Narr, C. F. | bioRxiv Science

bioRxiv2026

Shifts in consumer assemblages are linked to nutrient availability and ecosystem metabolism

Nutrient availability, ecosystem productivity, and consumer assemblages are intricately linked through complex interactions and feedbacks. Nutrients influence the diversity and functional roles of consumers via shifts in resource quality and quantity, and consumers can alter ecosystem production and nutrient availability. However, our understanding of how characteristics of consumers respond to and influence concomitant shifts in nutrient availability and production is limited. We quantified the response of well-studied consumer assemblages (benthic invertebrates and zooplankton) to realistic nutrient loads that altered gross primary production (GPP) and ecosystem respiration (ER). We fertilized 14 outdoor experimental ponds for 2 months and monitored total water column carbon (TC), nitrogen (TN), and phosphorus (TP), GPP, ER, and net ecosystem production (NEP) weekly. Then, we evaluated how fertilization and the variation in nutrients and metabolism caused by fertilization were related to shifts in consumer assemblages. Fertilization increased water column TN and TP and reduced TC:TP ratios, TN:TP ratios, and rates of GPP and ER. However, consumer assemblages were more tightly linked to variation in nutrient availability and production across ponds than to fertilization. Greater declines in benthic diversity occurred in ponds with higher average TN:TP ratios during the experiment. Consistent with predicted effects of cladocerans on nutrient availability, shifts in cladoceran abundances were positively associated with average water column TN:TP ratios during the experiment. Finally, elevated GPP and ER were associated with greater increases in the abundance of benthic invertebrate predators, suggesting the possibility of top-down control. Our study highlights the critical role of consumer-mediated processes in the interaction between nutrient availability and production. Manuscript HighlightsO_LIFertilization reduced pond gross primary production and ecosystem respiration rates. C_LIO_LIInvertebrate predator abundance was inversely related to gross primary production. C_LIO_LIShifts in consumer assemblages were tightly linked to nutrients and production. C_LI

ecology↗

bioRxiv2024

Measuring the Stoichiometry of Microbial Parasite Infrapopulations One Cell at a Time using Energy Dispersive Spectroscopy

O_LIProgress in the field of ecological stoichiometry has demonstrated that the outcome of ecological interactions can often be predicted a priori based on the nutrient ratios (e.g., carbon: nitrogen: phosphorus, C:N:P) of interacting organisms. However, the challenges of accurately measuring the nutrient content of active parasites within hosts has limited our ability to rigorously apply ecological stoichiometry to host-parasite systems. Traditional nutrient analyses require high parasite biomasses, often preventing individual-level analyses. This prevents researchers from estimating variation in the nutrient content of individual parasites within a single host infrapopulation, a critical factor that could define how the ecology of the parasite affects the host-parasite interaction. C_LIO_LIHere, we explain how energy dispersive technology, a technique currently used to measure the elemental content of free-living microbes, can be adapted for parasitic microbial infrapopulations. We demonstrate the power of accurately quantifying the biomass stoichiometry of individual microbial parasites sampled directly from individual hosts. C_LIO_LIUsing this approach we show that the stoichiometric composition of two microbial parasites capable of infecting the same host are stoichiometrically distinct and respond to host diet quality differently. We also demonstrate that characteristics of the stoichiometric trait distributions of these infrapopulations were important predictors of host fecundity, a proxy for virulence in this system, and better predictors of parasite load than the mean parasite stoichiometry or our parasite and diet treatments alone. C_LIO_LIEDS provides a rigorous tool for applying ecological stoichiometry to host-parasite systems and enables researchers to explore the nutritional physiology of host-parasite interactions at a scale that is more relevant to the ecology and evolution of the system than traditional nutrient analyses. Here we demonstrate that this level of resolution provides useful insights into the diet-dependent physiology of microbial parasites and their hosts. We anticipate that this improved level of resolution has the potential to elucidate a range of eco-evo interactions in host-parasite systems that were previously unobservable. C_LI

ecology↗