Final Activity Report Summary - GECLIPDI (Geographical variation in effects of global climate change on the population dynamics of terrestrial isopods) Soil carbon decomposition and storage are one of the least understood elements of the global carbon cycle. Organic carbon storage in soils makes up about two-thirds of the total organic carbon in terrestrial ecosystems. Carbon exchange between the terrestrial biosphere and the atmosphere is one of the critical natural determinants of the future carbon concentration in the lower atmosphere. One aspect of soil carbon activity results from the decomposition rates and feeding behaviour of soil macrodecomposers, of which woodlice are a dominant component in many terrestrial ecosystems of the world. While the majority of the CO2 emitted from soils results from the metabolic activity of soil micro-fauna such as microbes, this process is strongly regulated by the numbers of, and the foraging behaviour of isopods and other soil macro-fauna. Possible future climate change effects may result in less rainfall, higher temperatures, and hence a periodic warming and drying out of the soil.The objectives of this research were to investigate 1) to compare the effects of predicted changes in rainfall along the trans-European climatic gradient on growth, survivorship and behaviour of oceanic, semi-continental and fully continental ecotypes of one species Porcellio scaber; 2) to compare the effects of predicted changes in rainfall and hence humidity in four species of terrestrial isopods contrasting in their morphological and physiological adaptations to the terrestrial environment. Considering the ecotypic differences for the four ecotypes tested in this study, Germany stands out with a distinctively different phenotype. This ecotype spends more time in the feeding arena and actually consumes more food, it spends more time walking on the arena and it survives better than all the other three ecotypes analysed. Spending more time walking and keeping higher survival rates will have higher energy costs which might be the reason why the German ecotype grows less despite eating more than the others. So in the face of global change, different ecotypes of one given species will probably respond differently and it is predictable that species distribution range might shift as a consequence.As for the interspecific comparison, the four species selected spent less time feeding and searching for food under conditions of lower humidity. This is because they had to spend more time sheltering to protect themselves from drying out thereby increasing their chances of survival. Some species were more affected than others, because of their morphological adaptations, but in all cases, the research provided clear evidence of the trade-off between optimal foraging and survivorship. This particular aspect of trade-off, namely shifts in the behaviour and fitness of the species for survival in the face of desiccation, is relatively under-researched. So this particular set of experiments is of considerable scientific significance.These important findings suggest that in warmer, drier conditions, woodlice will have slower growth rates, and consequently will produce fewer offspring, and will reduce their rates of decomposition activity. To avoid extinction the isopods will need to adapt to the new conditions. However, evolution is a slow process and if the rates of climate changes are too rapid it will be difficult for the woodlice to keep pace with it. Phenotypic plasticity will play a very important role. Animals will have to be more plastic to take advantage of the good conditions when they are available. It is predictable that opportunistic species will adapt better. Maybe they will even expand their ranges, while more specialised species may face extinction.More research is recommended in order to examine these aspects further. Given that these findings will have repercussions for CO2 release through lower microbial activity, this research suggests that climate change impacts could lower the future release of carbon dioxide from soils. Clearly, this is a finding of potentially considerable significance for the modelling of future carbon cycling in the atmosphere, and hence future rates of climate change.