BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

The regular large-scale population fluctuations that characterize many species of northern vertebrates have fascinated ecologists since the time of Charles Elton. There is still, however, no clear consensus on what drives these fluctuations. Throughout their circumpolar distribution, mountain hares Lepus timidus show regular and at times dramatic changes in density. There are distinct differences in the nature, amplitude and periodicity of these fluctuations between regions and the reasons for these population fluctuations and the geographic differences remain largely unknown. In this review we synthesize knowledge on the factors that limit or regulate mountain hare populations across their range in an attempt to identify the drivers of unstable dynamics. Current knowledge of mountain hare population dynamics indicates that trophic interactions--either predator-prey or host-parasite--appear to be the major factor limiting populations and these interactions may contribute to the observed unstable dynamics. There is correlative and experimental evidence that some mountain hare populations in Fennoscandia are limited by predation and that predation may link hare and grouse cycles to microtine cycles. Predation is unlikely to be important in mountain hare populations in Scotland as most hares occur on sporting estates where predators are controlled, but this hypothesis remains to be experimentally tested. There is, however, emerging experimental evidence that some Scottish mountain hare populations are limited by parasites and that host-parasite interactions contribute to unstable dynamics. By contrast, there is little evidence from Fennoscandia that parasitism is of any importance to mountain hare population dynamics, although disease may cause periodic declines. Although severe weather and food limitation may interact to cause periodic high winter mortality there is little evidence that food availability limits mountain hare populations. There is a paucity of information concerning the factors limiting or regulating mountain hare populations in the Alps of Central Europe or in the tundra and taiga belts of Russia. Future research on mountain hare population dynamics should focus on the interactions between predation, parasitism and nutrition with stochastic factors such as climate and anthropogenic management including harvesting.

The raccoon dog is a medium sized canid native to East-Asia. It was introduced to the western Soviet Union during the first half of the twentieth century, and has since then spread to, and established in, many European countries where it now is considered invasive. Raccoon dogs are suspected to have negative impacts on biodiversity, for example through nest predation, but empirical evidence is scarce. In this study we used GPS monitoring combined with camera traps on both artificial and natural nests to find out: (1) if raccoon dogs find and scavenge eggs from artificial nests, (2) if the scavenging from raccoon dogs is additive or compensatory to the scavenging from native species, and, (3) if raccoon dogs actively scare brooding birds off their nests and prey on their eggs. We found that raccoon dogs effectively located artificial nests and scavenged their eggs. There was a significantly higher scavenging frequency on experiment islands with both raccoon dogs and native scavengers, than on control islands with only native scavengers. There was no difference in native scavenging frequency on islands with versus without a raccoon dog, suggesting an additive effect from the raccoon dog on top of the native scavenging. GPStracked raccoon dogs moved intensively in the archipelago during the bird breeding season, swimming long distances to reach new islands if needed. Raccoon dogs that arrived on islands with natural nests actively scared brooding hens, up to the size of graylag goose, off their nests and preyed on their eggs. Raccoon dogs preyed on all the eggs they found, but discarded the egg shells. Not consuming the egg shells consequently leads to few visible traces of eggs in their stomachs or faeces, which in turn may explain why egg predation by raccoon dogs has been largely overlooked in previous studies. We discuss the potential impact of raccoon dogs on biodiversity, in the light of our new findings, and conclude that the raccoon dog may have a much larger effect on the breeding success of ground nesting sea birds than what has so far been the predominating view in the scientific literature.

We investigated the occurrence and distribution of multi-annual cycles in abundance of mountain hare populations across a wide area of their range in northern Europe. We analysed 125 time-series of mountain hare abundance indexed from hunting bag records and questionnaire responses from Scotland, Sweden, Finland and Switzerland. We also reanalysed 17 previously published time-series based on hunting bag records and snow track indices from mountain hare populations in Scotland, Norway, Sweden, Finland, Russia and Italy. Autocorrelation analysis showed that 45% of mountain hare populations showed evidence of cycles, characterised by significant negative autocorrelations at half or the whole cycle period. The amplitude and periodicity of cycles varied between and within countries. Time-series in Scotland were characterised by highamplitude weak cycles with a mean periodicity of nine years but with a range of 4 Á15 years. Norwegian and Swedish time-series revealed low amplitude weak cycles with a 3 Á7 year period. Finnish time-series showed low amplitude cycles with a 4 Á11 year period. Alpine time-series were predominantly non-cyclic, while the limited number of series from Russia showed high amplitude weak cycles with an 8 Á11 year period. The results reveal that mountain hare populations show a wide range of population dynamics with distinct regional differences in periodicity, amplitude and density dependent structure of cycles. These findings suggest that different factors may limit or regulate mountain hare populations in different regions of Europe thus supporting the results of recent field studies.