Four Burning Questions for Anthony Ricciardi, invasive species biologist
Anthony Ricciardi is an Associate Professor in the Redpath Museum and the Associate Director of Research in the McGill School of Environment. For the past 20 years, his research has examined the causes and consequences of the spread of alien species, and he teaches an undergraduate course on this subject (BIOL/ENVR 540 “Ecology of Species Invasions”). He coordinated, and spoke at, the recent McGill School of Environment Symposium, “Canada’s Environmental Future”, where invited experts presented their research findings and opinions concerning some major environmental problems likely to burden our country in the coming decades. Ricciardi’s presentation framed biological invasions as an issue of national security.
What is a biological invasion, and what causes it?
A biological invasion occurs when an organism (a plant, animal, or microbe) is introduced and establishes a population in a region where it did not exist historically. We refer to such organisms as ‘non-native’, ‘non-indigenous’, ‘exotic’, or ‘alien’. If the species spreads aggressively, or causes negative impacts, some people also refer to it as ‘invasive’.
Biological invasions have occurred throughout the history of life on Earth. Using natural mechanisms of dispersal, species can expand their ranges – but normally over short (intra-continental) spatial scales.
Then what, if anything, is special about biological invasions occurring today?
Under human influence, species are moving faster and farther than ever before. Even Antarctica – once considered remote and pristine – has been invaded by nearly two hundred alien species. Modern rates of invasion are tens of thousands of times higher than in the distant past. Whereas, in prehistoric times, mass invasions occurred only episodically (such as when two continents became connected by a land bridge), now the entire planet is swarming with species carried across great distances by human transportation mechanisms.
For example, ships plying the world’s oceans are loaded with literally millions of aquatic organisms in the water filling their ballast tanks, which can be discharged at a more distant port. On any given day, ships are likely transporting several thousands of species in this way. International tourists carry species in the form of fungal spores, plant seeds, and invertebrate eggs on their shoes and clothing. Moreover, several thousands of species are being moved intentionally between continents to be sold alive through the ornamental plant trade, the pet trade, and food markets. The bottom line is that enormous numbers of species are being introduced by humans to all but the remotest regions of the planet. This is an unprecedented form of global change.
So why should we be concerned?
Although many alien species do not appear to be harmful, and some are even desirable, the impacts of the vast majority of invasions are unknown. However, there is a large growing number of cases demonstrating that invasions can cause ecological disruptions that affect native biodiversity, the normal functioning of ecosystems, natural resources (including crops, forests, fisheries, water quality), and even human health.
Canada has experienced an increasing number of biological invasions in recent decades. At this moment, a virus (“Viral Hemorrhagic Septicemia”) is causing mass die-offs of fish in the Great Lakes, the world’s largest freshwater fishery; the virus is one of over 180 alien species that have invaded the region over the past two centuries. The Great Lakes remain at risk of further invasion by species such as Asian carp. Meanwhile, shellfish farms on P.E.I. are being smothered by ‘sea squirts’ – gelatinous invertebrates that foul aquaculture equipment and commercially important species. Off the coast of Nova Scotia, a Japanese seaweed is wiping out native kelp. Invasive beetles are killing trees in Ontario, Alberta and Nova Scotia; one of these, the Emerald Ash Borer, has expanded into Quebec. On the prairies, farmers are battling a weed called leafy spurge, which is toxic to cattle. City-dwellers there are also witnessing the western spread of Dutch elm disease. This is but a small number of examples of a phenomenon that growing as a consequence of globalization.
Unfortunately, we have little knowledge of how much damage these invasions are causing in terms of direct economic costs and the loss of ecosystem services. One published study estimated a projected cost to Canada of $13 billion per year for only a dozen well-documented species – a small fraction of the >1400 alien species that are known to have become established in this country. On a global scale, the annual cost may be as high as $1.4 trillion dollars, or 5% of the world’s economy.
Some intentionally introduced species have been beneficial, at least to some stakeholders; but even those species (e.g. European honey bees) are threatened by other introduced organisms. I suspect that we are experiencing a general erosion of ecosystem services as a result of the accumulating number of invasion threats. For example, several million North American bats have been killed in recent years by a European fungus that causes a fatal disease called “White Nose Syndrome”. Given their capacity to control pest insects (a single colony of 100 bats can consume over a million insects per year!), the loss of these insectivores could result in billions of dollars of damage to agriculture. An even more worrisome example is the potential global spread of a wheat-killing fungus (“Ug99”) that has emerged out of central Africa and can destroy entire grain fields.
So what can be done about this huge problem?
Based on the examples I have given, it is clear that we should be treating biological invasions as a national security issue. Countries such as New Zealand, Australia and South Africa have dedicated government agencies to handle “biosecurity” – the coordinated risk assessment and management of new invasive threats. I can think of no reason why Canada should not be giving this issue equally serious attention. We should identify and control emerging vectors and pathways of invasion, especially those that are unregulated, such as the “live trade” in species for the pet and food industries. We also need to work with other countries to create international monitoring networks to function as early-warning systems for high-risk invaders and to facilitate rapid information exchange.
Finally, we must develop better risk assessment methods for identifying and prioritizing high-risk invaders. This is a major goal for my lab; my students and I have aimed to develop a predictive understanding of the impacts of invasions, by using field and lab experiments to examine their highly contingent nature. We belong to a national research group (the Canadian Aquatic Invasive Species Network) that is assessing the risk of invasion to our inland and coastal waters. And recently, we have begun to collaborate with European colleagues to conduct experiments on the same invaders across a range of ecosystem types on both sides of the Atlantic, in order to gain more insight on the factors that contribute to variation in impact. Invasions pose a critical challenge for environmental scientists and managers, particularly as climate change, international trade, and human travel continue to alter the vulnerability of Canada’s landscape to this stressor. Clearly, we need to become more creative in our research efforts to meet this challenge.