Malte Jochum

Arthropods drive essential ecosystem processes such as pollination, decomposition, and nutrient cycling and are widely used as indicators of ecosystem condition and function. Among various arthropod-derived metrics, body weight is a key variable in functional ecology and frequently assessed as dry body weight. However, drying arthropod specimens limits the samples’ future potential for research, as it prevents further processing such as trait measurements or species identification. Here, we present AWET (Arthropod Weight Estimation Tool), an open-source application for automated estimation of individual fresh body weight and extraction of morphometric measurements from standardized images of pre-sorted arthropod samples. AWET combines automated image analysis with taxon-specific allometric regression models to estimate fresh body weight while simultaneously quantifying body length, width, area, and specimen abundance. The software operates with standard imaging equipment, requires no machine-learning-based classification or segmentation, and allows users to define taxonomic groupings according to their objectives. By preserving specimens for downstream analyses while processing large numbers of individuals within milliseconds, AWET provides an efficient, non-destructive, and cost-effective workflow for high-throughput arthropod phenotyping. The software is a practical and expandable tool for biodiversity monitoring projects investigating changes in arthropod biomass, abundance and individual morphometric measures.

Biodiversity change has elicited widespread concern over the consequences for functions and services provided by ecosystems^1-3. Despite extensive evidence for a positive effect of biodiversity on ecosystem functioning within a single trophic level^4,5, how this biodiversity effect varies with multi-trophic food web structure remains unresolved⁶ even though most ecosystems contain two to six trophic levels⁷. We investigate how food web complexity modulates biodiversity-ecosystem functioning relationships in nature by quantifying energy fluxes as proxies for two principal ecosystem functions⁸-primary consumption and predation-in 318 highly resolved, complex food webs from marine, lake, stream and soil ecosystems. Ecosystem functioning increased consistently with taxon richness across all trophic levels and ecosystems, which arose from greater vertical diversity (that is, maximum trophic level⁹) and trophic complementarity of predators in more taxonomically diverse food webs. Furthermore, predator trophic complementarity^10,11 increased predation fluxes in all freshwater ecosystem types. These findings highlight the threat of trophic downgrading to critical ecosystem functions (for example, biological control and maintenance of biodiversity and ecosystem stability) provided by predators^12,13, which are typically most vulnerable to anthropogenic disturbances^14,15. Our study demonstrates that the consequences of biodiversity change are deeply entangled within the web of life, emphasizing the need to conserve the trophic complexity underlying biodiversity-ecosystem function relationships.

Soil fauna regulates litter decomposition and soil organic matter transformation, acting as both litter and microbial feeders. Whether these feeding modes shift along environmental gradients remains unclear. We tested if microbivory increases with decreasing litter quality and in colder climates, both factors limiting detritus digestion by fauna. Using stable isotope composition (δ ¹³ C, δ ¹⁵ N) of 7408 soil invertebrate samples from 228 forest sites across temperate to tropical biomes, we determined δ ¹⁵ N values are positively associated with litter C:N ratio and mean annual temperature, indicating a shift from detritivory toward microbivory under low litter quality with additional modulation by climate. In contrast, δ ¹³ C values showed no consistent association with litter C:N ratio or climate, reflecting context dependent microbial carbon routing. Our findings highlight litter quality as the primary driver of the detritivory‐to‐microbivory shift in soil fauna, with implications for predicting changes in climate and plant communities on carbon cycling in terrestrial ecosystems.

Increasing aridity is predicted to alter the structure and functioning of soil food webs, yet its impacts on grassland food-web energetics and the resulting consequences for soil carbon sequestration remain poorly understood. Here, we quantified energy fluxes in soil food webs along a natural aridity gradient using data from 240 observations across 30 grassland ecosystems in the eastern Eurasian Steppe, spanning temperate (Loess and Inner Mongolian Plateaus) and alpine (Tibetan Plateau) regions. We found that increasing aridity decreases total energy flux through whole food webs across all study regions, largely driven by species losses and weakened trophic interactions. Energy flux to herbivory-based “green” channels declined more sharply than microbivory-based “brown” channels with increasing aridity, resulting in greater dominance of brown energy channels under more arid conditions across temperate grasslands. This broad-scale “browning” of soil food webs aligns with declining soil organic carbon (SOC) storage in temperate grasslands, suggesting that carbon loss through decomposition outpaces plant-derived carbon inputs under increasing aridity. In contrast, alpine grasslands showed increased SOC when the energy flux ratio of herbivory to microbivory was below the threshold of ~1, likely because lower temperatures constrain microbe-based decomposition and energy transfer to microbivory channels under more arid conditions. Understanding the context-dependent metabolic processes that underlie energy reallocation across soil food webs can augment modeling efforts to predict change to Earth’s carbon cycle.

