Density-dependent responses of fawn cohort body mass in two contrasting roe deer populations

We investigated the influence of population density on juvenile body mass in two contrasting roe deer populations, in Sweden (Bogesund) and France (Chizé), in which density was monitored for ≥15 years. We investigated the effect of population density and climatic conditions on cohort performance. We predicted that: (1) body mass of growing fawns should be sensitive to environmental changes, showing marked between-year variation (i.e., cohort effects), (2) fawns in the less productive (weakly seasonal, weakly predictable summer weather) habitat of Chizé should show stronger density-dependent responses due to more severe food competition during summer than fawns in the more productive (markedly seasonal, moderately predictable summer weather) habitat of Bogesund, and (3) fawns at Bogesund should be heavier both in absolute terms and relative to their size than their conspecifics in Chizé due to a higher degree of fat accumulation in northern environments. In both study sites we found marked cohort variation and clear effects of density, with body mass varying by as much as 29% over years. While neither summer nor winter climate influenced fawn body mass at Bogesund, fawns tended to be lighter after summers with high temperatures at Chizé. In addition, fawns were heavier after acorn mast years experienced in utero at Bogesund. As expected, the strength of the density-dependent response of fawn body mass was greater at Chizé than at Bogesund. For a given density, male fawns were consistently heavier than females in both sites. Lastly, both sexes at Bogesund had higher absolute body mass and were larger for a given body size than in Chizé. Our results clearly demonstrate that absolute density is a poor predictor of roe deer performance and supports the view that habitat quality has an overwhelming importance for determining fawn body mass in roe deer populations.     

Using a proxy of plant productivity (NDVI) to find key periods for animal performance: the case of roe deer

Animals in seasonal environments are affected by climate in very different ways depending on season and part of the climatic effects operates indirectly through the plants. Vegetation conditions in spring and summer are regarded as decisive for the reproductive success and the offspring's condition of large herbivores, but objective ways to determine key periods during the growing season have not been done often due to limitations in plant data. Using satellite data (NDVI), we determined how plant productivity from birth to fall influences the following winter body mass of roe deer fawns. We do this in two populations, the first inhabiting the low productive Chizé reserve in south western France with an oceanic climate and the second from Trois Fontaines, a highly productive forest with continental climate in east France. The effect of plant productivity was similar for male and female fawn mass, as expected from the weak intensity of sexual selection in roe deer life history traits. We found contrasting results between sites, with a strong effect of plant productivity in spring (April-May) in the Chizé population, but no effect in the Trois Fontaines population. The relatively low variability in winter fawn body mass could account for the absence of NDVI effects at Trois Fontaines. However, such results might also point to a limitation in the use of the NDVI, since the relationship between the canopy and the plant productivity at the ground level might be weak in the highly productive forest of Trois Fontaines.     

Bigger teeth for longer life? Longevity and molar height in two roe deer populations

The role of tooth wear as a proximate cause of senescence in ruminants has recently been highlighted. There are two competing hypotheses to explain variation in tooth height and wear; the diet-quality hypothesis predicting increased wear in low-quality habitats, and the life-history hypothesis predicting molar height to be related to expected longevity. We compared tooth height and wear from roe deer of known age from two contrasting populations of roe deer (Capreolus capreolus) in France: Trois Fontaines (TF) with good habitat and shorter animal life expectancy and Chizé (CH) with poor habitat and longer animal life expectancy. There was no population difference in tooth wear, leading to rejection of the diet-quality hypothesis. However, despite their smaller body size, initial molar height for animals from CH was larger than for animals from TF. This provides the first evidence that variation in longevity between populations can lead to differences in molar height within a species.     

