Groupe Ecologie et Conservation, Université d'Angers, Angers, France.
PLoS One. 2012;7(3):e34678. doi: 10.1371/journal.pone.0034678. Epub 2012 Mar 30.
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.
尽管有大量关于运动的研究，但分组对运动决策的限制在很大程度上仍未得到探索，即使对于高度社会化的物种也是如此。然而，这些限制对于理解生活在群体融合-裂变系统中的物种的动态和空间组织可能是关键。我们研究了自由放养的狍（Capreolus capreolus）在一个农业景观中的冬季运动（速度和扩散系数），该景观的特点是食物和无食物斑块的镶嵌。大多数群体是短暂的单位，在一天的过程中经常合并和分裂。当鹿群在食物斑块丰富的地区、靠近主要道路和山顶以及远离森林的地方旅行时，它们会降低速度和扩散率。虽然我们的研究考虑了这些对栖息地特征的行为调整，但也揭示了群体觅食所施加的一些限制：大群体比小群体更快地达到扩散率的极限。因此，随着群体规模的增大，个体在斑块减少后快速移动到新觅食地点的能力会下降。我们的研究结果强调了在预测群体融合-裂变社会中个体运动时，既要考虑栖息地异质性，也要考虑群体动态的重要性。此外，我们提供了经验证据，表明群体凝聚力可以限制运动，从而限制群体成员探索环境的速度。当由于运动限制而保持凝聚力会降低觅食收益时，离开群体可能成为一个有利于适应的决策，特别是当个体可以加入附近的其他群体时，这将倾向于维持高度动态的群体融合-裂变系统。我们的研究结果还为解释广泛的生态模式提供了基础，例如报道的较大食草动物群体的更广泛的饮食和更长的居留时间。
