Abstract North American moose (Alces alces) populations along the southern extent of their range have been experiencing high levels of calf mortality in recent years. In New England, this phenomenon has been linked to extensive blood loss resulting from extreme winter tick (Dermacentor albipictus) parasitism. Moose are symbolic of the region and generate income through tourism and the auction of hunting permits; thus, successive years of greater than 50% calf mortality (epizootics) are of concern to wildlife managers and others. It is hypothesized that high localized moose density coupled with climate change are the driving forces behind moose-winter tick epizootics; however, the impact that variable combinations of these and other factors have on the occurrence and magnitude of epizootics has not been previously simulated. We, therefore, developed and implemented a spatially explicit agent-based model with two model environments, each representative of a distinct location within an ongoing field study site in northern New Hampshire that differed in the proportional availability of optimal moose habitat. Three experiments were devised to test the sensitivity of the outcome variables, calf infestation level and calf mortality, to 1) winter tick abundance, 2) winter tick aggregation, and 3) moose density, for the length of the winter tick questing period. Each experiment was conducted in both model environments. This model generated similar mortality levels to those measured in the field study under representative moose density and weather conditions. Additionally, the modeled moose agents and the radio-collared moose in the field reflect comparable habitat usage. While the infestation levels reported by calf agents are considered conservative, we believe that future versions of this model, parameterized with more accurate estimates of winter tick abundance and moose density, may be an effective tool for managing moose against winter tick parasitism.

中文翻译：

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使用基于代理的模型来了解驼鹿冬季蜱寄生的动态

摘要 近年来，北美驼鹿 (Alces alces) 种群的分布范围南部一直在经历高水平的小牛死亡率。在新英格兰，这种现象与极端冬季蜱（Dermacentor albipictus）寄生导致的大量失血有关。驼鹿是该地区的象征，通过旅游业和狩猎许可证拍卖产生收入；因此，连续数年超过 50% 的小牛死亡率（流行病）引起了野生动物管理者和其他人的关注。据推测，高本地驼鹿密度加上气候变化是驼鹿冬季蜱流行的驱动力；然而，这些因素和其他因素的可变组合对流行病的发生和严重程度的影响以前没有模拟过。因此，我们 开发并实施了一个空间明确的基于代理的模型，该模型具有两个模型环境，每个环境都代表新罕布什尔州北部正在进行的实地研究站点内的不同位置，其在最佳驼鹿栖息地的比例可用性方面有所不同。设计了三个实验来测试结果变量、小牛感染水平和小牛死亡率对 1) 冬季蜱丰度、2) 冬季蜱聚集和 3) 驼鹿密度在冬季蜱探查期的长度的敏感性。每个实验都在两种模型环境中进行。该模型产生的死亡率水平与在具有代表性的驼鹿密度和天气条件下的实地研究中测得的死亡率水平相似。此外，建模的驼鹿代理人和野外戴无线电项圈的驼鹿反映了可比较的栖息地使用情况。