Øystein Holand

The relative role of winter and spring conditions: linking climate and landscape-scale plant phenology to alpine reindeer body mass

The relative importance of winter harshness and early summer foraging conditions are of prime interest when assessing the effect of global warming on artic and mountainous ecosystems. We explored how climate and vegetation onset (satellite-derived Normalized Difference Vegetation Index data) determined individual performance in three reindeer populations (data on 27 814 calves sampled over 11 years). Snow conditions, spring temperatures and topography were the main determinants of the onset of the vegetation. An earlier onset positively affected the body mass of calves born the following autumn, while there was no significant direct negative impact of the previous winter. This study underlines the major impact of winter and spring climatic conditions, determining the spring and summer food availability, and the subsequent growth of calves among alpine herbivores.

Good reindeer mothers live longer and become better in raising offspring.

Longevity is the main factor influencing individual fitness of long-lived, iteroparous species. Theories of life history evolution suggest this is because increased longevity allows individuals to (i) have more breeding attempts (time component), (ii) accumulate experience so as to become better able to rear offspring (experience component) or (iii) because individuals reaching old age have above-average quality (quality component). We assess empirically the relative influences of time, experience and quality on the relationship between longevity and individual fitness among female reindeer. Fitness increased with longevity due to all three processes. All females increased in success with age up to their penultimate year of life (experience component), the success of the terminal-breeding occasion was strongly dependent on longevity. Long-lived females had more successful breeding attempts during their life (time component), and had higher reproductive success at all ages, especially during the last year of life (individual quality component) than short-lived females. Our study reveals a more complex relationship between longevity and fitness in large mammals than the simple increase of the number of reproductive attempts when living longer.

Effects of age, density and sex ratio on reproductive effort in male reindeer (Rangifer tarandus)

In sexually dimorphic ungulates, male reproductive success depends on fighting with other males for access to females during a brief rutting season. Large body size is necessary for success in intrasexual competition, and af ew large-sized males are often able to monopolize access to female groups. Earlier studies have reported that reproductive effort increases with age until prime-age is reached, and one study that population density lowered effort in (older) males. No study has directly assessed whether there is within-age-class variation in effort resulting from varying levels of intra-male competition. It is reported here the weight loss during the rutting season of 54 individual male reindeer Rangifer tarandus coming from eight herds with varying density (3.3–6.0 deer/km 2 ) and sex ratio (4–28% males). In agreement with earlier studies, reproductive effort was lower for young (1- to 2-year-old) than for prime-aged (3- to 5-year-old) males both on an absolute and relative scale. Among 1-year-old males (n = 33), effort was lower as sex ratio became closer to even, but density during the rutting season had no effect. This suggests that yearling males take a more active role when prime-aged males are absent. In addition to the insight into male ungulate life history, understanding male rutting behaviour may also have implications for population dynamics.

Comparative response of Rangifer tarandus and other northern ungulates to climatic variability

To understand the factors influencing life history traits and population dynamics, attention is increasingly being given to the importance of environmental stochasticity. In this paper, we review and discuss aspects of current knowledge concerning the effect of climatic variation (local and global) on population parameters of northern ungu¬lates, with special emphasis on reindeer/caribou (Rangifer tarandus). We also restrict ourselves to indirect effects of climate through both forage availability and quality, and insect activity. Various authors have used different weather variables; with sometime opposite trends in resulting life history traits of ungulates, and few studies show consistent effects to the same climatic variables. There is thus little consensus about which weather variables play the most sig¬nificant role influencing ungulate population parameters. This may be because the effects of weather on ungulate pop¬ulation dynamics and life history traits are scale dependent and it is difficult to isolate climatic effects from density dependent factors. This confirms the complexity of the relationship between environment and ecosystem. We point out limits of comparability between systems and the difficulty of generalizing about the effect of climate change broadly across northern systems, across species and even within species. Furthermore, insect harassment appears to be a key climate-related factor for the ecology of reindeer/caribou that has been overlooked in the literature of climatic effects on large herbivores. In light of this, there is a need for further studies of long time series in assessing effects of climate variability on reindeer/caribou.

Use of climatic data to assess the effect of insect harassment on the autumn weight of reindeer (Rangifer tarandus) calves

Considerable behavioural evidence supports harassment by insects as the most important causal link between warm summer temperatures and low body condition of reindeer Rangifer tarandus, and that insect activity is influenced by weather condition. However, much less is known about the effect of insect harassment on individual performance, measured as reduced weight gain during summer, and the related consequences on both the reindeer pastoral economy and reindeer as a biological resource. Using climatic data, this paper develops a simple index for the analysis of insect harassment that takes into consideration weather variables known to significantly affect insect activity and/or the level of insect harassment. The insect harassment index, which is based on mid-day ambient temperature ≥13 °C, wind speed <6 m/s and cloud cover <40%, is further used to test the hypothesis that insect harassment has a negative effect on reindeer performance during summer in three Norwegian populations. Results show that harassment by insects negatively affects the autumn weight of reindeer calves, most probably through reduced grazing time and increased energy expenditure, but also indirectly by negatively influencing milk production of the dam. Moreover, female calves were more vulnerable to insect harassment than males. Insect harassment may have consequences on future reproductive performance, calving time, calf birth weight and hence neonatal mortality, and thus affect reindeer productivity. The presented index is easy to estimate and may be used to quantify and compare harassment levels on various reindeer summer grazing areas for management purposes. Our results also suggest that the expected temperature increase in the course of global warming may increase the insect-related stress on reindeer.

