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Factors affecting behaviour of avian predators to hoverflies (Syrphidae) and their models (Aculeata)
Truhlářová, Marie ; Exnerová, Alice (advisor) ; Sedláček, František (referee)
Batesian mimicry is an antipredator strategy used by harmless species to mimic dangerous models by their appearance. The so-called imperfect mimics are a phenomenon within Batesian mimicry. It would be expected that Batesian mimics are selected to resemble the model as perfectly as possible. However, in some species the resemblance is very poor. The aim of this study was to test reaction of predators towards a textbook example of Batesian mimics with imperfect mimicry, i.e., hoverflies (Syrphidae) and to verify some of the hypotheses describing imperfect mimicry. We conducted two experiments in which the model predators were great tits (Parus major). The topic of the first experiment was the effect of diversity of models on categorization and generalization of hoverflies. Birds were divided into two groups, with the first group receiving high diversity of models (10 species of Hymenoptera) and second group receiving low diversity of models (2 species of Hymenoptera). There were two parts of this experiment. Categorization training when great tits learn to discriminate between two categories of prey, palatable and unpalatable and generalization test, when great tits generalized their experience from categorization training to novel prey. Palatable prey was represented by non-mimetic flies (Diptera),...
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Seasonality in reproduction and abundance of birds in African savannas
Kučminová, Veronika ; Hořák, David (advisor) ; Remeš, Vladimír (referee)
Seasonality of climate is a crucial factor that determines the existence of African savannas. Especially, the rainfall seasonality is a key factor in the abundance and reproduction of bird species of the savannas. Precipitation determines the timing of reproduction directly, but mainly indirectly through the influence of the environment, phenology, and productivity of plants. The vegetation determines the availability of resources and shelters. However, the widespread distribution of the savannas across the continent means that the seasonality and consequently the environment varies considerably from one area to another due to the different timing, size, and duration of wet and dry seasons. Breeding, as well as the abundance of savanna birds, is clearly influenced by the availability of food, which is determined by seasonal rainfall. For most species, the rainy season is an ideal time for reproduction, but there are also other groups of birds, that prefer a dry season for breeding and nesting. The birds must cope with unfavourable conditions outside the breeding season or leave their breeding areas. The abundance of birds in savannas is also significantly affected by the presence of palearctic migrants. Migration is therefore an important factor of the seasonal abundance of the savanna avifauna....
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Food competition between waterbirds and fish
Bečvář, Viktor ; Hořák, David (advisor) ; Musil, Petr (referee)
Food competition between waterbirds and fish can be a crucial factor in todays wetland ecosystems. In certain situations it can be decisive if a specific site is still suitable for waterbirds or not. Large aquatic invertebrats are often shared food resource. Situations where specific waterbirds and fish compete for this resource were described in many wetland habitats. Fish are often much more effective in acquiring food to the point when this relationship can be described as asymetrical competition. The level of competition can be also influenced by various envirometal factors or different attributes of waterbird and fish populations. The knowledge obtained by studing this relationship can be then used in management of protected areas and comercially used waterbodies.
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Influence of external conditions on egg incubation in lapwings (genus Vanellus) in temperate and subtropical climate
Pešková, Lucie ; Šálek, Miroslav (advisor) ; Hořák, David (referee)
During incubation, most birds require the presence of at least one parent to ensure suitable incubation conditions for embryo development. The main factors that affect the development of the embryo are temperature, humidity and egg turning. In this work, incubation conditions were investigated in two biparental Lapwing species (genus Vanellus), the Northern Lapwing (Vanellus vanellus), which faces the risk of egg cooling in temperate areas, and the Red-wattled Lapwing (Vanellus indicus), which faces the risk of egg overheating in the subtropics. A laboratory experiment testing the thermal properties of the Red-wattled Lapwing nest lining showed that it selects lining material that slows down temperature growth during egg heating, thus ensuring suitable thermal conditions during parental absence at high ambient temperatures. Temperature and egg turning during incubation were recorded by an artificial egg with a built-in sensors placed in the nests of both target species; data collected by the sensors were stored by a base-station located nearby. The average egg temperature was 32.5 řC for the Northern Lapwing, and 35.0 řC for the Red-wattled Lapwing. Egg temperature in both species fluctuated significantly, affected by many factors. Egg temperature increased with increasing ambient temperature, it...
