Fachbereich 7
Refine
Year of publication
Document Type
- Doctoral Thesis (58)
- Article (2)
- Bachelor Thesis (1)
Keywords
- Agriculture (2)
- Bestäubung (2)
- Biodiversität (2)
- Ecotoxicology (2)
- Grundwasserfauna (2)
- Landwirtschaft (2)
- Pesticides (2)
- Pflanzenschutzmittel (2)
- Weinbau (2)
- decomposition (2)
Institute
Wild bees are essential for the pollination of wild and cultivated plants. However, within the
last decades, the increasing intensification of modern agriculture has led to both a reduction and fragmentation as well as a degradation of the habitats wild bees need. The resulting loss of pollinators and their pollination poses an immense challenge to global food production. To support wild bees, the availability of flowering resources is essential. However, the flowering period of each resource is temporally limited and has different effects on pollinators and their pollination, depending on the time of their flowering.
Therefore, to efficiently promote and manage wild bee pollinators in agricultural landscapes, we identified species-specific key floral resources of three selected wild bee species and their spatial and temporal availability (CHAPTERS 2, 3 & 4). We examined, which habitat types predominantly provide these resources (CHAPTERS 3 & 4). We also investigated whether floral resource maps based on the use of these key resources and their spatial and temporal availability explain the abundance and development of the selected wild bees (CHAPTERS 3 & 4) and pollination (CHAPTER 5) better than habitat maps, that only indirectly account for the availability of floral resources.
For each of the species studied, we were able to identify different key pollen sources, predominantly woody plants in the early season (April/May) and increasingly herbaceous plants in the later season (June/July; CHAPTERS 2, 3 & 4). The open woody semi-natural habitats of our agricultural landscapes provided about 75% of the floral resources for the buff-tailed bumblebees, 60% for the red mason bees, and 55% for the horned mason bees studied, although they accounted for only 3% of the area (CHAPTERS 3 & 4). In addition, fruit orchards provided about 35% of the floral resources for the horned mason bees on 4% of the landscape area (CHAPTER 3). We showed that both mason bee species benefited from the resource availability in the surrounding landscapes (CHAPTER 3). Yet this was not the case for the bumblebees (CHAPTER 4). Instead, the weight gain of their colonies, the number of developed queen cells and their colony survival were higher with increasing proximity to forests. The proximity to forests also had a positive effect on the mason bees studied (CHAPTER 3). In addition, the red mason bees benefited from herbaceous semi-natural habitats. The proportion of built-up areas had a negative effect on the horned mason bees, and the proportion of arable land on the red mason bees. The habitat maps explained horned mason bee abundances equally well as the floral resource maps, but red mason bee abundances were distinctly better explained by key floral resources. The pollination of field bean increased with higher proportions of early floral resources, whereas synchronous floral resources showed no measurable reduction in their pollination (CHAPTER 5). Habitat maps also explained field bean pollination better than floral resource maps. Here, pollination increased with increasing proportions of built-up areas in the landscapes and decreased with increasing proportions of arable land.
Our results highlight the importance of the spatio-temporal availability of certain key species as resource plants of wild bees in agricultural landscapes. They show that habitat maps are ahead of, or at least equal to, spatio-temporally resolved floral resource maps in predicting wild bee development and pollination. Nevertheless, floral resource maps allow us to draw more accurate conclusions between key floral resources and the organisms studied. The proximity to forest edges had a positive effect on each of the three wild bee species studied. However, besides pure food availability, other factors seem to co-determine the occurrence of wild bees in agricultural landscapes.
Agriculture covers one third of the world land area and has become a major source of water pollution due to its heavy reliance on chemical inputs, namely fertilisers and pesticides. Several thousands of tonnes of these chemicals are applied worldwide annually and partly reach freshwaters. Despite their widespread use and relatively unspecific modes of action, fungicides are the least studied group of pesticides. It remains unclear whether the taxonomic groups used in pesticide risk assessment are protective for non-target freshwater fungi. Fungi and bacteria are the main microbial decomposers converting allochthonous organic matter (litter) into a more nutritious food resource for leaf-shredding macroinvertebrates. This process of litter decomposition (LD) is central for aquatic ecosystem because it fuels local and downstream food webs with energy and nutrients. Effects of fungicides on decomposer communities and LD have been mainly analysed under laboratory conditions with limited representation of the multiple factors that may moderate effects in the field.
