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Death is a common outcome of infection, but most disease models do not track hosts after death. Instead, these hosts disappear into a void. This assumption lacks critical realism, because dead hosts can alter host–pathogen dynamics. Here, we develop a theoretical framework of carbon-based models combining disease and ecosystem perspectives to investigate the consequences of feedbacks between living and dead hosts on disease dynamics and carbon cycling. Because autotrophs (i.e. plants and phytoplankton) are critical regulators of carbon cycling, we developed general model structures and parameter combinations to broadly reflect disease of autotrophic hosts across ecosystems. Analytical model solutions highlight the importance of disease–ecosystem coupling. For example, decomposition rates of dead hosts mediate pathogen spread, and carbon flux between live and dead biomass pools are sensitive to pathogen effects on host growth and death rates. Variation in dynamics arising from biologically realistic parameter combinations largely fell along a single gradient from slow to fast carbon turnover rates, and models predicted higher disease impacts in fast turnover systems (e.g. lakes and oceans) than slow turnover systems (e.g. boreal forests). Our results demonstrate that a unified framework, including the effects of pathogens on carbon cycling, provides novel hypotheses and insights at the nexus of disease and ecosystem ecology.

Recent studies have documented global declines in insects and their relatives, but the exact mechanisms explaining these patterns are not fully understood. A potential driver underlying arthropod population declines are increases in anthropogenic inputs of nitrogen (N) and phosphorus (P). Here, we synthesize the effects of N, P, and combined N+P enrichment on the abundance of hexapods (insects and collembola) and arachnids from 901 experiments reported in 84 studies. We found that N and combined N+P enrichment caused significant decreases in the abundance of these groups overall. While arthropod responses to nutrient enrichment across aquatic and terrestrial habitats and in temperate as well as tropical climatic zones differed in magnitude, our results suggest that arthropods are decreasing similarly in response to nitrogen and phosphorus enrichment. Further, despite previously shown differences in the nutrient demands of different insect metamorphosis groups, we found consistent negative effects of N+P enrichment on all groups. Our results also showed that the negative effects of nutrient additions are stronger for aquatic insects that are considered more sensitive to changes in physical-chemical parameters in their environments, Ephemeroptera, Plecoptera, and Trichoptera (EPT), compared to other aquatic insects. In addition, N+P enrichment reduced the abundance of above- and below-ground arthropods, suggesting a similar mechanism driving arthropod community change is acting on both groups. These findings suggest that changes in elemental cycles are a potential cause of the ongoing global decline of arthropods and underscore the serious effects of nutrient enrichment on ecological systems. This article is protected by copyright. All rights reserved.

Human-driven changes in nitrogen (N) and phosphorus (P) inputs are modifying biogeochemical cycles and the trophic state of many habitats worldwide. These alterations are predicted to continue to increase, with the potential for a wide range of impacts on invertebrates, key players in ecosystem-level processes. Here, we present a meta-analysis of 1679 cases from 207 studies reporting the effects of N, P, and combined N + P enrichment on the abundance, biomass, and richness of aquatic and terrestrial invertebrates. Nitrogen and phosphorus additions decreased invertebrate abundance in terrestrial and aquatic ecosystems, with stronger impacts under combined N + P additions. Likewise, N and N + P additions had stronger negative impacts on the abundance of tropical than temperate invertebrates. Overall, the effects of nutrient enrichment did not differ significantly among major invertebrate taxonomic groups, suggesting that changes in biogeochemical cycles are a pervasive threat to invertebrate populations across ecosystems. The effects of N and P additions differed significantly among invertebrate trophic groups but N + P addition had a consistent negative effect on invertebrates. Nutrient additions had weaker or inconclusive impacts on invertebrate biomass and richness, possibly due to the low number of case studies for these community responses. Our findings suggest that N and P enrichment affect invertebrate community structure mainly by decreasing invertebrate abundance, and these effects are dependent on the habitat and trophic identity of the invertebrates. These results highlight the important effects of human-driven nutrient enrichment on ecological systems and suggest a potential driver for the global invertebrate decline documented in recent years.

