New and not so new projects ahead

Shortly before Christmas, a letter from the DFG (German Research Foundation) finally arrived, which makes it official: The Biodiversity Exploratories and with them the Core Project Arthropods will be funded for three further years (2023-2026). This will be the seventh phase for this unique long-term research project focusing, among other topics, on the influence of land-use intensity and biodiversity and ecosystem processes. Since my move to Darmstadt in 2020, the Biodiversity Exploratories have been my main occupation and I am really happy that I will be able to continue in the great Core Arthropods Team together with Nico Blüthgen, Rafael Achury and Wolfgang Weisser. We have been working on several interesting publications that are close to getting published.

The year 2023 will also see the start of the DFG-funded research unit MultiTroph, which will continue the old BEF-China project. Within the research unit, I am leading a subproject on trophic interactions of ants. My PhD student Joshua Spitz has already started with his research. We are all really looking forward to be able to come back to China soon, after the long Covid-19-induced hiatus of our work in the BEF-China Experiment.

Forest dung beetles don’t like gaps

In a new open access study from the Biodiversity Exploratories project, we could experimentally show that dung beetles avoid gaps in forests, which reduces their main ecosystem function in gaps, the removal of mammalian feces. This is the first study published from the full-factorial multi-site FOX (FOrest gap eXperiment), that was established within the Biodiversity Exploratories to disentangle two important factors related to forest management — gap creation and deadwood availability — and their influence on biodiversity and ecosystem functioning.

Overview on the rationale and design of the FOX experiment. In three regions of Germany, a full-factorial experiment with the treatments Gap (gap of ~30 m diameter, felled trees removed), Gap + Deadwood (gap of ~30 m diameter, deadwood left in place), Deadwood (deadwood addition in otherwise unmodified forest) and Control (no gap and no deadwood) was established at a total of 29 sites. Figure from Staab et al., 2022, Journal of Animal Ecology.

In this experiment, we sampled dung beetles and measured dung removal, which were the respective Bachelor thesis of Hendrik Mohr and Veronika Irmscher that are coauthors of the now published research. We consistently found lower dung beetle diversity, biomass and dung removal in gaps than in controls. For example, dung removal was reduced to 48.5% in gaps from 61.9% in controls. This treatment effect was primarily driven by dung beetle biomass, but not by dung beetle diversity.

Path diagram illustrating how experimental manipulations (Gap, Deadwood) and covariates affect dung removal. Treatment effects were both direct (in path model terminology), but also mediated indirectly, especially by lowered dung beetle biomass in gaps. Figure from Staab et al., 2022, Journal of Animal Ecology.

The findings do not confirm complementarity effects related to different dung beetle species linked to biodiversity-ecosystem functioning relationships that have been shown in several ecosystems. Rather, an identity effect related to a large-bodied key forest species was found. Gaps reduced the abundance of Anoplotrupes stercorosus without indication for compensatory recruitment of open land species to gaps. While I do not question that gaps and deadwood are important for many forest organisms such as saproxylic beetles, dung beetles responded negatively. This study, which is freely available to everyone, is in my opinion a great example for how spatially replicated experiments allow testing hypotheses on the interrelation between land use, biodiversity and ecosystem functioning.

Talk at the German Federal Agency for Nature Conservation

Now that the Corona situation has eased, the first in person meetings and conferences are thankfully taking place. I have really missed the direct contact to the scientific community, which can only partly be replaced by virtual meetings. Last week, I had the pleasure to be invited to the International Nature Conservation Academy (INA) of the German Federal Agency for Nature Conservation. On the beautiful island of Vilm, near Rügen in the Baltic Sea, three interesting and informative days were spent on ‘Insektenschutzmaßahmen und Potentiale für derartige Maßnahmen in Großschutzgebieten‘ (Insect conservation in protected areas). I met many interesting people, both from science and practice, and presented my work on insect population trends in the Biodiversity Exploratories. As a bonus, I was lucky enough to spot my first ever Eurasian otters (Lutra lutra) in the wild.

Field work in the Biodiversity Exploratories

Recently, I had the pleasure to conduct extensive field work in the field sites of Biodiversity Exploratories located in Hainich-Dün (central Germany), Schorfheide-Chorin (north-east Germany) and Schwäbische Alb (south-west Germany). Together with my team, we measured the ecological processes seed removal, dung removal and predation in forest and grassland sites. Process measurements are part of a time series with the aim to test whether temporal variation in process rates is related to land use intensity. Furthermore, I sampled the newly established grassland experiments with suction sampling (‘biocenometer’) to get a quantitative picture of the arthropod community in the grasslands, and to test whether the reduction in fertilization, mowing and grazing is influencing species communities.

