Latest Findings: Warming Lakes Make Trout More Alike — and Ecosystems Less Resilient
Lake trout. Image courtesy of Eric Engbretson (USFWS).
As northern lakes heat up, Canada’s lake trout are losing their individuality — and with it, a key source of ecological resilience. A new study in Ecology led by Cassandra Kotsopoulos at the University of Guelph examined lake trout across 52 boreal lakes in Ontario in an attempt to answer the question: Do individuals within the same species change their feeding patterns in similar ways when the environment changes? Using chemical isotope analysis to trace diets, the researchers found that trout in warmer, smaller lakes feed in increasingly similar ways.
In cooler lakes, some trout specialize in deep-water prey while others forage near the shore, but as temperatures rise, they’re forced into the same cold, offshore zones. That diversity of behaviour disappears. This loss of intraspecific variation — the natural differences among individuals in a species — could make ecosystems less stable. Ecologist Dr. Kevin McCann, a co-author, likens it to an investment portfolio: “When individuals use different resources, it spreads ecological risk. If they all behave the same way, the whole population becomes vulnerable.”
Because lake trout link nearshore and deep-water food webs, their reduced flexibility can disrupt how energy and nutrients flow through lakes. The study suggests warming may not just stress cold-water fish directly, but also compress the ecological networks that depend on their diversity. As climate change continues to heat northern waters, large, cool lakes could become vital strongholds of resilience — places where individuality still helps ecosystems adapt to a changing world.
Kotsopoulos, Cassandra J., Marie Gutgesell, Matthew M. Guzzo, Thomas A. Johnston, Tyler D. Tunney, Timothy J. Bartley, Bailey C. McMeans, Kevin S. McCann, et al. (2025). Reduced intraspecific variation in lake trout food webs under warmer temperatures and smaller ecosystem sizes. Ecology 106(10): e70222.