Population Ecology of the Water Vole (Arvicola terrestris L.) in West Siberia. IV. Intra-Population Variability in Food Digestibility.
V. I. EVSIKOV, L. E. OVCHINNIKOVA
Institute of Animal Systematic and Ecology Siberian Branch
of the Russian Academy of Sciences, Frunze Str., 11, Novosibirsk 630091, Russia
Pages: 89-98
Abstract
Inter-annual, seasonal and individual variations in food digestibility were studied in a cyclic population of water vole. Digestibility was calculated from the data on the indigestible component (lignin + acid-insoluble ash) in food and feces. Samples were collected in natural habitats and from captured water voles maintained on a natural diet for 3-5 days after capture. Estimates of food quality were based on the data for forage fibber.
Seasonal changes in digestibility were determined by seasonal alterations in the forage but found to differ at different phases of population dynamics. After the peak there was a relative loss of digestibility in animals with no loss of food quality. This is suggested to be caused by adoptions to eating un-preferable food against a background of food depletion in winter habitats overgrazed at high density. Digestibility values started to rise at low density and these inter-annual changes in over wintered animals were positively correlated with the cyclic-related changes in the mean body weight and negatively with the plasma level of free fatty acids. Relations between the digestibility and the individual body weight, social status and breeding conditions were found. Among animals over wintered at numbers decline, dominant males and pregnant females digested food more efficiently in contrast to subordinate and non-pregnant ones. It was concluded that adjustments of digestive system of animals, among other nutritional factors, may affect the population dynamics through changes in population and individual fitness.
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