In this thesis a field study was conducted in a German vineyard area to characterise recurrent episodic exposure to fungicides in agricultural streams (chapter 2) and its effects on decomposer communities and LD (chapter 3). Additionally, potential interaction effects of nutrient enrichment and fungicides on decomposer communities and LD were analysed in a mesocosm experiment (chapter 4).
In the field study event-driven water sampling (EDS) and passive sampling with EmporeTM styrene-divinylbenzene reverse phase sulfonated disks (SDB disks) were used to assess exposure to 15 fungicides and 4 insecticides. A total of 17 streams were monitored during 4 rainfall events within the local application period of fungicides in 2012. EDS exceeded the time-weighted average concentrations provided by the SDB disks by a factor of 3, though high variability among compounds was observed. Most compounds were detected in more than half of the sites and mean and maximum peak (EDS) concentrations were under 1 and 3 µg/l, respectively. Besides, SDB disk-sampling rates and a free-software solution to derive sampling rates under time-variable exposure were provided.
Several biotic endpoints related to decomposers and LD were measured in the same sampling sites as the fungicide monitoring, coinciding with the major litter input period. Our results suggest that polar organic fungicides in streams change the structure of the fungal community. Causality of this finding was supported by a subsequent microcosm experiment. Whether other effects observed in the field study, such as reduced fungal biomass, increased bacterial density or reduced microbial LD can be attributed to fungicides remains speculative and requires further investigation. By contrast, neither the invertebrate LD nor in-situ measured gammarid feeding rates correlated with water-borne fungicide toxicity, but both were negatively associated with sediment copper concentrations. The mesocosm experiment showed that fungicides and nutrients affect microbial decomposers differently and that they can alter community structure, though longer experiments are needed to determine whether these changes may propagate to invertebrate communities and LD. Overall, further studies should include representative field surveys in terms of fungicide pollution and physical, chemical and biological conditions. This should be combined with experiments under controlled conditions to test for the causality of field observations.
Carabids, which are frequently distributed in agricultural landscapes, are natural enemies of different pests including slugs. Semi-natural habitats are known to affect carabids and thus, their potential to support natural pest control.
The impact of semi-natural habitats was investigated on carabids and slugs within different non-crop habitats (chapter 2). Most carabids and Deroceras reticulatum showed preferences for herbaceous semi-natural habitats, while Arion spp. occured mainly in woody habitats. An increase of predatory carabid abundance, which was linked to an inclining amount of semi-natural habitats in the landscape, and a decrease of Arion spp. densities, indicated a high potential for slug control in structural rich landscapes.
Effects of semi-natural habitats were investigated on predatory carabids and slugs in 18 wheat fields (chapter 3). Predatory carabid species richness was positively affected by the increasing amount of semi-natural habitats in the landscape, whereas predatory carabid abundance was neither influenced by adjacent habitat type nor by the proportion of semi-natural habitats in the landscape. The target pest species showed divergent patterns, whereas Arion spp. densities were highest in structural poor landscapes near woody margins. D. reticulatum was not affected by habitat type or landscape, reflecting its adaptation to agriculture. Results indicate an increased control of Arion spp. by carabids in landscapes with a high amount of semi-natural habitats.
Effects of semi-natural habitats and the influence of farming system was tested on carabid distribution within 18 pumpkin fields (chapter 4). Carabid species richness generally increased with decreasing distance to the field margins, whereas carabid abundance responded differently according to the adjacent habitat type. Farming system had no effect on carabids and landscape heterogeneity only affected carabids in organic pumpkin fields.
Slug and slug egg predation of three common carabid species was tested in single and double species treatments in the laboratory (chapter 5). Results show additive and synergistic effects depending on the carabid species. In general, semi-natural habitats can enhance the potential of slug control by carabids. This counts especially for Arionid slugs. Semi-natural habitats can support carabid communities by providing shelter, oviposition and overwintering sites as wells as complementary food sources. Therefore, it is important to provide a certain amount of non-crop habitats in agricultural landscapes.
The aquatic environment is exposed to multiple environmental pressures and mixtures of chemical substances, among them petroleum and petrochemicals, metals, and pesticides. Aquatic invertebrate communities are used as bioindicators to reflect long-term and integral effects. Information on the presence of species can be supplemented with information on their traits. SPEAR-type bioindicators integrate such trait information on the community level.
This thesis aimed at enhancing specificity of SPEAR-type bioindicators towards particular groups of chemicals, namely to mixtures of oil sands-derived compounds, hydrocarbons, and metals.
