Global fine-resolution data on springtail abundance and community structure.

Springtails (Collembola) inhabit soils from the Arctic to the Antarctic and comprise an estimated ~32% of all terrestrial arthropods on Earth. Here, we present a global, spatially-explicit database on springtail communities that includes 249,912 occurrences from 44,999 samples and 2,990 sites. These data are mainly raw sample-level records at the species level collected predominantly from private archives of the authors that were quality-controlled and taxonomically-standardised. Despite covering all continents, most of the sample-level data come from the European continent (82.5% of all samples) and represent four habitats: woodlands (57.4%), grasslands (14.0%), agrosystems (13.7%) and scrublands (9.0%). We included sampling by soil layers, and across seasons and years, representing temporal and spatial within-site variation in springtail communities. We also provided data use and sharing guidelines and R code to facilitate the use of the database by other researchers. This data paper describes a static version of the database at the publication date, but the database will be further expanded to include underrepresented regions and linked with trait data.

The seafloor from a trait perspective. A comprehensive life history dataset of soft sediment macrozoobenthos.

Biological trait analysis (BTA) is a valuable tool for evaluating changes in community diversity and its link to ecosystem processes as well as environmental and anthropogenic perturbations. Trait-based analytical techniques like BTA rely on standardised datasets of species traits. However, there are currently only a limited number of datasets available for marine macrobenthos that contain trait data across multiple taxonomic groups. Here, we present an open-access dataset of 16 traits for 235 macrozoobenthic species recorded throughout multiple sampling campaigns of the Dutch Wadden Sea; a dynamic soft bottom system where humans have long played a substantial role in shaping the coastal environment. The trait categories included in this dataset cover a variety of life history strategies that are tightly linked to ecosystem functioning and the resilience of communities to (anthropogenic) perturbations and can advance our understanding of environmental changes and human impacts on the functioning of soft bottom systems.

Globally invariant metabolism but density-diversity mismatch in springtails.

Soil life supports the functioning and biodiversity of terrestrial ecosystems. Springtails (Collembola) are among the most abundant soil arthropods regulating soil fertility and flow of energy through above- and belowground food webs. However, the global distribution of springtail diversity and density, and how these relate to energy fluxes remains unknown. Here, using a global dataset representing 2470 sites, we estimate the total soil springtail biomass at 27.5 megatons carbon, which is threefold higher than wild terrestrial vertebrates, and record peak densities up to 2 million individuals per square meter in the tundra. Despite a 20-fold biomass difference between the tundra and the tropics, springtail energy use (community metabolism) remains similar across the latitudinal gradient, owing to the changes in temperature with latitude. Neither springtail density nor community metabolism is predicted by local species richness, which is high in the tropics, but comparably high in some temperate forests and even tundra. Changes in springtail activity may emerge from latitudinal gradients in temperature, predation and resource limitation in soil communities. Contrasting relationships of biomass, diversity and activity of springtail communities with temperature suggest that climate warming will alter fundamental soil biodiversity metrics in different directions, potentially restructuring terrestrial food webs and affecting soil functioning.

Disentangling the effects of plant species invasion and urban development on arthropod community composition.

Urban development and species invasion are two major global threats to biodiversity. These threats often co-occur, as developed areas are more prone to species invasion. However, few empirical studies have tested if both factors affect biodiversity in similar ways. Here we study the individual and combined effects of urban development and plant invasion on the composition of arthropod communities. We assessed 36 paired invaded and non-invaded sample plots, invaded by the plant Antigonon leptopus, with half of these pairs located in natural and the other half in developed land-use types on the Caribbean island of St. Eustatius. We used several taxonomic and functional variables to describe community composition and diversity. Our results show that both urban development and A. leptopus invasion affected community composition, albeit in different ways. Development significantly increased species richness and exponential Shannon diversity, while invasion had no effect on these variables. However, invasion significantly increased arthropod abundance and caused biotic homogenization. Specifically, uninvaded arthropod communities were distinctly different in species composition between developed and natural sites, while they became undistinguishable after A. leptopus invasion. Moreover, functional variables were significantly affected by species invasion, but not by urban development. Invaded communities had higher community-weighted mean body size and the feeding guild composition of invaded arthropod communities was characterized by the exceptional numbers of nectarivores, herbivores, and detritivores. With the exception of species richness and exponential Shannon diversity, invasion influenced four out of six response variables to a greater degree than urban development did. Hence, we can conclude that species invasion is not just a passenger of urban development but also a driver of change.

Food Web Uncertainties Influence Predictions of Climate Change Effects on Soil Carbon Sequestration in Heathlands.

Carbon cycling models consider soil carbon sequestration a key process for climate change mitigation. However, these models mostly focus on abiotic soil processes and, despite its recognized critical mechanistic role, do not explicitly include interacting soil organisms. Here, we use a literature study to show that even a relatively simple soil community (heathland soils) contains large uncertainties in temporal and spatial food web structure. Next, we used a Lotka-Volterra-based food web model to demonstrate that, due to these uncertainties, climate change can either increase or decrease soil carbon sequestration to varying extents. Both the strength and direction of changes strongly depend on (1) the main consumer's (enchytraeid worms) feeding preferences and (2) whether decomposers (fungi) or enchytraeid worms are more sensitive to stress. Hence, even for a soil community with a few dominant functional groups and a simulation model with a few parameters, filling these knowledge gaps is a critical first step towards the explicit integration of soil food web dynamics into carbon cycling models in order to better assess the role soils play in climate change mitigation.

