This project explores the relationship between environmental heterogeneity in streams and the effect of herbivory on the ecosystem processes of algal accrual and removal. Spatial heterogeneity plays an important role in most, if not all ecosystems; however, few empirical investigations have explicitly examined how environmental heterogeneity influences ecological processes via its affect on species interactions. By addressing how heterogeneity in near-bed current regulates algal accrual through its influence on producer-consumer dynamics, this project will make an important contribution to community ecology in general and stream ecology in particular. Because stream flows are being altered worldwide to meet human needs there exists a pressing need for ecologists to provide society with an understanding of what flows are necessary to prevent species loss and allow streams to provide essential ecosystem services. By exploring the relationship between stream flow, heterogeneity, and herbivory, this project provides a basis for understanding the relationship between stream discharge and function; by examining how stream flow and heterogeneity influence species contributions to stream function, it provides a basis for understanding the causes and consequences of species loss. Ultimately, the project has the potential to provide resource managers with a process-based measure for establishing minimum stream flows.
Stream flows are being altered worldwide to meet human demands and there exists a pressing need for ecologists to provide society with an understanding of what flows are necessary to maintain aquatic habitats, prevent species loss, and allow streams to provide essential ecosystem services. By exploring the relationship between stream discharge and species interactions in streams, my project provides a basis for understanding the relationship between stream flow and function. More specifically, my project has examined how discharge influences stream current and the ability of the organisms that inhabit different current velocities to feed, survive and reproduce. I found that as discharge is reduced, current velocity not only slows, it becomes less varied across the streambed. This affects the ability of stream insects such as mayfly and stonefly nymphs -- important food for trout and other stream fish -- to feed effectively and to perform ecological functions such as algal removal. As current decreases and becomes more homogeneous, for example, some mayflies become less effective at feeding on and removing streambed algae. In fact, Mayflies feeding under conditions of very low flow actually facilitate the growth and accumulation of streambed algae, which has implications not only for the appearance of the stream, but its ability to sustain diverse communities or organisms. Thus, by examining how stream flow and heterogeneity influence stream function, my research provides a basis for understanding the causes and consequences of species loss and has the potential to provide resource managers with a process-based measure for establishing minimum stream flows.
