The sediment of Lake Balaton (Hungary) provides important information about the lake's history, particularly with regard to eutrophication. In this study, we used fossil pigment analysis and subfossil Cladocera remains preserved in a dated sediment core to identify trophic stages from *250 BC to present. Dates of the most recent eutrophic events are in good agreement with previously published data. In general, the abundance and diversity of the Cladocera community increased with eutrophication and decreased with oligotrophication. The sediments of Lake Balaton were characterised by Chydoridae remains, of which Alona species were the most abundant. Of these, Alona quadrangularis and Alona affinis accounted for 40 and 20% of the total Cladocera remains, respectively.

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Capsule The use of plasticine eggs coated with a thin layer of rubber instead of entirely plasticine eggs in dummy nests reduced the unnaturally high nest predation rate caused by attracted small mammals, while also enabling the identification of nest predators.

The water level of Lake Balaton (a large, shallow lake) was extremely low in 2003, after a dry period of several years. Due to the intensive precipitation in 2004, a regeneration period commenced. Stones of the littoral zone were sampled near the water surface and from the lake bottom four times in both years at four sampling stations. Malacostraca in the encrustation of the stones were represented by Ponto-Caspian immigrants: the invasive amphipods Chelicorophium curvispinum and Dikerogammarus spp. (D. haemobaphes and D. villosus), the mysid Limnomysis benedeni and the isopod Jaera istri. The amphipods dominated in both years. Species of the amphipod genus Dikerogammarus were relatively less abundant than the amphipod C. curvispinum in the regeneration period as compared to the drought period of 2003. Maximal density of Malacostraca (ind. m -2 stone surface) was 69,953 in 2003 and 82,465 in 2004. Vertical stratification of animal numbers and specific taxa occurred in May 2003 and throughout the year in 2004, with some exceptions. Many more Malacostraca individuals were recorded at the lake bottom than near the water surface.

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Abstract. In this paper we investigate a single-server retrial queueing system with collision of the customer and an unreliable server. If a customer finds the server idle, he enters into service immediately. The service times are independent exponentially distributed random variables. During the service time the source cannot generate a new primary call. Otherwise, if the server is busy, an arriving (primary or repeated) customer involves into collision with customer under service and they both moves into the orbit. The retrial time of requests are exponentially distributed. We assume that the server is unreliable and could be break down. When the server is interrupted, the call being served just before server interruption goes to the orbit. Our interest is to give the main steady-state performance measures of the system computed by the help of the MOSEL tool. Several Figures illustrate the effect of input parameters on the mean response time.

Abstract. The aim of the present paper is to build a simulation program to investigate finite-source retrial queuing system with collision of the customers where the server is subject to random breakdowns and repairs depending on whether it is idle or busy. All the random variables involved in the model construction are assumed to be independent and generally distributed. The novelty of the investigation is to carry sensitivity analysis of the performance measures using various distributions. Several figures show the effect of different distributions on the performance measures such as mean and variance of number of customers in the system, mean and variance of response time, mean and variance of time a customer spent in service, mean and variance of sojourn time in the orbit.