The implementation of Wastewater Treatment Plants (WWTPs) brought great improvement in river ecological status. However, WWTP effluents still contain a complex cocktail of pollutants whose environmental effects might go unnoticed, masked by other stressors in the receiving waters or by spatiotemporal variability. We conducted a BACI (Before-After/Control-Impact) ecosystem manipulation experiment to assess the effects of a well-treated and highly diluted effluent on diversity and food web dynamics in an unpolluted stream. Although effluent toxicity was low, it reduced diversity, increased primary production and herbivory, and reduced energy fluxes associated to terrestrial inputs. Altogether, the effluent decreased total energy fluxes in stream food webs, showing that treated wastewater can lead to important ecosystem-level changes, affecting the structure and functioning of stream communities even at high dilution rates. Our study highlights the need for further efforts to treat polluted waters to conserve aquatic food webs.

Increasing human pressures threaten fish diversity, with potentially severe but unknown consequences to the functioning of riverine food webs. Using a 17-years dataset from multi-trophic fish communities, we investigated the long-term effects of human pressure (represented by human footprint) on the species richness and energy flux across fish food webs, a measure of ecosystem functioning. Combining metabolic scaling theory and ecological network principles, we calculate the annual energy flux through varying trophic compartments (i.e., top-carnivore, mesocarnivore, detritivore, and omnivore). Species richness across all trophic compartments was positively associated with energy flux. However, species richness decreased over time, alongside with the energy flux at the whole-network level, which reduced by 75%. Human pressure negatively affected both species richness and energy flux, and the negative impacts of human pressure have intensified over time. These results illustrate how human pressure can reduce diversity and erode the energy flux through food webs, with long-term negative implications for the functioning of natural ecosystems

The relationship of plant diversity and several ecosystem functions strengthens over time. This suggests that the restructuring of biotic interactions in the process of a community’s assembly and the associated changes in function differ between species-rich and species-poor communities. An important component of these changes is the feedback between plant and soil community history. In this study, we examined the interactive effects of plant richness and community history on the trophic functions of the soil fauna community. We hypothesized that experimental removal of either soil or plant community history would diminish the positive effects of plant richness on the multitrophic functions of the soil food-web, compared to mature communities. We tested this hypothesis in a long-term grassland biodiversity experiment by comparing plots across three treatments (without plant history, without plant and soil history, controls with ~20 years of plot specific community history). We found that the relationship between plant richness and belowground multitrophic functionality is indeed stronger in communities with shared plant and soil community history. Our findings indicate that anthropogenic disturbance can impact the functioning of the soil community through the loss of plant species but also by preventing feedbacks that develop in the process of community assembly.

Plant community productivity generally increases with biodiversity, but the strength of this relationship exhibits strong empirical variation. In meta-food-web simulations, we addressed if the spatial overlap in plants' resource access and movement of animals can explain such variability. We found that spatial overlap of plant resource access is a prerequisite for positive diversity-productivity relationships, but causes exploitative competition that can lead to competitive exclusion. Movement of herbivores causes apparent competition among plants, resulting in negative relationships. However, movement of larger top predators integrates sub-food-webs composed of smaller species, offsetting the negative effects of exploitative and apparent competition and leading to strongly positive diversity-productivity relationships. Overall, our results show that spatial overlap of plant resource access and animal movement can greatly alter the strength and sign of such relationships. In particular, the scaling of animal movement effects opens new perspectives for linking landscape processes without effects on biodiversity to productivity patterns.

1.     Species-rich communities exhibit higher levels of ecosystem functioning compared to species-poor ones, and this positive relationship strengthens over time. One proposed explanation for this phenomenon is the reduction of niche overlap among plants or animals, which corresponds to increased complementarity and reduced competition. 2.     In order to examine the potential of increased complementarity among plants or animals to strengthen the relationship between diversity and ecosystem functions, we integrated models of bio-energetic population dynamics and food-web assembly. Through the simulation of various scenarios of plant and animal complementarity change, we sought to elucidate the mechanisms underlying the observed increases in (1) primary productivity, (2) control of herbivores by predators, and (3) reduction of herbivore pressure on plants in species-rich communities.3.     Our findings reveal that increased niche complementarity of plants can steepen the diversity-function relationships if it does not increase their intraspecific competition, while increasing complementarity among animals during community assembly can also have a positive effect but with considerable variability. 4.     The study highlights the importance of trait variation both among and within species, and the interplay between intra- and interspecific competition strength in shaping the functioning of ecosystems over time. These results offer insights into the mechanisms underpinning the diversity-functioning relationship, and have practical implications for ecosystem management and conservation efforts.

