A cornerstone of biodiversity—ecosystem functioning (BEF) research is that species diversity, often as species richness, is an important determinant of ecosystem functions such as productivity. In contrast, allometric theory is generally agnostic to taxonomy, focusing rather on organism size as a driver of ecosystem process. Together, BEF and allometric frameworks represent complementary perspectives to understand the controls on patterns within and across ecosystem. For example, allometric theory predicts that organism abundance (N) should scale with organism mass (M) as, N~M^-1 in multitrophic food webs. However, variation around this prediction may be associated with species diversity due to the mechanisms highlighted by BEF research (e.g., niche complementarity). Here, we present a continental-scale overview of the connections between total assemblage diversity, biomass, and body size distributions in macroinvertebrate and fish food webs of the National Ecological Observatory Network (NEON) stream ecosystems. We compare the total abundance, mean body size, and standing stock biomass across NEON, to test the prediction that more diverse assemblages (i.e., higher species richness) will exhibit higher biomass for a given body size distribution. Initial analyses show that both total abundance and mean assemblage body size ranged ~3 orders of magnitude while species richness varies 2-fold. Total assemblage biomass showed no bivariate relationship with species richness. Accounting for mean assemblage body size, residual variation around a constant yield also showed little association with species diversity. We extend this analysis to relate key environmental variables, temperature and resource supply, in a structural equation model framework to disentangle the causal relationships among environmental drivers, species diversity, and the over/under-yielding of food web standing stock. Lastly, we will draw connections among multiple size-abundance relationships at varying levels of organization to enrich the understanding of the connections between ecosystem structure and function.