CEFS, Université de Toulouse, INRA, Castanet-Tolosan, France.
Centre d'Ecologie et des Sciences de la Conservation (CESCO), Muséum national d'Histoire naturelle, Centre National de la Recherche Scientifique, Sorbonne Université, Paris, France.
J Anim Ecol. 2020 Jan;89(1):173-185. doi: 10.1111/1365-2656.13098. Epub 2019 Sep 21.
Dispersal is a key mechanism enabling species to adjust their geographic range to rapid global change. However, dispersal is costly and environmental modifications are likely to modify the cost-benefit balance of individual dispersal decisions, for example, by decreasing functional connectivity. Dispersal costs occur during departure, transience and settlement, and are levied in terms of energy, risk, time and lost opportunity, potentially influencing individual fitness. However, to the best of our knowledge, no study has yet quantified the energetic costs of dispersal across the dispersal period by comparing dispersing and philopatric individuals in the wild. Here, we employed animal-borne biologgers on a relatively large sample (N = 105) of juvenile roe deer to estimate energy expenditure indexed using the vector of dynamic body acceleration and mobility (distance travelled) in an intensively monitored population in the south-west of France. We predicted that energy expenditure would be higher in dispersers compared to philopatric individuals. We expected costs to be (a) particularly high during transience, (b) especially high in the more fragmented areas of the landscape and (c) concentrated during the night to avoid disturbance caused by human activity. There were no differences in energy expenditure between dispersers and philopatric individuals during the pre-dispersal phase. However, dispersers expended around 22% more energy and travelled around 63% further per day than philopatric individuals during transience. Differences in energy expenditure were much less pronounced during the settlement phase. The costs of transience were almost uniquely confined to the dawn period, when dispersers spent 23% more energy and travelled 112% further than philopatric individuals. Finally, the energetic costs of transience per unit time and the total distance travelled to locate a suitable settlement range were higher in areas of high road density. Our results provide strong support for the hypothesis that natal dispersal is energetically costly and indicate that transience is the most costly part of the process, particularly in fragmented landscapes. Further work is required to link dispersal costs with fitness components so as to understand the likely outcome of further environmental modifications on the evolution of dispersal behaviour.
扩散是物种调整其地理范围以适应快速全球变化的关键机制。然而，扩散是有代价的，环境的改变可能会改变个体扩散决策的成本效益平衡，例如通过降低功能连接性。扩散成本发生在离开、过渡和定居期间，以能量、风险、时间和失去的机会为代价，可能会影响个体的适应性。然而，据我们所知，目前还没有研究通过比较野外扩散和留守个体来量化整个扩散期间的扩散成本。在这里，我们使用动物携带的生物标记物对法国西南部一个密集监测的种群中的 105 只幼年狍进行了相对较大样本的研究，以估计使用动态身体加速度和移动性向量（旅行距离）索引的能量消耗。我们预测扩散者的能量消耗会高于留守个体。我们预计成本会（a）在过渡期间特别高，（b）在景观破碎化程度较高的地区特别高，（c）集中在夜间以避免人类活动引起的干扰。在预扩散阶段，扩散者和留守个体的能量消耗没有差异。然而，在过渡期间，扩散者每天消耗的能量多 22%，旅行距离多 63%。在定居阶段，能量消耗的差异就不那么明显了。过渡阶段的成本几乎完全局限于黎明时期，此时扩散者比留守个体多消耗 23%的能量，多旅行 112%的距离。最后，过渡期间的单位时间内的扩散成本以及找到合适的定居范围的总旅行距离在道路密度较高的地区更高。我们的结果为扩散是能量密集型的假设提供了强有力的支持，并表明过渡是这个过程中最昂贵的部分，尤其是在破碎化的景观中。需要进一步的工作将扩散成本与适应性成分联系起来，以了解进一步的环境改变对扩散行为进化的可能影响。