The survival of animals under global warming strongly depends on their individual thermal niches, which result from the balance between energy loss and gain. Active movement is an important component of this energetic balance, as it affects not only energy gain via food intake but also energy loss via activity metabolism. Here, we develop a novel trait-based approach for how thermal niches arise from temperature-dependent movement. Therefore, we used image-based tracking to quantify the unimodal responses of the movement speed of carabid beetles to temperature. We used these empirical data to parameterize a mathematical model based on metabolic and predator-prey theory for net energy gain to derive a general mechanistic concept of thermal niches. This trait-based approach allows a relatively rapid and cost-effective assessment of climate change vulnerability for a wide range of animal taxa on broad geographic scales.

Global change alters ecological communities with consequences for ecosystem processes. Such processes and functions are a central aspect of ecological research and vital to understanding and mitigating the consequences of global change, but also those of other drivers of change in organism communities. In this context, the concept of energy flux through trophic networks integrates food-web theory and biodiversity-ecosystem functioning theory and connects biodiversity to multitrophic ecosystem functioning. As such, the energy flux approach is a strikingly effective tool to answer central questions in ecology and global-change research. This might seem straight forward, given that the theoretical background and software to efficiently calculate energy flux are readily available. However, the implementation of such calculations is not always straight forward, especially for those who are new to the topic and not familiar with concepts central to this line of research, such as food-web theory or metabolic theory. To facilitate wider use of energy flux in ecological research, we thus provide a guide to adopting energy-flux calculations for people new to the method, struggling with its implementation, or simply looking for background reading, important resources, and standard solutions to the problems everyone faces when starting to quantify energy fluxes for their community data. First, we introduce energy flux and its use in community and ecosystem ecology. Then, we provide a comprehensive explanation of the single steps towards calculating energy flux for community data. Finally, we discuss remaining challenges and exciting research frontiers for future energy-flux research.

Resource-use complementarity of producer species is often invoked to explain their generally positive diversity-productivity relationships. Additionally, multi-trophic interactions that link processes across trophic levels have received increasing attention as a possible key driver. Given that both are integral to natural ecosystems, their interactive effect should be evident but has remained hidden. We address this issue by analyzing diversity-productivity relationships in a simulation experiment of primary producer communities nested within complex food-webs, manipulating resource-use complementarity and multi-trophic animal richness. We show that both mechanisms' joint contribution to positive diversity-productivity relationships generally exceeds their individual effects, as both interactively create diverse communities of complementary producer species. Specifically, multi-trophic interactions in animal-rich ecosystems increase complementarity the most when resource-use complementarity is low. The interdependence of top-down and bottom-up forces in creating biodiversity-productivity relationships highlights the importance to adopt a more multi-trophic perspective on biodiversity-ecosystem functioning relationships.

Global change drivers like warming and changing nutrient cycles have a substantial impact on ecosystem functioning. In most modelling studies, organism responses to warming are described through the temperature dependence of their biological rates. In nature, however, organisms are more than their biological rates. Plants are flexible in their elemental composition (stoichiometry) and respond to variance in nutrient availability and temperature. An increase in plant carbon-to-nutrient content means a decrease in food quality for herbivores. Herbivores can react to this decrease by compensatory feeding, which implies higher feeding rates and higher carbon excretion to optimize nutrient acquisition. In a novel model of a nutrient-plant-herbivore system, we explored the consequences of flexible stoichiometry and compensatory feeding for plant and herbivore biomass production and survival across gradients in temperature and nutrient availability. We found that flexible stoichiometry increases plant and herbivore biomasses, which results from increased food availability due to higher plant growth. Surprisingly, compensatory feeding decreased plant and herbivore biomasses as overfeeding by the herbivore reduced plants to low densities and depleted their resource. Across a temperature gradient, compensatory feeding caused herbivore extinction at a lower temperature, while flexible stoichiometry increased its extinction threshold. Our results suggest that compensatory feeding can become critical under warm conditions. In contrast, flexible stoichiometry is beneficial for plants up to a certain temperature threshold. These findings demonstrate the importance of accounting for adaptive and behavioural organismal responses to nutrient and temperature gradients when predicting the consequences of warming and eutrophication for population dynamics and survival.

Most studies of plant--animal mutualistic networks have been temporally static. This approach has revealed many general patterns in the structure of complex webs of mutualistic interactions, but limits our ability to understand the ecological and evolutionary processes that shape these networks, and to predict the consequences of natural and human-driven disturbance on species interactions. The growing availability of temporally explicit data is allowing ecologists to move beyond this static perspective. We review the growing literature dealing with temporal dynamics in plant--animal mutualistic networks including pollination, seed dispersal and ant defence mutualisms. We identify general patterns of temporal variation in these networks across temporal scales. We discuss potential mechanisms underlying variation in interactions, ranging from behavioural and physiological processes at the narrowest temporal scales to ecological and evolutionary processes operating over much broader temporal scales. We conclude by discussing priorities for future research, including an improved understanding of the abiotic and biotic factors driving temporal network change, and further development and refinement of analytical tools. Our review highlights the key role of the importance of considering the temporal dimension for our understanding of the ecology and evolution of complex webs of mutualistic interactions.