Forschung Weisser-Gruppe
Am Lehrstuhl für Terrestrische Ökologie wird Forschung zu einer Reihe aktuellen Themen durchgeführt. Hier finden Sie die Kurzbeschreibung der Forschungsthemen sowie Beispiele für wichtige Ergebnisse. Eine genauere Beschreibung der einzelnen Forschungsprojekte findet sich auf der englischen Seite. Die Verweise auf dieser Seite führen deshalb oft zu englischen Texten.
Unsere Forschung wird von verschiedenen öffentlichen Geldgebern gefördert. Der Hinweis auf die Förderer findet sich ebenfalls bei der genaueren Beschreibung der Forschungsprojekte.
Land use and biodiversity
The abundance and diversity of natural populations are under threat from mechanisms including habitat loss and fragmentation, climate change and land use change. Although multiple mechanisms often overlap and there are synergies, land use change is considered one of the main drivers behind the aggressive transformation and loss of biodiversity. Changes in land use - along natural and anthropogenic land cover gradients - modify the composition and diversity of ecosystems, as well as their ecological processes and services. Our research capitalizes on the multilevel measurement (e.g. species interactions, abiotic factors, or evolutionary processes) of ecosystem transformation to address fundamental questions in ecology: how changes in species composition contribute to concomitant effects on ecosystem processes. We are therefore also interested in making projections and recommendations under certain scenarios related with ecosystem management, and the maintenance of biological, economic and social benefits of biodiversity. Below we describe primary areas of research topics developed in our research group:
Biodiversity Exploratories
Arthropods contribute significantly to the maintenance of terrestrial ecosystems and provide a variety of ecosystem services. A major challenge of conservation biology lies in understanding the effects of management practices on insect communities. This challenge is further complicated as responses to land use change may be species specific, might vary temporally and/or change in different habitats. Subsequently, the Biodiversity Exploratories project (https://www.biodiversity-exploratories.de/en/) provides a monitoring platform in grassland and forest ecosystems for large-scale field research to address crucial questions about the effects of different intensities of land use on insect biodiversity and ecosystem processes. The long-term nature of this experiment also allows for the examination of how biodiversity influences different ecosystem processes over time, such as pest control, biomass accumulation or deadwood decomposition.
BELongDead
Our group is also responsible for the coordination of the BELongDead experiment that takes place in the 30 “VIP” (very intensive plots) in the three Biodiversity Exploratories. Initiated by Ernst-Detlef Schulze of the Max-Planck-Institute of Biogeochemistry in Jena, logs (diameter 30-40cm, length 4m) of 13 different tree species were placed in triplicate in each of the plots in 2008. Since then we study insect colonization of these logs using emergence traps. Other groups study fungi, mites, other organisms or log decomposition, e.g. DOC flow. This unique experiment allows disentangling the effect of tree species from the effect of the surrounding forest in shaping the communities using deadwood and also decomposition.
Douglas-Fir and biodiversity of beech forests
Germany's forests face unprecedented challenges due to drought-induced tree mortality, highlighting the urgent need for adaptive forestry practices in the face of climate change. The collaborative project, "Future Potential of Douglas Fir and Silver Fir Mixtures," is led by the Technical University of Munich (TUM) and the University of Göttingen, with support from the Bavarian State Institute of Forestry (LWF). At the Chair of Terrestrial Ecology, we are examining the ecological implications of incorporating Douglas fir and silver fir into managed European beech forests, which are predicted to have high future potential.
Our primary goal is to understand the impact of these mixed stands on native biodiversity, specifically focusing on taxonomic and functional diversity within communities of birds, bats, and insects. To achieve this, we conducted extensive field research across 63 plots (30 Douglas-fir-beech, 23 silver fir-beech, and 10 beech plots as control) in Lower Franconia (Spessart) during 2023-2024. The mixture plots represent a gradient of conifer proportions within the beech stands. Our data collection methodology for the diversity analysis includes:
• Arthropod Collection: Utilizing Malaise and light traps to measure biomass and species richness of arthropods and nocturnal moths.
• Bird and Bat Monitoring: Deploying audio recorders to analyze activity and diversity.
• Bird Reproductive Success: Monitoring blue tit breeding in nest boxes installed on both beech and conifer trees to assess habitat quality.
