Red grouse (<I>Lagopus lagopus scoticus </I>Lath.) populations often show cycles in numbers. It has been suggested that these are caused by positive feedback between population kin structure and recruitment of young cocks to the territorial population, and by negative feedback between population density and recruitment. In previous studies of red grouse in north-east Scotland, recruitment was the key demographic factor affecting population change. Changes in recruitment were the result of changes in breeding success and changes in the proportion of young cocks establishing territories in autumn. This thesis investigates the differences between those young males which successfully established a territory and those that did not, on a heather moorland on the edge of the Cairngorm mountains, north-east Scotland. It describes the behaviour and movements of young cocks during the period of territory establishment. In particular it is shown that young cocks which had more close relatives as neighbours were more likely to establish a territory. However, investigation of the effect of relatedness on the aggressive interactions between cocks did not reveal any robust behavioural mechanism by which this relationship might have come about. Relatedness between individuals was estimated from microsatellite genetic data. Young cocks which established territories had larger supra-orbital combs than those which did not. This suggests that hormonal status is important in determining recruitment success, since comb size is an indicator of the level of circulating androgens of an individual. Territory establishment by young cocks took place rapidly in mid-September following the break up of broods. Young cocks were never observed to win encounters with old established cocks during territory establishment. Persistence in engaging in encounters may be more important than winning them.

Arctic food webs are characterized by multi-year predator-prey cycles. Arctic foxes (Vulpes lagopus) feed primarily on rodents, but also on avian and marine prey when rodents are scarce. I examined temporal variation in the arctic fox diet related to food availability and stress hormones (i.e. cortisol). Lemmings (Dicrostonyx richardsoni), goslings, and goose eggs were important components of the fall and winter diet. Goslings were important in fall, even when rodents were abundant. Lemmings were most important in winter, even when lemming densities were low. Consuming stored eggs did not reduce cortisol concentrations, suggesting that arctic foxes do not prefer stored eggs to lemmings. I also found that prey hormones increased fecal hormone concentrations of captive arctic foxes, introducing an additional caution for hormone studies involving predators. Nonetheless, relationships between stress hormone concentrations and changes in food availability can provide insight regarding the importance of food sources to consumer populations.

The aim of the study was to find out the character of abundance fluctuations in a field vole population on immission clearings in the Krušné (Ore) Mountains during a 25 year series of trapping. Another aim was to find out the influence of climaticconditions on these cycles, concretely the influence of local climatic condition and the influence of North-Atlantic oscillation

The topic of the presented thesis is evolution of the arvicoline rodents (Cricetidae) using the phylogenetic approach. Phylogenetic relationships within the Arvicolinae were examined based on two genes (mitochondrial cytb, nuclear GHR exon 10) and approx. 470 morphological, developmental, behavioural, ecological and cytogenetic characters. The thesis consists of four related topics: (i) Phylogeny of arvicoline rodents (Robovský et al. 2008: Zool. Scr. 37: 571-590); (ii) Fossils, phylogeny and morphological evolution in the Arvicolinae (Rodentia: Cricetidae); (iii) Enamel, diet and habitat evolution in arvicoline rodents (Cricetidae); and (iv) Vole population cycles: evolutionary history or actual life histories?.