The phenological optimum in space and time

对于生活在季节性环境中的许多动植物来说，掌握关键生命周期事件的正确时机至关重要。以食虫的林地鸟类为例，它们必须在春天早早下蛋，以确保它们的幼鸟在食物最丰富的时候孵化和生长，比如毛虫。因为从开始产卵到雏鸟的最大食物需求之间隔了整整一个月，这些鸟利用早春环境中的线索，如温度，来预测春天晚些时候会发生什么。因此，雌性个体在产卵时间上可以相当灵活，如果春季温度升高1摄氏度，那么产卵时间就会提前大约2-5天(取决于物种)，这种能力我们称之为可塑性。然而，雌性对未来状况的预测仍然不完美；小鸡通常会在错误的时间被饲养，导致几乎没有羽毛。随着春季气温的上升，食物高峰的速度可能会快于单个鸟类所能跟上的速度。因此，一个物种可能需要进化出更早的产卵日期，如果这不可能，它最终可能灭绝。预测气候变化将如何影响物种已经被证明是非常困难的。如果我们知道温度升高1摄氏度的最佳时间会发生多大的变化，我们知道一个物种可以通过可塑性跟踪这种变化的程度，我们就可以计算出进化需要弥补的范围。无论是鸟类产卵、青蛙产卵、植物开花还是树木开叶，测量时间对温度反应的可塑性都相对容易。更困难的是计算出一个物种需要改变其时机以跟踪理想条件的数量。事实上，这只针对一个物种，即大山雀。我们将确定春季温度与第二个物种--蓝山雀--的最佳时间之间的关系。蓝山雀是大山雀的近亲。我们将在爱丁堡以北200公里的50个地点的四个泉水中监测蓝山雀的产卵情况和毛虫的可获得性。我们将进行一项巨大的实验，在孵化的雌性鸟巢之间交换数百只幼崽，以确定何时是产卵的最佳时间。我们认为，蓝山雀的最佳产卵日期可能取决于温度和毛虫可获得性高峰之间的关系。然而，像许多物种一样，蓝山雀是一个栖息地和取食多面手，随着不同的毛虫物种变得或多或少地丰富，春季温度和最佳产卵时间之间的关系可能会因地而异。我们将测试这一想法，如果我们找到支持它，这意味着对于多面手物种，我们可能需要在每次考虑不同的种群或栖息地时重新确定温度和最佳时间之间的关系。显然，我们不能指望这种巨大的时间或资源投入花费在少数几个分类群上，但我们需要知道温度与许多分类群的最佳时间之间的关系。我们已经开发出一种方法，可以从对时间的观察类型中推断出这种关系，公民科学项目，如自然日历和BTO Nest记录计划，在收集时间方面非常有效。这可能会极大地增加我们可以确定这种关系的物种的数量。然而，在我们鼓励更广泛地使用这种方法之前，我们首先需要改进统计方法，并测试它所要求的假设在蓝山雀中是否有效。

For the many animals and plants that live in seasonal environments, getting the right timing to key life cycle events is vital. To take insectivorous woodland birds as an example, they must lay their eggs early in spring to ensure that their chicks will hatch and grow when food, such as caterpillars, is most plentiful. Because a full month elapses between starting to lay eggs and the maximum food demand of their chicks, the birds use cues in the environment in early spring, such as temperature, to predict what will happen later in the spring. An individual female can therefore be quite flexible in the timing of egg-laying, advancing the time by about two - five days (depending on the species) if spring temperatures are 1C warmer, an ability that we call plasticity. The prediction that the female makes about future conditions remains imperfect however; chicks will often be reared at the wrong time, resulting in few, if any, fledging. With rising spring temperatures the food peak may advance at a rate that is faster than individual birds can keep up with. Therefore, to keep up a species may need to evolve an earlier egg-laying date or, if this is not possible, it may ultimately go extinct.Predicting how climate change will affect species has proven very difficult. If we know how much the optimum timing will shift for a 1C rise in temperature and we know how much a species can track this shift via plasticity, we can work out the amount of ground that evolution will need to make up. Measuring plasticity of timing in response to temperature, whether it be bird egg-laying, frog spawning, plant flowering or tree leafing, is relatively easy. Much more difficult is to work out the amount by which a species needs to shift its timing to track ideal conditions. In fact this has been done for just a single species, the great tit.We will identify the relationship between spring temperatures and optimum timing for a second species, the blue tit, a close relative of the great tit. We will monitor blue tit egg-laying and the availability of caterpillars in four springs and across 50 sites that stretch north of Edinburgh for 200km. We will conduct a huge experiment, swapping hundreds of clutches between the nest boxes of incubating females, to establish when is the best time to lay. We think that the best laying date for a blue tit is likely to be governed by the relationship between temperature and the peak availability of caterpillars. However, the blue tit, like many species is a habitat and feeding generalist and it is possible that the relationship between spring temperature and the best time to lay will vary from one site to another as different caterpillar species become more or less abundant. We will test this idea and if we find support for it this implies that for generalist species we may need to identify the relationship between temperature and the optimum timing anew every time we consider a different population or habitat.Clearly, we cannot expect this huge investment of time or resources to be expended on more than a handful of taxa and yet we need to know how temperature relates to the optimum timing for many taxa. We have developed a method that can infer this relationship from the type of observations on timings that citizen science projects like Nature's Calendar and the BTO Nest Record Scheme have been so effective at collecting. This could greatly increase the number of species for which we can identify this relationship. However, before we encourage much wider use of this method we need first to improve the statistical method and test whether the assumptions it requires are valid in the blue tit.