Through these investigations, we additionally aim to identify potential thresholds for positive or negative impacts on faunal diversity associated with varying conifer proportions. Ultimately, our research will provide more insight into the ecological implications of these mixtures and guidance for forest managers to make informed decisions for resilient and biodiverse forests in the face of climate change.
Completed projects:
Spongy moth outbreaks and forest biodiversity
Every year, the control of spongy moths in mixed oak forests is the subject of public debate when they reproduce en masse. On the one hand, high densities of spongy moth caterpillars can lead to defoliation of oak and other tree species. This should be prevented by timely control measures to protect forest owners from damage and even destruction of their stands. On the other hand, mixed oak forests are very species-rich and home to a large number of endangered butterflies, moths, birds and other species, so there is concern that these will suffer in the short or long term from the use of insecticides. However, the spongy moth outbreak itself also has negative consequences for other species in an oak forest, as the species community is dominated by a single species, the pest, for some time. While the biology of the spongy moth is well known and there are already many good studies on the effects of defoliation on oak trees, there are still some gaps in our knowledge that are important for risk management, e.g. with regard to the short- and long-term effects of the spongy moth on oak growth depending on the location. There are also too few studies comparing the short- and long-term effects on non-target organisms between untreated areas (with high spongy moth densities) and treated areas (with reduced spongy moth densities). Finally, some international results cannot be easily transferred to Bavaria. The interactions between spongy moth densities, site conditions, the chosen management approach and the responses of oak forests and their communities can only be investigated in years of mass reproduction, as is expected in the coming years.
In order to gain further insights that are important for spongy moth management, the Bavarian State Ministry of Food, Agriculture and Forestry (StMELF) is therefore funding a research project from 2019 to 2021 in which the Bavarian State Institute for Forest and Forestry (departments of forest protection, remote sensing, forestry and forestry economics) is participating. Agriculture and Forestry (StMELF) is therefore funding a research project from 2019 to 2021 involving the Bavarian State Institute for Forestry and Forest Management (Departments of Forest Protection, Remote Sensing, Biodiversity, Nature Conservation, Hunting), the Technical University of Munich (Forest Growth, Terrestrial Ecology) and the University of Würzburg (Institute of Zoology).
Biodiversity in mixed beech forests
In the past, studies on biodiversity in forests were mainly conducted in unmanaged forests. However, the majority of forest land in Germany is used for forestry. Integrative forestry aims to coordinate the use and protection of biodiversity, thereby enabling the preservation of species diversity across the entire forest area. Integrative forest management includes measures such as promoting biotope wood structures in the form of habitat trees and deadwood, designating stepping stone areas and preserving special sites with specific biodiversity. The project ‘Biodiversity in mixed beech forests’ helped to provide the scientific foundations for decision-making processes that have an impact on biodiversity in the course of forest management. Pure beech forests were compared with stands where beech was mixed with other species, such as spruce, oak, or other species. In addition, the role of small protected areas was considered.
Brazilian grasslands
Land-use changes such as conversion of semi-natural grasslands to agriculture, silviculture, or highintensity pastures affect biodiversity and ecosystem functions and services. However, which ecosystem functions are affected when highly diverse grasslands are converted remains largely unknown. As a model system, we studied 80 grasslands in Rio Grande do Sul, southern Brazil, comprising exceptionally diverse permanent grasslands that are traditionally managed with burning of accumulated biomass and moderate grazing, and four additional grassland types with different present or historical management: Permanent grasslands with reduced or increased current management intensity and secondary grasslands after past agricultural or silvicultural use. We measured ten ecosystem functions covering all major below- and aboveground ecosystem components and the processes that link them, using the novel rapid ecosystem function assessment approach.
BIOLOG Diva-Jena
The collaborative BIOLOG DIVA-Jena research project 'The relationship between Biodiversity and Ecosystem Functioning in Grassland Ecosystems' funded by the German Federal Ministry of Education and Research (BMBF) between 2000 and 2010 used extensively managed grasslands in the states of Thuringia and Bavaria as model ecosystems, to study the relationship between biodiversity and ecosystem functioning. Using a gradient in plant species richness a finding of the project was that there was a relationship between plant species richness and ecosystem variables also in these semi-natural ecosystems.
Agripopes
The importance of land-use intensity for biodiversity and ecosystem functioning was also the focus of the AGRIPOPES project, an ESF-funded network of 12 research teams across Europe. Using European agroecosystems, in particular wheat fields, as a model ecosystem, the project analyzed the effects of land use intensification parameters on biodiversity and the biocontrol potential of biodiversity. In a unique approach, more than 1300 wheat fields across were assessed and information about land use, biodiversity and ecosystem functioning assembled.