Spatial variation in springtime food resources influences the winter body mass of roe deer fawns

It is well established that the dynamics of mammalian populations vary in time, in relation to density and weather, and often in interaction with phenotypic differences (sex, age and social status). Habitat quality has recently been identified as another significant source of individual variability in vital rates of deer, including roe deer where spatial variations in fawn body mass were found to be only about a tenth of temporal variations. The approach used was to classify the habitat into blocks a priori, and to analyse variation in animal performance among the predefined areas. In a fine-grained approach, here we use data collected over 24 years on 1,235 roe deer fawns captured at known locations and the plant species composition sampled in 2001 at 578 sites in the Chizé forest to determine the spatial structure at a fine scale of both vegetation and winter body mass of fawns, and then to determine links between the two. Space and time played a nearly equal role in determining fawn body masses of both sexes, each accounting for about 20% of variance and without any interaction between them. The spatial distribution of fawn body mass was perennial over the 24 years considered and predicted values showed a 2 kg range according to location in the reserve, which is much greater than suggested in previous work and is enough to have strong effects on fawn survival. The spatial distribution and the range of predicted body masses were closely similar in males and females. The result of this study is therefore consistent with the view that the life history traits of roe deer are only weakly influenced by sexual selection. The occurrence of three plant species that are known to be important food items in spring/summer roe deer diets, hornbeam (Carpinus betulus), bluebell (Hyacinthoides sp.) and Star of Bethlehem (Ornithogalum sp.) was positively related to winter fawn body mass. The occurrence of species known to be avoided in spring/summer roe deer diets [e.g. butcher's broom (Ruscus aculeatus) and beech (Fagus sylvatica)], was negatively related to fawn body mass. We conclude that the spatial variation in the body mass of fawns in winter in this forest is as important as the temporal variation, and that the distribution of plant species that are actively selected during spring and summer is an important determinant of spatial variation in winter fawn body mass. The availability of these plants is therefore likely to be a key factor in the dynamics of roe deer populations.     

Maternal and individual effects in selection of bed sites and their consequences for fawn survival at different spatial scales

We examined the relationship between survival of roe deer (Capreolus capreolus) fawns at Trois Fontaines, Champagne-Ardennes, France, and factors related to bed-site selection (predator avoidance and thermoregulation) and maternal food resources (forage availability in the maternal home range). Previous studies have demonstrated that at small scales, the young of large herbivores select bed sites independently from their mothers, although this selection takes place within the limits of their mother’s home range. Fawn survival was influenced largely by the availability of good bed sites within the maternal home range, not by the fawn’s selection of bed sites; however, selection for thermal cover when selecting bed sites positively influenced survival of young fawns. Typical features of a good home range included close proximity to habitat edges, which is related to forage accessibility for roe deer. The availability of bed sites changed as fawns aged, probably due to an increased mobility of the fawn or a different use of the home range by the mother; sites offering high concealment and thermal protection became less available in favor of areas with higher forage accessibility. Despite the minor influence of bed-site selection on survival, roe deer fawns strongly selected their bed sites according to several environmental factors linked to predator avoidance and thermoregulation. Fawns selected for sites providing concealment, light penetration, and avoided signs of wild boar (Sus scrofa) activity. Avoidance of sites with high light penetration by young fawns positively affected their survival, confirming a negative effect on thermoregulation due to reduced thermal cover. Selection for light penetration by older fawns was less clear. We discuss these results in the context of cross-generational effects in habitat selection across multiple scales, and the potential influence of the ‘ghost of predation past’.     

Effects of cohort,sex, and birth date on body development of roe deer (Capreolus capreolus) fawns

We investigated the effects of the year of birth (cohort effect), sex and birth date on the variations observed in birth weight and postnatal growth rate in 209 newborn fawns marked during eight consecutive fawning seasons from a highly productive roe deer population under good nutritional conditions. Roe deer exhibited a fast body development with a birth weight of 1628 g and a postnatal growth rate of 139 g/day constant over the first 20 days of their life. As previously reported for dimorphic and polygynous ungulates, there was a marked cohort effect on the rate of body development. This variability was partly explained by climatic conditions during late gestation. When fewer than 5 days with rainfall over 5 mm occurred in April, fawns were heavier. High temperatures during April and during the winter could also be involved in fast body development of roe deer fawns. Sex of fawn did not affect roe deer growth pattern. This was expected on the basis of low sexual dimorphism in size and low polygyny level characteristic of roe deer. Lastly, the date of birth did not affect the body development of roe deer fawns. High constancy of mean birth dates and high synchrony of births observed in this population could account for this result.     

