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Food webs of glacier-fed streams.
Komárková, Julie ; Kopalová, Kateřina (advisor) ; Fuksa, Josef (referee)
This work focuses on glacier-fed stream ecosystems, with the centre of attention being on the community composition and characterization of their food web structure. Glacier-fed streams are harsh environments in terms of their physicochemical characteristics. These streams exhibit low temperatures and specific flow regimes, with the peak of meltwater generation, and thus discharge, in the summer. In turn, streamwater nutrient concentrations, light availability, and turbidity all vary seasonally according to the flow regime. Compositionally, glacier-fed stream habitats host chemolithotrophic bacteria along with photoautotrophic producers, such as diatoms, Chrysophyceae, and Cyanobacteria, which together serve at the bottom of food webs as primary producers. These streams also host some fungal taxa, that together with heterotrophic bacteria, represent the primary decomposers. Macroinvertebrates, including the water larvae of species Diamesa and Pseudodiamesa, or from the Ephemeroptera or Plecoptera groups, are important secondary producers with high feeding plasticity; that is, they are mainly grazing biofilm or collecting/filtering organic matter, with the possibility of predation. Other than that, in glacier-fed streams, there is usually no presence of higher trophic levels with large- bodied...
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Beginning and duration of flowering period in selected arable weed species
Trefil, Daniel ; Holec, Josef (advisor) ; Václav, Václav (referee)
Arable weeds are usually perceived as harmfull organisms in crops. On the other hand, the weeds provide a stable source of food for insects and other invertabrates that feed on pollen and nectar. Majority of crops are not able to provide long-term food component for invertebrates because their flowering is synchronized. Arable weeds flower continously throughout the growing season. There is possible to find many flowering species for the whole year.
The main aim of the study was to determine the onset and duration time of flowering period for selected arable weed species. The observation was conducted at the Demonstration and experimental field of Faculty of Agrobiology, Food and Natural Resources neighbouring areas as well as demonstration plots with rare weed species that do not occur in fields naturally. Inventory of flowering species was performed weakly from 9th calendar week (after frost period) and finished at 48th calendar week. There were found and evaluated 160 plant species of which 67 were the rare species from demonstration plots.
First flowering weeds were photoperiodically neutral species, mainly from the group of winter annual weeds followed by ephemeral annual weeds. Among others, the late-flowering species were particulary from the group of summer annual weeds, but also some from perennial species.
During the first week of observation, 11 flowering species were found. The number gradually increased up to a maximum of 118 flowering species in the 27th calendar week; then the number of flowering plant species naturally decreased. Newly flowering species were being found until 36th calendar week. Weed differed significantly in onset of the flowering acording to perenniality, in most cases. Length of flowering period in individual species was in relation to particular families.
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Trophic relationships between insectivorous birds and insect in Papua New Guinea
TVARDÍKOVÁ, Kateřina
The thesis describes diversity of birds along a complete altitudinal gradient and in forest fragments in lowlands of Papua New Guinea. It focuses separately on the diversity of different feeding guilds, and discusses their links to habitat and food resources. More specifically, it focuses on forest insectivorous birds, their predation pressure on arthropods, feeding specializations and preferences, and some of the ways how insectivores search for food.
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The role of species traits in predator-prey interactions and food web structure
KLEČKA, Jan
This thesis deals with the role of species traits in predator-prey interactions and food web structure. I conducted laboratory experiments with predatory aquatic insects and their prey to reveal the traits determining who eats whom in small standing waters. I also focused on the possibility of incorporating the observed dependence of predator-prey interactions on body mass into existing food web models. Further, I developed a simple simulation model to explore the consequences of body mass dependent feeding and dispersal for food web assembly. Last, I show that four common methods for sampling aquatic insects differ in their selectivity, especially on the basis of body mass of sampled insects. In conclusion, I combined laboratory experiments, field work and mathematical models to evaluate the importance of body mass and other species traits, such as foraging behaviour and microhabitat selectivity, in predator-prey interactions and explored selected food web level consequences.
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