Abstract

Understanding intraspecific phenotypic variation in prey specialisation can help to predict how long-term changes in prey availability affect the viability of these phenotypes and their persistence. Generalists are favoured when the main food resources are unpredictable compared to specialists, which track the availability of the main prey and are more vulnerable to changes in the main food resource. Intraspecific heritable melanin-based colour polymorphism is considered to reflect adaptations to different environments. We studied colour morph-specific diet specialisation in a generalist predator, tawny owl (Strix aluco), during offspring food provisioning in relation to mammal prey density. We hypothesised that the grey morph, with higher fitness than the brown in Northern boreal conditions, is more specialised in mammalian prey than the brown morph, which in turn has higher fitness than the grey in the temperate zone. We found a higher diversity of prey delivered to the nest by brown fathers compared to grey ones, which also depended on the overall mammalian prey availability. Brown fathers provided proportionally fewer mammalian prey than grey in poor, but not in favourable mammal prey years. Our results suggest that the brown morph is more generalistic and reacts more strongly to variations in food supply than the grey morph, which may be a beneficial strategy in an unpredictable environment caused by environmental degradation.

Significance statement

Diet choice of a species may vary depending on fluctuations in the abundance of their food resource, but also within a population, there can be adaptations to use different food resources. The tawny owl exhibits a grey and a reddish-brown colour morph and is considered a generalist predator eating both mammal and bird prey. We find that the diet of the reddish-brown morph is more diverse than that of the grey. When the tawny owls’ main prey, small mammals, are abundant both colour morphs prey on mammals, but in years with less small mammals, the reddish-brown morph is more prone of switching to small bird predation than the grey. The generalist strategy of the brown morph is likely to be more favourable than a stricter specialisation in small mammals of the grey under recently reoccurring irregularities in small mammal dynamics.

中文翻译：

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黄褐色猫头鹰中具有颜色多态性的专家捕食协变量

摘要

了解猎物专业化的种内表型变异可以帮助预测猎物可用性的长期变化如何影响这些表型的生存能力及其持久性。与主要追踪猎物的供应量且更容易受到主要粮食资源变化的影响的专家相比，与主要专家相比，主要粮食资源难以预测时，通才将受到青睐。种内可遗传的基于黑色素的颜色多态性被认为反映了对不同环境的适应性。我们在通体捕食者黄褐色猫头鹰（Strix aluco），在与哺乳动物猎物密度有关的后代食物供应过程中。我们假设，在北方寒带条件下，具有比棕色更高适应性的灰色变体比棕色变体更适合哺乳动物的猎物，而棕色变体在温带地区具有比灰色更高的适应性。我们发现，与灰色父亲相比，棕色父亲​​运送到巢中的猎物具有更高的多样性，这也取决于整个哺乳动物猎物的可用性。在贫穷的情况下，布朗父亲提供的哺乳动物猎物比灰色的少，但在有利的哺乳动物猎物年中却没有。我们的结果表明，与灰色形态相比，棕色形态对食物供应的变化更具普遍性，并且对食物供应的变化反应更强烈，这在环境退化导致的不可预测的环境中可能是一种有益的策略。

重要性声明

一个物种的饮食选择可能会因其食物资源丰富度的波动而有所不同，但在一个种群中，可能会进行适应以使用不同的食物资源。黄褐色的猫头鹰表现出灰色和红棕色的肤色，被认为是通吃哺乳动物和鸟类的猎物的通体捕食者。我们发现，红棕色形态的饮食比灰色饮食的饮食更加多样化。当黄褐色的猫头鹰的主要猎物小型哺乳动物在哺乳动物身上有两种颜色的变形猎物，但是在小型哺乳动物较少的年份中，与棕色相比，红棕色的变形更倾向于捕食小型鸟类。在最近发生的小型哺乳动物动力学异常情况下，对于灰色小型哺乳动物，棕色变体的通才策略可能比更严格的专业化更为有利。