Climate change is restructuring ecosystems globally, yet its cumulative effect with biological invasions remains an underestimated problem. A recent study by researchers from Oregon State University shows the ways in which rising temperatures are not only diminishing the range of habitable territory for native organisms but also raising the competition and predation of non-native species. The combined danger, according to researchers, can cause local extinctions among sensitive native organisms.

The research, appearing in Global Change Biology, centers on the Pacific Northwest, where climate change already is changing freshwater ecosystems. Scientists discovered that with rising global temperatures, native and non-native fish species are being pushed into higher elevation habitats, where they encounter more competition and predation. The research tested the interaction among two invasive fish species—smallmouth bass and northern pike—and native salmonids, such as redband trout and bull trout.

Ivan Arismendi, a department associate professor in Oregon State's Department of Fisheries, Wildlife, and Conservation Sciences, pointed out the value of knowing these synergistic effects. "Climate change and invasions by non-native species are having more impact on ecosystems worldwide," Arismendi said. "It is essential to learn about their combined effects so we can predict and adjust management efforts that consider changing interactions between native and non-native species."

The research employed ecological niche models, computer programs that examine environmental data to forecast species' distributions in various climate scenarios. Researchers Guillermo Giannico and Arif Jan, along with Arismendi, created a framework to evaluate how shifting climate conditions affect ranges of habitats and species overlap.

Their conclusions are alarming. With increasing temperatures, the acceptable ranges for redband trout, bull trout, smallmouth bass, and northern pike will contract. The remaining available environments will migrate to higher altitudes, where colder water exists. But in doing so, native salmonids will be driven into habitats where invasive predators are also likely to succeed, thus new hotspots for species conflict will be established.

"Upstream cold water refuges will be sites where native and non-native fishes will converge," said Arif Jan, a doctoral candidate at Oregon State. "There have been previous studies demonstrating predatory behavior against salmonids by smallmouth bass and northern pike where habitat overlaps. This would imply possible year-round predation and competition stress on the early life stages of salmonids.

The impacts of these interactions may be severe. Invasive species such as northern pike are formidable predators that have been known to devastate native fish populations, and smallmouth bass have the ability to dramatically alter food webs by outcompeting native fish for food. The scientists worry that this heightened interaction may result in local extinctions of native salmonids, paralleling declines already seen in southeastern Alaska and elsewhere globally.

Recognition and mitigation of these changes will be vital for conservation. The findings of the study highlight the need for concerted management practices that account for both climate-induced habitat change and species interactions.

This research indicates the importance of management strategies for integrated approaches to both direct and indirect effects of species interactions," said Giannico, Oregon State professor of fisheries. "Our system is straightforward and inexpensive for setting priorities on habitats for the early detection and tracking of invasive species and their potential future effects on native species.

As climate change speeds ecosystem transitions, conservation must shift rapidly. The research presents a model that can be used outside the Pacific Northwest, informing researchers and policymakers about potential threats elsewhere and allowing them to anticipate and prepare to mitigate them. Conservationists might still be able to save native fish populations from an unknown future by actively monitoring threatened habitats and controlling invasive species.