Stoichiometric relationships between consumers and resources in detritus‐based ecosystems have received little attention, despite the importance of detritus in most food webs. We analysed carbon (C), nitrogen (N), and phosphorus (P) content of invertebrate consumers, and basal food resources in two forested headwater streams (one reference and the other nutrient‐enriched). We found large elemental imbalances between consumers and food resources compared with living plant‐based systems, particularly in regard to P content, which were reduced with enrichment. Enrichment significantly increased nutrient content of food resources (consistent with uptake of N and P by detritus‐associated microbes). P content of some invertebrates also increased in the enriched vs. reference stream, suggesting deviation from strict homeostasis. Nutrient content varied significantly among invertebrate functional feeding groups, orders and, to some extent, size classes. Future application of stoichiometric theory to detritus‐based systems should consider the potential for relatively large consumer‐resource elemental imbalances and P storage by insect consumers.

Inadequate supply of one or more mineral elements can slow the growth of animal consumers and alter their physiology, life history and behaviour. A key concept for understanding nutrient deficiency in animals is the threshold elemental ratio (TER), at which growth limitation switches from one element to another. We used a stoichiometric model that coupled animal bioenergetics and body elemental composition to estimate TER of carbon and phosphorus (TER(C:P)) for 41 aquatic consumer taxa. We found a wide range in TER(C:P) (77-3086, ratio by atoms), which was generated by interspecific differences in body C : P ratios and gross growth efficiencies of C. TER(C:P) also varied among aquatic invertebrates having different feeding strategies, such that detritivores had significantly higher threshold ratios than grazers and predators. The higher TER(C:P) in detritivores resulted not only from lower gross growth efficiencies of carbon but also reflected lower body P content in these consumers. Supporting previous stoichiometric theory, we found TER(C:P) to be negatively correlated with the maximum growth rate of invertebrate consumers. By coupling bioenergetics and stoichiometry, this analysis revealed strong linkages among the physiology, ecology and evolution of nutritional demands for animal growth.

Summary 1. Ecological stoichiometry deals with the mass balance of multiple key elements [e.g. carbon (C), nitrogen (N), phosphorus (P)] in ecological systems. This conceptual framework, largely developed in the pelagic zone of lakes, has been successfully applied to topics ranging from population dynamics to biogeochemical cycling. More recently, an explicit stoichiometric approach has also been used in many other environments, including freshwater benthic ecosystems. 2. Description of elemental patterns among benthic resources and consumers provides a useful starting point for understanding causes of variation and stoichiometric imbalance in feeding interactions. Although there is considerable overlap among categories, terrestrially‐derived resources, such as wood, leaf litter and green leaves have substantially higher C : nutrient ratios than other resources of both terrestrial and aquatic origin, such as periphyton and fine particulate organic matter. The elemental composition of these resources for benthic consumers is modulated by a range of factors and processes, including nutrient availability and ratios, particle size and microbial colonisation. 3. Among consumers in benthic systems, bacteria are the most nutrient‐rich, followed (in descending order) by fishes, invertebrate predators, invertebrate primary consumers, and fungi. Differences in consumer C : nutrient ratios appear to be related to broad‐scale phylogenetic differences which determine body size, growth rate and resource allocation to structural body constituents (e.g. P‐rich bone). 4. Benthic consumers can influence the stoichiometry of dissolved nutrients and basal resources in multiple ways. Direct consumption alters the stoichiometry of food resources by increasing nutrient availability (e.g. reduced boundary layer thickness on substrata) or through removal of nutrient‐rich patches (e.g. selective feeding on fungal patches within leaf litter). In addition, consumers alter the stoichiometry of resources and dissolved nutrient pools through the return of egested or excreted nutrients. In some cases, consumer excretion supplies a large proportion of the nutrients required by algae and heterotrophic microbes and alters elemental ratios of dissolved nutrient pools. 5. Organic matter decomposition in benthic systems is accompanied by significant changes in the elemental composition of organic matter. Microbial colonisation of leaf litter influences C : nutrient ratios, and patterns of microbial succession (e.g. fungi followed by bacteria) may be under some degree of stoichiometric control. Large elemental imbalances exist between particulate organic matter and detritivores, which is likely to constrain growth rates and invertebrate secondary production. Such imbalances may therefore select for behavioural and other strategies for dealing with them. Comminution of large particles by benthic consumers alters detrital C : nutrient ratios and can influence the stoichiometry of elemental export from whole catchments. 6. A stoichiometric framework is l...

Temperature and nutrient availability play key roles in controlling the pathways and rates at which energy and materials move through ecosystems. These factors have also changed dramatically on Earth over the past century as human activities have intensified. Although significant effort has been devoted to understanding the role of temperature and nutrients in isolation, less is known about how these two factors interact to influence ecological processes. Recent advances in ecological stoichiometry and metabolic ecology provide a useful framework for making progress in this area, but conceptual synthesis and review are needed to help catalyze additional research. Here, we examine known and potential interactions between temperature and nutrients from a variety of physiological, community, and ecosystem perspectives. We first review patterns at the level of the individual, focusing on four traits--growth, respiration, body size, and elemental content--that should theoretically govern how temperature and nutrients interact to influence higher levels of biological organization. We next explore the interactive effects of temperature and nutrients on populations, communities, and food webs by synthesizing information related to community size spectra, biomass distributions, and elemental composition. We use metabolic theory to make predictions about how population-level secondary production should respond to interactions between temperature and resource supply, setting up qualitative predictions about the flows of energy and materials through metazoan food webs. Last, we examine how temperature-nutrient interactions influence processes at the whole-ecosystem level, focusing on apparent vs. intrinsic activation energies of ecosystem processes, how to represent temperature-nutrient interactions in ecosystem models, and patterns with respect to nutrient uptake and organic matter decomposition. We conclude that a better understanding of interactions between temperature and nutrients will be critical for developing realistic predictions about ecological responses to multiple, simultaneous drivers of global change, including climate warming and elevated nutrient supply.