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Ecophysiological characteristics of key members of Betaproteobacteria in freshwater bacterioplankton
KASALICKÝ, Vojtěch
This thesis primarily focuses on one segment of freshwater Betaproteobacteria, the Limnohabitans genus (including the RBT lineage). As opposed to other recent research directions, the major aim was to recover the members of the previously uncultured RBT lineage through their isolation from various freshwater habitats. However, the results presented in this thesis have also ambitions to go far beyond the taxonomic descriptions only; the dissertation intends to contribute significantly to unveiling of important ecophysiological characteristics of the studied lineage in a set of both laboratory and field research. Therefore, understanding of growth characteristics, mortality, diversity and life strategies of aquatic microbes is of highest importance regarding profound human impact on water quality and increasing need of drinking water supplies.
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Aggregations as an antipredator strategy in common toad tadpoles (\kur{Bufo bufo}).
BODNÁR, Tomáš
Tadpoles of many anuran species use a huge number of behavioral modifications to avoid predators. Reduced activity in presence of predators is favorite strategy for common toad tadpoles (Bufo bufo). Responses against predator cues by tadpoles of Bufo bufo in the presence of another cue of larger tadpole aggregation were tested in this study. We observed that these tadpoles responded differently to predator chemical cues than tadpoles in a small group.
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Impacts of predation on dynamics of an age-structured population: mathematical modelling and applications
PAVLOVÁ, Viola
Predation is one of the basic mechanisms of population growth control. Using a mathematical model, we explore the impact of predation in a prey population structured into two age classes, juveniles and adults, assuming a generalist predator. The specific predation pressure is represented for each of the two age classes by either no predation or Holling type II or Holling type III functional responses in various combinations. We distinguish two scenarios. In the first one, we seek for potential Allee effects or multiple stable states in the prey population, and explore the conditions at which the predation is more effective on juveniles than adults and vice versa. The most interesting finding here is the occurrence of bistability, or a predator-pit-like behaviour, when predators consume only juvenile prey, via a Holling type II functional response, an observation not described previously. In case only adults or both age classes are killed by predators exhibiting a type II functional response, the Allee effect occurs frequently. Multiple positive stable states are commonly observed if one of the age classes is exploited via a type III functional response. In the second scenario, we assume that the prey feeds on a resource and that the resource together with the prey undergoes outbreak dynamics, and we examine possibilities of control of such outbreaks using age-specific predation. Predation was proven to be able to suppress the prey population successfully. In some cases, an oscillation-free resource-prey-predator coexistence was detected.
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Influence of starvation on willingness to risk in Great tit (\kur{Parus major}) and Blue tit (\kur{Parus caeruleus})
TUMOVÁ, Petra
In this work, I investigated influence of starvation on willingness to risk for food in presence of a predator. Experiments proceeded in winter when birds are not influenced by fear about clutch or brood and therefore the food becomes their priority. I tested birds in laboratory conditions where is possible to monitor and regulate food availability. Tits were tested for stuffed model of dangerous hunting specialist sparrow hawk (Accipiter nisus), nest predator jay (Garrulus glandarius) and harmless similar-sized bird pigeon(Columbia livia f. domestica). A control experiment without a model was conducted too. Each bird was tested for given model replete and hungry and each bird was tested only for one model. We were interested in differences in reactions to individual models and the influence of repletion rate; if the behaviour was different between replete and hungry birds, or in the {\clqq}accustom`` phase and in experiment itself. We also investigated, if there are differences in behaviour between Great Tits and Blue Tits.
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Impact of american mink on stone crayfish populations
PAVLUVČÍK, Petr
1. Impact of introduced American mink (Mustela vison) predation on endangered stone crayfish (Austropotamobius torrentium) was examined in western Bohemian middle-sized streams for two years. Mink diet selectivity and its impact on its prey abundance were been investigating as the main target of this study. 2. The mink diet was described from excrements which were found on the target areas. The importance of different types of prey was specified by their relative numeric contribution to diet. The number of hunted crayfish was elicited from the number of crayfish remains which were collected during two years. The crayfish abundance was determined by capture {--} recapture method. 3. The crayfish was most frequently observed component of mink diet. The rate of mink predation on crayfish was dependent on density of crayfish population. This observed rate was lower during winters than during summers. The mink preferred significantly longer crayfish than was the mean of this value in population. 4. Although the crayfish was important part of mink diet the trend of impact of mink on crayfish is still inexplicit. It would be important to continue in this research to determine correlation between these two species.
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The effect of ants predation risk for herbivorous insect
DRAG, Lukáš
This thesis is the first step to evaluate the relationship between ant activity (predation risk) and the leaf damage caused by herbivorous insects. Tuna baits which were used in 1, 2 and 3 hours intervals to attract different species of invertebrates. The degree of herbivory was measured as the proportion of leaves that had been chewed or mined by herbivores. The most abundant and frequent potential predators were ants. All ant species were determined and patterns of their activity analysed.
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How birds judge the risk of predation during winter
TVARDÍKOVÁ, Kateřina
I investigated how willingness to risk the exposure to a predator in order to gain access to food is expresed within a group of wintering tits (Paridae). Stuffed models of sparrowhawk, kestrel, thrush, jay, pigeon and a lump of cotton wool (similarly sized of a pigeon) were used as a potential predators ({\clqq}objects``) and were presented near a feeder. My data suggested that Paridae are able to recognise the danger of {\clqq}objects``. Birds risk exposure to sparrowhawk, kestrel and jay less than to other {\clqq}objects``. No significant relation existed between behaviour in presence of kestrel and sparrowhawks. Behaviour of Paridae on feeder is influenced by temperature and snow too.
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