For developing a bioindicator for discontinuous contamination with oil-derived organic toxicants, a field study was conducted in the Canadian oil sands development region in Northern Alberta. The traits ‘physiological sensitivity towards organic chemicals’ and ‘generation time’ were integrated to develop the bioindicator SPEARoil, reflecting the community sensitivity towards oil sands derived contamination in relation to fluctuating hydrological conditions.
According to the SPEARorganic approach, a physiological sensitivity ranking of taxa was developed for hydrocarbon contamination originating from crude oil or petroleum distillates. For this purpose, ecotoxicological information from acute laboratory tests was enriched with rapid and mesocosm test results. The developed Shydrocarbons sensitivity values can be used in SPEAR-type bioindicators.
To specifically reflect metal contamination in streams via bioindicators, Australian field studies were re-evaluated with focus on the traits ‘physiological metal sensitivity’ and ‘feeding type’. Metal sensitivity values, however, explained community effects in the field only weakly. Instead, the trait ‘feeding type’ was strongly related to metal exposure. The fraction of predators in a community can, thus, serve as an indicator for metal contamination in the field.
Furthermore, several metrics reflecting exposure to chemical cocktails in the environment were compared using existing pesticide datasets. Exposure metrics based on the 5% fraction of species sensitivity distributions were found to perform best, however, closely followed by Toxic Unit metrics based on the most sensitive species of a community or Daphnia magna.
Mathematical models of species dispersal and the resilience of metapopulations against habitat loss
(2021)
Habitat loss and fragmentation due to climate and land-use change are among the biggest threats to biodiversity, as the survival of species relies on suitable habitat area and the possibility to disperse between different patches of habitat. To predict and mitigate the effects of habitat loss, a better understanding of species dispersal is needed. Graph theory provides powerful tools to model metapopulations in changing landscapes with the help of habitat networks, where nodes represent habitat patches and links indicate the possible dispersal pathways between patches.
This thesis adapts tools from graph theory and optimisation to study species dispersal on habitat networks as well as the structure of habitat networks and the effects of habitat loss. In chapter 1, I will give an introduction to the thesis and the different topics presented in this thesis. Chapter 2 will then give a brief summary of tools used in the thesis.
In chapter 3, I present our model on possible range shifts for a generic species. Based on a graph-based dispersal model for a generic aquatic invertebrate with a terrestrial life stage, we developed an optimisation model that models dispersal directed to predefined habitat patches and yields a minimum time until these patches are colonised with respect to the given landscape structure and species dispersal capabilities. We created a time-expanded network based on the original habitat network and solved a mixed integer program to obtain the minimum colonisation time. The results provide maximum possible range shifts, and can be used to estimate how fast newly formed habitat patches can be colonised. Although being specific for this simulation model, the general idea of deriving a surrogate can in principle be adapted to other simulation models.
Next, in chapter 4, I present our model to evaluate the robustness of metapopulations. Based on a variety of habitat networks and different generic species characterised by their dispersal traits and habitat demands, we modeled the permanent loss of habitat patches and subsequent metapopulation dynamics. The results show that species with short dispersal ranges and high local-extinction risks are particularly vulnerable to the loss of habitat across all types of networks. On this basis, we then investigated how well different graph-theoretic metrics of habitat networks can serve as indicators of metapopulation robustness against habitat loss. We identified the clustering coefficient of a network as the only good proxy for metapopulation robustness across all types of species, networks, and habitat loss scenarios.
Finally, in chapter 5, I utilise the results obtained in chapter 4 to identify the areas in a network that should be improved in terms of restoration to maximise the metapopulation robustness under limited resources. More specifically, we exploit our findings that a network’s clustering coefficient is a good indicator for metapopulation robustness and develop two heuristics, a Greedy algorithm and a deducted Lazy Greedy algorithm, that aim at maximising the clustering coefficient of a network. Both algorithms can be applied to any network and are not specific to habitat networks only.
In chapter 6, I will summarize the main findings of this thesis, discuss their limitations and give an outlook of future research topics.
Overall this thesis develops frameworks to study the behaviour of habitat networks and introduces mathematical tools to ecology and thus narrows the gap between mathematics and ecology. While all models in this thesis were developed with a focus on aquatic invertebrates, they can easily be adapted to other metapopulations.
The increase in plastic particles (< 5 mm) in the environment is a global problem, which is in direct correlation to the increasing production quantity and variety. Through direct input (primary) or through the degradation of macroplastics (secondary), particles enter the environmental compartments water and/or soil via conventional material transportation paths. The research and development work on the sustainable removal of microplastic particles (inert organic chemical stressors, IOCS) from wastewater is based on the construction of polymer inclusion compounds. IOCS describe a group of organic chemical molecules, which demonstrate a high level of persistence upon entry in the ecosystem and whose degradation is limited.
