The ecology and ecophysiology of Marion Island house mice, Mus Musculus L.

[摘要] English: This thesis presents the results of a studv of the biotic and abiotic conditions experienced byhouse mice on Marion Island, their morphological and reproductional adaptations to islandconditions, the seasonal changes in their diet. and of the densities and biomasses of their preyitems.By establishing burrow systems and sheltered aboveground runways nuce experience amicroelimate that is far less harsh than the macroelimatie regime. In terms of warmth, thisextends the season of mouse activity significantly compared with what would be allowed bythe macroclimate.House mice are opportunistic feeders and this plays a major role in their survival under theharsh conditions on Marion Island. The mice are primarily carnivores and impact severely onsoil macroinvertebrate populations, annually removing up to several times the averageinstantaneous standing crop of some macroinvertebrate populations. Since macroinvertebratesare cardinal agents of ecosystem functioning by being the main mediators of nutrient cycling onthe island, their predation by mice has severe ecological implications. Between 1979/80 and1992/93 the densities and biomasses of the mouse's major invertebrate prey species havedecreased. The percentage composition of the various prey types in the macroinvertebratepopulation has also changed. These changes have caused changes in the composition of themouse's diet.Seasonal changes in reproductive status, sex ratio, age structure, body mass and length,kidney- and adrenal mass, and length and shape of intestines were determined, in order toprovide information concerning the house mouse's response to fluctuating environmentalparameters and to assess the levels of stress experienced by mice at different times of the year.Stress levels are influenced by population density, sex, reproductive status, temperature andavailability of food. In 1992/93 mice had significantly larger body to tail length ratios than in1979/80, despite the fact that the island warmed considerably in the interim. This warming hasallowed a significantly longer breeding season, perhaps by as much as two months. It is suggested that this is the reason that end of season densities are now considerably higher thanin 1979/80.

[发布机构] University of the Free State