alder have spread into the low Arctic tundra. Brightly colored tropical parrotfish and rabbitfish have arrived in the temperate kelp forests of the eastern Mediterranean. Elkhorn corals from the Caribbean sprout in thickets off the coast of Galveston, Texas.
The trend is expected to continue as the climate crisis deepens, with species that societies rely upon for a wide range of economic, cultural and recreational value shifting their ranges to survive. "The entire trajectory of natural capital, from aesthetic to economic," says University of Florida wildlife ecologist Brett Scheffers, "is going to be moving."
For decades, conservation biology has characterized the movement of species into new habitats as potential invasions of alien species with the capacity to threaten local ecosystems and already resident species, leading to the formulation of policies to reflexively repel the newcomers. This approach, and its underlying classification of wild species as either "native" (and thus worthy of protections) or "alien" (and thus likely not) has been the subject of growing controversy in recent years.
Critics such as author Emma Marris and Macalester College biologist Mark Davis have pointed out that only a small subset of "alien" species wreak damage on already resident species, and that the categorization of wild creatures as either "native" or "alien" obscures as much as it elucidates. Indeed, the influential, albeit contested "tens rule" in invasion biology, validated in a range of species and locales, holds that only 10 percent of alien species establish themselves in new habitats and only 10 percent of those are likely to cause unwanted harm to economies, ecosystems or human health.
Scheffers — along with University of Tasmania marine ecologist Gretta Pecl, who recently convened an international conference on climate-driven range shifts — has proposed an international Climate Change Redistribution Treaty that would create a transnational system to manage species shifting across geopolitical and biogeographical borders. Such a treaty could transform the conservation agenda.
Populations that would not attract the attention of conservation managers working under traditional nationwide conservation systems, such as today’s healthy populations of quiver trees in South Africa, likely would be deemed worthy of monitoring under a transnational one, in which the quiver tree’s shrinking numbers in neighboring Namibia are taken into account. Newly arrived species that would be ignored as vagrants or condemned as unwanted aliens under traditional conservation approaches might be proactively monitored and managed so that they can establish self-sustaining populations, such as the tropical fish species arriving in the temperate waters of Tasmania, which have been protected with bag limits placed on anglers.