Biology subjects

Scheu, S.

Publications and source records attributed to Scheu, S..

26 records · Page 2Linked to original sources

bioRxiv2020

Mixing conifers and deciduous trees (Fagus sylvatica): response of soil microorganisms

Tree - soil interactions depend on environmental conditions. Planting trees may strongly impact microorganisms in particular at unfavorable site conditions, compromising the functioning of soil microorganisms. To understand the effects of tree species composition on soil microorganisms, we quantified structural and functional responses of soil microorganisms to forest types across environmental conditions using substrate-induced respiration and phospholipid fatty acid analyses. Five forest types were studied including pure stands of native European beech (Fagus sylvatica), range expanding Norway spruce (Picea abies), and non-native Douglas-fir (Pseudotsuga menziesii), as well as the two conifer - beech mixtures. We found that microbial functioning strongly depends on site conditions, in particular on soil nutrients. At nutrient-poor sites, soil microorganisms were more stressed in pure and mixed coniferous forests, especially in Douglas-fir, compared to beech forests. By contrast, microbial structure and functional indicators in beech forests varied little with site conditions, likely because beech provided high amounts of root-derived resources for microbial growth. Since soil microbial communities are sensitive to Douglas-fir, planting Douglas-fir may compromise ecosystem functioning in particular at nutrient-poor sites. Overall, root-derived resources are important for determining the structure and functioning of soil microbial communities, and soil microorganisms sensitively respond to plantations containing tree species that may differ in the provisioning of these resources.

ecology↗

bioRxiv2019

Does metal pollution affect stoichiometry of soil-litter food webs?

To date the field of ecological stoichiometry has focused mainly on aquatic systems concentrating on macro-elements. We investigated terrestrial systems and included microelements to study the elemental transfer in the detritivorous food web. We compared food webs of six sites differing in the type and degree of metal pollution along two forest transects contaminated with copper or zinc. We measured 11 elements in litter, herbivores, detritivores, predators and omnivores. Based on elemental concentrations of elements differences between trophic groups were visualized using PCA. At all sites litter C:N, C:P, C:K and C:Na ratios were higher than in animals. Invertebrate trophic groups were significantly different from each other in C:Cu, C:Zn and C:Ca ratios. The calculated resource:consumer N:P ratio suggests that invertebrates in studied forests are N limited and not P limited. Similar patterns at all sites suggests that metal pollution at the studied intensity slightly affects the transfer of elements in the terrestrial macro-invertebrate food web.

ecology↗

bioRxiv2019

Plant traits are poor predictors of long-term ecosystem functioning

Earth is home to over 350,000 vascular plant species1 that differ in their traits in innumerable ways. Yet, a handful of functional traits can help explaining major differences among species in photosynthetic rate, growth rate, reproductive output and other aspects of plant performance2-6. A key challenge, coined "the Holy Grail" in ecology, is to upscale this understanding in order to predict how natural or anthropogenically driven changes in the identity and diversity of co-occurring plant species drive the functioning of ecosystems7, 8. Here, we analyze the extent to which 42 different ecosystem functions can be predicted by 41 plant traits in 78 experimentally manipulated grassland plots over 10 years. Despite the unprecedented number of traits analyzed, the average percentage of variation in ecosystem functioning that they jointly explained was only moderate (32.6%) within individual years, and even much lower (12.7%) across years. Most other studies linking ecosystem functioning to plant traits analyzed no more than six traits, and when including either only six random or the six most frequently studied traits in our analysis, the average percentage of explained variation in across-year ecosystem functioning dropped to 4.8%. Furthermore, different ecosystem functions were driven by different traits, with on average only 12.2% overlap in significant predictors. Thus, we did not find evidence for the existence of a small set of key traits able to explain variation in multiple ecosystem functions across years. Our results therefore suggest that there are strong limits in the extent to which we can predict the long-term functional consequences of the ongoing, rapid changes in the composition and diversity of plant communities that humanity is currently facing.

ecology↗

bioRxiv2019

The results of biodiversity-ecosystem functioning experiments are realistic

A large body of research shows that biodiversity loss can reduce ecosystem functioning, thus providing support for the conservation of biological diversity1-4. Much of the evidence for this relationship is drawn from biodiversity-ecosystem functioning experiments (hereafter: biodiversity experiments), in which biodiversity loss is simulated by randomly assembling communities of varying species diversity, and ecosystem functions are measured5-9. This random assembly has led some ecologists to question the relevance of biodiversity experiments to real-world ecosystems, where community assembly may often be non-random and influenced by external drivers, such as climate or land-use intensification10-18. Despite these repeated criticisms, there has been no comprehensive, quantitative assessment of how experimental and real-world plant communities really differ, and whether these differences invalidate the experimental results. Here, we compare data from two of the largest and longest-running grassland biodiversity experiments globally (Jena Experiment, Germany; BioDIV, USA) to related real-world grassland plant communities in terms of their taxonomic, functional, and phylogenetic diversity and functional-trait composition. We found that plant communities of biodiversity experiments have greater variance in these compositional features than their real-world counterparts, covering almost all of the variation of the real-world communities (82-96%) while also containing community types that are not currently observed in the real world. We then re-analysed a subset of experimental data that included only ecologically-realistic communities, i.e. those comparable to real-world communities. For ten out of twelve biodiversity-ecosystem functioning relationships, biodiversity effects did not differ significantly between the full dataset of biodiversity experiments and the ecologically-realistic subset of experimental communities. This demonstrates that the results of biodiversity experiments are largely insensitive to the inclusion/exclusion of unrealistic communities. By bridging the gap between experimental and real-world studies, these results demonstrate the validity of inferences from biodiversity experiments, a key step in translating their results into specific recommendations for real-world biodiversity management.

