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Reciprocal predation between non-native crayfish and salmonids Who eats whom?
MÜLLEROVÁ, Lucie
Signal crayfish (Pacifastacus leniusculus) is important invasive species in European freshwaters. Its influence on other freshwater organisms is well known from the literature, as well as direct and indirect impact on fish assemblages. This work was focused on the experimental evaluation of non-indigenous signal crayfish as a predator of salmonids compared to indigenous noble crayfish (Astacus astacus). Moreover, the possible importance of young-of-the-year signal crayfish as a prey for salmonids was assessed. There were carried out experiments using eggs and hatchings of grayling (Thymallus thymallus) as a prey for adult and subadult specimens of both, signal and noble crayfish. Next experiment used young-of-the-year signal crayfish as a prey for young-of-the-year of brown trout (Salmo trutta). Results showed that the danger of signal crayfish for grayling eggs is slightly higher. However, detected differences were surprisingly lower and in the majority of parameters even insignificant. In the case of grayling hatchings, was not detected any significant difference at all. The abilities of both tested species to prey on eggs and hatchings are therefore very similar, comparable. Even so, the effect of signal crayfish can be importantly higher in natural conditions because of its more dense populations, higher growth rate and fast maturation. In accordance to our findings, it is evident that brown trout has no so high effect of crayfish juveniles compared with crayfish effect on salmonids early developmental stages. Crayfish are therefore more likely able to limit salmonids than conversely.
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Mravenci Formica foreli a konkurenční prostředí v superkolonii na lokalitě Štěměchy
Ošlejšková, Kateřina
In this diploma thesis, the results of Formica foreli Bondroit, 1918, and other ant species in the area of Štěměchy, interspecies relations study are presented. The ant Formica foreli, belonging to subgenus Coptoformica, is a species occured only at stabil and biologicaly valuable sites. Nowadays it occures only in the six locations on the territory of the Czech Republic. Investigated complex of nests, located in Vysočina region, contains 654 nests and at present it is the largest polycalic complex of the nests of this type in the Czech Republic. Collection by ground traps results, confrontation of two worker ants in an artificial arena experiments and competitive interactions on the bait observation, demonstrated, that there is wide spectrum of other ant species in the area, which indicates of good trophy of the site. Further, the results promoted a hypothesis, that thanks to the polycalic nest character, Formica foreli species ocupies the supreme position in hierarchic organization of the whole area.
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