Intraspecific Variation and Ecosystem Function: Implications for more effective Post-Restoration Monitoring
The effectiveness of stream restoration is often measured by the recolonization of certain focal species. However, important information regarding intraspecific variation (e.g. size structure) of these species is often ignored. Recent research suggests that intraspecific variation such as body size can have profound effects on food web dynamics and ecosystem functioning. Specifically, intraspecific predator size variation has been posited as a major determinant of a species’ ability to control lower trophic levels and even has the potential to alter trophic cascade intensity. The importance of predator feeding strategy (e.g. omnivory) and changes with body size may also be an important factor controlling the pervasiveness of top-down control. Therefore, considering factors such as size structure and how these factors interact with feeding strategy will enable better restoration planning and better predictions post restoration. We sought to identify the effects of size and size structure on top-down control by omnivorous Speckled Dace, Rhinichthys osculus, and how these effects scaled with density. Within our study system, R. osculus inhabit small isolated beaver ponds, the conditions of which we replicated in 1000L cattle tanks. Size, size structure, and density of R. osculus were then manipulated within these tanks and resulting changes in invertebrate and algal communities were monitored over 8 weeks. Benthic algal biomass was significantly lower in the fishless control and lowest fish density treatment, indicating that R. osculus may have caused a trophic cascade that varied in intensity by treatment. Invertebrate samples are currently being processed and should provide insight into the specific pathways of this potential trophic cascade. Once completed, this research will contribute to a growing body of knowledge regarding the role of intraspecific variation in maintaining the full suite of complex interactions that constitute healthy ecosystems. Additionally, this research highlights the importance of considering density and size structure in designing and assessing stream restorations.