Following the principle of Cloud Point Technology, a novel separation technique has been developed which induces particle growth in microplastics and allows easier separation from the water by volume increase according to the state of the art. The concept for the sustainable removal of microplastics from Herbort and Schuhen is based on a three-step synthesis. This concept was further optimized as part of the research and adapted to the criteria of resource efficiency and profitability. The fundamental research is premised on the hypothesis that van der Waals forces with short ranges and localized hydrophobic interactions between precursors and/or material and the IOCS to be connected can induce a fixation through the formation of an inclusion compound with particle growth. Through the addition of silicon-based ecotoxicologically irrelevant coagulation and inclusion units, it is possible to initiate molecular self-organization with the hydrophobic stressors in an aggregation process induced through water. It results in adhesive particle growth around the polymer particles and between particles. Subsequently, the polymer extract can be separated from aquatic media through simple and cost-effective filtration processes (e.g. sand trap, grease trap), due to the 10,000 times larger volume microplastic agglomerates.
For a comprehensive understanding of evolutionary processes and for providing reliable prognoses about the future consequences of environmental change, it is essential to reveal the genetic basis underlying adaptive responses. The importance of this goal increases in light of ongoing climate change, which confronts organisms worldwide with new selection pressures and requires rapid evolutionary change to avoid local extinction. Thereby, freshwater ectotherms like daphnids are particularly threatened. Unraveling the genetic basis of local adaptation is complicated by the interplay of forces affecting patterns of genetic divergence among populations. Due to their key position in freshwater communities, cyclic parthenogenetic mode of reproduction and resting propagules (which form biological archives), daphnids are particularly suited for this purpose.
The aim of this thesis was to assess the impact of local thermal selection on the Daphnia longispina complex and to reveal the underlying genetic loci. Therefore, I compared genetic differentiation among populations containing Daphnia galeata, Daphnia longispina and their interspecific hybrids across time, space, and species boundaries. I revealed strongly contrasting patterns of genetic differentiation between selectively neutral and functional candidate gene markers, between the two species, and among samples from different lakes, suggesting (together with a correlation with habitat temperatures) local thermal selection acting on candidate gene TRY5F and indicating adaptive introgression. To reveal the candidate genes’ impact on fitness, I performed association analyses among data on genotypes and phenotypic traits of D. galeata clones from seven populations. The tests revealed a general temperature effect as well as inter-population differences in phenotypic traits and imply a possible contribution of the candidate genes to life-history traits. Finally, utilizing a combined population transcriptomic and reverse ecology approach, I introduced a methodology with a wide range of applications in evolutionary biology and revealed that local thermal selection was probably a minor force in shaping sequence and gene expression divergence among four D. galeata populations, but contributed to sequence divergence among two populations. I identified many transcripts possibly under selection or contributing strongly to population divergence, a large amount thereof putatively under local thermal selection, and showed that genetic and gene expression variation is not depleted specifically in temperature-related candidate genes.
In conclusion, I detected signs of local adaptation in the D. longispina complex across space, time, and species barriers. Populations and species remained genetically divergent, although increased gene flow possibly contributed, together with genotypes recruited from the resting egg bank, to the maintenance of standing genetic variation. Further work is required to accurately determine the influence of introgression and the effects of candidate genes on individual fitness. While I found no evidence suggesting a response to intense local thermal selection, the high resilience and adaptive potential regarding environmental change I observed suggest positive future prospects for the populations of the D. longispina complex. However, overall, due to the continuing environmental degradation, daphnids and other aquatic invertebrates remain vulnerable and threatened.
