In my thesis I have studied the distribution of the myrmecophilous butterfly Alcon Blue (Maculinea alcon) in Slovenia, its endangerment and means of reducing its endangerment. M. alcon has a very complex life cycle, in which it is dependent on the specific host-plant and the specific species of host-ant. If any of the two hosts disappear from its habitat, the species will become extinct. The reason for the loss of the host-plants and partly for the absence of the host-ant, is usually connected to the negative human impact. In some European countries extinction or endangerment of M. alcon has risen due to changes in farming practices (abandoning, intensification). In Slovenia it is classified as a protected species and it is listed on the Slovenian Red list as endangered (E). I have compared the distribution in three different time periods (<1950, 1950-1999, >1999), using the extent of occurrence and area of occupancy approach. Results were surprising, indicating the increase of distribution of M. alcon in Slovenia. In contradiction, the field studies of M. alcon indicate increasing endangerment in whole Europe. The reason for the mismatching results is most certainly uneven sampling as the systematic surveys of species distribution in Slovenia were carried out only after the year 1999. The endangerment of M. alcon could be reduced with postponed mowing (in September), when the caterpillars are already safely in the anthills. M. alcon is a very interesting indicator species that strongly contributes to ecological stability in habitats where other threatened plant or animal species co-occur and I believe that is a good enough reason to make an effort to maintain its existence.
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