Data from: Predator-prey interactions in the canopy
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Small mammal abundances are frequently limited by resource availability, but predators can exert strong lethal (mortality) and non-lethal (e.g., nest abandonment) limitations. Artificially increasing resource availability for uncommon small mammals provides a unique opportunity to examine predator-prey interactions. We used remote cameras to monitor 168 nest platforms placed in the live-tree canopy (n = 23 young forest stands), primarily for arboreal red tree voles (tree voles; Arborimus longicaudus), over three years (n = 15,510 monitoring-weeks). Tree voles frequently built nests and were detected 37% of monitoring-weeks, whereas flying squirrels (Glaucomys oregonensis) built nests infrequently but were detected 45% of monitoring-weeks. Most nest predators were detected infrequently (<1% of monitoring-weeks) and were positively correlated with tree vole presence. Weasels (Mustela spp.) were highly effective predators of tree voles (n = 8 mortalities; 10% of detections) compared to owls (n = 1), flying squirrels (n = 2), and Steller’s jays (n = 1). Tree vole activity decreased from 84.1 (95% confidence interval (CI): 56.2, 111.9) detections/week 1-week prior to a weasel-detection to 4.7 detections/week (95% CI: 1.7, 7.8) 1-week post detection and remained low for at least 12 weeks. Interpretations of predator-prey interactions were highly sensitive to how we binned continuously collected data and model results from our finest bin-width were biologically counter-intuitive. Average annual survival of female tree voles was consistent with a previous study (0.14; 95% CI: -0.04 [0.01], 0.32) and high compared to many terrestrial voles. The relative infrequency of weasel detections and inefficiency of other predators did not provide strong support for the hypothesis that predation per se limited populations. Rather, predation pressure, by reducing occupancy of already scarce nest-sites through mortality and nest abandonment, may contribute to long-term local instability of tree vole populations in young forests. Additional monitoring would be needed to assess this hypothesis.
小型哺乳动物的种群丰度通常受资源可获得性限制，但捕食者可施加强烈的致死性（致死）与非致死性调控作用，例如弃巢行为。人为提升稀有小型哺乳动物的资源可获得性，为研究捕食者-猎物相互作用提供了独特契机。本研究利用远程监测相机，对设置于活立木冠层的168个巢台（覆盖23处幼林样地）开展了为期三年的监测，累计监测时长15510监测周，监测对象主要为树栖红树田鼠（树田鼠；*Arborimus longicaudus*）。红树田鼠筑巢频率较高，在37%的监测周中被检测到；而俄勒冈飞鼠（*Glaucomys oregonensis*）筑巢频次较低，但在45%的监测周中被检测到。多数巢捕食者的检测频率不足监测周总数的1%，且与树田鼠的出现呈正相关。与鸮类（n=1）、飞鼠（n=2）以及斯特勒松鸦（n=1）相比，鼬属（*Mustela* spp.）是红树田鼠的高效捕食者，共记录8例捕食致死事件，占所有检测事件的10%。在鼬属动物被检测到的前1周，树田鼠的活动检测频次为84.1次/周（95%置信区间CI：56.2, 111.9）；而在检测到后的1周，该数值降至4.7次/周（95% CI：1.7, 7.8），且后续至少12周均维持在较低水平。捕食者-猎物相互作用的解读结果对连续采集数据的分组方式极为敏感，且采用最小组距得到的模型结果在生态学意义上违背直觉。雌性红树田鼠的年平均存活率为0.14（95%置信区间：-0.04 [0.01], 0.32），与此前一项研究结果一致，且相较于多数陆生田鼠而言处于较高水平。鼬属动物的检测频率相对偏低，且其他捕食者的捕食效率有限，这两点均无法为“捕食本身限制种群规模”这一假说提供有力支撑。相反，捕食压力通过致死事件与弃巢行为减少本已稀缺的巢位占用率，可能是导致幼林生境中红树田鼠种群长期局部不稳定的原因之一。未来需开展额外监测以验证该假说。
