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Institute
Non-Consumptive Effects of Spiders and Ants: Does Fear Matter in Terrestrial Interaction Webs?
(2014)
Most animals suffer from predators. Besides killing prey, predators can affect prey physiology, morphology and behaviour. Spiders are among the most diverse and frequent predators in terrestrial ecosystems. Our behavioural arena experiments revealed that behavioural changes under spider predation risk are relatively scarce among arthropods. Wood crickets (Nemobius sylvestris), in particular, changed their behaviour in response to cues of various spider species. Thereby, more common and relatively larger spider species induced stronger antipredator behaviour in crickets.
Behavioural changes under predation risk are expected to enhance predator avoidance, but they come at a cost. Crickets previously confronted with cues of the nursery web spider (Pisaura mirabilis) were indeed more successful in avoiding predation. Surprisingly, crickets slightly increased food uptake and lost less weight under predation risk, indicating that crickets are able to compensate for short-term cost under predation risk. In a following plant choice experiment, crickets strongly avoided plants bearing spider cues, which in turn reduced the herbivory on the respective plants.
Similar to spiders, ants are ubiquitous predators and can have a strong impact on herbivores, but also on other predators. Juvenile spiders increased their propensity for long-distance dispersal if exposed to ant cues. Thus, spiders use this passive dispersal through the air (ballooning) to avoid ants and colonise new habitats.
In a field experiment, we compared arthropod colonisation between plants bearing cues of the nursery web spider and cue-free plants. We followed herbivory during the experimental period and sampled the arthropod community on the plants. In accordance with the plant choice experiment, herbivory was reduced on plants bearing spider cues. In addition, spider cues led to changes in the arthropod community: smaller spiders and black garden ants (Lasius niger) avoided plants bearing spider cues. In contrast, common red ants (Myrmica rubra) increased the recruitment of workers, possibly to protect their aphids.
Although behavioural changes were relatively rare on filter papers bearing spider cues, more natural experimental setups revealed strong and far-reaching effects of predation risk. We further suggest that risk effects influence the spatial distribution of herbivory, rather than reduce overall herbivory that is expected if predators kill herbivores. Consequently, the relative importance of predation and risk effects is crucial for the way predators affect lower trophic levels.
Biodiversity is not only threatened by habitat loss, climate change and pollution, but also by invasive species. The impact of introduced species is immense and causes substantial ecological and economical costs worldwide. With the start of domestications of the African wildcat (Felis lybica) in the Near East, the transport of house cats (Felis catus) around the world as a commensal and domesticate began. The general aim of my thesis was to investigate the impact of invasive feral cats on native species as well as underlying population genetic structures, diversity and phylogeography. This was studied in the context of the demographic history in Australia and Hawai'i. My studies confirmed that the main introductions of cats to Australia began in the 19th century via ships of European settlers, traders and workers. Similarly, I was able to confirm cat introductions to Hawai'i by European traders and explorers; which has to the present a devastating effect on Hawaiian endemic species. Likewise, cats are widespread across Australia, can be found on most islands and are recognized as one of the major threats to Australian native species. A selective feeding behaviour by invasive predators was found in one of my studies. This study additionally gives an indication for possible population recovery of small Western Australianrnvertebrate species after predator removal. Advancement and the combination of various management techniques allow, if adequately funded, a more efficient planning and implementation of eradication campaigns. Population genetic approaches are able to give insights into population genetic structure, diversity and kinship, thereby enabling management campaigns to be more cost effective and successful. No pattern of isolation by distance between populations of Hawai"i and Australia indicated that trade routes, such as the "Golden Round" of the maritime fur trade, facilitated a link between far off global cat populations. Multiple introductions to Australia and intermixing with domestic breed cats resulted in feral cat populations which showrnno signs of reduced genetic variability. My studies also revealed the advantages of bioproxies in combination with phylogeography, which enable the inference and reconstruction of introduction routes, history and origin of invasive species. Genetic signals of historically introduced genotypesrnare still discernible on islands with low number of introductions over time and thereby low intermixing with domestic fancy breeds. Feral cats' adaptability as an invader was reconfirmed and possible underlying genetic mechanisms enabling their success as a global invader ("global supercat") are discussed. Research into the feralisation process of cats will provide new information regarding the domestication of cats, the genetic basis of feralisation and allow additional insights into cats" adaptive potential.
