O'Shea William, O'Halloran John, Quinn John L
School of Biological, Earth and Environmental Sciences, University College Cork, Distillery Fields, North Mall, Cork, Ireland.
Oecologia. 2018 Dec;188(4):953-964. doi: 10.1007/s00442-018-4155-x. Epub 2018 Jun 30.
Understanding how resource use and life history variation influence a population's response to modified, fragmented landscapes is a major challenge for ecologists. We investigated the phenology, life history decisions and provisioning behaviour of a generalist passerine-the great tit-across a heavily managed woodland landscape. Contrary to most previous studies on this species, reproductive investment and success were lower in deciduous than in coniferous woodland fragments. This could not be explained by differences in provisioning behaviour; instead population density was considerably higher in deciduous woodlands, suggesting birds did not follow an ideal free distribution. Clutch size declined with lay date amongst populations breeding in coniferous woodland fragments, but these populations also displayed pronounced seasonal declines in the proportion of fledglings produced per egg and fledgling mass. In contrast, and against patterns observed in other similar study systems, clutch size did not change with lay date in mixed-species deciduous woodland fragments. Furthermore, the proportion of young fledged and fledgling condition remained stable throughout the season, even though the quality of food provisioned to nestlings increased over the season. Local recruitment was negligible, suggesting that plasticity rather than natural selection played a key role in driving the patterns observed. The unusual patterns we report are likely explained by the fragmented nature of the landscape, and unreliable phenological cues in a mixed-species tree community coupled with low food availability. They contrast with those reported from most other populations situated in continuous woodland, demonstrating that caution is needed when generalising across different contexts and ecosystems.
了解资源利用和生活史变异如何影响种群对改造后的破碎化景观的响应，是生态学家面临的一项重大挑战。我们研究了一种通才雀形目鸟类——大山雀——在一个管理密集的林地景观中的物候、生活史决策和育雏行为。与此前关于该物种的大多数研究相反，落叶林片段中的繁殖投入和成功率低于针叶林片段。这无法通过育雏行为的差异来解释；相反，落叶林中的种群密度要高得多，这表明鸟类并没有遵循理想的自由分布。在针叶林片段中繁殖的种群中，窝卵数随产卵日期的推迟而减少，但这些种群每枚卵所产生的雏鸟比例和雏鸟质量也呈现出明显的季节性下降。相比之下，与其他类似研究系统中观察到的模式不同，在混合物种落叶林片段中，窝卵数并未随产卵日期而变化。此外，尽管整个季节为雏鸟提供的食物质量有所提高，但雏鸟出飞的比例和雏鸟状况在整个季节都保持稳定。本地补充率可忽略不计，这表明可塑性而非自然选择在驱动所观察到的模式中起关键作用。我们报告的这些异常模式可能是由景观的破碎化性质、混合物种树木群落中不可靠的物候线索以及食物供应不足所导致的。它们与大多数位于连续林地的其他种群所报告的模式形成对比，这表明在不同背景和生态系统中进行概括时需要谨慎。
