Chemical effects on ecological interactions within a model-experiment loop

We propose in this paper a method to assess the effects of a contaminant on a micro-ecosystem, integrating the population dynamics and the interactions between species. For that, we developed a dynamic model to describe the functioning of a microcosm exposed to a contaminant and to discriminate direct and indirect effects. Then, we get back from modelling to experimentation in order to identify which of the collected data have really been necessary and sufficient to estimate model parameters in order to propose a more efficient experimental design for further investigations. We illustrated our approach using a 2-L laboratory microcosm involving three species (the duckweed Lemna minor, the microalgae Pseudokirchneriella subcapitata and the daphnids Daphnia magna) exposed to cadmium contamination. We modelled the dynamics of the three species and their interactions using a mechanistic model based on coupled ordinary differential equations. The main processes occurring in this three-species microcosm were thus formalized, including growth and settling of algae, growth of duckweeds, interspecific competition between algae and duckweeds, growth, survival and grazing of daphnids, as well as cadmium effects. We estimated model parameters by Bayesian inference, using simultaneously all the data issued from multiple laboratory experiments specifically conducted for this study. Cadmium concentrations ranged between 0 and 50 μg.L-1 . For all parameters of our model, we obtained biologically realistic values and reasonable uncertainties. The cascade of cadmium effects, both direct and indirect, was identified. Critical effect concentrations were provided for the life history traits of each species. An example of experimental design adapted to this kind a microcosm was also proposed. This approach appears promising when studying contaminant effects on ecosystem functioning

Capturer les interactions écologiques en microcosme sous pression chimique à travers le prisme de la modélisation

Contaminant risk assessment is generally based on data collected during single species bioassays (including only one species). As a consequence, interactions between species that occur in ecosystems are not taken into account. To investigate the effects of contaminants on interacting species dynamics, this thesis aims at modelling the functioning of a 2-L laboratory microcosm with three species, the daphnid Daphnia magna, the duckweed Lemna minor and the microalgae Pseudokirchneriella subcapitata, exposed to cadmium contamination. We modelled the dynamics of the three species, their interactions and the effects of cadmium using a mechanistic model based on coupled ordinary differential equations. The main processes occurring in this three-species microcosm were thus formalized, including growth and survival of daphnids, growth and settling of algae, growth of duckweeds, grazing of algae by daphnids, interspecific competition between the algae and duckweeds, and the effects of cadmium on these processes. We estimated model parameters by Bayesian inference, using simultaneously all the data issued from multiple laboratory experiments specifically conducted for this study during the thesisL'évaluation du risque lié aux contaminants est généralement basée sur des données collectées au cours d'essais monospécifiques (à une seule espèce). Par conséquent, les interactions entre espèces, bien qu'elles structurent les écosystèmes, ne sont pas prises en compte. Pour explorer les effets des contaminants sur la dynamique des espèces en interaction, cette thèse vise à modéliser le fonctionnement d'un microcosme de laboratoire de deux litres incluant trois espèces, la daphnie Daphnia magna, la lentille d'eau Lemna minor et la microalgue Pseudokirchneriella subcapitata, exposées à une contamination par le cadmium. La dynamique des trois espèces ainsi que leurs interactions et les effets du cadmium ont été décrits par un modèle mécaniste basé sur des équations différentielles ordinaires couplées. Les principaux processus intervenant dans ce microcosme de trois espèces ont donc été formalisés, notamment la croissance et la survie des daphnies, la croissance et la sédimentation des algues, la croissance des lentilles, le broutage des algues par les daphnies, la compétition interspécifique entre algues et lentilles et les effets du cadmium sur ces différents processus. Les paramètres du modèle ont été estimés par inférence bayésienne, en utilisant simultanément toutes les données issues de différentes expérimentations en laboratoire, réalisées au cours de la thèse spécialement pour cette étud

Capturing ecological interactions within a microcosm under chemical pressure through the prism of modelling