Autotrophs play an essential role in the cycling of carbon and nutrients, yet disease-ecosystem relationships are often overlooked in these dynamics. Importantly, the availability of elemental nutrients like nitrogen and phosphorus impacts infectious disease in autotrophs, and disease can induce reciprocal effects on ecosystem nutrient dynamics. Relationships linking infectious disease with ecosystem nutrient dynamics are bidirectional, though the interdependence of these processes has received little attention. We introduce disease-mediated nutrient dynamics (DND) as a framework to describe the multiple, concurrent pathways linking elemental cycles with infectious disease. We illustrate the impact of disease–ecosystem feedback loops on both disease and ecosystem nutrient dynamics using a simple mathematical model, combining approaches from classical ecological (logistic and Droop growth) and epidemiological (susceptible and infected compartments) theory. Our model incorporates the effects of nutrient availability on the growth rates of susceptible and infected autotroph hosts and tracks the return of nutrients to the environment following host death. While focused on autotroph hosts here, the DND framework is generalizable to higher trophic levels. Our results illustrate the surprisingly complex dynamics of host populations, infection patterns, and ecosystem nutrient cycling that can arise from even a relatively simple feedback between disease and nutrients. Feedback loops in disease-mediated nutrient dynamics arise via effects of infection and nutrient supply on host stoichiometry and population size. Our model illustrates how host growth rate, defense, and tissue chemistry can impact the dynamics of disease–ecosystem relationships. We use the model to motivate a review of empirical examples from autotroph–pathogen systems in aquatic and terrestrial environments, demonstrating the key role of nutrient–disease and disease–nutrient relationships in real systems. By assessing existing evidence and uncovering data gaps and apparent mismatches between model predictions and the dynamics of empirical systems, we highlight priorities for future research intended to narrow the persistent disciplinary gap between disease and ecosystem ecology. Future empirical and theoretical work explicitly examining the dynamic linkages between disease and ecosystem ecology will inform fundamental understanding for each discipline and will better position the field of ecology to predict the dynamics of disease and elemental cycles in the context of global change.

An overlooked effect of ecosystem eutrophication is the potential to alter disease dynamics in primary producers, inducing disease‐mediated feedbacks that alter net primary productivity and elemental recycling. Models in disease ecology rarely track organisms past death, yet death from infection can alter important ecosystem processes including elemental recycling rates and nutrient supply to living hosts. In contrast, models in ecosystem ecology rarely track disease dynamics, yet elemental nutrient pools (e.g. nitrogen, phosphorus) can regulate important disease processes including pathogen reproduction and transmission. Thus, both disease and ecosystem ecology stand to grow as fields by exploring questions that arise at their intersection. However, we currently lack a framework explicitly linking these disciplines. We developed a stoichiometric model using elemental currencies to track primary producer biomass (carbon) in vegetation and soil pools, and to track prevalence and the basic reproduction number (R0) of a directly transmitted pathogen. This model, parameterised for a deciduous forest, demonstrates that anthropogenic nutrient supply can interact with disease to qualitatively alter both ecosystem and disease dynamics. Using this element‐focused approach, we identify knowledge gaps and generate predictions about the impact of anthropogenic nutrient supply rates on infectious disease and feedbacks to ecosystem carbon and nutrient cycling.

Temperature dependency of consumer–resource interactions is fundamentally important for understanding and predicting the responses of food webs to climate change. Previous studies have shown temperature‐driven shifts in herbivore consumption rates and resource preference, but these effects remain poorly understood for predatory arthropods. Here, we investigate how predator killing rates, prey mass consumption, and macronutrient intake respond to increased temperatures using a laboratory and a field reciprocal transplant experiment. Ectothermic predators, wolf spiders (Pardosa sp.), in the lab experiment, were exposed to increased temperatures and different prey macronutrient content (high lipid/low protein and low lipid/high protein) to assess changes in their killing rates and nutritional demands. Additionally, we investigate prey mass and lipid consumption by spiders under contrasting temperatures, along an elevation gradient. We used a field reciprocal transplant experiment between low (420 masl; 26°C) and high (2,100 masl; 15°C) elevations in the Ecuadorian Andes, using wild populations of two common orb‐weaver spider species (Leucauge sp. and Cyclosa sp.) present along the elevation gradient. We found that killing rates of wolf spiders increased with warmer temperatures but were not significantly affected by prey macronutrient content, although spiders consumed significantly more lipids from lipid‐rich prey. The field reciprocal transplant experiment showed no consistent predator responses to changes in temperature along the elevational gradient. Transplanting Cyclosa sp. spiders to low‐ or high‐elevation sites did not affect their prey mass or lipid consumption rate, whereas Leucauge sp. individuals increased prey mass consumption when transplanted from the high to the low warm elevation. Our findings show that increases in temperature intensify predator killing rates, prey consumption, and lipid intake, but the responses to temperature vary between species, which may be a result of species‐specific differences in their hunting behavior and sensitivity to temperature., An important issue in ecological theory is to understand how increased temperatures will affect trophic interactions and food web dynamics. Our study provides an important step towards understanding the consequences of rising temperatures and changes in prey macronutrient content on predator killing rates and prey macronutrient consumption.

