Invasions of the ecosystem

Invasions of the ecosystem

Sylvain Comeau | We live in a biological global village, according to Anthony Ricciardi, and the results can sometimes be disastrous.

	Professor Anthony Ricciardi PHOTO: Owen Egan

"Today you hear a lot about globalization, how economies and societies are mixing more than ever before. But there's another, more insidious form of globalization taking place. Wherever we travel and transport merchandise, we transport other species with us -- animals, plants, viruses and bacteria are being rapidly shuttled from continent to continent. We are living in a virtually borderless world, and that's what I call the biological global village."

Ricciardi is an assistant professor of biodiversity with joint appointments at the Redpath Museum and the McGill School of Environment. He is one of a growing number of researchers who study the phenomenon of invasion ecology, which is the study of the causes and consequences of biological invasions -- the introduction and spread of a species into a region outside its natural range.

These invasions are usually not successful, but occasionally a new, aggressive species ends up dominating or threatening other species, and the ecological integrity of its new environment.

People usually do not think about the fact that it is almost inevitable that they will carry some species with them when they travel or transport material.

"The question is whether this species is already present in the region in which they are moving. If it isn't, it could become established.

"People are travelling across the planet more than ever before, so there is more opportunity for things to jump continents. But even more important than that is trade; with the explosion of global trade, the number of documented ecological invasions is increasing exponentially over time."

These kinds of invasions can be a direct threat to many species -- including humans.

"There are numerous recent examples in Canada. The West Nile virus was first detected in Canada in the year 2000. At this moment, a Japanese seaweed is replacing valuable kelp beds along the coast of Nova Scotia, and a European beetle is killing spruce trees in Halifax, and could spread throughout the continent unless it's eradicated. In the Great Lakes, a voracious water flea which is native to the Black Sea is competing with larval fish for planktonic food, and could have a strong impact on a multibillion-dollar fishery. And [these examples] are just the tip of the iceberg."

Ricciardi points out that most newly introduced species have little or no effect on their new habitats. Some may even have a positive impact. But the sheer number of new species means that a few will become serious threats.

"My goal is to find ways to predict which species introductions are likely to succeed and which are likely to cause significant changes to the ecosystem," says Ricciardi.

While most invasions are unintentionally caused by commerce or travel, intentional, planned introductions of species from one part of the world to another can also go awry.

"There have been cases in which species of fish were introduced in the U.S. to control weeds in lakes. Well, they end up escaping the lakes and forming large populations in areas where they weren't intended, and chewing up weeds that are used as nursery habitats for other fish. The result was declining populations.

"The important point is that the law of unintended consequences reigns supreme in invasions; there are many examples of disasters in which species were introduced intentionally."

Ricciardi hopes that his efforts, and those of a growing number of researchers in this relatively new field, will educate people on the inherent dangers.

"Disasters like this occur in part because people don't understand the biology of invasive species. That is, species don't act the same way in a new environment as they did in their native habitat. You can't expect them to act the way you anticipated, based on how they performed in the habitat where they evolved.

"In their native habitat, there are co-evolved predators, pathogens and parasites that keep these species in check. In a new habitat, there may be a population explosion, because the only thing keeping them in check is the available food supply, until something else adapts to them."

Ricciardi is developing statistical models for predicting aquatic invasions, which is his sub-specialty.

"My goal is to find ways to predict which aquatic invasions are likely to succeed, and which of the successful ones are likely to cause significant changes to ecosystems." Questions he wants to tackle include "why some ecosystems are more invaded than others, why some species cause more problems than others, and whether we can predict them.

"I'm optimistic that we can, by tying together information from a large number of separate invasions."

The key is to look at invasions as a trend, in which past invasions offer clues as to what will happen in the future.

"For a long time, scientists have treated invasions as isolated ecological events, but I believe we can take the information from multiple invasions and discern predictable patterns from them. By doing that, we can establish generalizations; we can learn, for example, that if you introduce a predator into an environment, it will more likely cause damage than a detritivore -- a species that feeds on detritus.

"That's an easy example, but there are more-complicated ones, and I believe that we can tease out these patterns if we look at large data sets."

To that end, Ricciardi is developing a data base which will be a resource for other researchers, and will provide the information for the statistical models he is developing. He intends to make his results available on the web.

Ricciardi joined McGill last year from Dalhousie University, where he was a postdoctoral fellow. He has applied for NSERC funding to pursue the project; he is currently being funded by McGill. He expects to enlist graduate students to help him, and is launching a course based on his research.

He has published in the Canadian Journal of Fisheries and Aquatic Sciences, the Journal of Animal Ecology, and Bioscience, among others.