L'évaluation du risque lié aux contaminants est généralement basée sur des données collectées au cours d'essais monospécifiques (à une seule espèce). Par conséquent, les interactions entre espèces, bien qu'elles structurent les écosystèmes, ne sont pas prises en compte. Pour explorer les effets des contaminants sur la dynamique des espèces en interaction, cette thèse vise à modéliser le fonctionnement d'un microcosme de laboratoire de deux litres incluant trois espèces, la daphnie Daphnia magna, la lentille d'eau Lemna minor et la microalgue Pseudokirchneriella subcapitata, exposées à une contamination par le cadmium. La dynamique des trois espèces ainsi que leurs interactions et les effets du cadmium ont été décrits par un modèle mécaniste basé sur des équations différentielles ordinaires couplées. Les principaux processus intervenant dans ce microcosme de trois espèces ont donc été formalisés, notamment la croissance et la survie des daphnies, la croissance et la sédimentation des algues, la croissance des lentilles, le broutage des algues par les daphnies, la compétition interspécifique entre algues et lentilles et les effets du cadmium sur ces différents processus. Les paramètres du modèle ont été estimés par inférence bayésienne, en utilisant simultanément toutes les données issues de différentes expérimentations en laboratoire, réalisées au cours de la thèse spécialement pour cette étudeContaminant risk assessment is generally based on data collected during single species bioassays (including only one species). As a consequence, interactions between species that occur in ecosystems are not taken into account. To investigate the effects of contaminants on interacting species dynamics, this thesis aims at modelling the functioning of a 2-L laboratory microcosm with three species, the daphnid Daphnia magna, the duckweed Lemna minor and the microalgae Pseudokirchneriella subcapitata, exposed to cadmium contamination. We modelled the dynamics of the three species, their interactions and the effects of cadmium using a mechanistic model based on coupled ordinary differential equations. The main processes occurring in this three-species microcosm were thus formalized, including growth and survival of daphnids, growth and settling of algae, growth of duckweeds, grazing of algae by daphnids, interspecific competition between the algae and duckweeds, and the effects of cadmium on these processes. We estimated model parameters by Bayesian inference, using simultaneously all the data issued from multiple laboratory experiments specifically conducted for this study during the thesi

Fate, toxicity and bioconcentration of cadmium on Pseudokirchneriella subcapitata and Lemna minor in mid-term single tests

International audienc

Mechanistic modelling of daphnid-algae dynamics within a laboratory microcosm

International audienceOur study describes the functioning of a 2-L laboratory microcosm of two species, daphnids (Daphnia magna) and microalgae (Pseudokirchneriella subcapitata), in two abiotic phases (water column and sedi- ment). We modelled the dynamics of both species and their interactions using a mechanistic model based on coupled ordinary differential equations. The main processes occurring in this two-species microcosm were thus formalised, including growth and settling of algae and growth, survival and grazing of daph- nids. We estimated model parameters by Bayesian inference, using simultaneously all data from multiple experiments specifically conducted for this study. Two types of model verifications were performed: (1) internal verification to validate model structure and parameter estimation method using all data simul- taneously; and (2) external verification to validate the ability of the model to be applied under new sediment conditions. For all parameters, we obtained biologically realistic values and reasonable uncer- tainties. The first verification step allowed us to confirm the modelled processes and the benefits of our parameter estimation method. The second one confirmed the ability of the model to describe microcosm functioning under different abiotic conditions. This innovative combination of mechanistic modelling and model-guided experiments revealed successful to understand the algae-daphnid microcosm func- tioning. This approach appears promising and can be applied to various issues in the ecological and ecotoxicological fields

Tree potential growth varies more than competition among spontaneously established forest stands of pedunculate oak (Quercus robur)

Key message : Analyses of dendrochronological data from 15 recently established tablished stands of pedunculate oak (Quercus robur L.) revealed that functions describing potential tree growth in the absence of neighbours varied more between stands than functions describing competitive effects of conspecific neighbours. This suggests that competition functions can more easily be transferred among stands than potential growth functions.Context : The variability inherent in the natural establishment of tree stands raises the question whether one can find general models for potential growth and competition that hold across stands.Aims : We investigated variation in potential growth and competition among recently established stands of Q. robur and tested whether this variation depends on stand structure. We also tested whether competition is symmetric or asymmetric and whether it is density-dependent or size-dependent. Lastly, we examined whether between-year growth variation is synchronous among stands.Methods : Potential growth, competition and between-year growth variation were quantified with statistical neighbourhood models. Model parameters were estimated separately for each stand using exhaustive mapping and dendrochronology data.Results : Competition was best described with an asymmetric size-dependent model. Functions describing potential growth varied more among forest stands than competition functions. Parameters determining these functions could not be explained by stand structure. Moreover, annual growth rates showed only moderate synchrony across stands.Conclusion : The substantial between-stand variability in potential growth needs to be considered when assessing the functioning, ecosystem services and management of recently established Q. robur stands. In contrast, the relative constancy of competition functions should facilitate their extrapolation across stands

