Understanding aquatic Herbivore performance under changing regimes of thermal and nutritional Variance (HerbiVar)

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Recent studies predict important changes to the frequency, intensity and duration of climate extremes which will manifest in the higher statistical moments (e.g. variance and skewenness) of temperature spatial and temporal frequency distributions. Because of the non-linearities of ectotherm thermal reaction norms, changes in the thermal variance regimes are expected to impact ectotherms even more than mean temperature changes. The mean properties and likely the spatio-temporal variance of the food resources (in terms of energy, biochemical and mineral composition) available to the ectotherms will also be affected by climate change. Temperature dictates the energy acquisition and expenditure in ectotherms but also their structural requirements for specific nutrients. Hence, the concomitant changes of temperature and nutrition have to be considered simultaneously in any attempt to understand ongoing and future changes of ectotherm populations. To date, all research on food-temperature interactions focused on changes in their mean values. This project goes beyond mean values and aims to improve our understanding of how higher statistical moments of food and temperature interact with each other and with the means to affect the fitness of ectotherms. Using an aquatic ectotherm (Daphnia magna) as model organism, the first objective will be to develop theoretical models of the effects of food quantity, food quality (in terms of essential fatty-acids, cholesterol and phosphorous) and temperature variances and covariances on critical fitness components (mortality, development, reproduction). Based on these models, it will be possible to generate clear theory-driven hypotheses that can be experimentally tested. This work will bridge nutritional and thermal ecophysiology and place them within the context of spatio-temporal heterogeneity. It is anticipated that it will yield powerful insights into the challenges ectotherms are facing in the course of ongoing temperature and resource changes.