Data_Sheet_1_Bird Census Data Do Not Indicate a Lack of Impact on Songbirds From the Growth of Avian Predator Populations in Britain in the Late 20th Century.PDF

The possible role of avian predators in limiting songbird populations has been largely discounted since the publication of findings showing a lack of statistical association in United Kingdom bird census data between changes in prey species populations and those of a range of predatory species, including raptors and corvids. I re-applied the methodology behind these findings, covering a wider range of prey species and using site-level modeling to estimate predator abundance instead of a mixture of spatial modeling and raw count data. A significant aggregate predator effect was found in 33 out of 40 prey species, compared to only 10 out of 27 in the original study, as well as a higher rate of significant individual predator effects, with 41 significantly negative and 84 significantly positive effects out of a total of 320. The greater explanatory power of predator variables estimated using site-level modeling suggests that this has significant advantages over the use of predator variables derived from spatial modeling, which may not capture variation in predator abundance at a local scale, or from raw count data, which may lead to attenuation of effect estimates. The prevalence of positive associations between predators and prey is consistent with a common response to local habitat variation, which may absorb negative covariance resulting from the impact of predators on prey populations. Both positive and negative predator-prey associations may also occur as a result of independent demographic processes that manifest as sequential habitat occupation or withdrawal. Analyses of census data cannot discriminate among these possible scenarios and may therefore have limited value in determining whether predators have been limiting prey populations. Inference to a lack of impact of avian predators on prey populations from such analyses may therefore be unsafe, and a role for increased predator numbers remains a viable hypothesis with respect to bird population declines. The recent neglect of this possibility should therefore be urgently reversed, with a particular need for field experiments that can support strong inference regarding population limitation of songbirds by avian predators.

自发布关于英国鸟类调查数据中，猎物种群数量变化与包括猛禽和鸦科动物在内的多种捕食者种群数量变化之间缺乏统计关联的研究发现以来，鸟类捕食者在限制鸣禽种群中的可能作用在很大程度上被忽视。我重新应用了这些发现背后的方法，覆盖了更广泛的猎物种群范围，并使用基于地点的模型来估计捕食者数量，而非空间模型与原始计数数据的混合。在40种猎物种群中，有33种发现了显著的总体捕食者效应，相比之下，原始研究中只有27种中的10种发现了显著的效应，同时显著的单个捕食者效应的比率也更高，共计320个效应中，有41个显著负效应和84个显著正效应。使用基于地点的模型估计的捕食者变量的更高解释力表明，这种方法相较于来自空间模型的捕食者变量具有显著优势，后者可能无法捕捉到局部尺度上的捕食者数量变化，或来自原始计数数据，可能导致效应估计的衰减。捕食者与猎物之间普遍存在的正相关关系与对局部栖息地变化的共同响应一致，这可能吸收了捕食者对猎物种群影响的负协方差。正负捕食者-猎物关联也可能是由独立的人口学过程引起的，这些过程表现为连续的栖息地占用或撤退。由于无法区分这些可能情景，因此对调查数据的分析在确定捕食者是否限制了猎物种群方面可能价值有限。因此，从这种分析中推断鸟类捕食者对猎物种群没有影响可能是不安全的，捕食者数量增加在鸟类种群减少的背景下仍是一个可行的假设。因此，应立即纠正近年来对这一可能性的忽视，尤其需要现场实验来支持关于鸟类捕食者对鸣禽种群限制的强推断。