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)

68 NATURA SOMOGYIENSIS Fig. 5.: The time trends of Euphidryas mat urna population in Lankoci forest in the permanent sampling sites long run these figures might make the environmental changes detectable. The main changes in their habitats can be deducted from them. Euphydryas maturna In the first year of the investigation, in 2002, the species could be found in large number in the area (Fig. 5). By this time Its caterpillars had gorged on the leaves of Fraxinus excelsior creating bare patches in the canopy. Later on, the size of the population seemed to decrease. Since early exact numerical data is not available, it is impossible to state precisely whether we are facing a possible graduation phenomenon or not. In the following years, similar phenomenon did not occur according to my experience since the population size was reduced to an average level. In the following years during my fieldwork, the above described mass occurrence was not experienced and the population size reduced back to an average level. The time trends in population changes can be precisely described after investigation in years to come. Parnassius mnemosyne According to the results of the investigation, the population sampled in Bélavár is gradually reducing year by year (Fig. 6). This size change was so dramatic on the sampling sites during the biomonitoring, that in 2004 the relative population was only 10% of the relative population in year 2000. The relative population size of the investigated species near Péterhida was smaller than in Bélavar during the early years of the research work but it showed a gradual increase in the years of 2003 and 2004.