Biodiversity and ecosystem functioning
Over the past decades, an increasing number of studies has analyzed the relationship between biodiversity and ecosystem functioning triggered the documentation of a global and ongoing loss of biodiversity. We research the ecosystem consequences of biodiversity loss in various projects. The longest-running and still ongoing project is the DFG-funded Jena Experiment, a grassland biodiversity experiment (coordinated by our research group from 2002-2017) with large plots and up to 60 plant species. In 2020 we have established another biodiversity field experiment as part of a global network of experimental sites (LegacyNet) to study the functional effects of diverse grassland leys both during the grassland phase and during the following crop (legacy effects). In the BMBF-funded BIOLOG DIVA-Jena project (completed at the end of 2010), we studied semi-natural grasslands spanning a plant species richness gradient. A major conclusion that can be drawn from this research is that low diversity in an assemblage is often associated with a lowered mean (and an increase in the variance) in many of the ecosystem variables investigated. In the Jena Experiment, for example, about 40% of ecosystem variables are affected by plant species richness. One major shortcoming of the current state of knowledge is, however, that for many of the observed biodiversity effects we do not know the underlying mechanism. We are interested in how species interactions change with increasing plant species richness and how these changes underlie the observed biodiversity effects on ecosystem variables.
Jena experiment
The Jena Experiment is one of the largest and longest-running biodiversity experiments worldwide. Grasslands of controlled plant species richness that form a diversity gradient from monocultures over combinations of 2, 4, 8, and 16 species up to communities with 60 different plant species are investigated since the year 2002. We analyse how plant diversity changes functions and properties ranging from abiotic conditions to species interactions, from above- to belowground, and from plants to top predators. These analyses are based on a large pool of data collected during the last 18 years by members of the research unit and are currently continued within the doctoral thesis of Laura Argens. We measure rates of herbivory and predation investigating their relationship to plant diversity, plant traits, and changes in the community of aboveground consumers in the doctoral thesis of Maximilian Bröcher together with Anne Ebeling (FSU Jena) in Subproject 5: Plant-consumer interactions as cause and consequence of long-term BEF relationships.
LegacyNet
The benefits of multi-species mixtures for many ecosystem processes are well known from ecological research in grassland biodiversity experiments. Now, we wish to apply these findings to benefit agricultural practices. Therefore, LegacyNet (https://legacynet.scss.tcd.ie/) investigates how to best design grassland leys within crop rotations to maximize the function of the ley as a grassland, and to maximize the carry-over effect of the grassland (supply of symbiotically fixed nitrogen, soil health and fertility).
In 2020, we have established a field site with 60 plots of 3x7m in Freising as part of a network of experimental sites following a common experimental design. The main treatments are grassland mixtures consisting of grasses, legumes and herbs (from monoculture up to six species and 10 species high-diversity controls), and a follow-on cereal crop to quantify the legacy effect of the grassland composition. In addition to quantifying the grassland yield, we monitor the activity of insects and small mammals in the plots as well as quantifying proxies for ecosystem processes (pollination, predation, seed dispersal using REFA methods).
Urban ecology
Urbanization is a major contributor to habitat and biodiversity loss. At the same time urban areas provide opportunities for those species that are adapted, or can adapt, to the novel and ever-changing urban landscape.
The defining feature of urbanized areas is the intensive use by humans, as a place to sleep and work, but also for leisure time and recreational activities. This opens up the potential for ample contact among society and wildlife, including on the one hand conflicts and on the other hand interactions that increase human wellbeing and the quality of the city. Ongoing human migration into cities results in densification within cities and sprawl of cities into the surrounding landscapes contribute to the loss of wildlife habitat. Currently, it remains unclear which properties of urban spaces have the strongest effects on urban wildlife and how to maximize positive effects of urban green infrastructures. As the green infrastructure decreases with ongoing urban development, many cities are looking for strategies to reduce the loss of urban nature and to secure and develop green infrastructures as a means to retain the ecosystem services provided by nature.
