Fiola Marie-Line, Vernouillet Alizée, Villard Marc-André
Département de biologie Université de Moncton Moncton NB Canada.
Department of Biological Sciences University of Manitoba Winnipeg MB Canada.
Ecol Evol. 2017 Nov 7;7(24):10733-10742. doi: 10.1002/ece3.3581. eCollection 2017 Dec.
The ecological literature presents considerable evidence for top-down forcing on the maintenance of species diversity. Yet, in temperate forests, bottom-up forces often exert a strong influence on ecosystem functioning. Here, we report on the indirect influence of a pulsed resource, sugar maple () seed production, on nest survival in a migratory songbird. We hypothesized that seed production in year would determine daily nest survival rate in year +1 through its effects on seed-eating rodents. We used the density of sugar maple seedlings (with cotyledons) in year +1 as a proxy for seed production in year and predicted that it would be inversely related to songbird nest survival the same year. We estimated the density of sugar maple seedlings, eastern chipmunk () activity, and daily nest survival rate in the ovenbird () over four successive years in a northern hardwood forest of New Brunswick, Canada. Seedling density varied by two orders of magnitude between years, whereas an index of chipmunk activity changed by an order of magnitude. Both variables were positively correlated and negatively correlated to daily nest survival rate. A logistic-exposure model including only seedling density received the greatest level of support (lowest AIC). Previous studies have reported the effect of sugar maple masting on seed-eating rodent populations, but the strong link we report between seedling density and songbird nest survival is novel. A nocturnal seed-eating nest predator, deer mouse (), was not considered in our models, which may explain why chipmunk was not the best predictor of daily nest survival rate. The trophic linkages we observed are remarkably strong for a temperate forest ecosystem and might become more prevalent in northeastern North America, at least on calcium-rich soils, with the loss of large-diameter beech trees as a result of beech bark disease.
生态文献提供了大量证据，证明自上而下的作用力对物种多样性的维持具有重要影响。然而，在温带森林中，自下而上的作用力往往对生态系统功能产生强烈影响。在此，我们报告了一种脉冲资源——糖枫（）种子产量对一种候鸟巢穴存活率的间接影响。我们假设第年的种子产量将通过其对食种子啮齿动物的影响来决定第 +1 年的每日巢穴存活率。我们使用第 +1 年糖枫幼苗（带子叶）的密度作为第年种子产量的替代指标，并预测它将与同年鸣禽巢穴存活率呈负相关。我们在加拿大新不伦瑞克省的一片北方硬木森林中，连续四年估计了糖枫幼苗的密度、东部花栗鼠（）的活动以及灶巢鸟（）的每日巢穴存活率。不同年份间幼苗密度变化了两个数量级，而花栗鼠活动指数变化了一个数量级。这两个变量与每日巢穴存活率均呈正相关和负相关。仅包含幼苗密度的逻辑暴露模型获得了最高程度的支持（最低 AIC）。先前的研究报道了糖枫结实对食种子啮齿动物种群的影响，但我们所报告的幼苗密度与鸣禽巢穴存活率之间的紧密联系却是新颖的。我们的模型中未考虑夜间食种子的巢穴捕食者鹿鼠（），这或许可以解释为何花栗鼠并非每日巢穴存活率的最佳预测指标。对于温带森林生态系统而言，我们所观察到的营养联系非常紧密，并且随着山毛榉树皮病导致大直径山毛榉树的减少，这种联系在北美东北部可能会变得更加普遍，至少在富含钙的土壤上是如此。
