Effects of Esfenvalerate on Daphnia magna under multiple levels of biological complexity : the influence of time, competition and environmental stressors / Florian Schunck
VerfasserSchunck, Florian
KörperschaftHelmholtz-Zentrum für Umweltforschung ; Rheinisch-Westfälische Technische Hochschule Aachen
ErschienenLeipzig : Helmholtz-Zentrum für Umweltforschung GmbH - UFZ; Bibliothek, 2024
Umfang1 Online-Ressource (xx, 154 Seiten, 5,31 MB) : Diagramme, Illustrationen
HochschulschriftRheinisch-Westfälische Technische Hochschule Aachen, Dissertation, 2023
Tag der mündlichen Prüfung: 06. November 2023
Literaturverzeichnis: Seite 95-121
Sprache der Zusammenfassung: Englisch, Deutsch
SerieUFZ-Dissertation ; 2024, 1
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Effects of Esfenvalerate on Daphnia magna under multiple levels of biological complexity [5.31 mb]
Worldwide ecosystems are increasingly stressed due to rapidly changing environmental conditions. Simultaneously the nutritional needs of a growing world population require a highly productive agriculture which will still rely on fertilizers and pesticides in the forseeable future. Pesticides however are also one of the largest contributors to the global loss of invertebrate diversity biomass and the associated agriculturally relevant ecosystem functions. We are metaphorically speaking cutting the branch on which we all sit. In order to maintain this delicate balance it is essential to protect the ecosystems close to arable lands. Invertebrates in surface waters are very susceptible to pesticide runoff from the field. This leads to unpredictable effects in complex aquatic communities - effects that are often much larger than thresholds determined in single species laboratory tests. Despite the increased interest in the conservation of stressed ecosystems the mechanistic understanding of pesticide effects under higher levels of biological complexity is still limited. This work is therefore set out to understand the processes that regulate the effects of low concentrations of pesticides under environmental complexity. To this end a sequence of investigations was conducted increasing the complexity step by step from the individual level to the population level until the species–species competition level. To allow for comparisons between the investigations the standard model organism Daphnia magna (water flea) was exposed in all experiments to pulses of the insecticide esfenvalerate. In Chapter 3 the effects of interacting stressors on individuals of D. magna are described. Esfenvalerate was combined with ultraviolet- B (UV-B) radiation in varying order of exposure and with different pauses between exposures in order to identify the influence of time on stressor interactions. It was shown that increased temporal distance between an esfenvalerate pulse and an environmental stress pulse shifted the interaction between the stressors from antagonism to synergism on the individual level. It was also shown that low stressor doses elicited antagonistic responses while high doses led to synergistic responses. The next level of complexity investigated was that of the population (Chapter 4). D. magna populations were non-invasively monitored during a complete development cycle. When populations at carrying capacity were exposed to 1⁄3 of the half maximal effective concentration (EC50) 2 out of 4 replicates collapsed due to direct mortality effects of esfenvalerate. In contrast concentrations at 1⁄30 and 1⁄10 of the EC50 significantly increased the population biomass for up to 7 weeks after the exposure. It was hypothesized that population increases are due to a hormetic response where reduced intraspecific competition is the trade-off that enabled this response. In the final investigation (Chapter 5) populations of D. magna and Culex pipiens (mosquito larvae) competing for a limited amount of food were exposed to repeated pulses of esfenvalerate at extremely low concentrations (1/1000–1/10 of the EC50). This was done to test if the presence of a competitor changes the interspecific competition between co-existing species with a shared ecological niche. It was revealed that species-species correlations significantly increased after the exposure. This was associated with a decrease in interspecific com- petition. In contrast to the results shown in the previous investigation low concentrations of esfenvalerate did not provoke a stimulatory response in the density and biomass of either population. The level of ecological complexity had a substantial influence on the detected effects of esfenvalerate in this work. Ecological organization stressor timing and pesticide dose had strong influences on the stress response. Those non-linearities can help to explain why it is so difficult to predict effects of pesticides in the field. The approach taken in this work suggests that environmental risk assessment (ERA) should consider intraspecific and interspecific competition when assessing the effects of very low doses of pesticides on the biodiversity of ecologically similar species. By combining the results from Chapter 4 and Chapter 5 it was hypothesized that the stimulatory hormesis response which is an increasingly discussed phenomenon only emerges when associated trade-offs are not penalized by environmental conditions.