Cooperative Fish and Wildlife Research Units Program: Nebraska
Education, Research and Technical Assistance for Managing Our Natural Resources

The distribution of functional traits within and across spatiotemporal scales has been used to quantify and infer the relative resilience across ecosystems. In this study, we use explicit spatial modeling to evaluate the adequacy of within-and cross-scale patterns as surrogates of resilience in headwater streams, an ecosystem type with hierarchical and dendritic network structure. We assessed the cross-scale distribution of functional feeding groups of benthic invertebrates in Swedish headwater streams during two seasons. We evaluated functional metrics (Shannon diversity, species richness, and evenness) and the degree of redundancy within and across modeled spatial scales for individual feeding groups. We also estimated the correlates of environmental vs spatial factors of both functional composition and the taxonomic composition of functional groups for each spatial scale identified. Measures of functional diversity and within-scale redundancy of functions were similar during both seasons, but both within- and cross-scale redundancy were low, suggesting an apparent low relative resilience of the stream network. This apparent low resilience was partly due to a few dominant taxa explaining the spatial models. Two findings derive from our study. First, both environmental and spatial factors can correlate with the scale-specific functional and taxonomic composition, suggesting that resilience in stream networks emerges as a function of both local conditions and regional factors (habitat connectivity and invertebrate dispersal). Second, quantifying within- and cross-scale patterns may underestimate resilience, limiting their use as surrogates of overall resilience in streams. Rare taxa with stochastic spatial distributions might provide additional information and will need to be considered explicitly for complementing resilience assessments.