Variations in adult body mass in roe deer: the effects of population density at birth and of habitat quality

Body mass is a key determinant of fitness components in many organisms, and adult mass varies considerably among individuals within populations. These variations have several causes, involve temporal and spatial factors, and are not yet well understood. We use long-term data from 20 roe deer cohorts (1977-96) in a 2600 ha study area (Chizé, western France) with two habitats contrasting in quality (rich oak forest in the North versus poor beech forest in the South) to analyse the effects of both cohort and habitat quality on adult mass (i.e. median body mass between 4 and 10 years of age) of roe deer (Capreolus capreolus). Cohort strongly influenced the adult body mass of roe deer in both sexes: males born in 1994 were 5.2 kg heavier when aged between 4 and 10 years old than males born in 1986, while females born in 1995 were 4.7 kg heavier between 4 and 10 years old than females born in 1982. For a given cohort, adult males were, on average, 0.9 kg heavier in the rich oak forest than in the poor beech forest. A similar trend occurred for adult females (0.5 kg heavier in the oak forest). The effects of cohort and habitat were additive and accounted for ca. 40% of the variation observed in the adult mass of roe deer at Chizé (males: 41.2%; females: 40.2%). Population density during the spring of the birth accounted for about 35% of cohort variation, whereas rainfall in May-June had no effect. Such delayed effects of density at birth on adult body mass probably affect population dynamics, and might constitute a mechanism by which delayed density-dependence occurs in ungulate populations.     

High red deer density depresses body mass of roe deer fawns

Many previous studies have pointed out that, when resources are limited, the potential for competition should be high among sympatric species that display overlaps in habitat and nutritional niches. However, reliable evidence of competition between red deer (Cervus elaphus) and roe deer (Capreolus capreolus) has not been yet reported for life history traits directly measuring performance such as body mass, reproduction, or survival. From long-term monitoring of deer populations in the reserve of La Petite Pierre (France), we measured the sex-specific responses of roe deer fawn body mass to changes in red deer density after accounting for possible confounding effects of date of shooting, climatic conditions, and roe deer density. As expected under the hypothesis of competition, red deer density in a given year had a marked negative influence on body mass of roe deer fawns born the same year and the following year. Fawn mass of roe deer males and females responded in similar ways to changes in red deer density. Our study provides the first evidence of a negative response of roe deer performance to high red deer density.     

Winter fawn survival in black-tailed deer populations affected by hair loss syndrome

Overwinter fawn mortality associated with hair loss syndrome (HLS) is anecdotally thought to be important in declines of Columbian black-tailed deer (Odocoileus hemionus columbianus) populations in Washington and Oregon (USA). We determined prevalence of HLS in black-tailed deer, September and April fawn:doe ratios, and minimum overwinter survival rates of fawns for selected game management units (GMUs) in western Washington from 1999 to 2001. Prevalence of HLS ranged from 6% to 74% in fawns and 4% to 33% in does. Minimum fawn survival ranged from 0.56 to 0.83 and was unrelated to prevalence of HLS in either does (r=0.005, P=0.991) or fawns (r=-0.215, P=0.608). The prevalence of HLS in either does or fawns was also unrelated to either fall fawn:doe ratios (HLS does: r=-0.132, P=0.779; HLS fawns: r=0.130, P=0.760) or spring fawn:doe ratios (HLS does: r=-0.173, P=0.711; HLS fawns: r=-0.020, P=0.963). However, the prevalence of HLS in does and fawns was strongly related (r=0.942, P=0.002), and GMUs with high prevalence of HLS had lower deer population densities (fawns: r=-0.752, P=0.031; does: r=-0.813, P=0.026). Increased overwinter mortality of fawns because of HLS was not supported by our data. Decreased production of fawns, increased summer mortality of fawns, or both were seen in six of eight study GMU-year combinations. Observed rates of productivity and minimum fawn survival were inadequate to maintain population size in five of eight study GMU-year combinations, assuming an annual doe survival rate of 0.75. The influence of deer condition and population health on adult survival, fawn production, preweaning fawn survival, parasitism, and prevalence of HLS in both fawns and adults need to be clarified to identify what factors are limiting black-tailed deer productivity.     

