In Trout Lake, the rusty crayfish has slowly dispersed around the shoreline and is now found around the entire lake. As they dispersed, most rooted aquatic plants sequentially disappeared, two other related species of crayfish declined in abundance, and other changes in bottom living invertebrates and some fishes occurred. Secondly, the mechanisms of change are determined. Predation was so intense as the numbers of smelt increased that virtually none of the cisco survived their first summer. In Crystal Lake, the invading smelt and the native yellow perch had extensive overlap in what they ate and where they lived.
Crystal Lake is oligotrophic and little production of food occurs in the upper waters.
As the smelt became super abundant, competition for limited food resources caused the greatly reduced growth of larval and adult perch and the lack of survival of young perch through their first summer. So the mechanism is food competition between smelt and perch. In Trout Lake, the invading rusty crayfish became super abundant. They are omnivores that can eliminate their preferred food while they maintain their large population on alternate prey. First to go were the most vulnerable of the rooted aquatic plants, followed by some of the more vulnerable bottom-living invertebrates, and fish eggs which they also eat.