Inland waters play an active role in the global carbon cycle. They collect carbon from upstream landmasses and transport it downstream until it finally reaches the ocean. Along this path, manifold processing steps are evident, resulting in (permanent) retention of carbon by sediment burial as well as loss by evasion to the atmosphere. Constraining these carbon fluxes and their anthropogenic perturbation is an urgent need. In this context, attention needs to be set on a widespread feature of inland waters: their partial desiccation. This results in the emergence of formerly inundated sediments to the atmosphere, referred to as dry inland waters. One observed feature of dry inland waters are disproportional high carbon dioxide (CO2) emissions. However, this observation was so far based on local case studies and knowledge on the global prevalence and fundamental mechanisms of these emissions is lacking. Against this background, this thesis aims to provide a better understanding of the magnitude and mechanisms of carbon emissions from dry inland waters on the global and local scale and to assess the impact of dry inland waters on the global carbon cycle. The specific research questions of this thesis were: (1) How do gaseous carbon emissions from dry inland waters integrate into the global carbon cycle and into global greenhouse gas (GHG) budgets? (2) What effect do seasonal and long term drying have on the carbon cycling of inland waters? The thesis revealed that dry inland waters emit disproportional large amounts of CO 2 on a global scale and that these emissions share common drivers across ecosystems. Quantifying global reservoir drawdown and upscaling carbon fluxes to the global scale suggests that reservoirs emit more carbon than they bury, challenging the current understanding of reservoirs as net carbon sinks. On the local scale, this thesis revealed that both, heterogeneous emission pattern between different habitats and seasonal variability of carbon emissions from the drawdown area, needs to be considered. Further, this thesis showed that re-mobilization of buried carbon upon permanent desiccation of water bodies can explain the observed emission rates, supporting the hypothesis of a positive feedback-loop between climate change and desiccation of inland waters. Overall, the present thesis highlights the importance of adding emissions from dry inland waters as a pathway to the global carbon cycle of inland waters.
Diet-related effects of antimicrobials in aquatic decomposer-shredder and periphyton-grazer systems
(2022)
Leaf-associated microbial decomposers as well as periphyton serve as important food sources for detritivorous and herbivorous macroinvertebrates (shredders and grazers) in streams. Shredders and grazers, in turn, provide not only collectors with food but also serve as prey for predators. Therefore, decomposer-shredder and periphyton-grazer systems (here summarized as freshwater biofilm-consumer systems) are highly important for the energy and nutrient supply in heterotrophic and autotrophic stream food webs. However, both systems can be affected by chemical stressors, amongst which antimicrobials (e.g., antibiotics, fungicides and algaecides) are of particular concern. Antimicrobials can impair shredders and grazers not only via waterborne exposure (waterborne effect pathway) but also through dietary exposure and microorganism-mediated alterations in the food quality of their diet (dietary effect pathway). Even though the relevance of the latter pathway received more attention in recent years, little is known about the mechanisms that are responsible for the observed effects in shredders and grazers. Therefore, the first objective of this thesis was to broaden the knowledge of indirect antimicrobial effects in a model shredder and grazer via the dietary pathway. Moreover, although freshwater biofilm-consumer systems are most likely exposed to antimicrobial mixtures comprised of different stressor groups, virtually nothing is known of these mixture effects in both systems. Therefore, the second objective was to assess and predict diet-related antimicrobial mixture effects in a model freshwater biofilm-consumer system. During this thesis, positive diet-related effects of a model antibiotic on the energy processing and physiology of the shredder Gammarus fossarum were observed. They were probably triggered by shifts in the leaf-associated microbial community in favor of aquatic fungi that increased the food quality of leaves for the shredder. Contrary to that, a model fungicide induced negative effects on the energy processing of G. fossarum via the dietary pathway, which can be explained by negative impacts on the microbial decomposition efficiency leading to a reduced food quality of leaf litter for gammarids. For diet-related antimicrobial effects in periphyton-grazer systems, a model algaecide altered the periphyton community composition by increasing nutritious and palatable algae. This resulted in an enhanced consumption and physiological fitness of the grazer Physella acuta. Finally, it was shown that complex horizontal interactions among leaf-associated microorganisms are involved, making diet-related antimicrobial mixture effects in the shredder G. fossarum difficult to predict. Thus, this thesis provides new insights into indirect diet-related effects of antimicrobials on shredders and grazers as well as demonstrates uncertainties of antimicrobial mixture effect predictions for freshwater biofilm-consumer systems. Moreover, the findings in this thesis are not only informative for regulatory authorities, as indirect effects and effects of mixtures across chemical classes are not considered in the environmental risk assessment of chemical substances, but also stimulate future research to close knowledge gaps identified during this work.
This thesis examined two specific cases of point and diffuse pollution, pesticides and salinisation, which are two of the most concerning stressors of Germany’s freshwater bodies. The findings of this thesis were organized into three major components, of which the first component presents the contribution of WWTPs to pesticide toxicity (Chapter 2). The second component focuses on the current and future background salt ion concentrations under climate change with the absence of anthropogenic activities (Chapter 3). Finally, the third major component shows the response of invertebrate communities in terms of species turnover to levels of salinity change, considered as a proxy for human-driven salinisation (Chapter 4).