Ideal free distribution and natal dispersal in female roe deer

We investigated whether adult ( 2 years) female roe deer Capreolus capreolus conform to an ideal free or an ideal despotic distribution, in order to understand whether natal dispersal is voluntary or socially enforced. The study was undertaken in a high-density, free-ranging population close to Stockholm, Sweden, during 1989–1994. Data on population density, habitat quality, and five parameters on female reproduction and body condition, in addition to age distribution, were obtained in two nearby located areas, the field and the forest, representing contrasting habitats. Population density was estimated by faecal pellet group counting in addition to total counts of culled animals after a major deer harvest. Density in the field area was twice that in the forest area (66 vs 33 deer/km²). Habitat quality was determined by analysing the amount of faecal nitrogen from samples of faeces collected in the two areas, and by comparing size of summer home ranges for adults of both sexes with the aid of telemetry. Both estimates indicated a higher nutritional quality and resource abundance, respectively, in the field area, with faecal nitrogen content being higher (2.96 vs 2.43%), and ranges being smaller (12.9 vs 20.9 ha). No significant differences were found in any of the parameters on reproduction or body condition obtained from culled females, i.e. number of corpora lutea (1.8 vs 1.8), proportion of females with offspring (71 vs 56%), body mass (16.9 vs 17.3 kg), kidney fat index (91.9 vs 98.5), and length of the lower mandible (152.8 vs 151.4 mm). Neither did the age distribution among females, as determined from tooth wear, differ between the areas. These results are consistent with the prediction of the ideal free hypothesis. This, in turn, suggests that female dispersal in this species is voluntary, the underlying proximate cause being maximization of resource gain.     

Population density and sex do not influence fine-scale natal dispersal in roe deer

It is commonly assumed that the propensity to disperse and the dispersal distance of mammals should increase with increasing density and be greater among males than among females. However, most empirical evidence, especially on large mammals, has focused on highly polygynous and dimorphic species displaying female-defence mating tactics. We tested these predictions on roe deer, a weakly polygynous species of large herbivore exhibiting a resource-defence mating tactic at a fine spatial scale. Using three long-term studies of populations that were subject to the experimental manipulation of size, we did not find any support for either prediction, whether in terms of dispersal probability or dispersal distance. Our findings of similar dispersal patterns in both sexes of roe deer suggest that the underlying cause of natal dispersal is not related to inbreeding avoidance in this species. The absence of positive density dependence in fine-scale dispersal behaviour suggests that roe deer natal dispersal is a pre-saturation process that is shaped by heterogeneities in habitat quality rather than by density per se.     

Landscape fragmentation influences winter body mass of roe deer

Body size of large herbivores is a crucial life history variable influencing individual fitness‐related traits. While the importance of this parameter in determining temporal trends in population dynamics is well established, much less information is available on spatial variation in body size at a local infra‐population scale. The relatively recent increase in landscape fragmentation over the last century has lead to substantial spatial heterogeneity in habitat quality across much of the modern agricultural landscape. In this paper, we analyse variation in body mass and size of roe deer inhabiting a heterogeneous agricultural landscape characterised by a variable degree of woodland fragmentation. We predicted that body mass should vary in relation to the degree of access to cultivated meadows and crops providing high quality diet supplements. In support of our prediction, roe deer body mass increased along a gradient of habitat fragmentation, with the heaviest deer occurring in the most open sectors and the lightest in the strict forest environment. These spatial differences were particularly pronounced for juveniles, reaching >3 kg (ca 20% of total body mass) between the two extremes of this gradient, and likely have a marked impact on individual fates. We also found that levels of both nitrogen and phosphorous were higher in deer faecal samples in the more open sectors compared to the forest environment, suggesting that the spatial patterns in body mass could be linked to the availability of high quality feeding habitat provided by the cultivated agricultural plain. Finally, we found that adults in the forest sector were ca 1 kg lighter for a given body size than their counterparts in the more open sectors, suggesting that access to nutrient rich foods allowed deer to accumulate substantial fat reserves, which is unusual for roe deer, with likely knock‐on effects for demographic traits and, hence, population dynamics.     