SUMMARY 1. In many aquatic ecosystems, detritus is the main basal resource and is able to support highly productive food webs. However, detritus is a relatively poor-quality resource compared with living plants. Despite substantial research on how the nutrient content of living plants limits herbivores, there is little information on whether the nitrogen (N) and/or phosphorus (P) content of plant detritus similarly limits detritivore performance, especially under natural conditions. 2. We examined this question by rearing larval chironomids and caddisflies within detrital-based tank-bromeliad ecosystems on different food qualities. We manipulated detrital nutrient content by increasing N and P simultaneously or separately. 3. Chironomids and caddisflies showed faster growth rates when they fed on enriched detritus. Both N and P contents of the detritus limited the growth of chironomids, but combined effects were antagonistic (i.e. growth rates were less than expected according to single additions of N or P). By contrast, the growth of caddisflies was greater when fed on N-rich detritus, but was unaffected by P enrichment. These results suggest that under natural conditions, chironomids and caddisflies show reduced growth rates because they face strong nutrient limitation. 4. We also found that increased growth rates were correlated with an increase in the body P content of chironomids and caddisflies, which is consistent with the growth rate hypothesis. This hypothesis predicts that high body P content permits the rapid ribosomal RNA production needed for high growth rates. This study therefore provides some of the first direct evidence for the growth rate hypothesis in detrital systems. Although detritus quality was an important factor determining the growth of detritivores, it had no effect on the survival of these insects. 5. Our study highlights the importance of N and P additions as well as their interaction in constraining the growth of different consumers. Our findings point to the need for future studies integrating organism life history traits and ecological stoichiometry to better understand how food quality affects the functioning of detritus-based ecosystems.

Several mechanisms for biological invasions have been proposed, yet to date there is no common framework that can broadly explain patterns of invasion success among ecosystems with different resource availabilities. Ecological stoichiometry (ES) is the study of the balance of energy and elements in ecological interactions. This framework uses a multi-nutrient approach to mass-balance models, linking the biochemical composition of organisms to their growth and reproduction, which consequently influences ecosystem structure and functioning. We proposed a conceptual model that integrates hypotheses of biological invasions within a framework structured by fundamental principles of ES. We then performed meta-analyses to compare the growth and production performances of native and invasive organisms under low- and high-nutrient conditions in terrestrial and aquatic ecosystems. Growth and production rates of invasive organisms (plants and invertebrates) under both low- and high-nutrient availability were generally larger than those of natives. Nevertheless, native plants outperformed invasives in aquatic ecosystems under low-nutrient conditions. We suggest several distinct stoichiometry-based mechanisms to explain invasion success in low- versus high-nutrient conditions; low-nutrient conditions: higher resource-use efficiency (RUE; C:nutrient ratios), threshold elemental ratios (TERs), and trait plasticity (e.g. ability of an organism to change its nutrient requirements in response to varying nutrient environmental supply); high-nutrient conditions: higher growth rates and reproductive output related to lower tissue C:nutrient ratios, and increased trait plasticity. Interactions of mechanisms may also yield synergistic effects, whereby nutrient enrichment and enemy release have a disproportionate effect on invasion success. To that end, ES provides a framework that can help explain how chemical elements and energy constrain key physiological and ecological processes, which can ultimately determine the success of invasive organisms.