ecology↗

bioRxiv2018

Trophic consistency of supraspecific taxa in belowground invertebrate communities

1. Animals that have similar morphological traits are expected to share similar ecological niches. This statement applies to individual animals within a species and thus species often serve as the functional units in ecological studies. Species are further grouped into higher-ranked taxonomic units based on their morphological similarity and thus are also expected to be ecologically similar. On the other hand, theory predicts that strong competition between closely related species can lead to differentiation of ecological niches. Due to a high diversity and limited taxonomic expertise, soil food webs are often resolved using supraspecific taxa such as families, orders or even classes as functional units.\n\n2. Here we for the first time empirically tested the trophic consistency of supraspecific taxa across major lineages of temperate forest soil invertebrates: Annelida, Chelicerata, Myriapoda, Crustacea and Hexapoda. Published data on stable isotope compositions of carbon and nitrogen were used to infer basal resources and trophic level, and explore the relationship between taxonomic and trophic dissimilarity of local populations.\n\n3. Genera and families had normal and unimodal distributions of isotope niches, suggesting that supraspecific taxa are trophically consistent. The isotopic niche of populations across different localities is better predicted by species than by supraspecific taxa. However, within the same genus, the effect of species identity on stable isotope composition of populations was not significant in 92% of cases. The link to basal resources, i.e. plants or detritus, was convergent in different lineages, while trophic levels followed the Brownian motion taxonomic model. Virtually none of the studied taxa showed pronounced trophic niche conservatism within a lineage.\n\n4. Supraspecific taxa are meaningful as functional units in ecological studies, but the consistency varies among taxa and thus the choice of taxonomic resolution depends on the research question; generally, identification of taxa should be more detailed in more diverse taxonomic groups. We compiled a comprehensive list of mean {Delta}13C and {Delta}15N values of invertebrate taxa from temperate forest soils allowing to refine soil food-web models when identification to species level is not feasible.

ecology↗

bioRxiv2018

Applying generalised allometric regressions to predict live body mass of tropical and temperate arthropods

1. The ecological implications of body size extend from the biology of individual organisms to ecosystem-level processes. Measuring body mass for high numbers of invertebrates can be logistically challenging, making length-mass regressions useful for predicting body mass with minimal effort. However, standardised sets of scaling relationships covering a large range in body length, taxonomic groups, and multiple geographical regions are scarce.\n\n2. We collected 6293 arthropods from 19 higher-level taxa in both temperate and tropical locations to compile a comprehensive set of linear models relating live body mass to a range of predictor variables. For each individual, we measured live weight (hereafter, body mass), body length and width, and conducted linear regressions to predict body mass using body length, body width, taxonomic group and geographic region. Additionally, we quantified prediction error when using parameters from arthropods of a different geographic region.\n\n3. Incorporating body width into taxon- and region-specific length-mass regressions yielded the highest prediction accuracy for body mass. Using regression parameters from a different geographic location increased prediction error, causing over- or underestimation of body mass depending on geographical origin and whether body width was included.\n\n4. We present a comprehensive range of parameters for predicting arthropod body mass and provide guidance for selecting optimal scaling relationships. Given the importance of body mass for functional invertebrate ecology and a paucity of adequate regressions to predict arthropod body mass from different geographical regions, our study provides a long-needed resource for quantifying live body mass in invertebrate ecology research.

zoology↗

bioRxiv2017

Effective purifying selection in ancient asexual oribatid mites

Sex is beneficial in the long-term, because it can prevent mutational meltdown through increased effectiveness of selection. This idea is supported by empirical evidence of deleterious mutation accumulation in species with a recent transition to asexuality. Here, we studied the effectiveness of purifying selection in oribatid mites, which have lost sex millions of years ago and diversified into different families and species while reproducing asexually. We compared the accumulation of deleterious coding and non-coding mutations between three asexual and three sexual lineages using transcriptome data. Contrasting studies of young asexual lineages, we find evidence for strong purifying selection that is more effective in asexual compared to sexual oribatid mite lineages. Our results suggest that large populations likely sustain effective purifying selection and facilitate the escape of mutational meltdown in the absence of sex. Thus, sex per se is not a prerequisite for the long-term persistence of animal lineages.

evolutionary biology↗

bioRxiv2017

Combining molecular gut content analysis and functional response models shows how body size affects prey choice in soil predators

O_LIPredator-prey interactions are a core concept of animal ecology and functional response models provide a powerful tool to predict the strength of trophic links and assess motives for prey choice. However, due to their reductionist set-up, these models may not display field conditions, possibly leading to skewed results.\nC_LIO_LIWe tested the validity of functional response models for multiple prey by comparing them with empirical data from DNA-based molecular gut content analysis of two abundant and widespread macrofauna soil predators, lithobiid and geophilomorph centipedes.\nC_LIO_LIWe collected soil and litter dwelling centipedes, screened their gut contents for DNA of nine abundant decomposer and intraguild prey using specific primers and tested for different prey and predator traits explaining prey choice. In order to calculate the functional response of same predators, we used natural prey abundances and functional response parameters from published experiments and compared both approaches.\nC_LIO_LIMolecular gut content results showed that prey choice of centipedes is driven by predator body size and prey identity. Results of functional response models significantly correlated with results from molecular gut content analysis for the majority of prey species.\nC_LIO_LIOverall, the results suggest that functional response models are a powerful tool to predict trophic interactions in soil, however, species-specific traits have to be taken into account to improve predictions.\nC_LI

ecology↗