A modelling approach for conservation of European Eel (Anguilla anguilla) and related fisheries

Demographic models that have been proposed to describe the continental phase of eel life cycle can be divided into site specific and general models. Site specific models (see for example Vøllestad and Jonsson (1988) or De Leo and Gatto (1995)) are usually devised, calibrated and, in same cases, validated upon data from particular dataset. Such models help in describing local population dynamics but can be hardly applied to different populations. On the other hand, very general model (see Dekker, 2000 or Lambert and Rochard, 2007) can be easily applied to different contexts but usually neglect parameter calibration and prediction validation on field data. The aim of this thesis is to develop modelling approaches for describing eel demography that can be easily applied to different contexts where a suitable dataset is provided (chapters 2, 3, 4, 5 and 6). Then, I show the effectiveness of such models when defining management plans, requested by the new European regulation (EC 1100/2007), with particular emphasis on eel fisheries and multiobjective analyses (chapters 7 and 8)

An ecophysiological model of plant-pest interactions: the role of nutrient and water availability.

Empirical studies have shown that particular irrigation/fertilization regimes can reduce pest populations in agroecosystems. This appears to promise that the ecological concept of bottom-up control can be applied to pest management. However, a conceptual framework is necessary to develop a mechanistic basis for empirical evidence. Here, we couple a mechanistic plant growth model with a pest population model. We demonstrate its utility by applying it to the peach-green aphid system. Aphids are herbivores which feed on the plant phloem, deplete plants' resources and (potentially) transmit viral diseases. The model reproduces system properties observed in field studies and shows under which conditions the diametrically opposed plant vigour and plant stress hypotheses find support. We show that the effect of fertilization/irrigation on the pest population cannot be simply reduced as positive or negative. In fact, the magnitude and direction of any effect depend on the precise level of fertilization/irrigation and on the date of observation. We show that a new synthesis of experimental data can emerge by embedding a mechanistic plant growth model, widely studied in agronomy, in a consumer-resource modelling framework, widely studied in ecology. The future challenge is to use this insight to inform practical decision making by farmers and growers

No apparent genetic bottleneck in the demographically declining European eel using molecular genetics and forward-time simulations

No apparent genetic bottleneck in the demographically declining European eel using molecular genetics and forward-time simulations

Fishery-Induced Selection for Slow Somatic Growth in European Eel

Both theoretical and experimental studies have shown that fishing mortality can induce adaptive responses in body growth rates of fishes in the opposite direction of natural selection. We compared body growth rates in European eel (Anguilla anguilla) from three Mediterranean stocks subject to different fishing pressure. Results are consistent with the hypotheses that i) fast-growing individuals are more likely to survive until sexual maturity than slow-growing ones under natural conditions (no fishing) and ii) fishing can select for slow-growing individuals by removing fast-growing ones. Although the possibility of human-induced evolution seems remote for a panmictic species like such as the European eel, further research is desirable to assess the implications of the intensive exploitation on this critically endangered fish

An ecological model to analyze and control the dynamics of the leafminer pest Tuta absoluta on tomato (Solanum lycopersicum)

The South American insect Tuta absoluta is a significant leaf-mining pest for tomato plants ( Solanum lycopersicum ). In the last fifteen years, it has invaded and rapidly expanded across most European and African countries. This poses increasing threats to key tomato-growing regions worldwide. Despite the global significance of crop damages caused by T. absoluta , existing models have primarily focused on the developmental growth at the individual level, with limited consideration for population and community-level interactions, especially the plant-pest relationship. Here we introduce and discuss an ecological, process-based, mathematical model that accounts for the interdependent dynamics between a population of the herbivorous insect and the tomato plants it feeds on. The model explicitly integrates the impacts of water and nutrients availability, as well as temperature, on the growth of both insect and plant populations. After calibrating the model using empirical data, we find that its simulations can replicate different observed patterns. Leveraging the mechanistic nature of our approach, we analyze the combined effects of various temperature, fertilization/irrigation (fertigation) and biocontrol scenarios on ( i ) crop growth and ( ii ) the overall health of the production system. This enables us to identify knowledge gaps and to discuss the effectiveness and trade-offs associated with different management policies

A global viability assessment of the European eel

The global European eel (Anguilla anguilla) stock is critically endangered according to the IUCN, and the European Commission has urged the development of conservation plans aimed to ensure its viability. However, the complex life cycle of this panmictic species, which reproduces in the open ocean but spends most of its prereproductive life in continental waters (thus embracing a huge geographic range and a variety of habitat types), makes it difficult to assess the long-term effectiveness of conservation measures. The interplay between local and global stressors raises intriguing cross-scale conservation challenges that require a comprehensive modelling approach to be addressed. We developed a full life cycle model of the global European eel stock, encompassing both the oceanic and the continental phases of eel's life, and explicitly allowing for spatial heterogeneity in vital rates, availability of suitable habitat and settlement potential via a metapopulation approach. We calibrated the model against a long-term time series of global European eel catches and used it to hindcast the dynamics of the stock in the past and project it over the 21st century under different management scenarios. Although our analysis relies on a number of inevitable simplifying assumptions and on data that may not embrace the whole range of variation in population dynamics at the small spatiotemporal scale, our hindcast is consistent with the general pattern of decline of the stock over recent decades. The results of our projections suggest that (i) habitat loss played a major role in the European eel decline; (ii) the viability of the global stock is at risk if appropriate protection measures are not implemented; (iii) the recovery of spawner escapement requires that fishing mortality is significantly reduced; and (iv) the recovery of recruitment might not be feasible if reproductive output is not enhanced

Life history theory explains observed plasticity in Tuta absoluta age and size at pupation

We explore the observed plasticity in Tuta absoluta age and size at pupation in response to water and nutrients scarcity. Using a minimal theoretical model, we demonstrate that the observed plasticity can be viewed as a strategic adaptation of individuals aimed at maximizing their reproductive output under stressful environmental conditions. T. absoluta plasticity is then found to align with expectations from fundamental principles of life history theory

Modelling the effect of multi-year aphid infestation on fruit production in perennial trees

Aphids are commonly considered major agricultural pests because of their ability to alter host plant physiology and impair foliar growth. However, their effect on fruit production in perennial trees did not receive wide attention and few existing works have mainly focused on plant-aphid dynamics in a single growing season (i.e., few months). We modified an existing process based model for the peach tree Prunus persica - aphid Myzus persicae pathosystem, explicitly considering interactions between the two species under the influence of cultural practices (i.e., winter pruning and nitrogen fertilization), in order to consider multi-year dynamics. The new multi-year model suggests that consequences of aphid infestation, in terms of fruit production, become evident only when considering multi-year dynamics