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The length of growing season and adult sex ratio affect sexual size dimorphism in moose.

Laboratoire de Biométrie et Biologie Evolutive (UMR 5558), Centre National de la Recherche Scientifique (CNRS), Université Lyon 1, 43 boulevard du 11 novembre, 69622, Villeurbanne, France.
Ecology (Impact Factor: 5). 04/2006; 87(3):745-58. DOI: 10.1890/05-0584
Source: PubMed

ABSTRACT While factors affecting body growth have been extensively studied, very little is known about the factors likely to affect the sexual size dimorphism (SSD) in polygynous mammals. Based on the carcass mass of 24420 male and female moose recorded in 14 Norwegian populations, we examine three hypotheses to explain geographical variation in SSD. First, SSD is expected to decrease when the relative density of animals (for a given habitat quality) increases, because resource limitation at high population densities is assumed to affect body growth of males more than females. Second, because males are selected to invest in growth more than females, environmental seasonality and related improvement of the forage quality during the short and intense growing season are expected to increase SSD. Third, by decreasing the proportion of adult males in the population, resulting in start of rutting earlier in life, hunting may decrease the SSD by increasing the reproductive cost of young males. We found that males grew faster and for a longer time of their life than did females and thus were heavier (-24%) when they reached adulthood. Sexual size dimorphism was independent of density but was higher in areas with short growing seasons. The low SSD in populations with largely adult female-biased sex ratios (males per female) shows that male body growth decreases with a decreasing proportion of adult males in the population. Our results indicate that geographical variation in moose SSD is influenced by divergent responses in the sexes to ecological factors affecting body growth.

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    ABSTRACT: The National monitoring program for wild cervids (moose, Alces alces, red deer, Cervus elaphus, wild reindeer, Rangifer tarandus) in Norway was established in 1991. The program is funded by the Directorate for nature management (DN), and operated by the Norwegian institute for nature research (NINA). The data collected during the 21 years of monitoring represent a unique opportunity to follow the development in population condition (carcass mass, fecundity and recruitment rates), population density and population structure of representative populations of moose, red deer and wild reindeer. The monitoring is carried out in 17 monitoring areas distributed all over Norway (moose: 7, red deer: 3, reindeer: 7). In this report we show the trends of development during the 21 year period, with main focus on the results from the last contract period, 2007-2011. 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