DOI: 10.5061/dryad.f8qm2d7
title: Data from: Experimental N and P additions alter stream macroinvertebrate community composition via taxon‐level responses to shifts in detrital resource stoichiometry

description: 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 litter
 C:P to be a significant predictor of shredder biomass given the greater
 relative imbalances between shredder and litter C:P than C:N. Finally, we
 tested whether shredder responses to enrichment were related to other
 taxon-level traits, including body size and stoichiometry, larval lifespan
 and growth rate. 4. Whole-community composition shifted similarly across
 the five streams after enrichment, largely driven by increased shredder
 and predator biomass. These shifts were limited to the autumn/winter
 seasons and related to decreased leaf litter C:P, highlighting important
 links between the quality of seasonal litter subsidies and community
 phenology. 5. Among 10 taxa that drove structural shifts, two declined
 while other taxa from the same functional/taxonomic groups responded
 positively, suggesting that specific life-history traits may determine
 sensitivity to enrichment. 6. Increases in total shredder biomass, and in
 biomass of several common shredders, were associated with lower litter
 C:P. Body C:P did not predict shredder response to enrichment. However,
 weak negative relationships between shredder response and body size, and
 larval lifespan, suggest that small-bodied and short-lived taxa may be
 more responsive to shifting resource stoichiometry. 7. Moderate
 anthropogenic increases in N and P availability affect resource
 stoichiometry and can alter animal communities, influencing additional
 food-web and ecosystem properties. We provide support for ecological
 stoichiometry as a framework for predicting such outcomes based on changes
 in the elemental composition of resource pools.
description: Bg_byAnnualAnnual invertebrate biomass, by genus (or lowest practical taxonomic unit)Bg_bySeasonSeasonal (autumn/winter and spring/summer) macroinvertebrate biomass, by genus (or lowest practical taxonomic unit)Factors_byAnnualEnvironmental data (DIN, SRP, leaf litter biomass and stoichiometry); annual means.Factors_bySeasonEnvironmental data (DIN, SRP, leaf litter biomass and stoichiometry); seasonal (autumn/winter and spring/summer) means.