Forage quality's influence on mule deer fawns

In many mule deer (Odocoileus hemionus) populations, recruitment of fawns drives population dynamics. The quality of food available to females and their fawns in summer and autumn may play an important role in fawn recruitment. We examined direct links between digestible energy (DE) content of food and the DE intake of females on the nutrient concentration of milk and between the nursing behavior, DE intake, growth, and survival in captive mule deer fawns. We offered females and their fawns diets that simulated the natural decline in DE content of forage from mid-summer to late autumn in many western landscapes. Fawns fed a higher DE diet weighed 14% more at the onset of winter, had fewer unsuccessful nursing attempts, consumed milk with more protein and energy, and had higher survival than fawns fed a low DE diet. Differences between fawn performances among treatments were greatest when diet quality began decreasing earlier in the summer. Because our results indicate that summer and autumn nutrition is likely to influence fawn recruitment, wildlife biologists should include metrics for summer precipitation and late autumn fawn mass in population models, and land managers should focus on methods for improving the nutritional carrying capacity of summer and early autumn habitats. © 2011 The Wildlife Society.     

Immune Phenotype and Body Condition in Roe Deer: Individuals with High Body Condition Have Different,Not Stronger Immunity

An efficient immunity is necessary for host survival, but entails energetic costs. When energy is limited, immunocompetence and body condition should co-vary positively among individuals and, depending on body condition, individuals should allocate more either in innate immunity or in adaptive response. We tested whether immune phenotype depends on body condition in large mammals, using data from two contrasted populations of roe deer Capreolus capreolus in France. Roe deer living at Chizé, a forest with poor habitat quality, were expected to show lower values for body condition and immune parameters than roe deer at Trois Fontaines, a forest with high habitat quality. From 285 blood samples collected between December 2009 and March 2011, we measured seven metabolic parameters and ten immunological parameters. A Principal Component Analysis showed that all indicators of body condition co-varied positively and were lowest at Chizé. Several immunological indicators correlated to body condition and differed between Trois Fontaines and Chizé. However, high body condition was not associated to a high average level of immunocompetence, but instead to high levels of indicators of acute inflammatory innate response, while low body condition was associated to high levels of monocytes and lymphocytes, possibly reflecting adaptive immunity. Limited data suggest that the difference between populations was not related to the presence of specific parasite species, however parasite exposure and stress have to be investigated to gain a more complete understanding of the determinants of immunity.     

What shapes intra‐specific variation in home range size? A case study of female roe deer

Spatial distribution in mammals, and thereby home range size, is influenced by many different factors including body size, sex, age, reproductive status, season, availability of forage, availability of water, fragmentation of landscape, trophic level and intra- and inter-specific competition. Using linear mixed models, we looked for factors shaping the variation in size of spring-summer and winter home ranges for 51 radio-collared adult female roe deer at Trois Fontaines forest, Champagne–Ardenne, France (1996–2005). Home range size of females was larger in winter than in spring–summer, decreased with age, and decreased with increasing quality. Females in low quality areas adjusted the size of their home range to include more patches of habitat so that all female deer obtained similar amounts of food resources (total biomass of 6.73±2.34 tons (mean±SE) for each home range). Such adjustments of home range size in response to patchiness of resources led to marked between-female variation in home range size. Our results demonstrate that roe deer females have different tactics of habitat use according to spatial variations in habitat quality so that females get similar food resources in highly productive environments such as the Trois Fontaines forest.     

Population density and phenotypic attributes influence the level of nematode parasitism in roe deer

The impact of parasites on population dynamics is well documented, but less is known on how host population density affects parasite spread. This relationship is difficult to assess because of confounding effects of social structure, population density, and environmental conditions that lead to biased among-population comparisons. Here, we analyzed the infestation by two groups of nematodes (gastro-intestinal (GI) strongyles and Trichuris) in the roe deer (Capreolus capreolus) population of Trois Fontaines (France) between 1997 and 2007. During this period, we experimentally manipulated population density through changes in removals. Using measures collected on 297 individuals, we quantified the impact of density on parasite spread after taking into account possible influences of date, age, sex, body mass, and weather conditions. The prevalence and abundance of eggs of both parasites in females were positively related to roe deer density, except Trichuris in adult females. We also found a negative relationship between parasitism and body mass, and strong age and sex-dependent patterns of parasitism. Prime-age adults were less often parasitized and had lower fecal egg counts than fawns or old individuals, and males were more heavily and more often infected than females. Trichuris parasites were not affected by weather, whereas GI strongyles were less present after dry and hot summers. In the range of observed densities, the observed effect of density likely involves a variation of the exposure rate, as opposed to variation in host susceptibility.     

