Spatial components of plasticity in tit phenology: responses, constraints and amelioration

生物体应对环境变化的可能方式有三种：(1)它们可能分散或迁移；(2)它们可能进化以适应新环境；(3)随着环境的变化，它们可能产生不同的表型——换句话说，表现出表型的可塑性。一个当代的例子与了解人口对气候变化的反应有关。迄今为止的研究表明，尽管这三种机制不是排他性的，但种群对气候变化的反应通常涉及表型可塑性。因此，理解作用于可塑性的进化力量对于我们理解面对气候变化的生存能力至关重要。大多数研究只是将种群的平均表型与环境的单一值（通常是一整年的水平）联系起来，这阻碍了对表型可塑性及其在适应不断变化的环境中的作用的理解。只有当生物体对环境线索的反应是非常大规模的线索，从种群中个体的角度来看变化很小时，这才有意义。然而，我们知道许多生物只经历了环境的有限部分，而且环境可能在相当小的空间尺度上变化。尽管如此，我们不明白动物是如何平衡这些小的和大的线索的。因此，本研究的中心目标是确定环境的空间尺度如何在理解表型可塑性的进化中发挥重要作用。我们的模型系统涉及小型林地鸟类的繁殖行为——在牛津附近的威瑟姆森林繁殖的大山雀——它们在强烈的自然选择下，将繁殖时间与蛾子毛虫（例如冬蛾）的丰度高峰相吻合，这些蛾子毛虫适应以落叶树新出现的叶子为食。在种群水平上，鸟类繁殖的时间与毛虫丰度的高峰吻合较好，但在很小的空间尺度上，这些事件的时间在每一年都有很大的变化。此外，我们有证据表明，尽管有共同的温度趋势，但不同人群的反应速度不同。因此，总体水平的汇总统计掩盖了几个重要的变化水平。我们将使用关于繁殖行为和适应性的长期数据，以及详细的环境数据来分析鸟类繁殖时间变化的空间尺度，并检验尺度对适应性和种群动态的影响的假设。然后，我们将用在规则网格位置收集的新数据来补充这些数据，以确定发芽和毛虫丰度的物候，从而表征鸟类能够在不同尺度上匹配环境中事件时间的程度。因为我们期望多个尺度是重要的，我们可以预测，最佳表型是小尺度和大尺度可塑性之间的平衡，因此，适应在孤立的任何一个尺度上都不可能是完美的。由于环境是斑驳的，我们可以进一步预测，适应小型和大规模的线索将导致一些斑块比其他斑块具有更高的生产力；因此，空间尺度的可塑性将导致种群内部的种群动态变化。在地面收集环境数据非常耗时，而且只能覆盖有限的区域；因此，我们将测试卫星图像在多大程度上可以用于估计与自然界生物体相关的尺度上的物候。最后，我们将进行实验测试，以确定鸟类与环境之间的物候不匹配是否会在更多样化的环境中得到缓解，这种不匹配与某些物种的种群下降有关。

There are three potential ways in which organisms can respond to changing environments: (1) they may disperse, or migrate, (2) they may evolve so that they adapt to the new environment, or (3) they may produce different phenotypes - in other words display phenotypic plasticity - as the environment changes. A contemporary example relates to understanding responses of populations to climate change. Work to date suggests that, despite the three mechanisms being non-exclusive, population responses to climate change usually involve phenotypic plasticity. Hence, understanding the evolutionary forces acting on plasticity is of central importance in our understanding of viability in the face of climate change. Understanding of phenotypic plasticity and its role in adaptation to changing environments is hampered by the fact that most studies simply correlate an average phenotype for the population with a single value for the environment, most often at the level of an entire year. This only makes sense if the environmental cues to which organisms respond are very large-scale cues, varying little from the perspective of individuals within populations. However, we know that many organisms experience only a limited part of the environment, and that the environment may vary over quite small spatial scales. Despite this, we don't understand how animals balance these small- and large-scale cues. The central aim of this research is thus to determine how the spatial scale of the environment is important in understanding the evolution of phenotypic plasticity.Our model system involves reproductive behaviour in small woodland birds - great tits, breeding in Wytham Woods near Oxford - which are under strong natural selection to time their reproduction to coincide with peaks in abundance of moth caterpillars (e.g. the winter moth) that are adapted to feed on newly emerged leaves of deciduous trees. At the population level there is a good match between the timing of birds' breeding and the peak of caterpillar abundance, but there is tremendous variation within each year in the timing of these events over quite a small spatial scale. Furthermore, we have evidence that, despite a common temperature trend, different parts of the population are responding at different rates. Hence, the population level summary statistics disguise several important levels of variation.We will use long term data on breeding behaviour and fitness, together with detailed environmental data to analyse the spatial scales at which variation in bird reproductive timing can best be explained, and to test hypotheses about the influence of scale on fitness and population dynamics. We will then supplement these data with new data collected across a regular grid of locations to determine phenology of bud-burst and caterpillar abundance, and hence characterise the extent to which birds are able to match the timing of events in their environment at different scales. Because we expect multiple scales to be important, we can make the prediction that the optimal phenotype is a balance between small- and large-scale plasticity, and hence that adaptation will not be perfect at either scale in isolation. Because the environment is patchy, we can further predict that adjusting to small- as well as large-scale cues will lead to some patches having higher productivity than others; hence the spatial scale of plasticity will lead to within population variation in population dynamics. Collecting environmental data on the ground is very time-consuming, and only limited areas can be covered; therefore we will test the extent to which satellite images can be used to estimate phenology at scales that are relevant to organisms in nature. Finally, we will carry out experimental tests of whether mis-matches in phenology between birds and the environment, which have been implicated in population declines in some species, are alleviated by being in more varied environments.