By the work presented in this thesis, the CH4 emissions of the River Saar were quantified in space and time continuously and all relevant processes leading to the observed pattern were identified. The direct comparison between reservoir zones and free-flowing intermediate reaches revealed, that the reservoir zones are CH4 emission hot spots and emitted over 90% of the total CH4. On average, the reservoir zones emitted over 80 times more CH4 per square meter than the intermediate reaches between dams (0.23 vs. 19.7 mol CH4 m-2 d-1). The high emission rates measured in the reservoir zones fall into the range of emissions observed in tropical reservoirs. The main reason for this is the accumulation of thick organic rich sediments and we showed that the net sedimentation rate is an excellent proxy for estimating ebullitive emissions. Within the hot spot zones, the ebullitive flux enhanced also the diffusive surface emissions as well as the degassing emissions at dams.
To resolve the high temporal variability, we developed an autonomous instrument for continuous measurements of the ebullition rate over long periods (> 4 weeks). With this instrument we could quantify the variability and identify the relevant trigger mechanisms. At the Saar, ship-lock induces surges and ship waves were responsible for over 85% of all large ebullition events. This dataset was also used to determine the error associated with short sampling periods and we found that with sampling periods of 24 hours as used in other studies, the ebullition rates were systematically underestimated by ~50%. Measuring the temporal variability enabled us to build up a conceptual framework for estimating the temporal pattern of ebullition in other aquatic systems. With respect to the contribution of freshwater systems to the global CH4 emissions, hot spot emission sites in impounded rivers have the potential to increase the current global estimate by up to 7%.
Engineered nanoparticles (ENP) are widely used in different industrial fields and products. In the last years, the risk potential for the release of ENP in the environment has increased as never before. ENP are expected to pass the wastewater-river-topsoil-groundwater pathway. In the terrestrial and aquatic environment ENP can undergo aging and transformation processes which can influence fate, transport and toxicological effects to different living organisms.
The scope of this workshop is to gather researchers, scientists, experts and specialists from nanoparticle and colloid science, soil and environmental chemistry, ecotoxicology or neighbouring disciplines to discuss the latest results and findings in the field of aging, fate, transport and toxicological effects of nanoparticles in the environment.
Larvae of Cx.pipiens coocurred with Cladocera, but the latter established delayed in time. Biotope structure influenced time of species occurrence with ponds at reed-covered wetlands favouring crustacean development, while ponds at grassland biotopes favoured colonization by mosquito larvae. The mechanisms driving the negative effect of crustaceans on mosquito larvae were investigated within an experiment under artificial conditions. Crustacean communities were found to reduce both oviposition and larval development of Cx.pipiens. Crustacean communities of high taxa diversity, including both predatory and competing crustaceans, were more effective compared with crustacean communities dominated by single taxa. Presence of crustacean communities characterised by high taxa diversity increased the sensitivity of Cx.pipiens larvae towards Bti and prolonged the time of recolonization. In a final step the combined approach, using Bti and crustaceans, was evaluated under field conditions. The joint application of Bti and crustaceans was found to reduce mosquito larval populations over the whole observation period, while single application of Bti caused only short-term reduction of mosquito larvae. Single application of crustaceans had no significant effect, because high abundances of prior established mosquito larvae impeded propagation of crustaceans. At combined treatment, mosquito larvae were reduced by Bti application and hence crustaceans were able to proliferate without disturbance by interspecific competition. In conclusion, natural competitors were found to have a strong negative impact on mosquito larval populations. However, a time span of about 2 weeks has to be bridged, before crustacean communities reached a level sufficient for mosquito control. Results of a combined approach, complementing the short-term effect of the biological insecticide Bti with the long-term effect of crustaceans, were promising. Using natural competitors within an integrated control strategy could be an important tool for an effective, environmentally friendly and sustainable mosquito management.
Mathematical Modelling of GIS Tailored GUI Design with the Application of Spatial Fuzzy Logic
(2014)
This PhD thesis is situated within the framework of the Research-Group Learning and Neurosciences (ReGLaN)-Health and Logistics project. The goal of this project is the optimisation of health service delivery in the rural areas of South Africa. Cooperation takes place between ReGLaN-Health and Logistics and the South African Council for Scientific and Industrial Research (CSIR) Meraka Institute, with Prof Dr Dr Marlien Herselman of Pretoria, South Africa, as the central contact person. This thesis deals with the mathematical modelling of Geographic Information System (GIS)-tailoredrnGraphical User Interface (GUI) design with the application of spatial fuzzy logic. This thesis considers the mathematical visualisation of risk and resource maps for epidemiological issues using GIS and adaptive GUI design for an Open Source (OS) application for digital devices. The intention ofrnthis thesis is to provide spatial decision support tailored to different user groups. In order for the GUI elements to be evaluated and initialised, empirical teaching-learning-research on dealing with geomedia and GUI elements was conducted.
