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Influence of biotic and abiotic factors on population dynamics of a critically endangered species Spiranthes spiralis
IPSER, Zdeněk
A population of a critically endangered species Spiranthes spiralis was discovered in 1980 in the National Natural Monument Pastviště u Fínů near village Albrechtice, close to Sušice city. Since 1985 the number of flowering individuals in this population has been annually monitored. Since autumn 1998 all the specimen found there have been marked and biometrically measured. During these periods (12 or 26 years, respectively), large year-on-year fluctuations in the number of flowering plants and in the survival of the individual rosettes have been recorded. The main aim of my work was to assess the effect of weather conditions (temperature, precipitation, the number of days of snow) on the population dynamics and on the fitness of plants (leaf area, probability of flowering and probability of death). The year-round lower temperature and the wet end of autumn during the previous year (t-1) together with the wet spring of the following year (t) had a positive effect on the leaf area during the period of maximal rosette growth (end May in the year t). The probability of flowering was positively affected by the lower temperatures in May and June in the previous year (t-1) and in August just before flowering (year t). The probability of death (in the year t) was increased when the March precipitation (in t) and October temperatures (in t-1) were low. The average number of seeds in the capsule was 1528 ? 885 (s.d.). The number of flowers was positively correlated with the number of mature capsules. However, it did not affect the ratio of mature capsules. Capsules developed on average from 44% ? 24.6 % (s.d.) of the flowers. The average life time of individual plant cohorts was 4.7 years. The number of rosettes per each position was variable from 1 to 7 rosettes (73.2% positions had only 1 rosette). The annual life cycle of the underground organs is described at the end of the thesis.
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