Vadadi-Fülöp et al.: Evalution of climate change scenarios based on aquatic food web modelling -1 -APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 6(1): 1-28. Abstract. In the years 2004 and 2005 we collected samples of phytoplankton, zooplankton and macroinvertebrates in an artificial small pond in Budapest. We set up a simulation model predicting the abundance of the cyclopoids, Eudiaptomus zachariasi and Ischnura pumilio by considering only temperature as it affects the abundance of population of

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... the previous day. Phytoplankton abundance was simulated by considering not only temperature, but the abundance of the three mentioned groups. This discrete-deterministic model could generate similar patterns like the observed one and testing it on historical data was successful. However, because the model was overpredicting the abundances of Ischnura pumilio and Cyclopoida at the end of the year, these results were not considered. Running the model with the data series of climate change scenarios, we had an opportunity to predict the individual numbers for the period around 2050. If the model is run with the data series of the two scenarios UKHI and UKLO, which predict drastic global warming, then we can observe a decrease in abundance and shift in the date of the maximum abundance occurring (excluding Ischnura pumilio, where the maximum abundance increases and it occurs later), whereas under unchanged climatic conditions (BASE scenario) the change in abundance is negligible. According to the scenarios GFDL 2535, GFDL 5564 and UKTR, a transition could be noticed. APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 6(1): 1-28. Our main aims were the following: • Description of the phytoplankton, zooplankton and macroinvertebrate assemblages in the examined pond. • Working out and adopting a sampling method regularly carried out, that provides accurate data of the temporal change of the examined objects. • Elaborate a simple simulation model, which is able to generate similar patterns to the observed ones. Testing the model. • Running the model with the data series of different internationally recognized climate change scenarios, supplying and interpreting of the predictions. Comparative estimating of the alternative climate change scenarios with classical statistical methods. We chose an artificial and small pond to examine, as we thought it is simpler and more closed than natural freshwaters, and the operation of the system could be easier understood. We expected the model to indicate real patterns like the observed data series, thus the climate change scenarios could be valued. By means of a simple simulation model we were able to generate similar patterns like the observed one. Running the model with the data series of different climate change scenarios, we got a prospective notion of the abundance of the examined objects, which must be handled watchful. The aim of the process is not the prediction, but the comparative appreciation of the possible effects of the different, international climate change scenarios, with the aid of a real model situation. Review of literature Climate change, climate change scenarios Climate change is considered, when the fluctuation range of climatic elements shifts appreciably to the higher or lower values, and this state remains for a long period (Varga-Haszonits, 2003) . General Circulation Models (GCM) were developed at first to modelling the atmosphere's processes. Later also the atmosphere's interactions with biosphere, hydrosphere, litosphere and criosphere were taken into consideration, and these models were accounted as Global Climate Models (GCM). These models use 3D space, tracking horizontal and vertical movements and cover the surface with grid (Varga-Haszonits, 2003) . Two types of GCM are distinguished: equilibrium and transient models. The equilibrium model calculates with doubled level of carbon-dioxid in the atmosphere. The model is run till then it set in an equilibrium state, namely a state when it evolves a stable temperature on the surface. By gradually increasing level of carbon-dioxid, transient models make it possible to determine the gradually changing climatic conditions (Varga-Haszonits, 2003) . The claim to apply GCM for regional levels demands using the method of downscaling. The kernel of downscaling is considering the results of GCM's for great areas, and setting statistical correspondence between the climatic variables of great and minor areas (Varga-Haszonits, 2003) . Climate change scenario can be defined as a likely combination of the change of climatic conditions, which is able to use for testing the possible effects and asses the reactions for them (Varga-haszonits, 2003) . These models are based on the simulations of General Circulation Models and regional climate models. Some remarkable institutes for developing GCMs are the undermentioned: the Geophysical Fluid Dynamics Laboratory (GFDL), the Goddard Institute for Space Studies (GISS), the National APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 6(1): 1-28.