Soil fauna contributes to a wide range of ecosystem functions via their trophic activities. Here we investigate how trophic diversity of soil animals varies across functional groups and major biomes. We use stable isotope analysis ( ¹³ C/ ¹² C and ¹⁵ N/ ¹⁴ N ratios) of 17,306 samples of 28 high-rank taxa from 456 sites across 19 countries to inspect the variability in trophic diversity across climate regions and land-use types. Trophic diversity of soil animal communities is higher for microbial feeders than for detritivores and predators, in agricultural ecosystems compared with woodlands (+32%) and in tropical compared with temperate climates (+40%). Higher trophic diversity is related to more diverse basal resources and longer trophic chains, which could reflect greater niche partitioning in resource-limited environments. Our findings suggest that soil animals could broaden their trophic niches under agricultural land use and possibly in response to warming, but whether such foraging flexibility may offset the loss of trophic specialists remains to be investigated.

Ecologists have long debated the universality of the energetic equivalence rule, which posits that population energy use should be invariant with average body size due to negative size–density scaling. We explore size–density and size–energy use scaling across 183 geographically–distributed soil invertebrate food webs (comprising 55,054 individual soil invertebrates) to investigate the universality of these fundamental energetic equivalence rule assumptions across trophic levels and varying food web structure. Additionally, we compare two measures of energy use to investigate size–energy use relationships: population metabolism and energy fluxes. We find that size–density scaling does not support energetic equivalence in soil communities. Furthermore, evidence of energetic equivalence is dependent on the estimate of energy use applied, the trophic level of consumers, and food web properties. Our study demonstrates a need to integrate food web energetics and trophic structure to better understand how energetic constraints shape the body size structure of terrestrial ecosystems.

The elemental content of organisms links cellular biochemistry to ecological processes, from physiology to nutrient dynamics. While plant stoichiometry is thought to vary with climate and nutrient availability across latitudes, the consistency of these patterns across trophic groups and realms remains unclear. Using the StoichLife database, which includes nitrogen and phosphorus content data for 5443 species across 1390 sites, we examine how solar energy (temperature, radiation) and nutrients (nitrogen and phosphorus) influence stoichiometric variation. We find that plant stoichiometry in terrestrial and freshwater ecosystems is more strongly associated with environmental gradients, particularly nitrogen deposition, than animal stoichiometry. Contrary to expectations, temperature, radiation, and labile P show limited global effects. Latitudinal patterns in stoichiometry are more closely associated with species turnover rather than intraspecific variation. Given the strong links between stoichiometry and organismal performance, these findings underscore the need to predict the ecological consequences of anthropogenic disruption to global biogeochemical cycles.

Soil fauna regulates litter decomposition and soil organic matter transformation, acting as both litter and microbial feeders. Whether these feeding modes shift along environmental gradients remains unclear. We tested if microbivory increases with decreasing litter quality and in colder climates, both factors limiting detritus digestion by fauna. Using stable isotope composition (δ13C, δ15N) of 7,408 soil invertebrate samples from 228 forest sites across temperate to tropical biomes, we determined δ15N values are positively associated with litter C:N ratio and mean annual temperature, indicating a shift from detritivory toward microbivory under low litter quality with additional modulation by climate. In contrast, δ13C values showed no consistent association with litter C:N ratio or climate, reflecting context dependent microbial carbon routing. Our findings highlight litter quality as the primary driver of the detritivory-to-microbivory shift in soil fauna, with implications for predicting changes in climate and plant communities on carbon cycling in terrestrial ecosystems

Global change alters abiotic and biotic conditions across the globe with unprecedented consequences for the functional integrity of affected ecosystems. However, most studies addressing global-change impacts focus on a very limited number of environmental variables, taxa, and ecosystem functions. Evidence is mounting that many belowground ecosystems are subject to an underappreciated aspect of global change: the invasion of earthworms. While we know that earthworm invasion can impact the physical, chemical, and biological properties of invaded ecosystems, it remains poorly understood how these changes are interconnected and how they concurrently affect the overall functioning of an ecosystem. To fill this gap, we collected data on six environmental variables, ten functional groups of microbes, plants, and animals, and 16 ecosystem functions from four forests in the USA and Canada, well-known hotspots of earthworm invasion. We used a multi-step Structural-Equation Modeling approach to disentangle the direct and indirect effects of earthworm invasion on environmental conditions and the ecosystem multidiversity and multifunctionality of invaded forests at different levels of resolution. Our analysis revealed that earthworm invasion reduced total multidiversity (combined microbial, plant, and animal multidiversity). Ecosystem multifunctionality was reduced via a combination of direct and indirect effects, with the latter involving both effects mediated by altered environmental conditions and by total multidiversity. In contrast, when resolving total multidiversity into taxon-specific multidiversity indices for microbes, plants, and animals, the above-mentioned effects of earthworm invasion on multifunctionality via multidiversity disappeared. Invasion effects on single ecosystem functions differed in their mediators but were net negative across the board. Given these differences across the differently-resolved analyses, the results suggest that a whole- ecosystem perspective is paramount to comprehensively understanding the impacts of biological invasions. Combining a multi-step analytical design with multiple biodiversity indices and multiple ecosystem functions assessed at the same time and place, our study represents the most complete assessment of the mechanisms and ecosystem-level consequences of earthworm invasion to date.