We research green infrastructure development and its effect on human well-being, as well as conflicts arising from co-inhabitation of the urban habitat. For example (https://www.bayklif.de/verbundprojekte/baysics/teilprojekt-7/), we study how the urban context changes attitudes towards animals in the city, and how urbanization affects the phenology of animals such as hedgehogs. in the 100 squares project [LINK], we investigate the abundance and diversity of various animal groups depend on the size, distance to the city centre, and greenness on and in the surrounding of public squares in the city of Munich as a model system. Moreover, in our ALAN project, we focus on the effects of artificial light at night on plant functioning, and how this influences interactions with plant-associated organisms in the phytobiome, such as insects and microbes. With Animal-Aided Design, we aim to integrate the development of buildings with nature conservation, such that conflict is minimized and the ecosystem services provided to society are maximized. In [link] Ecolopes we go one step further, and envision the building’s outer surface as an ecosystem, in which the needs of plants, animals, microbes and society are equally considered.
100-Squares Project
Rural land use is threatening biodiversity and cities have been suggested as an alternative habitat for wildlife with a potential for species conservation. However, urbanisation increases worldwide due to the migration of humans into cities. Resulting densification within cities and sprawl of cities into the surrounding landscapes contribute to the loss of wildlife habitat. Currently, it remains unclear which properties of urban spaces have the strongest effects on urban wildlife and how to integrate these properties into city planning. We investigate these questions using public squares in the city of Munich as a model system. In the 100-squars project, we have selected 103 that are a representative sample of all squares in Munich, which span gradients in size, distance to the city centre, and greenness on and in the surrounding of the squares. We monitor the abundance and diversity of various animal groups to investigate the effects of square properties on urban biodiversity. We demonstrate positive effects of an increasing greenness (proportion of grassy surface area, number of trees, shrub volume) on the abundance and diversity of various taxa.
Plant-mediated interactions between organisms
Plants play an important role in most terrestrial ecosystems, in which they serve as the basal resource for most of the higher trophic levels in the food chain. Plants are mostly sessile, and therefore, in contrast to most animals, have very few means to physically ‘fight or flight’. This does, however, not mean that plants have evolved to be sitting ducks, waiting to be devoured by anything that passes by. In fact, most plants have evolved a broad range of structural adaptations and chemical compounds to interact with their living environment. These can be used to keep away or deter antagonists, but also to keep close or attract beneficial organisms. Plants are highly plastic in both their structural and chemical properties, and hence, the environment plays an important role in a plant’s physical shape or health status. In the ‘Plant-mediated Interactions’ theme, we investigate how both biotic (e.g. multiple attackers) and abiotic factors (light pollution, climatic variation, pesticides) affect phytochemistry and plant growth (i.e., quality and quantity), and how the consequential changes in these properties affect other interactions occurring on the plant.
Artificial Light at Night (ALAN) effects on plants
Humans lit up the world. Over the course of the past century, we have introduced light into countless terrestrial and aquatic environments that traditionally experience prolonged stretches of darkness through the earth’s predictable day-night patterns. In many terrestrial ecosystems, man-made lamps are lighting up the night, and the problem of artificial light at night (ALAN) is still quickly expanding. It is evident from the research of the past two decades that ALAN has strong impacts on animals, for instance via sleep disruption, behavioral attraction or deterrence, or even impacts on physiology. In plants, it has long been clear that light is important, as a resource, and as a mediator of many signaling pathways. However, the research on the effects of ALAN on plants is limited. Several studies indicate effects of ALAN on phenological processes, and the insect food web, but there are only a small handful of studies that have investigated the effects of ALAN on plants and interactions with, or within the phytobiome. In this line of research, we study the effects of ALAN on plant performance, plant defenses, plant-insect interactions and dynamics within plant communities.
Ongoing projects: Robin Heinen
Above-belowground interactions between beneficial microbes, plants, and insects
During their growing phase, most plants have to deal with attack by insects. Although some do well by chemical defenses alone, many species also recruit help from beneficial microbes in the soil. Interactions with mutualist microbes, which may for instance be various types of rhizobacteria, or mycorrhizal fungi, can in many cases strengthen the plant’s defense response, leading to outcomes similar to those of vaccines in humans. Plants with such beneficial microbes often are more resistant to pests, or pathogens, than plants without these beneficials. Although the concept is known for many years, the exact mechanisms through which this resistance arises are not clear, and it is likely specific to both the plant and microbial species. At the Terrestrial Ecology Group, in collaboration with Dr. Sharon Zytynska at Liverpool University, we study the interactions between a beneficial bacterium extracted from the roots of barley plants, Acidovorax radicis, barley plants, and colonization by aphids. These bacteria have growth-promoting properties in several barley cultivars, and lead to a higher resistance against cereal aphids, Sitobion avenae in most cultivars. Our work aims at unravelling mechanisms through which the bacteria communicate with the plants, and understanding how these interactions operate in a changing world.
