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 present study investigated altitudinal variation in sexual size dimorphism of a Tibetan frog Nanorana parkeri. Size dimorphism was female‐biased in all populations, although this bias became less at higher altitudes because of a steeper altitudinal decrease in female size than male size. Operational sex ratios, an indicator of the opportunity for sexual selection on larger males, changed independently of altitude. Clutch volume, an indicator of the strength of fecundity selection on larger females, was positively with female size, and tended to decrease approaching high altitudes. Females lived longer and grew more slowly than males, and the mean age in both sexes increased and growth rate decreased altitudinally, although the changes were more rapid in females than males. These results suggest that, relative to males, females (i.e. the sex that typically bears greater reproductive costs and experiences stronger directional selection for larger size to take fecundity advantages) should be more sensitive to environments, attaining a larger size via enhancing growth under favourable lower‐latitude conditions but a smaller size as a result of retarding growth when conditions become harsher at higher altitudes. This supports the condition‐dependence hypothesis with respect to intraspecific variation in sexual size dimorphism. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••–••.
    Biological Journal of the Linnean Society 11/2012; 107(3). DOI:10.1111/j.1095-8312.2012.01953.x · 2.54 Impact Factor
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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. During the period 1991-2011, there was a steady increase in the number of harvested red deer and a reduction in the number of harvested wild reindeer at a national level, whereas the number of harvested moose was relatively stable. For moose and red deer, a similar development is reflected in the number of traffic kills. On a regional level the population density and harvest of moose increased from Sør-Trøndelag to Finnmark, while the harvest decreased from Buskerud to Vest-Agder. Further east, as well as in Oppland, the harvest numbers show less of a linear trend. In the same period there was a general decrease in calf recruitment rates based on hunter observations (seen moose) in most counties. This was particularly evident in the counties from Buskerud to Vest-Agder. Despite a significant reduction in population density in these counties, recruitment rates are still low. Higher recruitment rates are still found in Østfold and in the counties from Sør-Trøndelag to Finnmark. Within monitoring areas, moose densities increased or were relatively stable in Troms, Nordland, Nord-Trøndelag and Hedmark during the period 1991-2011, and decreased in Oppland, Vestfold/Telemark and Vest-Agder. In the same period carcass weights and/or recruitment rates decreased in all areas, apart from Oppland and Troms. The recruitment rates from hunter observations did not always co-vary with the fertility rates based on ovary analyses, possibly because of hunting selection and methodological problems. The decrease in moose carcass weights and recruitment rates was most evident in areas with the highest moose densities in the early 1990’s, and is likely to be a consequence of density dependent food limitations. However, a subsequent decrease in moose density in these areas has not led to an increase in carcass weights or recruitment rates. The lack of response may be due to the fact that a major part of the reproductive females are individuals born during the high density years, and/or because the per capita available food is still limited despite a significant population reduction. A general reduction in food quality following increased summer temperatures in central and southern Norway may also have had a negative impact on body weights and recruitment rates. By the use of cohort analysis and age-at-death data we reconstructed the moose population development during the period 1991-2011 and show that the reconstructed population closely correlate with the number of moose seen per hunter day, as well as with the annual moose harvest. In addition, we found that the reconstructed female age structure was increasing or relatively stable in most areas. In all areas there was also an increase in the average age of harvested adult males. This is in accordance with an increasing proportion of males observed in Norwegian moose populations during the last 15 years. In the three monitoring areas for red deer, the population during 1991-2011 was characterized by i) increasing densities, ii) decreasing body weights and iii) reduced fertility among two year old females. The reduced fertility rates are linked to the reduction in body weights, which in turn is likely to be a consequence of density-dependent food limitation. During the period 1991- 2011 most sex and age categories showed a 10-15 % reduction in body weights. The strongest reduction in productivity among two year olds was found in Hordaland (Kvinnherad), a decrease by 80 %. This represents a significant reduction of the overall population productivity. The decrease was lower in Sogn og Fjordane and Møre og Romsdal/Sør-Trøndelag, but was following the same trend. The negative trend is likely to continue unless the population growth is stopped. The red deer observations from hunters in Kvinnherad indicate that deer density is currently decreasing, while it seems to be rather stable in the two other monitoring areas. Following a reduction in the harvest pressure of males, the female-male ratio has become less female-biased in all monitoring areas during the last 