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Dynamics of orchid occurrence in highlands
Černocká, Veronika ; Kindlmann, Pavel (advisor) ; Křenová, Zdeňka (referee)
All species of orchids are sensitive plants and records of their distribution are rare. Their rarity is related to their complex biology and their sensitivity to changes in the environment. It is necessary to pay attention to these threatened species, so that we could preserve them from extinction. For their effective protection we need to know the main causes of extinction of their localities. It is also useful to know the factors, which determine their distribution, so that we could find new localities, where they occur. In this thesis I analyzed some climatic, geographic and ecological factors in the Jeseníky mountains and their surroundings. First, I visited localities of orchids, which were registered in large databases of their presence in the past. The four most numerous species were analyzed using the program MaxEnt. Based on the revisions, existence of 2/3 of the revised localities was confirmed, 8% of the revised localities became extinct because of overgrowth or due to human intervention in the landscape. From the MaxEnt results it is clear, that for all species the most important factor at the 50 × 50 m scale, is the type of biotope and heterogeneity of the countryside. The most suitable biotopes are floodplain and wetland forests, mesophile meadows, natural scrubs, peat bogs and...
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Biodiversity of chironomid fauna in mountain lakes and streams influenced by acidification and recovery from acidification.
Černocká, Veronika ; Stuchlík, Evžen (advisor) ; Frouz, Jan (referee)
This thesis examines the influence of acidification on the largest group of macroinvertebrates in mountain lakes and running waters - chironomids. The diversity of chironomids has been associated with temperature, the concentration of dissolved oxygen in the water, the amount of nutrients, and also with the ability to survive in conditions (e.g. extreme pH) that are not suitable for other taxa. Because of this the family Chironomidae has become a dominant group of macrozoobentos in many assemblages affected by acidification. The Bohemian Forest lakes and the Tatra Mountain lakes belong to the most frequently studied locations, which were affected by acidification. The peak of acidification was in the 1980s. It turned out that, during the acidification, the number of chironomids changed and also the species composition of their assemblages. The main reason was a change of trophic status, which chironomids reflected more than a change of pH. A decrease in the number of species occurred after the pH dropped below 5. Until then, only their relative abundance had been affected. Chironomids are also influenced by the toxic effect of Al. The most important factor affecting chironomids fauna is not the value of pH, but the change of food supply. Acid stream food webs are often viewed as being...
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