Energy Models for the Common Vole Microtus arvalis: Energy as a Limiting Resource for Reproductive Output

Abstract

A mathematical model for energy requirements of individual, non-reproducing and reproducing female small rodents is developed. Employing data on the metabolism of the commone vole M. arvalis during reproduction, the parameters are estimated by least square techniques. In all measurements applied the temperature was held constant at 20.degree. C. The best mathematical representation of the data was found by analysis of variance and error-term analysis. The models so found represent the data without systemic deviations. Some predictive variable other than weight, number of days from conception and number in each litter is needed to predict the metabolic rate more accurately. Such identification represents an important bioenergetic field of study. The deductions of precise mathematical functions representing the data facilitate a detailed analysis of how metabolic rates depend on weight of mother, time in reproductive period and number of young per litter. During gestations the total metabolic rate is not increased greatly relative to non-reproductive state. The increased total energetic cost due to pregnancy decreases with increasing initial weight of mother and an initial drop in total metabolic rate during the first 1/3 of pregnancy is observed. During lactation a marked increase in metabolic rate is seen, although no marked change occurs just at the time of parturition. Survival of fetuses and sucklings is discussed on the basis of the bioenergetic cost due to reproduction; energy might be a limiting resource for demographic features such as survival.