Bonar Maegwin, Ellington E Hance, Lewis Keith P, Vander Wal Eric
Department of Biology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
School of Environment and Natural Resources, Ohio State University, Columbus, Ohio, United States of America.
PLoS One. 2018 Feb 21;13(2):e0192204. doi: 10.1371/journal.pone.0192204. eCollection 2018.
In ungulates, parturition is correlated with a reduction in movement rate. With advances in movement-based technologies comes an opportunity to develop new techniques to assess reproduction in wild ungulates that are less invasive and reduce biases. DeMars et al. (2013, Ecology and Evolution 3:4149-4160) proposed two promising new methods (individual- and population-based; the DeMars model) that use GPS inter-fix step length of adult female caribou (Rangifer tarandus caribou) to infer parturition and neonate survival. Our objective was to apply the DeMars model to caribou populations that may violate model assumptions for retrospective analysis of parturition and calf survival. We extended the use of the DeMars model after assigning parturition and calf mortality status by examining herd-wide distributions of parturition date, calf mortality date, and survival. We used the DeMars model to estimate parturition and calf mortality events and compared them with the known parturition and calf mortality events from collared adult females (n = 19). We also used the DeMars model to estimate parturition and calf mortality events for collared female caribou with unknown parturition and calf mortality events (n = 43) and instead derived herd-wide estimates of calf survival as well as distributions of parturition and calf mortality dates and compared them to herd-wide estimates generated from calves fitted with VHF collars (n = 134). For our data, the individual-based method was effective at predicting calf mortality, but was not effective at predicting parturition. The population-based method was more effective at predicting parturition but was not effective at predicting calf mortality. At the herd-level, the predicted distributions of parturition date from both methods differed from each other and from the distribution derived from the parturition dates of VHF-collared calves (log-ranked test: χ2 = 40.5, df = 2, p < 0.01). The predicted distributions of calf mortality dates from both methods were similar to the observed distribution derived from VHF-collared calves. Both methods underestimated herd-wide calf survival based on VHF-collared calves, however, a combination of the individual- and population-based methods produced herd-wide survival estimates similar to estimates generated from collared calves. The limitations we experienced when applying the DeMars model could result from the shortcomings in our data violating model assumptions. However despite the differences in our caribou systems, with proper validation techniques the framework in the DeMars model is sufficient to make inferences on parturition and calf mortality.
在有蹄类动物中，分娩与运动速率的降低相关。随着基于运动的技术的发展，出现了开发新技术的机会，以评估野生有蹄类动物的繁殖情况，这些技术侵入性较小且能减少偏差。德马斯等人（2013年，《生态与进化》3:4149 - 4160）提出了两种有前景的新方法（基于个体和基于种群的；德马斯模型），该模型利用成年雌性北美驯鹿（Rangifer tarandus caribou）的GPS定位间隔步长来推断分娩和幼崽存活情况。我们的目标是将德马斯模型应用于可能违反模型假设的北美驯鹿种群，以便对分娩和幼崽存活情况进行回顾性分析。在通过检查全群分娩日期、幼崽死亡日期和存活情况的分布来确定分娩和幼崽死亡状态后，我们扩展了德马斯模型的应用。我们使用德马斯模型来估计分娩和幼崽死亡事件，并将其与已知的佩戴项圈成年雌性（n = 19）的分娩和幼崽死亡事件进行比较。我们还使用德马斯模型来估计分娩和幼崽死亡事件，这些事件来自佩戴项圈但分娩和幼崽死亡情况未知的雌性北美驯鹿（n = 43），并由此得出全群幼崽存活情况的估计值以及分娩和幼崽死亡日期的分布，然后将它们与佩戴甚高频（VHF）项圈的幼崽（n = 134）得出的全群估计值进行比较。对于我们的数据，基于个体的方法在预测幼崽死亡方面有效，但在预测分娩方面无效。基于种群的方法在预测分娩方面更有效，但在预测幼崽死亡方面无效。在群体层面，两种方法预测的分娩日期分布彼此不同，且与从佩戴VHF项圈幼崽的分娩日期得出的分布也不同（对数秩检验：χ2 = 40.5，自由度 = 2，p < 0.01）。两种方法预测的幼崽死亡日期分布与从佩戴VHF项圈幼崽观察到的分布相似。然而，基于VHF项圈幼崽的情况，两种方法都低估了全群幼崽的存活率，不过，基于个体和基于种群的方法相结合得出的全群存活估计值与佩戴项圈幼崽得出的估计值相似。我们在应用德马斯模型时遇到的局限性可能是由于我们的数据存在违反模型假设的缺点所致。然而，尽管我们研究的北美驯鹿系统存在差异，但通过适当的验证技术，德马斯模型中的框架足以对分娩和幼崽死亡情况进行推断。
