Species Community Structure and Functional Redundancy in Swedish Headwater Streams Local versus Regional Control

Streams and rivers only contain a small proportion of the Earth’s freshwater, but nevertheless harbour much biodiversity. Headwater streams are the most prevalent running water environments, but despite their wide distribution, they are often excluded from important freshwater legislation and national monitoring programmes. This thesis investigated biodiversity patterns of benthic macroinvertebrates and diatoms in headwater streams and the relative importance of local and regional control of community structure. Functional redundancy (i.e. the relative resilience) of a headwater catchment was also assessed. Alpha and beta diversity made significant contributions to the gamma diversity of the investigated headwaters. Local control of community structure peaked in first order streams and at small spatial extents. Also, biological predictors were able to detect additional local control of diatom assemblage structure. Regional control of community structure was less consistent, and depended on macroinvertebrate dispersal abilities and diatom growth form and size. System-specific spatial variables were also able to detect additional regional control of macroinvertebrate assemblage structure. Results indicated low functional redundancy, and that community structure within invertebrate functional feeding groups was, with a few exceptions, the result of both local and regional control. I conclude that we are likely to underestimate biological assets (including both alpha and beta diversity) if headwater streams are not included in bioassessment and management programmes. The conservation of this diversity is likely to be most effective when management targets environmental conditions across multiple local sites within relatively small catchments. However, as regional control was detected at both small and large spatial scales, it is important to manage regional conditions (e.g. landscape connectivity), in addition to local site conditions, irrespective of the scale targeted by management. This is especially important because conservation of headwater functions (in addition to biodiversity) is likely dependent on both. Finally, we can increase the accuracy and performance of predictive models by including additional local and regional predictors which are specific to the system and organism studied.