Eruption patterns of permanent front teeth as an indicator of performance in roe deer

In most species of vertebrates, teeth play a central role in the long-term performance of individuals. However, patterns of tooth development have been little investigated as an indicator of animal performance. We filled this gap using data collected during long-term capture-mark-recapture monitoring of 1152 roe deer fawns at Chizé, western France. This population fluctuated greatly in size during the 27 years of monitoring, offering a unique opportunity to assess how the eruption patterns of front teeth perform as indicator of animal performance. We used three indices of the eruption of permanent front teeth, the simplest being whether or not incisor I₂ has erupted, and the most complex being a 12-level factor distinguishing the different stages of tooth eruption. We also assessed the relevance of these indices as compared to fawn body mass, a widely used indicator of animal performance of deer populations. Dental indices and body mass were positively correlated (all r > 0.62). Similarly to body mass, all indices based on tooth eruption patterns responded to changes of population size and can be reliably used to assess the relationship between roe deer and their environment. We found a linear decrease in body mass with increasing population size (r² = 0.54) and a simultaneous delay in tooth development (r² = 0.48–0.55 from the least to the most accurate indicator). However, tooth development would be not further delayed in years with the highest densities (>15 adult roe deer/100 ha). A path analysis supported the population density effect on tooth eruption patterns being mainly determined by the effect of population size on body mass. Our study provides managers with simple indices (e.g., presence-absence of I₂) that provide a technically more easy way to standardize measurements of deer density-dependent responses over large geographical and temporal scales than would be possible with body mass.     

Spatial patterns and density dependence in the dynamics of a roe deer (<Emphasis Type="Italic">Capreolus capreolus</Emphasis>) population in central Italy

The demography of roe deer living in a mountain area of central Italy was studied from 1995 to 1999 with 104 radio-tagged animals, including fawns and adults of both sexes. From spring surveys we estimated population density by mark-resighting (average: 53.8dž.8 individuals km^-2) and found an average fawn/doe ratio of 0.75ǂ.4. The fawn/doe ratio was negatively correlated to density suggesting density-dependent regulation in this population. Using culled and net-trapped individuals we evaluated the dressed body weights of adult males (23.1ǃ.0 kg) and females (22.0ǃ.0 kg), which indicated a low level of sexual dimorphism. The potential litter size (1.44ǂ.1 embryos) depended on female body weight and a threshold of 20.9ǃ.4 kg separated adult females carrying one or two embryos. Both fawn (0.38ǂ.07) and adult survival (0.90ǂ.07) were evaluated from radiotagged individuals and no gender effect was observed in either age class. During the study period we recorded a population decline in one part of the study area and an increasing fawn mortality, which was attributed to the spreading of an enteropathogenic desease. The study revealed an unexpected spatial structure in population dynamics at a scale of few square kilometres. In the two studied subareas, which are very close and ecologically similar, we documented significant differences in several demographic parameters: females in the subarea with the highest deer density produced smaller litters and allocated their reproductive effort preferentially to males, which is consistent with the hypothesis that local resource competition determines sex allocation in roe deer. The importance of spatial variability with respect to roe deer demography was overlooked in previous studies and our results raise new interesting research questions relative to the study of population equilibria which are also relevant for the management of this important game species.     

Evaluation of the importance of roe deer fawns in the spring–summer diet of red foxes in southeastern Norway

Red fox Vulpes vulpes predation on roe deer Capreolus capreolus fawns has the potential to strongly affect prey population dynamics, but it is unclear whether this relationship is symmetrical or not. We analysed the spring–summer diet of adult foxes and of their cubs in a fragmented agricultural area of southeastern Norway, where a parallel study showed that the predator kills annually 25% of the radio-monitored roe deer fawns. The overall diet was highly varied and was dominated by small mammals (33% volume), especially Microtus agrestis, and medium-large mammals (25%), largely represented by fawns. The frequency of occurrence (FO) of fawns in the diet of adult foxes was highest in early spring, thus, supporting previous studies showing that the predator started actively hunting for fawns from the very beginning of the birth season. During the summer, the FO of both fawns and small mammals markedly declined, while that of berries and invertebrates increased. As expected for central-place foragers, cubs consumed a higher proportion of large prey items compared to adults. In particular, 25% of scats from cubs—versus 9% from adults—contained roe deer remains, suggesting a high profitability of fawns for vixens raising offspring. However, considering the wide food spectrum and the availability of several large prey items in our study area, it seems unlikely that the importance of fawns to the diet and population dynamics of red foxes could be as great as the impact of the predator on roe deer populations. This asymmetrical relationship implies that there are unlikely to be any stabilising feedback mechanisms in the predator–prey relationship.     

