Effects of seasonal, ontogenetic, and genetic factors on lifespan of male and female progeny of Arvicola amphibius

Population dynamics of an island population of water voles Arvicola amphibius (Linnaeus, 1758) with one major predator, the eagle owl Bubo bubo (Linnaeus, 1758), in northern Norway

Predator–prey relationships are of great significance to ecosystems, and their effects on the population dynamics of voles and lemmings (Microtinae) in Boreal and Arctic environments have long been of particular interest. A simple ecosystem with one major prey and one major predator could be an ideal setting for a study of their interactions. This is the situation on several small islands on the coast of northern Norway just below the Arctic Circle, with populations of water voles Arvicola amphibius preyed upon by the eagle owl Bubo bubo. The population dynamics of the water vole was studied by trapping and tagging in 2003–2018, eagle owl pellets were collected for analyses, eagle owl breeding attempts were recorded, and some weather variables collected from official recordings. After having been introduced well into the study period, the number of sheep Ovis aries was also recorded. Water voles were the main prey of the eagle owl, with 89% occurrence in pellets, with an overrepresentation of adults and males. Both predation, sheep grazing and extreme weather events influenced the vole population. Predator exclusion, as happened in three summers due to an intensive radio tracking study, especially increased the number of surviving young (in particular from the early cohorts) and the mass of adults. Extreme weather events, such as flooding in summer and deeply frozen ground in winter, most significantly reduced vole populations. Sheep grazing may exacerbate the effects of predation. A similar multitude of factors may affect populations of other rodent species as well.

Reproduction and mortality rates in ecologically distinct species of murid rodents

The trade-off between reproduction and somatic maintenance is one of the most studied concepts of modern evolutionary ecology. This theory predicts a negative relationship between maximum species longevity and total reproductive output. However, studies performed on natural animal populations have found contradictory results, probably due to the unlikelihood of wild animals gaining both maximum longevity and maximum potential fecundity. A comparison of the mortality rates and reproductive output of four ecologically distinct rodent species of Cricetidae family that were maintained in the laboratory in controlled conditions revealed the different life-history tactics of subterranean social mole voles and three related aboveground species: hydrophilic water voles, arid dwarf hamsters and steppe lemmings. Regardless of the relatively higher mortality rates at early ages in mole voles, this species has considerably higher maximum species longevity and smaller litter sizes that do not depend on calendar age, whereas in dwarf hamsters and water voles clear negative correlations between female age and litter size were detected. Steppe lemmings, as a semi-social arid species, shared some life-history tactics with both mole voles and aboveground non-social rodents.