Eric Bideau

Herd Size in Large Herbivores: Encoded in the Individual or Emergent?

In large mammalian herbivores, the increase of group size with habitat openness was first assumed to be an adaptive response, encoded in the individual. However, it could, alternatively, be an emergent property: if groups were nonpermanent units, often fusing and splitting up, then any increase of the distance at which animals perceive one another could increase the rate of group fusion and thus mean group size. Dynamical models and empirical data support this second hypothesis. This is not to say that adaptive modifications of mean herd size cannot occur. However, this changes the way in which we can envisage the history of gregariousness in large herbivores during the Tertiary.

Effects of Age and Sex on Space Occupation by European Roe Deer

The effects of age and sex on annual home-range characteristics of European roe deer ( Capreolus capreolus ) were investigated by means of radiotracking individuals from a high-density population within a deciduous forest. Subadult males often used more diffuse home ranges than did adults and subadult females, whereas old males exhibited the most concentrated pattern of space occupation. Subadult males also showed a higher dispersal than did subadult females. Such results contrast with those obtained at low densities and suggest that population density influences the process of range acquisition in a sex-dependent way, probably because of the retention of territoriality by adult males at high densities.

Temporal dynamics of seed excretion by wild ungulates: implications for plant dispersal.

Dispersal is a key process in metapopulation dynamics as it conditions species’ spatial responses to gradients of abiotic and biotic conditions and triggers individual and gene flows. In the numerous plants that are dispersed through seed consumption by herbivores (endozoochory), the distance and effectiveness of dispersal is determined by the combined effects of seed retention time in the vector’s digestive system, the spatial extent of its movements, and the ability of the seeds to germinate once released. Estimating these three parameters from experimental data is therefore crucial to calibrate mechanistic metacommunity models of plant–herbivore interactions. In this study, we jointly estimated the retention time and germination probability of six herbaceous plants transported by roe deer (Capreolus capreolus), red deer (Cervus elaphus), and wild boar (Sus scrofa) through feeding experiments and a Bayesian dynamic model. Retention time was longer in the nonruminant wild boar (>36 h) than in the two ruminant species (roe deer: 18–36 h, red deer: 3–36 h). In the two ruminants, but not in wild boar, small and round seeds were excreted faster than large ones. Low germination probabilities of the excreted seeds reflected the high cost imposed by endozoochory on plant survival. Trait-mediated variations in retention time and germination probability among animal and plant species may impact plant dispersal distances and interact with biotic and abiotic conditions at the release site to shape the spatial patterns of dispersed plant species.

Short-term browsing by roe deer has little effect on survival and growth of sessile oak seedlings

We studied the effect of roe deer (Capreolus capreolus) browsing on the growth and mortality of sessile oak (Quercus petraea) seedlings. First, we measured the height and basal diameter, and counted the number of shoots of the 849 seedlings of an experimental plantation, 60 of which were individually protected by fencing. We then introduced two tame roe deer females every day for three weeks from late May to mid-June. Measurements and counts were repeated after roe deer removal, then once again the following winter. We found no significant effect of browsing on mortality, total height, or basal diameter of the seedlings. However, the browsed seedlings exhibited a lower number of shoots despite regrowth observed after roe deer removal. We propose to use the tolerance of oak to deer browsing to promote natural and inexpensive methods, to protect oak during regeneration, such as the spatial arrangement of plants or the use of slash or surrounding vegetation in favourable environments.

Is dominance the only factor determining access to food in an agonistic context? An experiment with captive male mouflon

In fulfilling their daily activities, animals must expend the least amount of energy possible while feeding in order to optimise their energy balance. Food is removed by congeners as a result of exploitation competition. When a resource becomes limited, an increase in the probability of interference competition (direct competition for the resource) is triggered. While a high social rank may increase foraging time and resource access, this status also has detrimental facets. To explore the benefits of dominance/aggression in a context where true monopolisation of resources could be advantageous, we tested three hypotheses related to the patchiness of resources, agonistic activity (i.e. dominance and aggression) and individual attributes (i.e. morphology and behaviour) in a group of captive mouflon males (Ovis ammon musimon). Feeding performance was analysed using linear mixed models based on predictors about patchiness of the resource, and behavioural and morphological indices. No clear relationship was found between dominance and feeding performance. However, the general pattern showed (i) a decrease in overall feeding performance with the dispersion of the resource; (ii) that the discrepancy in feeding performance among individuals was maximal when confronted with intermediate conditions; and (iii) that alternative tactics allowed subordinate individuals to achieve a similar feeding performance to dominants. The results of this study suggest that, over and above agonistic behaviour and dominance, the motivation of individuals and its variation over time, though difficult to evaluate, could be key to understanding the coexistence of alternative behavioural tactics.

Experimental evidence of socio-spatial intolerance between female roe deer

Female roe deer tend to live in mixed-sex groups in winter but in solitary manner on reduced home ranges in spring. This tendency is commonly related in the literature to the rearing of hiding fawns. We studied the socio-spatial relationships between six female roe deer, introduced at 1 year of age into a partly wooded 14.2-ha enclosure. Animals were monitored with GPS telemetry collars for a period of 3 years, a male being added at the end of the 2nd year. Females did not share large overlapping home ranges. In the absence of any male and offspring, they spread out in May–June (birthing season) and in July-August (rutting season). During these seasons, the size and overlap of their home ranges were minimal, while the mean distance between the arithmetic centres of their respective locations reached its maximum value and was greater than expected under the hypothesis that the females positioned their ranges independently of one another. Related females were not preferentially associated beyond 2 years of age. Moreover, the introduction of a male affected this spatial organisation only slightly. Overall, the socio-spatial organisation of female roe deer appears to be almost independent of their reproductive status, and very similar to that of males, as is the case in a number of other small-bodied ruminants.