Ábrahám Levente: Biomonitoring a Dráva folyó magyarországi szakasza mentén 2000-2004 - Natura Somogyiensis 7. (Kaposvár, 2005)
Ábrahám, Levente.: Biomonitoring of the butterfly fauna in the Drava region (Lepidoptera: Diurna) - Nappali lepkék biomonitoring vizsgálata a Dráva mentén (Lepidoptera: Diurna)
71 The significance of biomonitoring of this species along the River Drava is indisputable since the construction plans of the dam will presumably put this butterfly species at risk the most. Bélavár, the habitat of the biggest population of this species is the most endangered area where the forming of a new riverbed could cause the end of soft wood. The construction of the dam could also result in low level ground water, in changes of the seasonal water current, and in reducing water supply of the backwater through the pebbles etc, which will all have an effect on the size of the population. The artificially maintained constantly high water level could disturb the feeding, sucking and mating habits of the butterflies which are used to gathering on the sandy river banks during low water level. The investigation proved that Maculinea teleius has a large population living on the oligitrophic humid grasslands surrounding the Lankoci forests. According to the data from sampling, it is highly presumable that 2001 was a remarkably successful year for Maculinea teleius therefore the relative population doubled compared to the following years. I have experienced similar phenomenon before in other habitats, but long sequence data of biomonitoring are not available for this species (CZIGÁNY and ÁBRAHÁM 2000, MacMan project). The biomonitoring process of this species started in 2003 and it was conducted in accordance with the NBmR standards, therefore the local and countrywide tendencies will be comparable only in the future. The population of Maculiea nausithous is considerably smaller therefore this species is endangered to a greater extent. The growth of the population could probably be stimulated by the extension of forests fringes i.e. the appearance of willow bush and alder tree groups. The survey of Lycaena dispar along the River Drava is very likely not suitable to demonstrate the effects caused by the construction of the dam on the environment since this species is absent in patches and lives a migrant lifestyle. The relative fluctuation of Euphydryas maturna population could be estimated after evaluating the results of the investigation in the following years. The population of this species in Hungary can be found in the southwest of the Euro-Siberian distribution area. The population being satellite population has gone through an isolation process and taxonomical separation can be observed (VARGA & SÁNTHA 1972-73). In the region of the Transdanubian Hills and along the River Drava, a subspecies, Euphydryas maturna idunides (Fruhstorfer, 1917) which is typical of wet forests (hard wood and riverine woodlands) can be found. This species would become more endangered if the dam is to be constructed. Several observations suggest that the population of the species tends to be fluctuating country wide. The size of Parnasius mnemosyne population is fluctuating in time and space as well. The dynamic changes of the population are due to the natural successions but also influenced by different farming activities for example clear cutting. In the sampling area around Bélavár, where the host plant of this species grows in the underwood of beech forest patches, after partial clear cutting, a succession process started and resulted in decrease of a 10 year-old young population. The other cause of the reducing population lies in degradation which, on the sampling site, manifests itself in the extensive growth of Robinia pseudo-acacia and Ailanthus altissima trees covered land. However, in order to evaluate the position of the species from the environmental point of view, the situation shows negative tendencies only in the permanent sampling sites. But 1-1.5 km south of the sampling area I have discovered a population of the species which settled in the region at the turn of the millennium and seems to have been growing continuously since then. I have not encountered a similar phenomenon since my
