Data from: Food availability modulates differences in parental effort between dispersing and philopatric birds

Dispersal entails costs and might have to be traded off against other life-history traits. Dispersing and philopatric individuals may thus exhibit alternative life-history strategies. Importantly, these differences could also partly be modulated by environmental variation. Our previous results in a patchy population of a small passerine, the collared flycatcher, suggest that, as breeding density, a proxy of habitat quality, decreases, dispersing individuals invest less in reproduction but maintain a stable oxidative balance, whereas philopatric individuals maintain a high reproductive investment at the expense of increased oxidative stress. In this study, we aimed at experimentally testing whether these observed differences between dispersing and philopatric individuals across a habitat quality gradient were due to food availability, a major component of habitat quality in this system. We provided additional food for the parents to use during the nestling rearing period and we measured subsequent parental reproductive effort (through provisioning rate, adult body mass, and plasmatic markers of oxidative balance) and reproductive output. Density-dependent differences between dispersing and philopatric parents in body mass and fledging success were observed in control nests but not in supplemented nests. However, density-dependent differences in oxidative state were not altered by the supplementation. Altogether, our results support our hypothesis that food availability is responsible for some of the density-dependent differences observed in our population between dispersing and philopatric individuals but other mechanisms are also at play. Our study further emphasizes the need to account for environmental variation when studying the association between dispersal and other traits.

扩散过程存在适应性成本，且往往需要与其他生活史特征发生权衡。因此，扩散个体与留巢个体往往呈现出截然不同的生活史策略。尤为关键的是，这些差异还可能部分受到环境变异的调控。我们此前针对小型雀形目鸟类领姬鹟（collared flycatcher）的斑块种群开展的研究结果表明：当作为生境质量替代指标的繁殖密度降低时，扩散个体的繁殖投入会有所下降，但可维持稳定的氧化平衡；而留巢个体则会保持较高的繁殖投入，却以加剧氧化应激为代价。本研究旨在通过实验验证：在生境质量梯度下观测到的扩散个体与留巢个体间的上述差异，是否由食物可获得性所导致——食物可获得性正是本研究系统中生境质量的核心组成部分。我们为育雏期的亲本个体提供额外食物，并测定了后续的亲本繁殖投入（通过喂食率、成体体重以及氧化平衡血浆标志物）与繁殖产出。在对照巢中，我们观测到扩散亲本与留巢亲本的体重及出飞成功率存在密度依赖的差异，但在食物补充巢中未发现此类差异。然而，食物补充并未改变氧化状态的密度依赖差异。综上，本研究结果支持我们提出的假说：食物可获得性是导致本种群中扩散个体与留巢个体间部分密度依赖差异的原因，但其他作用机制也同样存在。本研究还进一步强调，在探究扩散与其他性状间的关联时，有必要将环境变异纳入考量范畴。