Allozyme variability and differentiation in Serbian roe deer populationsCapreolus capreolus

The present study investigates the genetic structure of 12 roe deerCapreolus capreolus Linnaeus, 1758 population samples from Serbia, by screening a total of 334 individuals. We examined whether genetic differentiation exists in local populations in Serbia, and addressed the question whether management policies may affect genetic structure. The populations were analysed by multilocus protein electrophoresis, with 33 protein loci examined. Screening of 20 enzymes and one group of general proteins revealed polymorphism at the following 12 loci: Sdh, Mdh-1, Me-1, Idh-2, 6-Pgd-1,αGpd, Ak, Pgm-1, Pgm-2, Ca, Mpi andGpi. Among samples, the proportion of polymorphic loci varied between 3–15.2% (mean 11.9%), while the average gene diversity was in the range of 1.1–4.2%. The overall genetic differentiation was low (θ = 0.03). The comparison of two regional population groups (northern-southern, separated by the Danube River) showed an absence of genetic differentiation between regions. Gene flow was estimated at 8.96 migrants per generation, and was higher in the lowland than in the highland group. Three loci (Ca, 6-Pgd andGpd-1) showed clinal variation along a geographical gradient. Additional five alleles of four loci (Ak, Pgm-1, Gpi, 6-Pgd) showed significant spatial autocorrelation. Genetic distances were small (D = 0–0.004). Northern and southern populations clustered separately. For at least three populations game management practices provide evidence for outlying genetic parameters. The observed heterogeneity in the inbreeding level was deemed more under the influence of non-random mating strengthened by game management, than by overall selective pressure.     

Patterns of dispersal and seasonal migration in roe deer (Capreolus capreolus)

Roe deer ( Capreolus capreolus ) spacing behaviour, during the period between mother-fawn separation and home range establishment, was studied in southern Sweden during 1987–1992. Data were collected, using telemetry, in two non-hunted populations. Females dispersed either as yearlings, or as 2- or 3-year-olds after having migrated between non-overlapping summer and winter ranges for one and two seasons, respectively. Seasonal migration usually ended with permanent settlement in the new summer area. Males dispersed as one- or two-year-olds, or remained philopatric. Median distance moved was c. 2 km with no significant sex-bias. Both populations underwent one increase, and one stable phase. During the increase phase, the frequency of yearling dispersal was 70% in one of the populations, but dropped to 20% at high density. This drop paralleled a 14% decrease in yearling winter weights. In the other population, yearling dispersal frequency was 56% during the increase phase. This population stopped increasing at an intermediate density and dispersal frequency was kept at 75%. Weights remained high in this population. In neither of the populations, at intermediate and high densities, was a sex-bias in dispersal among yearlings evident. Dispersers were on average heavier than philopatrics. High juvenile winter weight did not predestinate yearlings to dispersal, whereas low weight seemed to prevent dispersal. On the basis of these relationships, we propose a hypothesis relating dispersal to body condition, in order to explain dispersal tendency at different population densities. Further, we suggest the reason for female migration is the advantage of residing in a group during winters when predation risk is high. Since it is difficult for females (but not for males) to join non-relatives, dispersers must go back to the natal area as long as they have too few offspring to form their own matriarchal group.     

Landscape connectivity influences gene flow in a roe deer population inhabiting a fragmented landscape: an individual-based approach

Changes in agricultural practices and forest fragmentation can have a dramatic effect on landscape connectivity and the dispersal of animals, potentially reducing gene flow within populations. In this study, we assessed the influence of woodland connectivity on gene flow in a traditionally forest-dwelling species--the European roe deer--in a fragmented landscape. From a sample of 648 roe deer spatially referenced within a study area of 55 x 40 km, interindividual genetic distances were calculated from genotypes at 12 polymorphic microsatellite loci. We calculated two geographical distances between each pair of individuals: the Euclidean distance (straight line) and the 'least cost distance' (the trajectory that maximizes the use of wooded corridors). We tested the correlation between genetic pairwise distances and the two types of geographical pairwise distance using Mantel tests. The correlation was better using the least cost distance, which takes into account the distribution of wooded patches, especially for females (the correlation was stronger but not significant for males). These results suggest that in a fragmented woodland area roe deer dispersal is strongly linked to wooded structures and hence that gene flow within the roe deer population is influenced by the connectivity of the landscape.     

Genetic and environmental influences on natal dispersal distance in a resident bird species

We analyzed more than 1,600 dispersal events from two populations of a North American cooperatively breeding woodpecker species to determine what factors influence natal dispersal distance and whether distance traveled affects reproduction later in life. We found significant heritability of natal dispersal distance, in both males and females, indicating substantial additive genetic variance for this behavioral trait. Natal dispersal distance additionally was affected by social and ecological factors: individuals dispersing in their first year of life moved longer distances than those staying on their natal site as helpers for a prolonged time prior to dispersal, and increasing territory isolation led to longer dispersal distances. Successful dispersers incurred fitness costs, with lifetime fledgling production (in both sexes) and lifetime production of recruits to the breeding population (in females only) decreasing with increasing natal dispersal distance. We conclude that natal dispersal distance has a genetic basis but is modulated by environmental and social factors and that natal dispersal distance in this species is (currently) under selection.     

