Barraquand Frédéric, Høye Toke T, Henden John-André, Yoccoz Nigel G, Gilg Olivier, Schmidt Niels M, Sittler Benoît, Ims Rolf A
Department of Arctic and Marine Biology, University of Tromsø, Tromsø, 9037, Norway.
Arctic Research Centre, Aarhus University, Aarhus, DK-8000, Denmark.
J Anim Ecol. 2014 Mar;83(2):375-87. doi: 10.1111/1365-2656.12140. Epub 2013 Oct 15.
Environmental variability, through interannual variation in food availability or climatic variables, is usually detrimental to population growth. It can even select for constancy in key life-history traits, though some exceptions are known. Changes in the level of environmental variability are therefore important to predict population growth or life-history evolution. Recently, several cyclic vole and lemming populations have shown large dynamical changes that might affect the demography or life-histories of rodent predators. Skuas constitute an important case study among rodent predators, because of their strongly saturating breeding productivity (they lay only two eggs) and high degree of site fidelity, in which they differ from nomadic predators raising large broods in good rodent years. This suggests that they cannot capitalize on lemming peaks to the same extent as nomadic predators and might be more vulnerable to collapses of rodent cycles. We develop a model for the population dynamics of long-tailed skuas feeding on lemmings to assess the demographic consequences of such variable and non-stationary prey dynamics, based on data collected in NE Greenland. The model shows that populations of long-tailed skua sustain well changes in lemming dynamics, including temporary collapses (e.g. 10 years). A high floater-to-breeder ratio emerges from rigid territorial behaviour and a long-life expectancy, which buffers the impact of adult abundance's decrease on the population reproductive output. The size of the floater compartment is affected by changes in both mean and coefficient of variation of lemming densities (but not cycle amplitude and periodicity per se). In Greenland, the average lemming density is below the threshold density required for successful breeding (including during normally cyclic periods). Due to Jensen's inequality, skuas therefore benefit from lemming variability; a positive effect of environmental variation. Long-tailed skua populations are strongly adapted to fluctuating lemming populations, an instance of demographic lability in the reproduction rate. They are also little affected by poor lemming periods, if there are enough floaters, or juveniles disperse to neighbouring populations. The status of Greenland skua populations therefore strongly depends upon floater numbers and juvenile movements, which are not known. This reveals a need to intensify colour-ringing efforts on the long-tailed skua at a circumpolar scale.
环境变异性，通过食物可获得性或气候变量的年际变化，通常对种群增长不利。它甚至可能导致关键生活史特征的稳定性，尽管也存在一些例外情况。因此，预测环境变异性水平的变化对于预测种群增长或生活史进化很重要。最近，一些周期性的田鼠和旅鼠种群出现了巨大的动态变化，这可能会影响啮齿动物捕食者的种群统计学或生活史。贼鸥是啮齿动物捕食者中的一个重要案例研究对象，因为它们的繁殖生产力强烈饱和（它们只产两枚卵）且忠诚度很高，这与在啮齿动物数量丰富的年份养育大量幼崽的游牧捕食者不同。这表明它们无法像游牧捕食者那样充分利用旅鼠数量的峰值，可能更容易受到啮齿动物数量周期崩溃的影响。我们基于在格陵兰东北部收集的数据，建立了一个以旅鼠为食的长尾贼鸥种群动态模型，以评估这种可变且非平稳的猎物动态的种群统计学后果。该模型表明，长尾贼鸥种群能够很好地承受旅鼠数量动态的变化，包括暂时的崩溃（例如持续10年）。由于严格的领地行为和较长的预期寿命，出现了高比例的非繁殖者与繁殖者，这缓冲了成年个体数量减少对种群繁殖输出的影响。非繁殖者群体的规模受到旅鼠密度均值和变异系数变化的影响（但不是周期幅度和周期本身）。在格陵兰，旅鼠的平均密度低于成功繁殖所需的阈值密度（包括在正常的周期阶段）。由于詹森不等式，贼鸥因此从旅鼠数量的变异性中受益；这是环境变化的一个积极影响。长尾贼鸥种群强烈适应旅鼠数量的波动，这是繁殖率中种群统计学易变性的一个例子。如果有足够的非繁殖者，或者幼鸟扩散到邻近种群，它们也很少受到旅鼠数量不佳时期的影响。因此，格陵兰贼鸥种群的状况在很大程度上取决于非繁殖者的数量和幼鸟的移动情况，而这些情况尚不清楚。这表明有必要在环极范围内加强对长尾贼鸥的彩色环志工作。