A brief review on models for birds exposed to chemicals

International audience"A Who's Who of pesticides is therefore of concern to us all. If we are going to live so intimately with these chemicals eating and drinking them, taking them into the very marrow of our bones-we had better know something about their nature and their power."-Rachel Carson, Silent Spring.In her day, Rachel Carson was right: plant protection products (PPP) like all the other chemical substances that humans increasingly release into the environment without further precaution, are among our worst enemies today. All compartments of the biosphere, air, soil and water, are potential reservoirs within which all species that live there are impaired. Birds are particularly concerned: PPP are recognized as a factor in the decline of their abundance and diversity predominantly in agricultural landscapes. Due to the restrictions on vertebrates testing, \textit{in silico} based approaches are an ideal choice alternative given input data are available. This is where the problem lies as we will illustrate in this paper. We performed an extensive literature search covering a long period of time, a wide diversity of bird species, a large range of chemical substances and as many model types as possible to encompass all our future need to improve environmental risk assessment of chemicals for birds. In the end, we show that poultry species exposed to pesticides are the most studied at the individual level with physiologically based toxicokinetic models. To go beyond, with more species, more chemical types, over several levels of biological organization, we show that observed data are crucially missing. As a consequence, improving existing models or developing new ones could be like climbing Everest if no additional data can be gathered, especially on chemical effects and toxicodynamic aspects

A brief review on models for birds exposed to chemicals

International audience"A Who's Who of pesticides is therefore of concern to us all. If we are going to live so intimately with these chemicals eating and drinking them, taking them into the very marrow of our bones-we had better know something about their nature and their power."-Rachel Carson, Silent Spring.In her day, Rachel Carson was right: plant protection products (PPP) like all the other chemical substances that humans increasingly release into the environment without further precaution, are among our worst enemies today. All compartments of the biosphere, air, soil and water, are potential reservoirs within which all species that live there are impaired. Birds are particularly concerned: PPP are recognized as a factor in the decline of their abundance and diversity predominantly in agricultural landscapes. Due to the restrictions on vertebrates testing, \textit{in silico} based approaches are an ideal choice alternative given input data are available. This is where the problem lies as we will illustrate in this paper. We performed an extensive literature search covering a long period of time, a wide diversity of bird species, a large range of chemical substances and as many model types as possible to encompass all our future need to improve environmental risk assessment of chemicals for birds. In the end, we show that poultry species exposed to pesticides are the most studied at the individual level with physiologically based toxicokinetic models. To go beyond, with more species, more chemical types, over several levels of biological organization, we show that observed data are crucially missing. As a consequence, improving existing models or developing new ones could be like climbing Everest if no additional data can be gathered, especially on chemical effects and toxicodynamic aspects

A brief review on models for birds exposed to chemicals

International audience"A Who's Who of pesticides is therefore of concern to us all. If we are going to live so intimately with these chemicals eating and drinking them, taking them into the very marrow of our bones-we had better know something about their nature and their power."-Rachel Carson, Silent Spring.In her day, Rachel Carson was right: plant protection products (PPP) like all the other chemical substances that humans increasingly release into the environment without further precaution, are among our worst enemies today. All compartments of the biosphere, air, soil and water, are potential reservoirs within which all species that live there are impaired. Birds are particularly concerned: PPP are recognized as a factor in the decline of their abundance and diversity predominantly in agricultural landscapes. Due to the restrictions on vertebrates testing, \textit{in silico} based approaches are an ideal choice alternative given input data are available. This is where the problem lies as we will illustrate in this paper. We performed an extensive literature search covering a long period of time, a wide diversity of bird species, a large range of chemical substances and as many model types as possible to encompass all our future need to improve environmental risk assessment of chemicals for birds. In the end, we show that poultry species exposed to pesticides are the most studied at the individual level with physiologically based toxicokinetic models. To go beyond, with more species, more chemical types, over several levels of biological organization, we show that observed data are crucially missing. As a consequence, improving existing models or developing new ones could be like climbing Everest if no additional data can be gathered, especially on chemical effects and toxicodynamic aspects