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Aktivita raka mramorovaného v závislosti na reprodukčním cyklu
MARKOVÁ, Kateřina
The aim of this thesis was to elaborate a literature review on the topic of crayfish activity, in particular their feeding activity and the use of shelters, including an emphasis on the role of sex and the reproductive cycle. I also focused on the characteristics of the marbled crayfish, Procambarus virginalis Lyko, 2017 and its usability as a model organism. The experimental part of the thesis focused on comparing three groups of female marbled crayfish (with ovulum, with glair glands and without ovulum). Experiments have been carried out using a method for ecological assessment of feeding behavior and predator-prey relationship in various prey densities in the form of larvae of buzzer midge Chironomus plumosus (Linnaeus, 1758) by functional response analysis and subsequently tested for the effect of shelter presence at uniform prey densities levels. In our experiment, all three groups of tested females showed a type II functional response typical of predators. The results indicate that females without ovulum have been the most active in terms of food collection in all cases, with a generally positive effect of the presence of shelter. Females with employed ovulum are generally less active in terms of consumption, processing and overall aktivity due to hormonal, physiological and consequently behavioural changes. Females with glair glands behaved similarly to females with ovulum in our experiments, being more cautious and less active than females without ovulum. This was probably due to their increased gonadosomatic index (GSI) and, conversely, their decreased hepatopankreas to total body weight ratio, which renders these females unable to physiologically ingest large amounts of submitted food. Female GSI decreases again after ovulation, nevertheless, even females with already employed ovulum did not consume more food, as females prefer safety at this stage of the reproductive cycle. They are less active, move more slowly, spend more time in a shelter, tend to their eggs, and thus cannot devote themselves fully to hunting and prey processing. Regarding its life strategy, the marbled crayfish is a generally suitable model organism for use in various areas of research, however, it is important to take into account its rapid life and reproductive cycle and adapt the conditions of the given experiments to this fact, as the parallel use of female marbled crayfish at various stages of the reproductive cycle can modulate results in terms of their activity. Certain differences in the presented results may also be due to the origin of the experimental animals, as with very few exceptions all performed experiments with marbled crayfish have been carried out using laboratory individuals. A number of conditions that change seasonally in nature have been kept constant in the laboratory. Therefore, it is important to keep in mind that in wild, crayfish are also exposed to both biotic (predation pressure of various species of fish, birds or mammals) and abiotic (changes in temperature and water chemistry) factors that can influence food activity. Nevertheless, we assume that the patterns observed here will also be valid for female crayfish living in the wild nature. However, the lack of similar experiments leading to the elucidation of female activity depending on the stage of the reproductive cycle provides a room to investigate other, not just crayfish species.
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Odhad ekologického vlivu hlaváče černoústého (Neogobius melanostomus) na makrozoobentos dolního Labe pomocí funkční odpovědi potravního chování: vliv velikosti predátora
RYTÍŘ, Jan
The round goby Neogobius melanostomus (Pallas, 1814) originally from the Ponto - Caspian region, has remarkably expanded in recent decades in areas of the North American Great Lakes and European river systems. This small benthic fish represents for the invaded aquatic ecosystems a serious threat, through both competition for food sources, habitats, and direct predation on benthic organisms. The aim of the B. Sc. thesis was to summarize the available information in the field of biological invasions and non-native species, with a special emphasis on the round goby and issue of the functional response. In the practical part, a potential impact of the round goby as the predator and its size (3 size cohorts: small individuals = 3.0 - 3.5 g; medium individuals = 5 - 5.5 g; large individuals = 8.0 - 8.5 g) on the waterlouse, Asellus aquaticus (Linnaeus, 1758) (tested in 6 concentrations: 2, 8, 20, 35, 60, 90 individuals.box-1) as a selected representative of macrozoobenthos forming an important food component of the round goby diet was evaluated using a series of "functional response" experiments. All size cohorts of the round goby exhibited a functional response type 2. The highest efficiency in prey search (search rate) was found in the large individuals. Statistically significantly lower values were achieved in this parameter in medium and small individuals (p 0.001). The smallest individuals processed a food for the longest time. Statistically significantly lower values were reached in case of handling time in medium and large individuals (p 0.001). In large individuals, a curve of the functional response showed a steeper slope and faster attainment of the limit value (curve asymptote). Per capita impact of the medium and large individuals (based on the value of the asymptote of a functional response) did not differ. However, small individuals have reached a lower value. In summary, it can be concluded that a size cohort of the large individuals of the round goby could represent the highest potential impact upon macrozoobenthos communities. Nevertheless, for a more accurate estimation and evaluation of the real impact of this fish predator on benthic invertebrate communities of the Elbe river, it is necessary to combine the results of the B.Sc. thesis with the field data on the total size of the predator population, the size composition and seasonal variability.
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Potravní chování hlaváčovitých ryb v závislosti na komplexitě prostředí
KOVÁŘ, Petr
Round goby Neogobius melanostomus (Pallas, 1814) and western tubenose goby Proterorhinus semilunaris (Heckel, 1837) are two benthic fish species, which have recently expanded from their native ranges of Ponto-Caspian Region to Europe and North America. While the ecological impact of round goby is widely documented, western tubenose goby receives little attention and its effect on aquatic communities has not yet been quantified. The main aims of present B.Sc. thesis are assessment and comparison of ecological impact and feeding behavior of both alien predatory fish species upon larvae of common carp (Cyprinus carpio, Linnaeus, 1758). The feeding behavior was tested in three habitats with different complexities: sandy and rocky substratum and habitat with plant. Present experiments were accomplished using comparative functional response, which has been successfully applied in assessment and comparison of ecological impact of alien species and their feeding behavior. Interspecific comparison between round goby and western tubenose goby showed similar handling times in rocky substratum and in habitat with plant suggesting similar per capita ecological impact of both predators. Intraspecific comparison showed significantly lower handling time in rocky habitats compared to others, and hence the ecological impact of both predators in such environments could elevate. Both, round goby and western tubenose goby showed type II FR in all treatments. Our results highlight the importance of complex actions in management of biological invasions, as the elimination of invasive round goby can boost the population growth of another alien species, e.g. western tubenose goby, which was not considered invasive until that time.
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Influence of visibility in water column on predation pressure in predatory aquatic insects
PODHRADSKÁ, Eliška
The influence of abiotic factors on predation behaviour in predatory aquatic animals is reviewed. The most important factors are turbidity, light intensity and complexity of the environment. These abiotic factors are often combined with biotic factors. The second important part of thesis is the description of functional responses and influence of changes of visibility on individual components of predation behaviour. The review is complemented by laboratory experiments on two selected species of aquatic insects.
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