Ongoing projects: Oriana Sanchez (PhD candidate Jan ‘19)
Intraspecific phytochemical diversity
Ongoing projects: Lina Ojeda (PhD candidate May ‘21), Annika Neuhaus (PhD candidate Nov ‘21), Robin Heinen.
Although most plants use ‘roughly’ the same chemical machinery to make them function wherever they grow (i.e., primary metabolism), many plants are extremely diverse in their secondary (defense) chemical composition. Obviously, there is a huge variation between species in what chemicals can be found in tissues. However, in the past years, it has become quite evident that there is tremendous variation in secondary metabolism within species. Work at the Terrestrial Ecology Group and elsewhere has revealed strong effects of differences in phytochemical profiles on insects, such as plant colonization by aphids, attendance by ants, and attraction of natural enemies. Our group is involved in the DFG FOR3000 research unit, in which we specifically focus on the effects of intraspecific phytochemical diversity on the assembly of insect communities. Our main model system for this work is Tansy (Tanacetum vulgare), an aromatic plant that shows extraordinary variation in their terpenoid profiles.
Ecological side effects of agricultural pesticides
Industrial agriculture in its current form uses many different forms of pesticides to ensure a healthy crop with a maximized yield. Among these commercial products there are fungicides, herbicides and insecticides, to name a few. Although most products are marketed as environmentally safe, with limited unwanted side effects, a much more likely description would be ‘we have no idea of the full scope of side effects’ for most of them. It is likely that many pesticides have undesirable side effects, for instance on the protective plant microbiome, and via this, likely influence associated pests. At the Terrestrial Ecology Group, we investigate the impacts that fungicides in particular have, on the pathogens they are intended to suppress, on the plant-associated microbiome, and ultimately on interactions with insect pests.
Ongoing projects: Stephan Grassl (PhD candidate May ‘21)
Soil legacy effects
This part of the theme is a legacy effect in and of itself. This line of work originated during Robin Heinen’s PhD project – studying soil legacy effects on plants and insects – at the Netherlands Institute of Ecology. Soil legacies are changes, either abiotic or biotic, in the soil wrought by plants. Plant species drive soil conditions in different directions. Through this they may influence plants that grow later in the same soil (i.e., plant-soil feedback), or anything that interacts with these plants (e.g., insects). The term ‘soil legacy effects’ is an umbrella term that includes any form of memory that persists in the soil and affects subsequent organisms.
Ongoing projects: Robin Heinen
Tansy chemotypes, including completed project
Tansy research unit
Joachim, C., I. Vosteen and W. W. Weisser. 2014. The aphid alarm pheromone (E)-beta-farnesene does not act as a cue for predators searching on a plant. Chemoecology in press.
Joachim, C. and W. W. Weisser. 2013. Real-Time Monitoring of (E)-beta-Farnesene Emission in Colonies of the Pea Aphid, Acyrthosiphon pisum, Under Lacewing and Ladybird Predation. Journal of Chemical Ecology 39:1254-1262. PDF
Hatano, E., J. Baverstock, G. Kunert, J. K. Pell and W. W. Weisser. 2012. Entomopathogenic fungi stimulate transgenerational wing induction in pea aphids, Acyrthosiphon pisum (Hemiptera: Aphididae). Ecological Entomology 37:75-82. PDF
Kunert, G., S. Otto, U. S. R. Rose, J. Gershenzon and W. W. Weisser. 2005. Alarm pheromone mediates production of winged dispersal morphs in aphids. Ecology Letters 8:596-603. PDF
Kunert, G. and W. W. Weisser. 2003. The interplay between density- and trait-mediated effects in predator-prey interactions: a case study in aphid wing polymorphism. Oecologia 135:304-312. PDF
Sloggett, J. J. and W. W. Weisser. 2002. Parasitoids induce production of the dispersal morph of the pea aphid, Acyrthosiphon pisum. Oikos 98:323-333. PDF
Weisser, W. W., C. Braendle and N. Minoretti. 1999. Predator-induced morphological shift in the pea aphid. Proceedings of the Royal Society of London Series B-Biological Sciences 266:1175-1181. PDF