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Effects of Altering Sex Ratio Structure on the Demography of an Isolated Moose Population

Bernt-Erik Sæther, Erling Johan Solberg and Morten Heim
The Journal of Wildlife Management
Vol. 67, No. 3 (Jul., 2003), pp. 455-466
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3802703
Stable URL: http://www.jstor.org/stable/3802703
Page Count: 12
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Effects of Altering Sex Ratio Structure on the Demography of an Isolated Moose Population
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Abstract

We examined the effects on life-history characteristics of altering the age distribution and proportion of male moose (Alces alces) present in an isolated island population. We expected that such changes in population structure would reduce the mean adult male body mass because of increased energetic expenditure during the rut at younger age. We also expected delayed parturition and/or reduced fecundity in females, due to a lack of acceptable males during the rut. We first studied variation in body mass and fecundity in an unmanipulated (unhunted) population for 3 years. We then manipulated the age composition of the male segment of the population, leaving only young (≤2.5-yr-old) males as potential breeders during 2 rutting seasons. Finally, we reduced the adult sex ratio in the population to about 25% males during the last 3 years of the project. We found no effects from the manipulation of male age composition on age-specific variation in body growth of males, age at maturity of females, or fecundity rate. However, a delay in the mean parturition date occurred when the composition of the male segment was manipulated. Moreover, the structural changes in the male segment affected calf body mass the winter following birth, as mass decreased with parturition date. Such a decrease may produce long-term demographic effects on the population because variation in many life-history traits of ungulates is closely related to the body mass of young females. Our results indicate that manipulation of the composition of the male segment of an ungulate population may have important demographic consequences, which should be considered when choosing harvest strategies.

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