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Causes of limitation of plant reproduction by pollen and resource availability
Kalousková, Petra ; Janovský, Zdeněk (advisor) ; Sklenář, Petr (referee)
Plant seed production depends on many factors: their life history, the environment they grow in, and other factors such as biotic interactions. However, the immediate cause of the reduction in seed production is the lack of partners or the lack of resources available for seed production. This bachelor thesis aims to summarize and analyze the mechanisms of action and the relative importance of individual causes of limitation of plant seed production. Most plants are pollen limited at least in some seasons or in some localities, in the rest of the situations are plants resource limited. Pollen limitation can be quantitative (low pollen deposition) or qualitative (low quality of pollen). Existing theoretical models of pollen and resource limitation compare use of resources either to attract pollinators (increased flower size, increased number of rewards) and increase the chances of encountering them (change of phenology or prolongation of flowering) or to produce seeds. Plants can sometimes be seemingly pollen limited, with the pollen supplementation increasing seed production at the cost of reducing reproductive effort in the upcoming years. However, the most significant feature of pollination, which is often reflected in the alternation of reduced seed production due to insufficient pollen...
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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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