8-9 years. This is probably also the reason why the mean age of harvested adult stags (> 1 years old) has increased. The change in sex ratio and male age structure is the result of a systematic shift in harvest pattern following local management decisions. The management goal for the wild reindeer herds has been to stabilise population densities at relatively moderate levels. Monitoring data shows that this is achieved in Snøhetta, Knutshø, Rondane and Forolhogna, where populations have mostly been fluctuating around the mean density during the last two decades. In contrast, managers in Setesdal Ryfylke and Hardangervidda attempted to increase body mass, reproductive performance and quality of winter rangers by reducing reindeer densities during the 1980’s and 1990’s. Monitoring data suggest that these populations have responded to reduced densities by an increase in body mass and calf recruitment. Despite the relatively stable reindeer densities, there has recently been a marked reduction in body weights and jaw lengths in Forolhogna and Knutshø, and in Knutshø we also see a pronounced decrease in number of calves per 100 females and yearlings. In the report we discuss several factors that can explain these rather surprising results. In the monitoring area on Svalbard, the reindeer population shows erratic fluctuations in density following large annual variations in recruitment and natural mortality rates. For two decades (1979-1999) the population fluctuated around a mean of about 450 animals, but then increased in density after several years with higher than average recruitment. Since year 2000 the population has been fluctuating around an average of 800 animals. During the last contract period, 2007-2011, we also examined in a pilot study to what extent data provided by the national forest inventory can be used for monitoring the variation in food availability and browsing pressure in forest habitats. The results presented show that browsing pressure and food availability varies extensively among areas, and that moose carcass weights and recruitment rates are generally higher in areas with low browsing pressure and a higher number of available foraging trees. We concluded that the data are able to provide a good reflection of the moose forage conditions at a regional scale and that they also might be used to monitor the forage conditions for red deer. In the next 5-year period NINA will continue the National monitoring program for wild cervids much as before in all monitoring areas. However, following the increasing distribution of red deer in eastern Norway, we will establish two new monitoring areas for red deer in this part. In addition, we will continue the close collaboration with the national forest inventory and integrate the monitoring of forest food availability and browsing pressure as a part of the monitoring program. For reindeer, we will start a similar monitoring of the winter grazing conditions at Hardangervidda.
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    ABSTRACT: Body condition has a strong influence on reproduction and survival. Consequently, understanding spatiotemporal variation in body condition may help identify processes that determine life history, and thus demography. The effect of environmental variables on individuals' body condition, although widely documented, is generally achieved by investigating habitat, plant phenology, or density separately, such that cumulative or interactive effects can rarely be considered. We investigated how spatial and annual variation in habitat composition, deer density, and vegetation productivity influenced white-tailed deer (Odocoileus virginianus) body condition during the breeding period. We detailed changes in body condition using several indices, including body mass, peroneus muscle mass, rump fat, kidney fat index, and antler size in >4,000 male and female deer of different ages harvested during September-December, 2002-2006 on Anticosti Island, Quebec, Canada. Overall, females and yearlings harvested in fir forests were in poorer condition than those harvested in peatlands or spruce forests, whereas body condition of adult males was greater when open habitats were highly available. High deer density reduced autumn gains in fat, muscle mass, and body mass in males and yearlings, and in fat for females. Surprisingly, density positively affected the size of male antlers. High density at birth favored fat accumulation in adult females, suggesting strong selective pressure that removed low-quality individuals in early age at high deer density. Low Normalized Difference Vegetation Index (NDVI) in spring was associated with delayed but rapid spring green-up, and favored higher body condition in autumn. Reproduction affected most parameters of body condition; lactating females had less mass, fat, and muscle than non-lactating females, whereas mass and fat of males >4 years old steeply declined during the rut. Body mass and fat reserves showed a stronger response to density, habitat, NDVI, and reproduction than muscle mass. Body mass was a good integrating measure of fat and muscle mass, although allocation between muscle growth and energy storage was confounded. Our study highlighted the influence of environmental conditions on individual fat reserves, muscle mass, and body mass in autumn, with potential effects on reproduction and winter survival. Appropriate monitoring of body-condition indices in the fall can track the effect of environmental variables and management practices on animal populations. (C) 2014 The Wildlife Society
    Wildlife Monographs 06/2014; 187(1). DOI:10.1002/wmon.1010 · 2.83 Impact Factor

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