Our interest in invasion biology is primarily in its application, specifically to “restoration” projects. Therefore, as science revises the assumptions of invasion biology we are equally interested in the implications for ecological restorations.
Professor Scott Carroll (UC Davis) is a particularly good candidate to lead the way in revising ecological restoration practices, as informed by current scientific theories of invasion biology. His study of rapid evolution of the native soapberry bug to accommodate use of non-native vegetation puts him in the forefront of the effort to integrate evolutionary theory into invasion biology.
And so we introduce to our readers, Professor Carroll’s proposal that we turn from efforts to eradicate non-native species in favor of a new approach which manages the co-existence of native and non-native species. He calls this approach Conciliation Biology.*
Conciliation Biology is based on these premises:
- The environment has been radically altered by the activities of humans
- The environment will continue to change in the future.
- It is not feasible to eradicate non-native species.
- The cost of attempting to do so is prohibitive.
These are familiar themes on Million Trees and we will not belabor them in this post. Rather we will focus on those aspects of Professor Carroll’s proposal that are new to us.
Rapid evolution can resolve apparent ecological problems
Garlic mustard is an invasive non-native plant which tolerates shade and emits a powerful root toxin known to inhibit the germination of other plants, notably forest trees. This chemical tool to reduce competition is known as allelopathy, a weapon used by many plant species, both native and non-native.
Since garlic mustard arrived first in the eastern US and spread slowly west, scientists compared the allelopathic toxicity of a population of garlic mustard known to have arrived 50 or more years ago with a population which arrived only 10 years ago. The toxicity of the recently arrived garlic mustard was significantly greater than that of the older population. In fact, the understory and seedling germination were rebounding in the forest with the older population of garlic mustard.
In other words, science informs us that ecological problems caused by the arrival of new exotic species can resolve themselves over time.
New exotic species are sometimes better adapted to the changed environment
Professor Carroll cites a study of two aquatic species (Phragmite and Hydrilla) which provide superior ecological services than their native counterparts because of changes in the environment. The extreme weather events associated with climate change are subjecting our coasts to unprecedented storm surges. Native species of marsh grass are not as successful in protecting the coast against the ravages of these storm surges.
We have our own local example of the same phenomenon. Non-native Spartina marsh grass is being eradicated along the entire west coast of the country. It grows taller and thicker than native Spartina and it does not die back during the winter months as the native species does. Since storm surges occur during the winter months, surely the non-native Spartina provides superior protection to our coast. We have yet to see a scientific experiment which proves this point, but common sense tells us that it is a study that needs to be done, particularly since ornithologists have reported that the eradication of non-native Spartina has been harmful to our dwindling population of endangered California Clapper Rail.
The harmful effects of eradication efforts
We have seen many such harmful consequences of eradication efforts, but Professor Carroll provides his own example. Iberian rabbits are native to Spain. They were intentionally imported to Australia where they quickly became a problem. The Australians imported a virus from South America that killed the rabbits. The virus was also introduced to Britain for the same purpose. The virus has spread back to Spain where it is killing the rabbits in their native range. The rabbits are prey of several rare species of animals in Spain, including the Iberian lynx. The absence of their prey is now decimating those native predator populations as well.
Biological controls are one of many dangerous games being played by those who share in the fantasy that it is possible to eradicate non-native species without paying a price. Sometimes that price is greater than whatever cost may be associated with the non-native species.
Simply eradicating non-native species will not necessarily result in the return of natives
Professor Carroll tells us the story of the failed attempt to save the Large Blue butterfly in Britain from extinction to illustrate this point. This was apparently a spectacularly beautiful butterfly, and so the British spent 50 years trying to bring it back from extinction. They failed because they figured out too late that the butterfly is dependent upon an ant which lives only in heavily grazed vegetation. The ant population no longer existed within the range of the butterfly because grazing had long ago been abandoned.
How many other pointless efforts to reintroduce endangered species are there? We recently told our readers about the effort to reintroduce the endangered Mission Blue butterfly to Twin Peaks in San Francisco. This is a radically altered environment with high levels of nitrogen and carbon dioxide associated with the urban environment. The annual brush fires of pre-settlement San Francisco are no longer capable of sustaining the scrub required by the butterfly and the prescribed burns, which are the artificial equivalent, are not allowed in San Francisco. The scrub is therefore maintained with repeated applications of pesticides which are unlikely to benefit the endangered butterfly.
What is Conciliation Biology
Conservation biology has been “constrained by often futile efforts to restore historical communities, and [does] not appreciate the unavoidable and dynamic contributions of ongoing adaptive evolution.” * Conciliation biology proposes to address these shortcomings by:
- Taking a longer-term view of the chronic effects of changes in the environment.
- Making greater use of evolutionary theory
- Fostering ongoing adaptation by accepting the hybridization that increases genetic variability
- Identifying and supporting community mechanisms that increase resiliency
- Improving the effectiveness of the science of invasion biology by using a multidisciplinary approach
How long will It take for this new approach to filter into the minds of those who are busily destroying non-native vegetation and damaging the environment in the process? How much damage will be done before these destructive methods are abandoned in favor of an approach that accommodates the reality, inevitability, and often the advantages of change?
*Carroll, Scott, “Conciliation biology: the eco-evolutionary management of permanently invaded biotic systems,” Evolutionary Applications, 2011, 184-199.