A black swan is a beauty to behold. It is used often as a metaphor for rare events that have a massive impact and invalidate common thinking; for example, a single swan with black plumage invalidates the premise that all swans are white. This metaphor was popularized by Nicholas Nassein Taleb who, instead of dismissing such events because of their rarity, argued that they result in the most long-term of changes, such as scientific discoveries and historic events. Photo by Dick Daniels.

Black swans and the detection of ecological collapse

The motivation Black swan events are surprising, unexplainable occurrences that happen without prior notice and usually wreak havoc on society. We are most familiar with the black swan events of banking collapses, devastating earthquakes, and other major surprises in financial, social, and natural systems. But what about black swan events in ecological systems? Until now, no one has taken a good look at the prevalence and causes of such events in the biosphere.

The discovery – Animal populations fluctuate from year to year. In a recent study, the Dulvy Group at Simon Fraser University and collaborators from the University of Washington surveyed these oscillations, specifically focusing on extreme crashes and outbreaks.  The team discovered that drastic changes in population sizes occurred in about four percent of the animals they reviewed, most commonly in birds. Usually, these black swan events were population crashes, and they tended to be driven by external factors, such as parasites, severe winters, predators, or climate. And furthermore, most of these external factors will likely become more extreme under climate change.

Its significance – Like banking crashes, ecological black swan events have profound consequences for people. The collapse of Atlantic Cod populations in the 1990s – due to overfishing – resulted in massive unemployment, out-migration, and the loss of the main income source for 24,400 fishers and factory workers in 400 coastal communities. The ramifications were felt by all Canadians, through the diversion of tax revenues to provide income assistance totaling more than $3 billion. While rare, these extreme ecological events have profound effects. The lead author of this study – Sean Anderson – is working to develop new fisheries forecasts that anticipate and account for black swan events.

Read the paper“Black-swan events in animal populations” by Anderson SC, Branch TA, Cooper AB, Dulvy NK. Proc. Natl. Acad. Sci. U.S.A. 114: 3252-3257 (2017). DOI: 10.1073/pnas.1611525114.

Website article compiled by Jacqueline Watson with Theresa Kitos