Group Dynamics and Landscape Features Constrain the Exploration of Herds in Fusion-Fission Societies: The Case of European Roe Deer

Despite the large number of movement studies, the constraints that grouping imposes on movement decisions remain essentially unexplored, even for highly social species. Such constraints could be key, however, to understanding the dynamics and spatial organisation of species living in group fusion-fission systems. We investigated the winter movements (speed and diffusion coefficient) of groups of free-ranging roe deer (Capreolus capreolus), in an agricultural landscape characterised by a mosaic of food and foodless patches. Most groups were short-lived units that merged and split up frequently during the course of a day. Deer groups decreased their speed and diffusion rate in areas where food patches were abundant, as well as when travelling close to main roads and crest lines and far from forests. While accounting for these behavioural adjustments to habitat features, our study revealed some constraints imposed by group foraging: large groups reached the limit of their diffusion rate faster than small groups. The ability of individuals to move rapidly to new foraging locations following patch depression thus decreases with group size. Our results highlight the importance of considering both habitat heterogeneity and group dynamics when predicting the movements of individuals in group fusion-fission societies. Further, we provide empirical evidence that group cohesion can restrain movement and, therefore, the speed at which group members can explore their environment. When maintaining cohesion reduces foraging gains because of movement constraints, leaving the group may become a fitness-rewarding decision, especially when individuals can join other groups located nearby, which would tend to maintain highly dynamical group fusion-fission systems. Our findings also provide the basis for new hypotheses explaining a broad range of ecological patterns, such as the broader diet and longer residency time reported for larger herbivore groups

Investigating differences in vigilance tactic use within and between the sexes in eastern grey kangaroos

Peer reviewedPostprin

Local Extinction in the Bird Assemblage in the Greater Beijing Area from 1877 to 2006

Recent growth in industrialization and the modernization of agricultural activities, combined with human population growth, has greatly modified China’s natural environment, particularly in the vicinity of large cities. We compared avifauna checklists made between 1877 and 1938 with current checklists to determine the extent of local bird extinctions during the last century in the greater Beijing area. Our study shows that of the 411 bird species recorded from 1877–1938, 45 (10.9%) were no longer recorded from 2004–2006. Birds recorded as ‘rare’ in 1938 were more likely to have disappeared in subsequent years. Migrant status also influenced the probability of local bird extinction with winter migrants being the most affected class. Moreover, larger birds were more likely to have disappeared than smaller ones, potentially explained by differential ecological requirements and anthropogenic exploitation. Although our habitat descriptions and diet classification were not predictors of local bird extinction, the ecological processes driving local bird extinction are discussed in the light of historical changes that have impacted this region since the end of the 1930 s. Our results are of importance to the broader conservation of bird wildlife

Incorporating biodiversity responses to land use change scenarios for preventing emerging zoonotic diseases in areas of unknown host-pathogen interactions

The need to reconcile food production, the safeguarding of nature, and the protection of public health is imperative in a world of continuing global change, particularly in the context of risks of emerging zoonotic disease (EZD). In this paper, we explored potential land use strategies to reduce EZD risks using a landscape approach. We focused on strategies for cases where the dynamics of pathogen transmission among species were poorly known and the ideas of “land-use induced spillover” and “landscape immunity” could be used very broadly. We first modeled three different land-use change scenarios in a region of transition between the Cerrado and the Atlantic Forest biodiversity hotspots. The land-use strategies used to build our scenarios reflected different proportions of native vegetation cover, as a proxy of habitat availability. We then evaluated the effects of the proportion of native vegetation cover on the occupancy probability of a group of mammal species and analyzed how the different land-use scenarios might affect the distribution of species in the landscape and thus the risk of EZD. We demonstrate that these approaches can help identify potential future EZD risks, and can thus be used as decision-making tools by stakeholders, with direct implications for improving both environmental and socio-economic outcomes

Does sex affect both individual and collective vigilance in social mammalian herbivores: the case of the eastern grey kangaroo?

International audienceIn several vertebrate taxa, males and females differ in the proportions of time they individually devote to vigilance, commonly attributed to sex differences in intra-specific competition or in absolute energy requirements. However, an effect of sex on collective vigilance is less often studied (and therefore rarely predicted), despite being relevant to any consideration of the adaptiveness of mixed- vs single-sex grouping. Controlling for group size, we studied the effect of sex on vigilance in the sexually dimorphic eastern grey kangaroo Macropus giganteus, analysing vigilance at two structural levels: individual vigilance and the group’s collective vigilance. Knowing that group members in this species tend to synchronise their bouts of vigilance, we tested (for the first time) whether sex affects the degree of synchrony between group members. We found that females were individually more vigilant than males and that their vigilance rate was unaffected by the presence of males. Collective vigilance did not differ between female-only and mixed-sex groups of the same size. Vigilance in mixed-sex groups was neither more nor less synchronous than in single-sex groups of females, and the presence of males seemed not to affect the degree of synchrony between females. Sixty-six percent of vigilant acts were unique (performed when no other kangaroo was alert), and only about one unique vigilant act in every three induced a collective wave of vigilance. The proportions of vigilant acts that were unique were 60% for females but only 46% for males. However, the sexes differed little in the rates at which their unique vigilant acts were copied. This limited study shows that the differences in vigilance between male and female kangaroos had no discernible effect upon collective vigilance.</p

On the dynamics of predation risk perception for a vigilant forager.

