Invasive species often compete so successfully in new ecosystems that they displace native species and disrupt important ecosystem processes. For example, brook trout (Salvelinus fontinalis) are native to most of eastern North America, but they have become highly invasive to western rivers. In the Northern Rocky Mountains, nonnative brook trout are considered a significant contributor to the decline or extirpation of native cutthroat trout (Oncorhynchus clarkii) in headwater streams. Effects on aquatic systems produced by climate change suggest that large numbers of cool-water fishes and other kinds of invasive aquatic organisms (such as crayfish, mussels, and amphibians) will become issues. The RMRS Invasive Species Working Group published a Research Summary and Expertise Directory that describes the programs' research priorities and future direction in regards to strategically dealing with invasive species.