Structure of soil organic matter (SOM) is a hot topic of discussion among scientific community for several decades. The mostly discussed models, among many, are polymer model and supramolecular model. While the former considers SOM as macromolecules consisting of amorphous and crystalline domains, the latter explains SOM as a physicochemical entity dominated by weak hydrophobic and H-bond interactions in the secondary level, which holds individual molecules of primary structure together. The weak forces in secondary level impart characteristic mobility of SOM. Very important consequence of this multidimensional formulation is that physicochemical structure plays a crucial role in most biogeochemical functions of SOM, apart from the chemical composition. Recently introduced concept of cation and water molecule mediated bridges between OM molecular segments (CaB and WaMB, respectively) evolved from physicochemical understanding of SOM structure. Even though several indirect evidences were produced for CaB and WaMB during last years, no clear-cut understanding of these processes has been achieved yet. Experimental difficulty due to overlapping effects of equally important CaB-governing parameters such a pH and competing cations raises huge challenge in investigating CaB-related influences. This thesis, therefore, aims to validate an experimental set-up for inducing CaB within OM structures and assessing it from various chemical and physicochemical aspects.
The method involved removal of omnipresent cations and adjustment of pH before cation addition. This helped to separate pH effects and cation effects. Based on results obtained on two different types of organic matter, it can be deduced that multivalent cations can cross-link SOM, given that functional group density of the SOM material is enough for the functional groups to be arranged in sufficient spatial proximity to each other. Physicochemical structural reorganisation during aging causes formation of more and/or stronger CaB and WaMB. As for inducing CaB directly after cation treatment, cationic size and valency were found determinant also for aging effect. A strongly cross-linked system in the beginning is less vulnerable to structural changes and undergoes aging with lower intensity, than an initially weakly cross-linked system. Responsible for the structural changes is, the inherent mobility of SOM within its physicochemical assemblage. Thus the information on structural requirement of CaB and its consequences on OM matrix rigidity will help to obtain insight into the physicochemical SOM structure. Additionally, organic matter quality (assessed by thermal analysis) and pore structure of SOM formed in a set of artificial soils showed that mineral materials are important for the chemical nature of SOM molecules, but not for the physical structure of organo-mineral associations, at least after several months of SOM development.
Furthermore, nanothermal analysis using atomic force microscopy (AFM-nTA) was implemented in soils for the first time to reveal nanoscale thermal properties and their spatial distribution in nano- and micrometer scales. This helped to identify physicochemical processes, such as disruption of WaMB, in low-organic soils, in which bulk methods fail due to their low sensitivity. Further, various types of materials constituting in soils were distinguished with high resolution by advanced application of the method, in combination with other AFM parameters. Attempts were done to identify various materials, with the usage of defined test materials. Above all, the method is potent to reveal microspatial heterogeneity on sample surfaces, which could help understanding process-relevant hotspots, for example.
This thesis thus contributes to the scientific understanding on physicochemical structural dynamics via cross-linking by cations and via nanoscale thermal properties. Direct investigation on CaB demonstrated here will potentially help making a big leap in knowledge about the interaction. The observed aging effects add well to the understanding of supramolecular consideration of SOM. By introducing nanothermal analysis to the field of soil science, it is made possible to face the problem of heterogeneity and spatial distribution of thermal characteristics. Another important achievement of AFM-nTA is that it can be used to detect physicochemical processes, which are of low intensity.
