The length of growing 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: 4.66). 04/2006; 87(3):745-58. DOI: 10.1890/05-0584
Source: PubMed


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.

Download full-text


Available from: Ivar Herfindal
  • Source
    • "The degree of SSD in Norwegian moose (Alces alces) populations varied with ecological factors affecting body growth. Males are, on average, larger than females, although the degree of dimorphism was lowest in populations with adult female-biased sex ratios (Garel et al., 2006). Consistent with one of the suggestions of Owen-Smith (1993) for other ungulates , it was proposed that the decreased SSD observed was a result of a smaller proportion of adult males in those populations and its effect on mate competition during the rut. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The attainment of sexual maturity has been shown to affect measures of sexual size dimorphism (SSD) and adult sex ratios in several groups of vertebrates. Using data for turtles, we tested the model that sex ratios are expected to be male-biased when females are larger than males and female-biased when males are larger than females because of the relationship of each with the attainment of maturity. Our model is based on the premise that the earlier-maturing sex remains smaller, on average throughout life, and predominates numerically unless the sexes are strongly affected by differential mortality, differential emigration, and immigration, or biased primary sex ratios. Based on data for 24 species in seven families, SSD and sex ratios were significantly negatively correlated for most analyses, even after the effect of phylogenetic bias was removed. The analyses provide support for the model that SSD and adult sex ratios are correlated in turtles as a result of simultaneous correlation of each with sexual differences in attainment of maturity (bimaturism). Environmental sex determination provides a possible mechanism for the phenomenon in turtles and some other organisms. © 2014 The Authors. Biological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London, Biological Journal of the Linnean Society, 2014, ●●, ●●–●●.
    Full-text · Article · May 2014 · Biological Journal of the Linnean Society
  • Source
    • "The areas cover representative parts of the distributional range of moose in Norway. We used data only from calves and yearlings, as their body masses are not affected by regional differences in reproductive tactics (Garel et al. 2006). During the period 1980–2009, data on 44,926 calves and yearlings were collected within the study area. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Large-scale geographical variation in phenotypic traits within species is often correlated to local environmental conditions and population density. Such phenotypic variation has recently been shown to also be influenced by genetic structuring of populations. In ungulates, large-scale geographical variation in phenotypic traits, such as body mass, has been related to environmental conditions and population density, but little is known about the genetic influences. Research on the genetic structure of moose suggests two distinct genetic lineages in Norway, structured along a north-south gradient. This corresponds with many environmental gradients, thus genetic structuring provides an additional factor affecting geographical phenotypic variation in Norwegian moose. We investigated if genetic structure explained geographical variation in body mass in Norwegian moose while accounting for environmental conditions, age and sex, and if it captured some of the variance in body mass that previously was attributed to environmental factors. Genetic structuring of moose was the most important variable in explaining the geographic variation in body mass within age and sex classes. Several environmental variables also had strong explanatory power, related to habitat diversity, environmental seasonality and winter harshness. The results suggest that environmental conditions, landscape characteristics, and genetic structure should be evaluated together when explaining large-scale patterns in phenotypic characters or life history traits. However, to better understand the role of genetic and environmental effects on phenotypic traits in moose, an extended individual-based study of variation in fitness-related characters is needed, preferably in an area of convergence between different genetic lineages.
    Full-text · Article · Jan 2014 · Oecologia
  • Source
    • "Recent studies showed that NDVI has been successfully used to link plant phenology (as a proxy of vegetation quality) and life history traits in various species of ungulates in open habitats (Pettorelli et al. 2005, 2007; Garel et al. 2011). Again, limited information is available regarding the ability of NDVI to forecast resource quality in forested areas [but see Garel et al. (2006) "
    [Show abstract] [Hide abstract]
    ABSTRACT: Quantifying available plant biomass is a crucial step towards improving our understanding of herbivore ecology and trophic interactions. Thanks to the development of satellite-derived vegetation indices such as the normalized difference vegetation index (NDVI), ecologists have been provided with indirect estimates of primary production at various temporal and spatial scales. When it comes to forested ecosystems, most mammalian herbivores predominantly rely on the ground vegetation, yet little is known regarding the suitability of NDVI to predict this component of forest vegetation cover. This study compares the relationship between NDVI and ground vegetation biomass in two contrasting habitats (field and forest) in Eastern Poland over the spring and summer seasons (2007–2008). Results indicate that seasonality shapes the relationship between NDVI and ground vegetation biomass for each habitat type. In the field habitat, NDVI and ground vegetation biomass were positively related, with a stronger correlation between the two variables occurring in summer. In the forest habitat, a switch in the direction of the correlation between biomass and NDVI (from positive in spring to negative in summer) was detected. The timing of the switch was related to the timing of full development of tree and shrub leaves (late May–early June). This suggests that the usefulness of NDVI as a predictor of ground vegetation biomass is dependent upon the habitat considered and the targeted season.
    Full-text · Article · Oct 2013 · European Journal of Wildlife Research
Show more