Biological invasions of non-native species are one of the most serious factors threatening global biodiversity. Their negative impacts are particularly evident in the case of freshwater ecosystems and native crayfish populations that live there. Generally, the higher dominance of non-native crayfish species over the native species is relatively well known, but the interactions between non-native crayfish species are significantly less investigated. Although their distribution is increasingly more important and it is obvious that non-native crayfish species will dominate in European waters. However, it is not yet clear which of these crayfish will be more successful. The aim of this diploma thesis was to create a literature review on the topic of interspecific interactions in crayfish with emphasis on native and non-native crayfish species occurring in Europe. The experimental part of the thesis was focused on the comparison of direct interactions and competition for shelter between the widespread spiny-cheek crayfish Faxonius limosus (Rafinesque, 1817) and the newly increasingly occurring marbled crayfish Procambarus virginalis Lyko, 2017. These species are becoming increasingly common in the European wild, but about their mutual direct interactions and competition is largely unknown. During agonistic interactions the marbled crayfish won in significantly more fights than the spiny-cheek crayfish in the absence as well as presence of the shelter. The marbled crayfish established a significantly greater dominance over the females of the spiny-cheek crayfish in the absence and in the presence of shelter, but not over the males. It is also important to say that the presence of the shelter reduces the number of fights and their total duration. There was no significant difference in dominance established by occupation of shelter between the marbled crayfish and the spiny-cheek crayfish. Still, thanks to its aggressiveness, marbled crayfish is able to compete with other non-native species or displace them from freshwater ecosystems.

This diploma thesis deals with non-native species of crustaceans, which are already present not only in Europe but also successfully inhabit the territory of the Czech Republic. The species that this work deals with is the signal crayfish (Pacifastacus leniusculus), marbled crayfish (Procambarus fallax f. virginalis) and the killer shrimp (Dikerogammarus villosus). The main goal of this study was to demonstrate the ability of killer shrimp to attack and prey on the crayfish eggs and hatchlings of above mentioned species, which were used not only for theuir presencein Czech Republic but also as model representatives of families Astacidae and Cambaridae. It was therefore the confirmation of high aggressiveness of killer shrimp and point out, that this species is capable of negatively influencing even the bigger invertebrates by direct predation on their early developmental stages. Another aim was to assess whether the killer shrimp can be a suitable prey for a crayfish. As the experiments have shown, killer shrimp is able to predate on crayfish eggs and hatchlings even directly on females abdomens wehre they are incubated and protected. The results confirmed the theory of killer shrimp hazards to aquatic ecosystems and its potential to directly influence the populations of larger organisms. At the same time, it has been found that killer shrimp may be a suitable prey for adult and subadult individuals of signal crayfish and adults of marbled crayfish.

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