All three process measurements in one shot. Seeds are placed on a plastic tray, dummy caterpillars pinned on the ground and dung is placed on cellulose paper. After 48 h, missing seeds are counted, dummy caterpillars collected and remaining dung retrieved. (picture by Genny Walther)

In some forest sites dung beetles (particularly Anoplotrupes stercorosus shown here) are very common. Hardly any dung is remaining after 48 h. (picture by Robin Fuchs)

Myself sampling an experimental grassland site with the biocenometer in the Hainich region. All arthropods in a defined (and caged) square meter are sucked in our amazing custom-made machine. (picture by Genny Walther)

Phylogenetic diversity paper published

This has been a long way coming. I have been working on this project for almost four years. It has been a bumpy road with several detours, from which I have learned a lot. But it was certainly worth the effort, as the final paper now published in Functional Ecology (read the article here, it is Open Access) went out really well. For this work, I have synthesized a large dataset of arthropods and fungi from plots in the Gutianshan National Nature Reserve. Acquiring this database was a group effort to which very many people have contributed over the years. I have to thank them all.

The data for this study have been collected in the beautiful and diverse forests of Gutianshan.

Ecosystems with more plant species usually harbor more species of other organisms such as insects. However, counting species is just one of many ways to describe the diversity of ecosystems. Many other possibilities exist, among which the present study focuses on ‘phylogenetic diversity’ (PD), a statistical measure that takes account of evolutionary relatedness. In other words, if two ecosystems have the same number of species, the one where the species are more distantly related has the higher PD. Using a large dataset from subtropical Chinese forests, we tested whether the number of tree species present in a forest stand or the PD of those trees is the better predictor of the diversity and species composition of the associated insects, herbaceous plants and microscopic fungi. Following our expectations, we found that tree PD but not the number of tree species relates to the composition of the associated organisms. Also, there were more species of predatory but fewer species of herbivorous insects in forests with higher PD. While our study was necessarily limited in scale and scope, the results point to the important role of plant PD in maintaining biologically diverse species assemblages. As during global change often the evolutionary most distinct (plant) species disappear first, the consequent reduction in PD will likely have far-reaching consequences for entire ecological communities.

Conceptual overview of the core predictions this study is testing.

Exotic garden plants are well-integrated in plant-pollinator interaction networks

Exotic plants are ubiquitous in gardens, where they are usually deliberately planted, for example to achieve a continuous flowering over the entire growing season. As at least in Central Europe, relatively few native plants flower in the end of the season, exotic plants often dominate gardens in late summer and autumn.

In a study freshly published in Oecologia (Open Access Link), we (Michael Staab, Helena Maria Pereira-Peixoto, Alexandra-Maria Klein) investigated if seasonal changes in the availability of flowers from native vs. exotic plant species affect flower visits, visitor diversity and plant-pollinator interaction networks.

While flower visitor species richness decreased over the course of the season, gardens with higher proportions of flowering exotic plants relative to natives partly compensated the seasonal decrease in flower-visitor species richness. Plant-pollinator interaction networks were not influenced by exotic species. Thus, later in the season when only few native plants were flowering, exotic garden plants have at least partly substituted native flower resources without apparent influence on plant-pollinator network structure.

This research suggests that as long as exotic plants are appropriately managed and risk of naturalization is minimized, late-flowering exotic garden plants may provide floral resources to support native pollinators when native plants are scarce.

Seasonal changes in plant-pollinator networks and related quantitative network indices. (a) Exemplary bipartite plant-pollinator interaction networks from a single garden. Width of bars corresponds to flower cover per plant species in the lower and to the number of visits by each flower-visiting species in the higher level (species identities can be resolved with the numerical codes in Table S1 of the publication); width of arrows corresponds to the number of interactions between two species, with the most narrow bars and arrows indicating single interactions each (note that the number of interactions varied: April=229, June=20, August=33, October=13). Arrows narrowing from top to bottom indicate that a plant species was more often visited than expected solely from the cover of this plant among all plants. In turn, arrows that widen from top to bottom indicate relatively less visited plant species. For plants, light grey bars and arrows indicate interactions of native plant species and red of exotic species, respectively. Non-visited plant species are included but do not have any interactions. While in April, most flowers were from native plants, this changed over the season and in October all interactions in the exemplary garden were with exotic plants. Both, (b) the Shannon diversity of species interactions and (c) the linkage density of networks peaked in summer. Regression lines in (b) and (c) indicate the bootstrapped (n=1000) predictions of quadratic lmms (significant at p<0.01) with 95% CI (dashed lines).