International audienceForaging animals often raise their head to scan for predators. Scanning intervals have variable durations, and occur more or less frequently, depending on ecological conditions. Our study relies on the assumption that temporal patterns of vigilance depend on the speed with which information concerning the likelihood of a predator's presence in the neighbourhood is gathered when an animal is vigilant, and lost when it is not. Using an analytical model, we study how the perceived level of risk progressively decreases, when the individual is vigilant and detects no predator, then increases again, when it lowers its head to feed, thereby losing most of its detection abilities. The speed of these variations is affected by the likelihood of the presence of a predator in the whole environment, by the mobility of this predator, and by the detection capacities of the prey. We show how, combined with the range of risk levels tolerated by this animal, this dynamics determines the frequency and the duration of its scanning intervals. The dynamics of risk perception can also explain particular behavioural patterns, such as the progressive decrease of vigilance that may occur after the arrival into a novel environment, and the central tendency in the distribution of inter scan durations reported by many studies. Next, we use the model to compute optimal vigilance strategies, taking into account the trade-off between feeding and limiting exposure to predators. The model predicts that a forager will scan more often, and for longer periods, when the likelihood of a predator's presence in the surrounding environment is increased. A similar response is expected when the mobility of the predator is increased. By contrast, when the detection capacities of the prey are reduced, it will increase its vigilance by scanning for longer periods, but scanning intervals will be separated by longer interscans

Does sex affect both individual and collective vigilance in social mammalian herbivores: the case of the eastern grey kangaroo?

In several vertebrate taxa, males and females differ in the proportions of time they individually devote to vigilance, commonly attributed to sex differences in intra-specific competition or in absolute energy requirements. However, an effect of sex on collective vigilance is less often studied (and therefore rarely predicted), despite being relevant to any consideration of the adaptiveness of mixed- vs single-sex grouping. Controlling for group size, we studied the effect of sex on vigilance in the sexually dimorphic eastern grey kangaroo 'Macropus giganteus', analysing vigilance at two structural levels: individual vigilance and the group's collective vigilance. Knowing that group members in this species tend to synchronise their bouts of vigilance, we tested (for the first time) whether sex affects the degree of synchrony between group members. We found that females were individually more vigilant than males and that their vigilance rate was unaffected by the presence of males. Collective vigilance did not differ between female-only and mixed-sex groups of the same size. Vigilance in mixed-sex groups was neither more nor less synchronous than in single-sex groups of females, and the presence of males seemed not to affect the degree of synchrony between females. Sixty-six percent of vigilant acts were unique (performed when no other kangaroo was alert), and only about one unique vigilant act in every three induced a collective wave of vigilance. The proportions of vigilant acts that were unique were 60% for females but only 46% for males. However, the sexes differed little in the rates at which their unique vigilant acts were copied. This limited study shows that the differences in vigilance between male and female kangaroos had no discernible effect upon collective vigilance

Le fonctionnement des groupes chez les grands herbivores sauvages (mécanismes et considérations évolutives)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Ticks or lions: trading between allogrooming and vigilance in maternal care

International audienceBehavioural adjustments to predation risk may impose costs on prey species. While the vigilance–foraging conflict has been extensively investigated, other important fitness-related behaviours exclusive to scanning, such as grooming, have been overlooked. Yet, risk perception is expected to be more accurately assessed in these contexts as food-related parameters should not interfere. We studied individually recognizable impalas, Aepyceros melampus, and questioned the factors that shape maternal decision making in two exclusive components of maternal care with high benefits and costs: scanning for predators and grooming offspring to remove parasites. While studies generally infer prey alertness level, used as a proxy of risk perception, from the observed investment in vigilance, the vigilance–allogrooming context gave us the opportunity to directly assess alertness during the time spent head-up, and then to investigate its sources of variation and its consequences for allogrooming probability. We found a strong decrease in allogrooming probability when maternal alertness increased. Mothers were more alert in open (grassland) than in closed (bushland) habitats at a large scale. Increasing group size led both to lower maternal alertness and higher proportion of suckling time spent allogrooming, but only when surrounded by low vegetation, the reverse being true in high vegetation. Finally, mothers suckling female calves were more alert. Our results underline the determinant role of habitat, shaping both offspring predation risk and the relative conspicuousness or protective value of group mates. We discuss the potential fitness costs associated with the antipredator–antiparasite trade-off faced during maternal care. Our results suggest that prey behaviours other than foraging are essential to identify factors shaping risk perception