Abstract
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.
Highlights
Living in groups presents an individual with benefits, including a decrease in predation risk due to dilution effects and collective detection of predators, an opportunity to increase foraging time by decreasing its own scanning rate in response to the vigilance of others, and an opportunity to glean information on the location of highquality food patches from the behaviour of competitors [1,2,3,4,5,6]
We found a strong relationship between group size (GS) and the log-transformed group lifetime (GL) (GL = 20.012GS2+0.019GS+0.671, F2–391 = 26.098, P,0.0001, R2 = 0.10)
Our results show that both landscape components and group features affect the movements of roe deer herds
Summary
Living in groups presents an individual with benefits, including a decrease in predation risk due to dilution effects and collective detection of predators, an opportunity to increase foraging time by decreasing its own scanning rate in response to the vigilance of others, and an opportunity to glean information on the location of highquality food patches from the behaviour of competitors [1,2,3,4,5,6]. Group living carries some well-known costs, such as the potential for aggression by conspecifics, an increase in resource competition and pseudo-interference, a risk of kleptoparasitism, and an increase in parasite burdens and disease transmission [7,8,9,10,11,12,13,14,15,16]. But less documented, cost of group living lies in the constraint imposed by group cohesion on the movements of individuals. Group cohesion can only exist if group members synchronise their movements. Considering groups as mobile units, they should become slower as their size increases because of the inertia that is generated by potentially conflicting path directions among an increasing number of group members. The capacity to explore landscapes, should vary as a function of group size
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
