Individual specialization in resource use by a far-ranging marine predator: incidence and implications

将一个种群中的所有个体视为生态上的等同是一种过于简单化的做法，而忽视个体之间的差异，特别是在资源利用方面的差异，可能会阻碍我们掌握一系列生态和进化过程的能力。饮食和觅食行为的个体专业化对生态学、进化（包括物种形成）和保护有着重要的影响，但对于大多数自由生活的消费者，特别是那些长途觅食的消费者来说，这在很大程度上仍未得到评估和了解。一些最长的觅食范围是在海洋捕食者中发现的，例如，远洋海鸟通常在一次旅行中从繁殖地飞行数十到数百公里。由于气候驱动的低营养水平的快速变化，加上工业和商业渔业对猎物物种的直接影响，海洋捕食者目前正面临前所未有的环境变化速度。此外，商业渔业目前以诱饵、小渔获物和内脏的形式为某些物种提供了大量的食物。不同物种对这些食物供应变化的反应已经在种群水平上得到了很好的记录，但这些数据通常掩盖了个体反应中大量无法解释的变化。在这里，我们建议研究北方塘鹅作为一种广泛以渔业废弃物和远洋鱼类为食的远距离海洋捕食者，在资源利用方面的个体变化的发生率和影响。个体的资源可得性经常受到与其他种群成员的竞争的强烈影响，然而令人惊讶的是，迄今为止很少有人尝试将海洋捕食者对环境变化的反应置于依赖于密度的资源利用模式的更广泛背景下。了解个体特化的本质对于预测渔业和气候相关变化对顶级海洋捕食者的反应和可能的后果也具有重要的保护意义。因此，在本项目中，我们将：(i)将塘鹅的饮食专业化与觅食地点、猎物搜索模式和捕获技术的个体差异联系起来；（ii）检查人口水平饮食广度和个体饮食和觅食行为专业化的密度依赖程度；（iii）确定个体专业化对生殖适合度不同组成部分的影响。除了回答有关多面手捕食者种群中个体专业化的产生和维持的基本问题外，我们还将提供关于不同种群中鸟类的觅食范围和核心觅食区域的重要信息。这些数据对于关注确定重要鸟类区和在欧洲水域建立海洋保护区的保护主义者和决策者具有重要价值。我们还将提供前所未有的详细资料，说明在不同的渔区依赖渔业弃物的发生率和后果，以及小型浅水鱼（例如沙鳗）的重要性。这些信息对于准确预测欧洲渔业丢弃做法拟议变化对种群水平的影响以及与气候有关的对天然饲料鱼可得性的影响至关重要。

Treating all individuals within a population as ecologically equivalent is an oversimplification and ignoring variation among individuals, particularly with respect to resource use, is likely to impede our ability to grasp a suite of ecological and evolutionary processes. Individual specialization in diet and foraging behaviour has important implications for ecology, evolution (including speciation) and conservation but remains largely unevaluated and poorly understood for most free-living consumers, particularly those that forage over long distances. Some of the longest foraging ranges are found among marine predators where, for instance, pelagic seabirds routinely travel tens to hundreds of kilometres from the breeding site on a single trip. Marine predators are currently facing an unprecedented rate of environmental change as a result of rapid climate-driven changes at lower trophic levels combined with direct effects of industrial and commercial fisheries on prey species. In addition, commercial fisheries currently provide huge quantities of food for some species in the form of bait, undersized catch and offal. Responses of different species to these changes in food availability have been well documented at population level but such data typically mask substantial unexplained variation in responses of individuals. Here we propose to examine the incidence and implications of individual variation in resource use by northern gannets as a model far-ranging marine predator that feeds extensively on both fishery discards and pelagic fish. Resource availability to individuals is often strongly affected by competition with other population members, yet surprisingly little attempt has been made to date to place the responses of marine predators to environmental change within the broader context of density-dependent patterns of resource use. Understanding the nature of individual specializations also has important conservation implications for predicting the response and likely consequences of fisheries and climate related change for apex marine predators. Accordingly in this project, we shall: (i) relate dietary specialization of gannets to individual variation in foraging locations, prey search patterns and capture techniques; (ii) examine the extent of density-dependence of both population-level dietary breadth and individual specialization in diet and foraging behaviour, and; (iii) determine the consequences of individual specialization for different components of reproductive fitness. In addition to answering fundamental questions concerning the generation and maintenance of individual specializations within populations of generalist predators, we shall provide vital information on the foraging ranges and core foraging areas of birds at different colonies. These data will be of great value to conservationists and policy makers concerned with the identification of Important Bird Areas and the establishment of Marine Protected Areas in European waters. We shall also provide information in unprecedented detail on the incidence and consequences of reliance on fisheries discards at different colonies as well as the importance of small shoaling fish (e.g. sandeels). This information is essential to make accurate predictions of population-level impacts of proposed changes to fishery discarding practices in Europe and climate related impacts on the availability of naturally occurring forage fish.