9632427 McIntosh This research will improve understanding of the influence of predators on stream communities. Predators often change the foraging behavior of their prey, because prey avoid dangerous situations. In Rocky Mountain streams trout feed on aquatic insects, such as mayfly larvae. In trout streams, mayflies avoid trout predation by foraging and moving mainly at night, when these visual predators are unable to see them. Thus, avoidance of trout restricts the amount of time that mayflies can spend foraging. Large predatory stoneflies also feed on mayflies and confrontations with stoneflies also disrupt mayfly foraging. Thus, both trout and stoneflies reduce the amount of food that mayflies are able to consume. Since mayflies eat algae, this reduction in grazing may also affect the distribution and abundance of algae when predators are present. Through observations and experiments conducted in natural streams and in stream-side channels, this research will measure the effects of trout and stoneflies on mayfly and algal distribution and abundance. It will also determine whether trout and stoneflies affect how mayflies respond to patchy distributions of their algal resources, and whether trout change the distribution of algae by modifying mayfly or stonefly behavior. Finally, data from these experiments will be used in a simulation model to predict how prey movement under different predator regimes affects algal patches over time. This work builds on a long-term data base from 20 years of research in Colorado streams. It will provide a more detailed understanding of how trout, aquatic insects, and algae function in balanced communities of pristine systems. This information will be useful in preserving the biotic integrity of those systems, and restoring the biotic integrity of more disturbed streams.