饲养林麝的种群特征和幼麝的存活研究

对饲养在上海崇明岛东平林场的林麝种群特征以及1998～2000 年间该种群所出生的74 只幼麝存活情况进行分析研究。结果表明: 该林麝种群中能繁殖的个体占51.1 % , 种群数量逐渐增长。种群存活率曲线呈C 型,说明林麝的死亡主要发生在幼麝时期。从不同年龄段性比变化来看, 初生幼麝的性比接近1∶1 , 由于雌幼麝比雄幼麝具有更高的存活率( P < 0.05) , 进入亚成体以后雄性比例逐渐下降, 显示幼麝时期存在偏雄性死亡。早出生幼麝的存活率明显高于晚出生幼麝( P < 0.05) 。引起幼麝死亡的主要原因是疾病(45. 9 %) 。     

Haematological parameters do senesce in the wild: evidence from different populations of a long‐lived mammal

Increasing evidence of senescence has been reported from long‐term studies of wild populations. However, most studies have focused on life‐history traits like survival, reproduction or body mass, generally from a single intensively monitored population. However, variation in the intensity of senescence across populations, and to a lesser extent between sexes, is still poorly understood. In addition, the pattern of age‐specific changes in haematological parameters remains virtually unknown to date for any population of vertebrate living in the wild. Using repeated blood samples collected from known‐aged (2–15 years of age) roe deer (Capreolus capreolus) from two populations facing highly different environmental conditions, we filled the gap. In particular, we investigated age‐specific changes in haematocrit, albumin and creatinine. We reported clear evidence of senescence in all haematological parameters. Moreover, senescence patterns differed between sexes and populations. The rate of senescence was higher in males than in females for haematocrit with no site difference. On the other hand, the rate of senescence in creatinine was higher at Trois Fontaines than at Chizé with no sex difference. Our findings provide a first demonstration of age‐specific declines in haematological parameters in wild populations of large herbivores and show that the process of senescence in vertebrates is not restricted to body mass or fitness components. We also demonstrate that the senescence pattern of haematological parameters is context dependent and varies both between sexes and according to environmental conditions.     

How does environmental variation influence body mass,body size,and body condition? Roe deer as a case study

We tested the influence of population density and of drought intensity (measured as the Gaussen Index in spring and summer of the year of birth) on winter body mass, hind foot length, and body condition of roe deer fawns. Body mass decreased with increasing density and increased with increasing Gaussen Index in summer, in a similar way for both males and females. Hind foot length of males showed the same response. On the other hand, hind foot length of females decreased with increasing density only after dry summers, hence when environmental conditions were very harsh. Body condition was affected neither by density nor by drought intensity. Our results indicate that body mass and size are much better indicators of phenotypic quality than body condition in roe deer. The sex-specific responses of body size to environmental conditions could correspond to a differential allocation in favour of daughters by heavier than average roe deer mothers.     

Variation in cohort mandible size as an index of roe deer (Capredus capreolus) densities and population trends

This paper examines the effects of increasing population density on the skeletal development of roe deer as indexed by variation in the size of the mandible. We tested for density-dependence in total jaw length and minimum diastema height among cohorts in a single, intensively studied population in France. A strong relationship of average adult jaw length of both males and females with deer density in the year of birth of a given cohort was observed, and presumably reflects inadequate nutrition of juveniles at high population density. No such relationship was observed for the minimum diastema height which remained constant over the range of densities studied. This relationship was exploited to investigate population trends of roe deer in Britain. In nine populations, where equivalent data were available for between 16 and 28 separate cohorts, a consistent pattern of variation in cohort jaw size was observed, with a decrease in average total length, but not diastema height, towards the present. This trend is discussed in relation to changes in habitat structure in the coniferous forests of Britain. The utility of cohort jaw length as a management tool to index population trends of roe deer is highlighted.