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Hatching synchrony in birds
Tippeltová, Zuzana ; Hořák, David (advisor) ; Riegert, Jan (referee)
This bachelor thesis is about hatching synchrony in birds. Generally, among birds there are two types of hatching - asynchronous and synchronous- and the type of hatching is primarily determined by the time of the onset of incubation. In many bird species, including most precocial ones, incubation does not begin until the last egg has been laid, which results in hatching of all the eggs within a few hours. In synchronously-hatched broods, all the chicks are about the same age. Thus no single individual has an advantage in size or strength over any of its siblings in the nest. The survival probability is then similar for all chicks which maximizes number of fledglings under favourable condition. In contrast many species of birds begin to incubate as soon as the first eggs is laid and hatch their eggs asynchronously over a period of days or weeks, handicapping last-hatched chicks with an age and size disadvantage. Many hypotheses have been proposed to explain why female birds start to incubate before clutch completion and some of those suggest that asynchronous hatching is a parental strategy for raising the largest number of offspring that food resources will allow when the abundance of food for the chicks cannot be predicted at the time that eggs are laid. The selective pressures leading to the evolution of...
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The use of stable isotopes in the trophic ecology of birds
Rusnáková, Michaela ; Hořák, David (advisor) ; Procházka, Petr (referee)
Recently, the use of stable isotope analysis has been becoming increasingly common in ecological studies of animals. This interesting method is based on the premise that the isotope composition of consumer's tissues is related to the isotope composition of the sustenance consumed. This allows us to explore the contribution of individual food sources to the diet of species, populations or individuals, and at the same time to study their position in the trophic chains. The method enables us to research even omnivores, consuming variable food with different nutrients and isotope composition. Nevertheless, isotope values can differ depending on diet preferences, species physiology and the tissue type used for the analysis. This review summarizes current knowledge and results in the topic of stable isotope analysis, particularly in ornithological studies where the approach in question has been used to study the diet and trophic position. Powered by TCPDF (www.tcpdf.org)
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Interspecific hybridization in birds: lessons for conservation
Štěpánková, Klára ; Reif, Jiří (advisor) ; Vokurková, Jana (referee)
Interspecific hybridization is quite common in recent years. Favorable factors are rarity of a species, limited time for partner selection, misdirected preference in mating partner selection of females, preference for males with more pronounced sexually selected traits, greater body size and habitat destruction. Factors which lead to the artificially interspecific hybridization due to habitat destruction include deforestation, fragmentation of the territory, urbanization, abandoning agricultural areas, as well as translocation of species into the regions where they did not originally occur. These species can later interbreed with the native species and if the latter are rare and the former aggressive, it can result in increased threat potentially leading to extinction of indigenous populations. Exceptionally, interbreeding can lead to the emergence of a new species; however, this type of origination of a new species is not common in animals. Hybridization is a natural phenomenon important for the evolution. Nevertheless, anthropogenically induced or assisted hybridization represents a serious problem for the species conservation. Finding a solution to overcome the negative impacts of such interspecific hybridization is difficult and there is no exact and universally applied methodology to date. Key...
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Incubation behaviour of birds in polar regions
Hromádková, Tereza ; Pavel, Václav (advisor) ; Praus, Libor (referee)
The climate in the polar regions is so extreme that it has led to a big number of special adaptations in life and reproduction of local animals. However, the disadvantages are compensated by several important aspects like much lesser activity of preadtors, long sunny polar day and an abundance of nutriments during spring and summer. I tis no wonder that many species of birds have adapted their life cycle and migrate annualy thousands of kilometres to the polar regions in order to increase their chance of successfully leading out their offspring. Birds in these areas nest during the polar summer. Only one species of nesting begins already during the polar winter, i tis an Emperor Penguin (Aptenodytes forsteri) in Antarctica. The broods of birds nesting in polar regions are bigger in quantity in average and they also incubated longer then their conterparts in temperate and tropical. The main difference is the incubation rhythm adjusting mainly the extension of sessions associated with a reduction of recesses. The only exception are songbirds who leaves their nests frequently but only for a short periods of time. The information about the incubation behaviour of the most of the bird species of the polar regions are still very limited and incomplete. Therefore, bachelor thesis contains so far...
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Adaptive evolution of Toll-like receptors in birds
Velová, Hana ; Vinkler, Michal (advisor) ; Elleder, Daniel (referee) ; Novák, Karel (referee)
Adaptive evolution of Toll-like receptors in birds Hana Velová, PhD thesis 6 Abstract Toll-like receptors (TLRs) are one of the key and presumably also evolutionary most original components of animal immune system. As Pattern recognition receptors they form the first line of innate immune defence against various pathogens. The proper receptor binding of pathogenic ligands is crucial for their correct recognition and for subsequent triggering of an appropriate immune response. Because there exists a direct interaction between the receptor surface and the pathogenic ligand, host-pathogen coevolution on molecular level can be predicted. Thus, through variability of their ligands, TLRs are exposed to extensive selective pressures that may be detected on both genetic and protein levels. Surprisingly, the variability we revealed in birds is even higher than previously expected based on the reports from other vertebrates, mainly mammals. In my doctoral thesis I summarise the results of my contribution to the avian TLR research. We were the first who experimentally verify the absence of functional TLR5 in several avian species and duplication of TLR7 in others. We finally resolved the origin of duplication in TLR1 and in TLR2 family. An important part of my research project focused on the prediction of potentially...
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