Adaptive adjustment of offspring sex ratio and maternal reproductive effort in an iteroparous mammal

Large mammals in seasonal environments have a pattern of high-reproductive synchrony in spring, but how the timing of reproduction affects resource allocation decisions at different stages of the reproductive cycle remains largely unexplored. By manipulating the timing of conception in reindeer (Rangifer tarandus), we tested how the timing of conception affected sex ratio, gestation length and weight development of mother and offspring. Females that conceived at their first ovulation within the rut had a 60.5% probability of producing a male; in contrast, females that conceived a cycle later had a 31.3% probability of producing a male. Late conceiving females had gestation times that were 10 days shorter and the calves were 0.6 kg (9.2%) lighter at birth and 7.4 kg (14.7%) lighter in autumn. Over the year, female weight changes was similar between the groups suggesting reindeer follow a bet-hedging strategy; reducing the quality of this years offspring to ensure their own future reproduction and survival. Harvesting is often selective leading to skewed sex ratios and age structure, which may influence the timing of reproduction due to females hesitation to mate with young males. Whenever this hesitation is strong enough to increase the frequency of recycling, harvesting is likely to have profound life history consequences.

The Effect of Sex Ratio and Male Age Structure on Reindeer Calving

In polygynous ungulates, biologists commonly assume that the role of males in population dynamics is negligible since the males physiological capacity to inseminate females normally will not be a limiting factor for calving rates. Recently, however, research indicates that the role of males may be more important than previously acknowledged because availability of males may affect conception dates and hence calving dates and synchrony. In many harvested or otherwise managed populations, a sex ratio highly skewed toward females and a young male age structure often exist. Both a skewed sex ratio and male age structure may affect conception times and may delay calving dates. We manipulated the sex ratio and male age structure in herds of reindeer (Rangifer tarandus) fenced in large-scale enclosures (14-15 km 2 ). We compared calving rates, dates, and synchrony as well as (1) birth and autumn weights of calves among a skewed sex ratio and yearling males only, (2) a skewed sex ratio and an even male age structure, and (3) an even sex ratio and even male age structure. As predicted, calving dates were earlier in the treatment with an even sex ratio and even male age structure compared to the 2 other treatments. Neither sex ratio nor male age structure impacted calving rates or birth synchrony. Timing of births is important for the survival of newborns, and this should be considered when harvesting or otherwise managing populations of polygynous ungulates.

Social rank in female reindeer (Rangifer tarandus): effects of body mass, antler size and age

In polygynous mammals, fitness differences may reflect differences in phenotypic quality as well as experience. This study determines dominance hierarchy among female reindeer Rangifer tarandus from two experimental herds (consisting of c. 45 animals in each) during 2 consecutive years. The influence of body mass, antler size and age on social rank in the herds was investigated, first using simple regression analysis. The combined effect of body mass, age and antler size on female rank was further assessed using principal component analysis, as these three parameters were significantly correlated. The improved Laundau linearity index of c. 0.5 (Pr < 0.001) in both herds indicated that a substantial part of the hierarchies was explained by their linearity properties. Consistently, body mass, female age and antler size, as well as their combined effect (measured by the scores on the main axis, PC1), influenced social rank in all four groups. It was concluded that both body mass and age are good predictors of social rank in female reindeer, whereas antler size in comparison plays a less important role in herds with a ‘normal’ female age structure. This suggests that female antlers may have evolved in intersexual rather than intrasexual competition. The temporal variations in the importance of body mass and age, probably owing to variation in female age structure between the 2 years, calls for conservative interpretations of whether body mass or age is more important in determining social rank among female reindeer. This is confirmed by the PCA analyses, where all three variables contributed more or less equally to the first component, the size variable, which on average explained more of the variation in female rank than body mass and age, suggesting that phenotypic quality expressed as the combination of the three variables is a better predictor of social rank than the variables per se. Hence, general conclusions about social rank based on single studies including few animals may not be credible.

Genetic analyses reveal independent domestication origins of Eurasian reindeer

Although there is little doubt that the domestication of mammals was instrumental for the modernization of human societies, even basic features of the path towards domestication remain largely unresolved for many species. Reindeer are considered to be in the early phase of domestication with wild and domestic herds still coexisting widely across Eurasia. This provides a unique model system for understanding how the early domestication process may have taken place. We analysed mitochondrial sequences and nuclear microsatellites in domestic and wild herds throughout Eurasia to address the origin of reindeer herding and domestication history. Our data demonstrate independent origins of domestic reindeer in Russia and Fennoscandia. This implies that the Saami people of Fennoscandia domesticated their own reindeer independently of the indigenous cultures in western Russia. We also found that augmentation of local reindeer herds by crossing with wild animals has been common. However, some wild reindeer populations have not contributed to the domestic gene pool, suggesting variation in domestication potential among populations. These differences may explain why geographically isolated indigenous groups have been able to make the technological shift from mobile hunting to large-scale reindeer pastoralism independently.

Male phenotypic quality influences offspring sex ratio in a polygynous ungulate

Evolutionary models of sex ratio adjustment applied to mammals have ignored that females may gain indirect genetic benefits from their mates. The differential allocation hypothesis (DAH) predicts that females bias the sex ratio of their offspring towards (more costly) males when breeding with an attractive male. We manipulated the number of available males during rut in a polygynous ungulate species, the reindeer (Rangifer tarandus), and found that a doubling of average male mass (and thus male attractiveness) in the breeding herd increased the proportion of male offspring from approximately 40 to 60%. Paternity analysis revealed indeed that males of high phenotypic quality sired more males, consistent with the DAH. This insight has consequences for proper management of large mammal populations. Our study suggests that harvesting, by generating a high proportion of young, small and unattractive mates, affects the secondary sex ratio due to differential allocation effects in females. Sustainable management needs to consider not only the direct demographic changes due to harvest mortality and selection, but also the components related to behavioural ecology and opportunities for female choice.