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Reactions of avian predators to automimicry in milkweed bugs (Heteroptera: Lygaeidae):
Stránská, Anna ; Exnerová, Alice (advisor) ; Baňař, Petr (referee)
Automimicry, or intraspecific variation in defence mechanisms in aposematic prey, is very common in nature. Especially in chemically protected prey. This study contains two experiments. The first experiment investigated the reaction of naive predators, which were Great tits (Parus major), to automimetic prey. The prey was the black-and-red-bug (Lygaeus equestris). The tits were divided into three experimental groups and each group was presented with three bugs that were fed on an artificial diet with different amounts of cardenolides. The control group was presented with prey that had no cardenolides in the diet. The group tested with the low concentration received bugs that fed on a diet with a low concentration of cardenolides and the group tested with the high concentration received bugs that fed on a diet with a high concentration of cardenolides. In a generalization test, all groups were then offered a single firebug (Pyrrhocoris apterus). It was found that the group tested with the high concentration experienced a higher rate of aversive learning. This group also killed and consumed fewer firebugs than the other two groups. The group tested with high concentration generalized most to novel red-and-black prey because they were least likely to attack the firebug. The second experiment tested...
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Reactions of predators towards species of red-and-black mimetic complex
Kotlíková, Lucie ; Exnerová, Alice (advisor) ; Baňař, Petr (referee)
The red-black mimetic complex in the Western Palaearctic region includes a large number of arthropod species. These species differ in the degree of their mimetic resemblance, as well as in defensive mechanisms and their effectiveness against various predators. This study is based on two experiments. The first experiment was carried out with adult great tits (Parus major) and artificial prey (photographs). The birds were divided into two experimental groups and were trained to discriminate between palatable and unpalatable prey. One group was trained with higher diversity in the coloration of unpalatable prey (ten species of subfamily Lygaeinae), while the other was trained with low diversity in the coloration of palatable prey (ten individuals of the same species, Lygaeus equestris). After ten learning blocks, two generalization blocks followed, in which both groups received the same prey that was completely different from the prey during learning phase. The rate of learning was not significantly different between the two groups. However, more effective generalization was observed in the group trained with higher prey diversity. However, this trend was only observed in the first generalization block. On the second day, both groups achieved similar generalization success. The second experiment was...
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Melanism in free living vertebrates
Slavíková, Ema ; Munclinger, Pavel (advisor) ; Exnerová, Alice (referee)
Melanism is an over-development of melanin in the skin and its cover that is described in a large number of species in vertebrates. Increasing number of studies observing melanistic traits in animal species tends to reveal genetical, physiological and behavioural characteristics associated with dark pigmentation. This bachelor thesis briefly summarizes knowledge about occurrence and characteristics of melanistic animals associated with their specific pigmentation. Presented are rules and theories associated with melanism in vertebrates, e.g., melanocortin theory, thermal hypothesis and Gloger's rule.
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Evolution and function of hidden anti-predator signals
Ziková, Magdaléna ; Exnerová, Alice (advisor) ; Pipek, Pavel (referee)
Hidden anti-predator signals (HAS) are hidden colour patterns in an otherwise cryptic prey; they are revealed upon encountering a predator. HAS include deimatic signals (DS) and flash signals (FS). DS are used when at risk of predation, typically after being discovered by a predator. Their position in the predation sequence (PS) differs by species. DS are often linked with deimatic behaviour, that boosts their efficiency. The use of DS in later stages of the PS occurs more often in defended prey, which may thus speed up predators' avoidance learning. In undefended prey, DS may trigger startle or fear responses, confusion or sensory overload in the predator, thereby pausing or stopping the attack. FS are exposed during the prey's escape, usually early in the PS before a predator detects the prey. This can cause a predator to form a wrong impression of the prey's appearance, making it harder to find. FS can also attract the predator's attention during pursuit, thus decreasing its chance of noticing an evasive manoeuvre. Dynamic FS, in which different colours alternate during movement, can make it hard to estimate the prey's position. The presence of both types of HAS is often linked with prey body size. The efficiency of FS is affected by the flight initiation distance. The efficiency of DS is related to...
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Performance of birds in model cognitive tasks: a cross-taxon comparison
Schlőglová, Nikola ; Exnerová, Alice (advisor) ; Kahounová, Hana (referee)
Bird cognition is an immensely complex topic. Many factors influence how birds acquire, process and act upon obtained information. Some bird groups outshine others regarding their cognitive skills, and the underlying reasons for these differences are extensively researched and discussed. Birds naturally face varying environmental factors that could have driven the evolution of specialised cognitive adaptations not generalisable across all contexts. In contrast, some birds perform well in a broad range of cognitive tasks and may possess general intelligence. Model cognitive tasks help us gain standardised data on birds' cognitive performances to compare them across different taxa, which enables us to identify potential parallels. This thesis covers selected model cognitive tasks: string-pulling tasks, reasoning by exclusion tasks, transitive inference tasks, tasks related to mirror use and reversal learning tasks, for which it analyses and compares the performance of both well-studied and understudied bird taxa. The thesis describes the selected cognitive tasks, summarises available data and highlights correlations between birds' performances and other factors while discussing possible explanations for their varying performances. Finally, the thesis addresses the question of general intelligence...
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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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Neophobia, neophilia, and dietary conservatism in birds
Beranová, Eliška ; Exnerová, Alice (advisor) ; Hotová Svádová, Kateřina (referee)
Birds` reactions towards novelty are demonstrated by two significant processes - neophobia and neophilia. These reactions often vary according to specific type of novel stimulus. Differences in levels of neophobia and neophilia enable birds to deal with potential costs and benefits arising from encountering a novel stimulus. Reactions towards novelty in birds may vary between different species as well as within them. In between species variability in levels of neophobia/neophilia may be related to dietary strategy and lifestyle. Differences in neophobia/neophilia of an individual bird may be related to sex, age, and personality. Long-term avoidance of novel food - dietary conservatism may follow the initial food neophobia. Again it varies a lot between species as well as within them. Key words: neophobia, neophilia, dietary conservatism, novel stimulus, novel object, novel food
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