Changes in population structure and reproduction during a 3-yr population cycle of voles [Microtus agrestis, Microtus rossiaemeridionalis, Clethrionomys glareolus, Sorex araneus]

• Published in: Oikos Vol. 96; no. 2; pp. 331 - 345
• Main Authors: Norrdahl, Kai, Korpimäki, Erkki
• Format: Journal Article
• Language: English
• Published: Copenhagen Munksgaard International Publishers 01.02.2002; Blackwell Publishers; Blackwell
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Breeding; CAMPAGNOL; CICLO VITAL; Clethrionomys glareolus; CYCLE DE DEVELOPPEMENT; Demecology; DINAMICA DE POBLACIONES; DYNAMIQUE DES POPULATIONS; FINLAND; FINLANDE; FINLANDIA; Fundamental and applied biological sciences. Psychology; LIFE CYCLE; Litter size; Mammalia; Mammals; Microtus; POPULATION DYNAMICS; Population growth rate; Predation; Predators; REPRODUCCION; REPRODUCTION; Shrews; Siblings; Sorex araneus; TOPILLOS; Vertebrata; VOLES; Europe; Finland; Population growth; Interspecific comparison; Trophic factor; Rodentia; Environmental factor; Population structure; Long term variation; Cycle; Population survey; Vertebrata; Clethrionomys glareolus; Sorex araneus; Mammalia; Seasonal variation; Muridae; Population dynamics; Density dependence; Dynamic model; Insectivora; Microtus agrestis; Ecological abundance
• ISSN: 0030-1299; 1600-0706
• DOI: 10.1034/j.1600-0706.2002.960215.x

Cyclic changes in population growth rate are caused by changes in survival and/or reproductive rate. To find out whether cyclic changes in reproduction are an important part of the mechanism causing cyclic fluctuations in small mammal populations, we studied changes in the population structure and reproduction of field voles (Microtus agrestis), sibling voles (M. rossiaemeridionalis), bank voles (Clethrionomys glareolus), and common shrews (Sorex araneus) in western Finland during 1984-1992, in an area with 3-yr vole cycles. We also modelled the population growth of voles using parameter values from this study. The animals studied were collected by snap trapping in April, May, June, August, September, and, during 1986-1990, also in October. We found several phase-related differences in the population structure (age structure, sex ratio, proportion of mature individuals) and reproduction (litter size, length of the breeding season) of voles. In non-cyclic common shrews, the only significant phase-related difference was a lower proportion of overwintered individuals in the increase phase. According to the analyses and the vole model, phase-related changes in litter size had only a minor impact on population growth rate. The same was true for winter breeding in the increase phase. The length and intensity of the summer breeding season had an effect on yearly population growth but this impact was relatively weak compared to the effect of cyclic changes in survival. The population increase rates of Microtus were delayed dependent on density (8-12-month time lag). Our results indicate that cyclic changes in reproduction are not an important part of the mechanism driving cyclic fluctuations in vole populations. Low survival of young individuals appeared to play an important role in the shift from the peak to the decline phase in late summer and early autumn.