Studies on the toxicity of chemical mixtures find that components at levels below no-observed-effect concentrations (NOECs) may cause toxicity resulting from the combined effects of mixed chemicals. However, chemical risk assessment frequently focuses on individual chemical substances, although most living organisms are substantially exposed to chemical mixtures rather than single substances. The concepts of additive toxicity, concentration addition (CA), and independent action (IA) models are often applied to predict the mixture toxicity of similarly and dissimilarly acting chemicals, respectively. However, living organisms and the environment may be exposed to both types of chemicals at the same time and location. In addition, experimental acquisition of toxicity data for every conceivable mixture is unfeasible since the number of chemical combinations is extremely large. Therefore, an integrated model to predict mixture toxicity on the basis of single mixture components having various modes of toxic action (MoAs) needs to be developed. The objectives of the present study were to analyze the challenges in predicting mixture toxicity in the environment, and to develop integrated models that overcome the limitations of the existing prediction models for estimating the toxicity of non-interactive mixtures through computational models. For these goals, four sub-topics were generated in this study. Firstly, applicable domains and limitations of existing integrated models were analyzed and grouped into three kinds of categories in this study. There are current approaches used to assess mixture toxicity; however, there is a need for a new research concept to overcome challenges associated with such approaches, which recent studies have addressed. These approaches are discussed with particular emphasis on those studies involved in computational approaches to predict the toxicity of chemical mixtures based on the toxicological data of individual chemicals. Secondly, through a case study and a computational simulation, it was found that the Key Critical Component (KCC) and Composite Reciprocal (CR) methods (as described in the European Union (EU) draft technical guidance notes for calculating the Predicted No Effect Concentration (PNEC) and Derived No Effect Level (DNEL) of mixtures) could derive significantly different results. As the third and fourth sub-topics of this study, the following two integrated addition models were developed and successfully applied to overcome the inherent limitations of the CA and IA models, which could be theoretically used for either similarly or dissimilarly acting chemicals: i) a Partial Least Squares-Based Integrated Addition Model (PLS-IAM), and, ii) a Quantitative Structure-Activity Relationship-Based Two-Stage Prediction (QSAR-TSP) model. In this study, it was shown that the PLS-IAM might be useful to estimate mixture toxicity when the toxicity data of similar mixtures having the same compositions were available. In the case of the QSAR-TSP model, it showed the potential to overcome the critical limitation of the conventional TSP model, which requires knowledge of the MoAs for all chemicals. Therefore, this study presented good potential for the advanced integrated models (e.g., PLS-IAM and QSAR-TSP), while considering various non-interactive constituents that have different MoAs in order to increase the reliance of conventional models and simplify the procedure for risk assessment of mixtures.
Chemical plant protection is an essential element in integrated pest management and hence, in current crop production. The use of Plant Protection Products (PPPs) potentially involves ecological risk. This risk has to be characterised, assessed and managed.
For the coming years, an increasing need for agricultural products is expected. At the same time, preserving our natural resources and biodiversity per se is of equally fundamental importance. The relationship of our economic success and cultural progress to protecting the environment has been made plain in the Ecosystem Service concept. These distinct 'services' provide the foundation for defining ecological protection goals (Specific Protection Goals, SPGs) which can serve in the development of methods for ecological risk characterisation, assessment and management.
Ecological risk management (RM) of PPPs is a comprehensive process that includes different aspects and levels. RM is an implicit part of tiered risk assessment (RA) schemes and scenarios, yet RM also explicitly occurs as risk mitigation measures. At higher decision levels, RM takes further risks, besides ecological risk, into account (e.g., economic). Therefore, ecological risk characterisation can include RM (mitigation measures) and can be part of higher level RM decision-making in a broader Ecosystem Service context.
The aim of this thesis is to contribute to improved quantification of ecological risk as a basis for RA and RM. The initial general objective had been entitled as "… to estimate the spatial and temporal extent of exposure and effects…" and was found to be closely related to forthcoming SPGs with their defined 'Risk Dimension'.
An initial exploration of the regulatory framework of ecological RA and RM of PPPs and their use, carried out in the present thesis, emphasised the value of risk characterisation at landscape-scale. The landscape-scale provides the necessary and sufficient context, including abiotic and biotic processes, their interaction at different scales, as well as human activities. In particular, spatially (and temporally) explicit landscape-scale risk characterisation and RA can provide a direct basis for PPP-specific or generic RM. From the general need for tiered landscape-scale context in risk characterisation, specific requirements relevant to a landscape-scale model were developed in the present thesis, guided by the key objective of improved ecological risk quantification. In principle, for an adverse effect (Impact) to happen requires a sensitive species and life stage to co-occur with a significant exposure extent in space and time. Therefore, the quantification of the Probability of an Impact occurring is the basic requirement of the model. In a landscape-scale context, this means assessing the spatiotemporal distribution of species sensitivity and their potential exposure to the chemical.
The core functionality of the model should reflect the main problem structures in ecological risk characterisation, RA and RM, with particular relationship to SPGs, while being adaptable to specific RA problems. This resulted in the development of a modelling framework (Xplicit-Framework), realised in the present thesis. The Xplicit-Framework provides the core functionality for spatiotemporally explicit and probabilistic risk characterisation, together with interfaces to external models and services which are linked to the framework using specific adaptors (Associated-Models, e.g., exposure, eFate and effect models, or geodata services). From the Xplicit-Framework, and using Associated-Models, specific models are derived, adapted to RA problems (Xplicit-Models).
Xplicit-Models are capable of propagating variability (and uncertainty) of real-world agricultural and environmental conditions to exposure and effects using Monte Carlo methods and, hence, to introduce landscape-scale context to risk characterisation. Scale-dependencies play a key role in landscape-scale processes and were taken into account, e.g., in defining and sampling Probability Density Functions (PDFs). Likewise, evaluation of model outcome for risk characterisation is done at ecologically meaningful scales.