Craniometric variability in two populations of roe deer (Capreolus capreolus) from Spain

Two populations of roe deer from Spain, approximately 300 km apart from each other and currently recognized as separate subspecies. were studied to analyse the nature of the morphological differences between these populations and to assess the validity of its taxonomic division. Sixty-one skulls of roc deer from the Occidental Cantabric Mountains (OCM) and 17 from the Northern lberic Mountains (NIM) were used. No significant sexual dimorphism allowed pooling of male and female samples, on which a large set of 53 measurements was taken. Skulls from the OCM population are, on average, 1·9% larger than those from the NIM population. Twenty-five out of the 53 characters showed some degree of significant differences between means of both populations, though only four showed highly significant differences. Mandible characters were the most variable traits, showing also significant differences between populations. Eight principal factors were extracted. explaining a total of 84·7% of the sample variance. An ANOVA of factor scores from each population revealed significant differences in PF 1 and PF 3. Interpretation of these two factors suggests that morphological differences between both populations can be summarized as specimens from OCM having larger mandibles and broader neurocranium than specimens from NIM. Mandible differences might reflect morphological adaptations to favour the consumption of ligneous plants, which are more frequently eaten by the OCM roe deer population, whereas a broader neurocranium might be related to antler size. It is concluded that biometric differences observed in skulls from these two populations only reflect minor morphological adaptations to different habitats, thus. there is a lack of morphological data to support the taxonomic distinction of the OCM population as a separate subspecies.     

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.     

Hormonal influences on natal dispersal in free-living Belding's ground squirrels (Spermophilus beldingi)

Preliminary identification of the physiological causes of natal dispersal in two populations of free-living Belding's ground squirrels (Spermophilus beldingi) was attempted in the Sierra Nevada of California. Two competing hypotheses, each suggesting a different endocrinological cause for natal dispersal in this species were tested. Data collected by observation, trapping, and telemetry during three field seasons (1979–1981) contradict predictions of the hypothesis that concurrent, high levels of circulating gonadal steroids cause natal dispersal. Rather the data suggest that perinatal exposure to androgen subsequently results in dispersal of treated individuals. The hormone may promote dispersal behavior through its mediating effects on juveniles' exploratory and social behaviors, and on their responsiveness to frightening stimuli. Possible interactions of endocrine mechanisms with other proximal and ultimate causes of dispersal are discussed.     

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.     

Intolerance amongst deer species at feeding: roe deer are uneasy banqueters

The function of inter-specific interactions in large herbivore assemblies is under debate. We have studied inter-specific interactions between roe and fallow deer on pastures, to assess whether competition between these Cervidae occurs through behavioural interference. Roe were displaced by fallow deer (i.e. the former moved away from the latter at a distance of >50 m) in 83% of cases (N = 127). Ninety-four percentage (N = 83) of displacement events occurred while roe deer were feeding; in 50% of these cases (N = 78), roe stopped grazing and left the feeding ground. Even when fallow deer did not show any sign of direct aggression to roe, these moved away from fallow in 72% of cases (N = 127). Vigilance rate was significantly greater in roe than in fallow deer, irrespectively of the presence of the other species. When roe and fallow deer grazed within 50 m from each other, vigilance rate increased significantly in roe, but not in fallow deer. Roe deer, in a group, were significantly more tolerant of the presence of fallow deer (even in group), than when solitary. Fallow deer seemed to be able to exclude roe deer from feeding sites through behavioural intolerance.     

Female-biased natal dispersal in the Siberian flying squirrel

Natal dispersal is usually sex biased in birds and mammals.Female-biased natal dispersal is the prevailing pattern in birdsbut is rare among mammals. Hypotheses explaining sex bias indispersal include the mate-defense mating hypothesis, whichpredicts male-biased dispersal, the resource-defense hypothesispredicting female-biased dispersal, and the competition hypothesis,which predicts that if dispersal is caused by competition forresources between sexes, then the subdominant sex will disperse.We studied natal dispersal of Siberian flying squirrels Pteromysvolans using radio telemetry in Southern Finland in 1996–2004.Of 86 juveniles that survived over the dispersal period, almostall young females dispersed from the natal site, whereas almost40% of males were philopatric. Dispersal was farther for femalesthan males. Females began dispersal on average 2 weeks earlierthan males and were lighter in mass at the onset of dispersalthan later dispersing males. No mate- or resource-defense matingsystem could be found among males, but females seemed to defendnest and apparently food resources, in contrast to the expectationof dispersal bias in resource-defense systems. Competition forresources between sexes does not explain female bias either:in the flying squirrel, the female seems to be the dominantsex. We propose that young females are subordinate to theirmothers and have to disperse to find a vacant, suitable sitefor reproduction.