New review on the relationship between tree diversity and natural enemies

Recently,  I compiled together with Andreas Schuldt (University of Göttingen) a review on the ‘enemies’ hypothesis for forests ecosystems. Our review paper has now been published open access in Current Forestry Reports (Staab & Schuldt 2020).

The ‘enemies’ hypothesis is a classical ecological concept postulating a positive relationship between plant diversity (and complexity) and natural enemies of herbivores, which, in turn, should increase top-down control in more diverse environments. While the ‘enemies’ hypothesis has abundant support from grasslands and agricultural ecosystems, outcomes from studies in forests are heterogeneous. Our synthesis of the literature suggests that the ‘enemies’ hypothesis does not unambiguously apply to forests. With trees as structurally complex organisms, even low-diversity forests may maintain a high degree of habitat heterogeneity and provide niches for predator and parasitoid species, blurring correlations between tree and natural enemy diversity.

Staab M, Schuldt A (2020) The influence of tree diversity on natural enemies – A review of the ‘enemies’ hypothesis in forests. Current Forestry Reports, online first. >> Open Access

Goodbye Freiburg, hello Darmstadt

After almost 7 years in Freiburg, I have recently moved to the Technical Universit of Darmstadt. I will work as a postdoc in the Ecological Networks group of Nico Blüthgen. There I have the great opportunity to join the Biodiversity Exploratories, a large research platform for functional (bio)diversity research funded by the Germany Research Foundation. At three sites spread over Germany (Schwäbische Alb, Hainich-Dün, Schorfheide) many research groups investigate a broad range taxa and ecosystem functions in forests and grasslands.

I am part of the Arthropod Core team headed by Wolfgang Weisser (Technical University Munich) and Nico Blüthgen (Technical University of Darmstadt) where a substantial part of my research will be dedicated to measuring ecosystem processes and synthesizing data collected in previous phases of the Biodiversity Exploratories.

Nevertheless, I will continue with some of my most exciting old projects and (hopefully) make regular updates here.

Paper recommended by F1000

Our paper ‘A tale of scale: Plot but not neighbourhood tree diversity increases leaf litter ant diversity’ published in the Journal of Animal Ecology has recently been recommended by F1000 as a highly important contribution in ecology. F1000 member Bernhard Schmid states that “This is a very important finding, because it demonstrates that tree diversity beyond the immediate neighbourhood can still affect sampling points within that neighbourhood, and in such cases, biodiversity effect should be evaluated at larger scales.” You can read the full recommendation here.

New PhD Position

I am recruiting a PhD student to work on the exiting project Sex determination and biomass allocation in response to habitat quality. The project is at the interface of ecology, entomology and evolutionary biology (PhD Position Insect Ecology Freiburg). Application deadline is 22 November 2019. The position is anticipated to start on 1 January 2020 (or as soon as possible thereafter) and is fixed-term for 36 months (until 31 December 2022). Payment is subjected to the German standard tariff (50% TVL13).

Project description

Changes in habitats do not only affect species diversity but also population structure within species. Evolutionary theory suggests that the ratio of females to males in offspring of sexually reproducing species responds to resource availability. In resource-poor habitats, it is expected that the share of the less costly sex (in insects usually males) increases, which may skew sex ratios and consequently affect population viability. Hymenoptera are due to their haplodiploid sex determination system exceptionally suitable organisms for studying sex ratios. The PhD student will investigate solitary bees and wasps with trap nests along a habitat gradient near Freiburg and test if local habitat quality influences resource allocation and sex ratios. Food resources will be quantified and foraging efficiencies will be measured. Furthermore, already existing data from a diverse geographical context will be synthesized. Taken together, this project at the interface of ecology, entomology and evolutionary biology will reveal if and how habitat quality influences sex ratios, which could be one mechanism for why insect populations are declining.

Your profile

• Excellent MSc in a relevant field (e.g. biology, ecology, conservation, entomology, evolution)
• Strong experience with statistical data analyses in R
• Interest in entomology and cross-disciplinary research
• Ability to work independently in the field and laboratory
• Experience with scientific writing in English; scientific working language is English; German language skills are required for field work
• Valid driving license class B
• Technical affinity (electronics, computer) is advantageous, as for parts of the experiments custom-made hardware will be build
• Basic knowledge of GIS systems is beneficial

Please submit your application in a single PDF document (maximum 5 MB) no later than 22 November 2019 to Dr. Michael Staab (michael.staab@nature.uni-freiburg.de), who may also be contacted for further information. Your application should include cover letter, short summary of research interests and experiences, CV, certificates, 1 page summary of the MSc thesis, and contacts of two potential referees. Interviews will tentatively be conducted at 9 December 2019. Note that the position is pending final funding approval and that application costs cannot be reimbursed.