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Seasonal Variations in the Body Composition and Nutrition of the Vole Microtus agrestis

Dianne M. Evans
Journal of Animal Ecology
Vol. 42, No. 1 (Feb., 1973), pp. 1-18
DOI: 10.2307/3403
Stable URL: http://www.jstor.org/stable/3403
Page Count: 18
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Seasonal Variations in the Body Composition and Nutrition of the Vole Microtus agrestis
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Abstract

(1) The aim of the study was to measure changes in the quality of the food of Microtus agrestis and to relate these to certain aspects of the animal's ecology. (2) The species composition of the diet of voles from two habitats, a young plantation and ungrazed limestone grassland, was determined by micro-analysis at monthly intervals. (3) The pepsin-soluble contents of the grasses eaten were measured at monthly intervals. (4) Carcass analyses (to estimate fat, protein and water contents) were made at monthly intervals on voles from the two habitats. In addition, live weights were obtained from monthly live trapping. (5) Although certain grasses were selected preferentially by the voles, the utilization of the different species bore no obvious relationship to their pepsin-soluble contents. (6) Grasses are at their most soluble for only a few weeks in the year, and most growth, moult and reproduction in the vole populations occurred outside this period. Only the increase in weight of male Microtus coincided with the spring increase in protein content of grass. (7) The water content (expressed as a percentage of the lean dry weight) of both sexes dropped slightly in the winter, coinciding with low body weight. (8) In both populations studied, winter fat reserves were very low. During the summer, breeding females maintained maximum fat levels, in spite of increased energy requirements at this time. (9) Certain differences in the sizes of various body components occurred between different populations. These may indicate other physiological differences between them, as have been demonstrated already for certain plasma proteins by Semeonoff & Robertson (1968).

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