Herbivore removal reduces influence of arbuscular mycorrhizal fungi on plant growth and tolerance in an East African savanna.

The functional relationship between arbuscular mycorrhizal fungi (AMF) and their hosts is variable on small spatial scales. Here, we hypothesized that herbivore exclusion changes the AMF community and alters the ability of AMF to enhance plant tolerance to grazing. We grew the perennial bunchgrass, Themeda triandra Forssk in inoculum from soils collected in the Kenya Long-term Exclosure Experiment where treatments representing different levels of herbivory have been in place since 1995. We assessed AMF diversity in the field, using terminal restriction fragment length polymorphism and compared fungal diversity among treatments. We conducted clipping experiments in the greenhouse and field and assessed regrowth. Plants inoculated with AMF from areas accessed by wild herbivores and cattle had greater biomass than non-inoculated controls, while plants inoculated with AMF from where large herbivores were excluded did not benefit from AMF in terms of biomass production. However, only the inoculation with AMF from areas with wild herbivores and no cattle had a positive effect on regrowth, relative to clipped plants grown without AMF. Similarly, in the field, regrowth of plants after clipping in areas with only native herbivores was higher than other treatments. Functional differences in AMF were evident despite little difference in AMF species richness or community composition. Our findings suggest that differences in large herbivore communities over nearly two decades has resulted in localized, functional changes in AMF communities. Our results add to the accumulating evidence that mycorrhizae are locally adapted and that functional differences can evolve within small geographical areas.

Heated communities: large inter- and intraspecific variation in heat tolerance across trophic levels of a soil arthropod community.

Temperature extremes are predicted to increase in frequency, intensity and duration under global warming and are believed to significantly affect community composition and functioning. However, the effect of extreme climatic events on communities remains difficult to predict, especially because species can show dissimilar responses to abiotic changes, which may affect the outcome of species interactions. To anticipate community responses we need knowledge on within and among species variation in stress tolerance. We exposed a soil arthropod community to experimental heat waves in the field and measured heat tolerance of species of different trophic levels from heated and control plots. We measured the critical thermal maximum (CTmax) of individuals to estimate inter- and intraspecific variation in heat tolerance in this community, and how this was affected by experimental heat waves. We found interspecific variation in heat tolerance, with the most abundant prey species, the springtail Isotoma riparia, being more sensitive to high temperatures than its predators (various spider species). Moreover, intraspecific variation in CTmax was substantial, suggesting that individuals within a single species were unequally affected by heat extremes. However, heat tolerance of species did not increase after being exposed to an experimental heat wave. We conclude that interspecific variation in tolerance traits potentially causes trophic mismatches during extreme events, but that intraspecific variation could lessen these effects by enabling partial survival of populations. Therefore, ecophysiological traits can provide a better understanding of abiotic effects on communities, not only within taxonomic or functional groups, but also when comparing different trophic levels.

Reciprocal rewards stabilize cooperation in the mycorrhizal symbiosis.

Plants and their arbuscular mycorrhizal fungal symbionts interact in complex underground networks involving multiple partners. This increases the potential for exploitation and defection by individuals, raising the question of how partners maintain a fair, two-way transfer of resources. We manipulated cooperation in plants and fungal partners to show that plants can detect, discriminate, and reward the best fungal partners with more carbohydrates. In turn, their fungal partners enforce cooperation by increasing nutrient transfer only to those roots providing more carbohydrates. On the basis of these observations we conclude that, unlike many other mutualisms, the symbiont cannot be "enslaved." Rather, the mutualism is evolutionarily stable because control is bidirectional, and partners offering the best rate of exchange are rewarded.

Gene expression analysis of collembola in cadmium containing soil.

Increasing concern about pollution of our environment calls for advanced and rapid methods to estimate ecological toxicity. The use of gene expression microarrays in environmental studies can potentially meet this challenge. We present a novel method to examine soil toxicity. We exposed the collembolan Folsomia candida to soil containing an ecologically relevant cadmium concentration, and found a cumulative total of 1586 differentially expressed transcripts across three exposure durations, including transcripts involved in stress response, detoxification, and hypoxia. Additional enrichment analysis of gene ontology (GO) terms revealed that antibiotic biosynthesis is important at all time points examined. Interestingly, genes involved in the "penicillin and cephalosporin biosynthesis pathway" have never been identified in animals before, but are expressed in F. candida's tissue. The synthesis of antibiotics can possibly be a response to increased cadmium-induced susceptibility to invading pathogens, which might be caused by repression of genes involved in the immune-system (C-type lectins and Toll receptor). This study presents a first global view on the environmental stress response of an arthropod species exposed to contaminated soil, and provides a mechanistic basis for the development of a gene expression soil quality test.