McGill scientists find invasive species affect lake ecosystems

October 07, 1999

McGill University scientists have documented profound changes in lake ecosystems following the introduction of two exotic species, smallmouth bass and rock bass, into Canadian lakes. What's more, these changes may threaten native fish populations, particularly lake trout. In an upcoming article to be published in the prestigious journal Nature, Jake Vander Zanden and Joseph Rasmussen, together with a colleague from the Ontario Ministry of Natural Resources, John Casselman, report that when bass are introduced into lakes, they prey aggressively on smaller fish, forcing lake trout to shift to energetically-poor foods such as invertebrates. "Bass consume many of the food organisms that the lake trout depend on and greatly reduce their abundance," explains Rasmussen.

"Human dominance over the Earth's ecosystems has been accompanied by the widespread introduction of exotic species, which has led to the extinction of native species, the collapse of native fisheries and the loss of ecological integrity and ecosystem functioning," write the authors in Nature. "Ecologists are far from being able to predict, detect or measure the ecological impacts of species invasions. This is not surprising because natural food webs are variable and complex."

Whether the bass are introduced intentionally to stimulate the local economy by enhancing fish stocks or whether they are introduced inadvertently by dumping unused live bait, the consequences on the "food-web dynamic" i.e. the relationship between plants, animals and fish life around Canadian lakes, may be dramatic. "We have to be much more sensitive to the potential impact of invasive predators," say Vander Zanden and Rasmussen. "Predicting the impact of species invasions and other perturbations in natural food webs presents a formidable challenge to ecology. If we want to understand and measure what happens to the environment when we tamper with it, we need more broad-scale, systemwide ecological approaches."

The biologists describe traditional methods for examining the impact of species invasions as laborious, difficulty and costly, and it has been a priority of the Rasmussen Lab at McGill to develop and apply stable isotope techniques to the study of environmental problems. These techniques are based on naturally occurring tracers and can identify pathways of energy flow efficiently and inexpensively. In this study, such techniques were applied to quantify the food-web consequences of recent invasions of bass in Canadian lakes. In their field sampling, Rasmussen and his colleagues believe they've developed a very sensitive indicator of environmental change.

McGill University

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