Experimental N and P additions alter stream macroinvertebrate community composition via taxon‐level responses to shifts in detrital resource stoichiometry

1. Increases in nitrogen (N) and phosphorus (P) availability are changing animal communities, partly by altering stoichiometric imbalances between consumers and their food. Testing relationships between resource stoichiometry and consumer assemblage structure requires ecosystem-level manipulations that have been lacking to date. 2. We analyzed patterns of macroinvertebrate community composition in five detritus-based headwater streams subject to experimental whole-stream N and P additions that spanned a steep gradient in dissolved N:P ratio (2:1, 8:1, 16:1, 32:1, 128:1) over two years, following a one-year pre-treatment period. 3. We predicted that shifts in leaf litter stoichiometry would drive overall patterns of community composition via greater responses of shredders to enrichment than other taxa, as shredders dominate primary consumer biomass and experience larger consumer-resource elemental imbalances than other functional groups in stream ecosystems. Specifically, we expected lit...