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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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