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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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Kompetice o úkryt mezi hlavačkou mramorovanou a hlaváčem černoústým
KREJČÍ, Miloslav
Non-native species very often causes reduction of quantity or they completely replace the native species. One of reasons of this phenomenon is competition for habitat and shelter. Shelter is essential for bentic and primarily for speleophilous fish species to keep stable populations. Non-native species compete for shelter not only with native fauna, but also with other non-natives species too. The aim of the B. Sc. thesis was experimental evaluation of shelter competition between western tubenose goby (Proterorhinus semilunaris) and round goby (Neogobius melanostomus) in dependence upon shelter type, time of the day, sex and species. The experiment was conducted in eleven trials with 16 repetitions (tanks) in each trial. Western tubenose goby was always the resident fish in each trial. Invader was either conspecific (intraspecific competition) or round roby (interspecific competition). Two types of shelter were used ("plant imitation" and "rocky substratum imitation"). Shelter occupancy was evaluated in four 1-hour intervals (two intervals during the day and two during the night). The course of experiment was recorded by cameras with infrared ilumination. Solitary fish (without intruder) spent significantly longer time in shelter during the day regardless of sex and shelter type. In the intraspecific competition (western tubenose goby vs. western tubenose goby), the resident fish spent more time in the shelter than the intruder. In the interspecific competition (western tubenose goby vs. round goby), the intruder spent more time in the shelter compared to situations when western tubenose goby was intruder. In conclusion, round goby could be considered more aggressive species than western tubenose goby. It could explain successful spread of round goby in the natural conditions.
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