Xplicit-Models can be designed to explicitly address risk dimensions of SPGs. Their definition depends on the RA problem and tier. Thus, the Xplicit approach allows for stepwise introduction of landscape-scale context (factors and processes), e.g., starting at the definitions of current standard RA (lower-tier) levels by centring on a specific PPP use, while introducing real-world landscape factors driving risk. With its generic and modular design, the Xplicit-Framework can also be employed by taking an ecological entity-centric perspective. As the predictive power of landscape-scale risk characterisation increases, it is possible that Xplicit-Models become part of an explicit Ecosystem Services-oriented RM (e.g., cost/benefit level).
This habilitation thesis deals with the effects of toxicants on freshwater ecosystems and considers different toxicant classes (pesticides, organic toxicants, salinity) and biotic endpoints (taxonomic community structure, trait community structure, ecosystem functions).
The thesis comprises 12 peer-reviewed international publications on these topics. All of the related studies rely on mesocosm or field investigations, or the analysis of field biomonitoring or chemical monitoring data. Publications I and II are devoted to passive sampling of a neonicotinoid insecticide and polycyclic aromatic hydrocarbons (PAHs), respectively. They show that biofouling and a diffusion-limiting membrane can reduce the sampling rate of the pulsed insecticide exposure and that receiving phases of different thicknesses can be used to assess the kinetic regime during field deployment of passive samplers. Publications III to VI mainly focus on trait-based approaches to reveal toxicant effects on invertebrates in streams. An overview on the framework and several applications of a trait-based approach to detect effects of pesticides (SPEARpesticides index) are given in publication III. Publication IV describes the development of a trait database for South-East Australian stream invertebrates and its successful application in the adaptation of SPEARpesticides as well as the development of a salinity index. Moreover, a conceptual model for the future development of trait-based biomonitoring indices is proposed. Publication V reports a mesocom study on the effects of a neonicotinoid insecticide on field-realistic invertebrate communities. The insecticide had long-term effects on the invertebrate communities, which were only detected when grouping the taxa according to their life-history traits. A comprehensive field study employing different pesticide sampling methods including passive sampling and biomonitoring of the invertebrate and microbial communities is presented in publication VI. The study did not find pesticide-induced changes in the microbial communities, but detected adverse effects of current-use pesticides on the invertebrate communities using the trait-based SPEARpesticides index. This index is also applied in a meta-analysis on thresholds for the effects of pesticides on invertebrate communities in publication VII. It is shown that there is a similar dose-response relationship between SPEARpesticides and pesticide toxicity over different biogeographical regions and continents. In addition, the thresholds for effects of pesticides are lower than derived from most mesocosm studies and than considered in regulatory pesticide risk assessment. The publications VIII to X use statistical data analysis approaches to examine effects of toxicants in freshwater ecosystems. Using governmental monitoring data on 331 organic toxicants monitored monthly in 4 rivers over 11 years, publication VIII finds that organic toxicants frequently occurred in concentrations envisaging acute toxic effects on invertebrates and algae even in large rivers. Insecticides and herbicides were the chemical groups mainly contributing to the ecotoxicological risk. Publication IX introduces a novel statistical method based on a similarity index to estimate thresholds for the effects of toxicants or other stressors on ecological communities. The application of the method for deriving thresholds for salinity, heavy metals and pesticides in streams is presented in three case studies. Publication X tackles the question of interactive effects between different toxicants using data from a field study on stream invertebrates in 24 sites of South-East Australia. Both salinity and pesticides exhibited statistically significant effects on the invertebrate communities, but no interaction between the stressors was found. Moreover, salinity acted on a higher taxonomical level than pesticides suggesting evolutionary adaptation of stream invertebrates compared to pesticide stress. Publications XI and XII concentrate on the effects of toxicants on biodiversity, ecosystem functions and ecosystem services, with publication XI summarising different studies related to the ecological risk assessment for these endpoints. A field study on the effects of pesticides and salinity on the ecosystem functions of allochthonous organic matter decomposition, gross primary production and ecosystem respiration is presented in publication XII. Both pesticides and salinity reduced the breakdown of allochthonous organic matter, whereas no effects on the other ecosystem functions were detected. A chapter following these publications synoptically discusses all studies of this habilitation thesis and draws general conclusions. It is stressed that in order to advance the understanding of effects of toxicants on freshwater ecosystems more ecological realism is needed in ecotoxicological approaches and that the spatiotemporal extent of toxicant effects needs more scrutiny.