Robert B. Weladji

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.

Conflict between people and protected areas within the Bénoué Wildlife Conservation Area, North Cameroon

Knowledge of conflicts between people and protected areas is required for the design of sustainable conservation strategies for the management of most protected areas. This study identifies the causes of conflicts between local people and the Benoue Wildlife Conservation Area (BWCA), which includes the Benoue National Park, in northern Cameroon. Informal interviews and questionnaires were administered to 114 households in three communities, and to 17 Park staff and seven professional hunting guides. Crop damage affected 86% of the surveyed households, with 31% of crop income lost on average, and with the damage varying significantly between communities. Elephants, baboons, patas monkeys, warthogs and green parrots accounted for 97% of crop damage, with the staple foods maize and millet being most affected. Of the respondents, 28% experienced livestock depredation, with 18% of livestock income lost on average. The civet cat was the main predator. The involvement of local people in illegal activities, their lack of access to natural resources, and damage by wildlife were identified as principal causes of conflicts. Local people, park staff and professional hunting guides had diverse and differing perceptions about the causes of the conflicts, and made various suggestions for reduction of wildlife damage including animal scaring and controlled shooting. We conclude that, under current wildlife policy, conflict between people and BWCA is difficult to resolve. To reduce conflicts and promote sustainable conservation, we suggest co-management of wildlife involving all stakeholders, establishment of crop damage control teams, and promotion of tangible benefits to local people. There may be a requirement for site-specificity inmanagement strategies.

Feedback effects of chronic browsing on life-history traits of a large herbivore.

1. Increasing ungulate populations are affecting vegetation negatively in many areas, but few studies have assessed the long-term effects of overbrowsing on individual life-history traits of ungulates. 2. Using an insular population of white-tailed deer (Odocoileus virginianus Zimmermann; Anticosti, Québec, Canada) introduced in 1896, and whose density has remained high since the first evidence of severe browsing in the 1930s, we investigated potential feedbacks of long-term and heavy browsing on deer life-history traits. 3. We assessed whether chronic browsing contributed to a decline of the quality of deer diet in early autumn during the last 25 years, and evaluated the impacts of reduced diet quality on deer body condition and reproduction. 4. Rumen nitrogen content declined 22% between two time periods, 1977-79 and 2002-04, indicating a reduction in diet quality. 5. After accounting for the effects of year within the time period, age and date of harvest in autumn, peak body mass of both sexes declined between the two time periods. At the end of November, males were on average 12% heavier and adult does 6% heavier in 1977-79 than in 2002-04. Hind foot length did not vary between time periods. 6. The probability of conception increased 15% between the two time periods, but litter size at ovulation declined 7%, resulting in a similar total number of ovulations in 2002-04 and in 1977-79. 7. Our results suggest that following a decline in diet quality, white-tailed deer females modified their life-history strategies to maintain reproduction at the expense of growth. 8. Deer appear to tolerate drastic reductions in diet quality by modifying their life history traits, such as body mass and reproduction, before a reduction in density is observed. Such modifications may contribute to maintain high population density of large herbivores following population irruption.

VARIATION IN CALF BODY MASS IN MIGRATORY CARIBOU : THE ROLE OF HABITAT, CLIMATE, AND MOVEMENTS

Abstract Individual differences in body mass exert a major influence on several life-history traits of mammals. We investigated the factors influencing variation in body mass of calves of migratory caribou (Rangifer tarandus) at birth (June, 19 years of data) and in autumn (October, 15 years of data) in the Rivière-aux-Feuilles (Feuilles, 1991–2003) herd and the Rivière-George (George, 1978–2003) herd in Québec and Labrador, Canada. Mass at birth (hereafter, birth mass) did not differ between herds, possibly because part of their winter ranges overlapped. However, Feuilles calves were smaller in autumn than George calves, possibly reflecting differences in summer ranges. The birth mass of calves also varied with year, likely as the outcome of both intrinsic and extrinsic factors. Birth and autumn body mass were influenced positively by habitat quality in June, estimated by the normalized difference vegetation index. The North Atlantic Oscillation of the previous winter was positively correlated with autumn mass of the George calves. Previous winter snowfall was negatively related to the mass of George calves, and daily movement rates in summer were negatively correlated with the mass of calves of both herds in autumn. Birth mass was positively related with productivity in October in the George herd and also with productivity 3 and 4 years later, which corresponds to the beginning of reproduction of females. We suggest that a mechanism of delayed quality effect of the calves could have been involved in the decrease of fall productivity and population size of the George herd.

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.

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.

Reproductive effort in relation to maternal social rank in reindeer (Rangifer tarandus)

In polygynous mammals, high-quality females may increase their fitness by providing superior care to their offspring. Based on the agonistic interactions of female reindeer in an experimental herd during two consecutive years (1997 and 1998), we tested whether maternal social rank influenced: (1) winter body-mass change of females, (2) preparturition reproductive effort (measured as fecundity, the birth mass and the birth date of their calves), (3) preweaning maternal effort (measured as calves’ preweaning mortality, early preweaning and late preweaning growth rate and September body mass of calves), and (4) postweaning maternal effort (measured as calves’ body-mass change during their first winter). In the models, we included September females’ body mass as a covariate to separate the effects of maternal rank and body mass. We also tested whether the effect of social rank on maternal efforts was dependent on offspring sex. High-ranked females gained body mass whereas low-ranked females lost weight during the winter. Fecundity was higher and date of birth was earlier in high-ranked females than in subordinates, whereas no effect of females’ rank on birth mass of calves was found. Early preweaning growth rate and September body mass of calves increased with increasing females’ social rank, whereas late preweaning daily growth rate of calves was not influenced by females’ rank. Calves’ preweaning mortality was only influenced by year, which also explained most of the variance in the winter body-mass change of calves. The effects of females’ rank on the reproductive-efforts parameters studied were not specific to offspring sex. These findings suggest that females’ rank influences reproductive effort during the preparturition, as well as the preweaning, period, the effect being sex independent.