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Bird Appearances and Similarities
Figura, Roman ; Komárek, Stanislav (advisor) ; Daněk, Tomáš (referee) ; Jaroš, Filip (referee)
The presented work deals with a striking, yet usually neglected phenomenon by researchers, the similarity between the forms of different (closely unrelated) bird taxa. It mainly concerns visual signs of the body surface, the work also deals with other signs, including behavioral ones. The thesis demonstrates that these are not a few curious similarities, but a truly robust phenomenon, which apparently cannot be fully explained from a unifying point of view. Only some characters, which the work deals with, help their bearers to crypsis, aposematism or mimesis. In many other cases, their function is unknown. They can carry different functions in the life of their bearers, but it is often not possible to determine a single cause of their occurrence. In terms of the information contained, the work belongs to the largest works dealing with this topic known to the author.
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Crypsis at dragonflies
Záhorová, Kristýna ; Černý, Martin (advisor) ; Hadrava, Jiří (referee)
Crypsis is one of the defens mechanisms used by animals to hide from predators. It is a form of coloring that allows prey to blend in with their surroundings or makes difficult for predators to see them due to disruptive coloration. Dragonflies utilize crypsis across different families and sometimes even within individual species in various types of environments, ranging from savannas to tropical rainforests. Crypsis also serves as a defense mechanism not only against predators, but also against members of their own species, where females avoid sexual harassment from males and young males avoid fighting with adult males. This is related to changes in coloration during ontogenetic development, as well as the sometimes pronounced sexual dimorphism that is relatively common in dragonflies. Additionally, larvae of dragonflies are often cryptically colored. This study focuses on cryptically colored dragonflies from around the world and in various types of environments. Rather unexpectedly there are not many studies focing on this phenomena at otherwise throroughly studied group of insects. Key words: dragonflies, crypsis, cryptic coloration, sexual dimorphism, dragonflies larvae
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Effect of body-margin shape on detectability of cryptic prey
Machalková, Kateřina ; Exnerová, Alice (advisor) ; Hotová Svádová, Kateřina (referee)
5 Abstract Subject of many studies dealing with interactions of predator and prey is behaviour and reactions of those predators who distinguish their prey by visual signals. The aim of the study was to compare the detectability of prey with a simple or structured body-margin shape of cryptically coloured true bugs Dysodius crenulatus and Dysodius lunatus (Aradidae) using a different type of background (tree bark of Acer, Gleditschia and Tilia). Background photos were presented in black and white and colour. The test was performed on naive birds and on the wild-caught adults of the Great Tits (Parus major) and the Blue Tits (Cyanistes caeruleus). The experiment was performed in the experimental cage with one-sided mirror glass. The influence of the body-margin shape of the prey was evident for certain groups, but the effect was depending on the age and specie of the birds and the type of the background. Different times of the search for prey were encountered as it was more difficult for birds to search for structured body-margin shape and the birds found faster preys with simple ones. When searching on the colour background the Great Tits were faster than on black and white background. Naive birds of the Great Tits were in search of prey faster than adults and vice versa with the Blue Tits. A separate task...
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Factors affecting prey detectability for visual predators
Machalková, Kateřina ; Exnerová, Alice (advisor) ; Javůrková, Veronika (referee)
The cryptic coloration is one of the main ways to protect prey before the visually directing predators. Most animals use two basic strategies of crypsis, background-matching and disruptive coloration. The aim of this thesis was to summarize and evaluate knowledge about different strategies of cryptic coloration. The study was mainly focused on the confrontation between insect prey and predator bird. Experimental studies are comparing the effectiveness of cryptic coloration of prey by a combination of background-matching and disruptive coloration with prey characteristics (inner pattern contrast, background contrast, shape and pattern distribution, symmetry) or background parameters (background complexity, multiple backgrounds, the distance between the prey and the predator) that affect detectability. The results of the study conclude that disruptive coloration pattern in cryptic prey has better effects than the strategy of background-matching. Prey characteristics can affect detectability, but the results of individual studies are not conclusive. Even the background parameters results were unambiguous, the highest efficiency for prey detection time was a combination of disruptive coloration and the background complexity. The issue of camouflage is so complex that the majority of studies do not have...
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Crypsis on the principles of disruptive coloration
Kopčiková, Kristýna ; Kreisinger, Jakub (advisor) ; Pecháček, Pavel (referee)
The crypsis gives the oportunity to an animal to become inconspicuous in its natural environment to avoid being detected by potential observer (Cott, 1940, Edmunds 1974 Merilaita 2003). But crypsis isn't unambiguous term, there are few ways to achieve being cryptic and disruptive coloration and background-matching are one of them. The aim of this thesis is to summarize empirical evidence for the inmportace, the function and the expansion of disruptive coloration in nature. This research also constitutes a fundamental experiments testing the principles of disruptive patterns. It turns out that this coloration could bring for the bearer some selective advantages, but the experiments are too uniform and they have important methodological failures. Results of them are unclear so scientists have no consistent conclusions. The issue of disruptive coloration is very complicated and still poorly explored. There is need to invest a lot of more labor and study to be certain whether or how disruptive coloration works in nature. Powered by TCPDF (www.tcpdf.org)
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