Among numerous anthropogenic impacts on terrestrial landscapes, expanding transportation networks represent one of the primary challenges to wildlife conservation worldwide. Larger mammals may be particularly vulnerable because of typically low densities, low reproductive rates, and extensive movements. Although numerous studies have been conducted to document impacts of road networks on wildlife, inference has been limited because of experimental design limitations. During the last decade, the North Carolina Department of Transportation (NCDOT) rerouted and upgraded sections of United States Highway 64 between Raleigh and the Outer Banks to a 4‐lane, divided highway. A new route was selected for a 24.1‐km section in Washington County. The new section of highway included 3 wildlife underpasses with adjacent wildlife fencing to mitigate the effects of the highway on wildlife, particularly American black bears (Ursus americanus). We assessed the short‐term impacts of the new highway on spatial ecology, population size, survival, occupancy, and gene flow of black bears. We tested our research hypotheses using a before‐after control‐impact (BACI) study design. We collected data during 2000–2001 (preconstruction phase) and 2006–2007 (postconstruction phase) in the highway project area and a nearby control area (each approx. 11,000 ha), resulting in 4 groups of data (i.e., pre‐ or postconstruction study phase, treatment or control area). We captured and radiocollared 57 bears and collected 5,775 hourly locations and 4,998 daily locations. Using mixed‐model analysis of variance and logistic regression, we detected no differences in home ranges, movement characteristics, proximity to the highway alignment, or habitat use between the 2 study phases, although minimum detectable effect sizes were large for several tests. However, after completion of the new highway, bears on the treatment area became less inactive in morning, when highway traffic was low, compared with bears on the control area (F_{1, 43} = 6.05, P = 0.018). We used DNA from hair samples to determine if population size and site occupancy decreased following highway construction. For each study phase, we collected black bear hair from 70 hair snares on each study area during 7 weekly sampling periods and generated genotypes using 10 microsatellite loci. We used the multilocus genotypes to obtain capture histories for 226 different bears and used capture‐mark‐recapture models to estimate population size. Model‐averaged estimates of population size decreased on the treatment area from 87.7 bears before construction to 31.6 bears after construction (64% reduction) and on the control area from 163.6 bears to 108.2 bears (34% reduction). Permutation procedures indicated this reduction was proportionally greater for the treatment area (P = 0.086). We also applied a spatially explicit capture‐recapture technique to test our research hypothesis. The model with the most support indicated a greater change in density on the treatment area (69% reduction) compared with the control area (24% reduction). We did not observe a treatment effect based on survival of radiocollared bears. We used bear visits to hair snares as detections in multi‐season occupancy models and found that occupancy decreased more on the treatment area (preconstruction: Ψ = 0.84; postconstruction: Ψ = 0.44; 48% decline) than the control area (preconstruction: Ψ = 0.91; postconstruction: Ψ = 0.81; 11% decline), primarily as a function of a greater probability of site extinctions (ε) on the treatment area (ε = 0.57) than the control area (ε = 0.17). Finally, individual‐ and population‐based analyses of contemporary gene flow did not indicate the highway was a barrier to movements. Black bear use of the 3 wildlife underpasses was infrequent (17 verified crossings based on remote cameras, track surveys, and telemetry). Only 4 of 8 bears with home ranges near the highway were documented crossing the highway (n = 36 crossings), of which 2 were killed in vehicle collisions. Six additional bears were killed in vehicle collisions from May 2007 to November 2008, after we completed field work. Harvest data indicated that hunting mortality alone could explain the population decline on the control area. On the treatment area, however, hunting mortality only accounted for an approximately 40% population decline; the additional 30% decline we observed likely was caused by other mortality. We speculate vehicle collisions were primarily responsible. We conclude that impacts of the new highway on resident black bears occurred at the population level, rather than the individual or genetic level, but that the impact was smaller than harvest mortality. Increased activity by remaining bears when traffic volumes were low indicated behavioral plasticity. Bear use of the underpasses seemed sufficient to maintain gene flow between areas north and south of the new highway. Effectiveness of wildlife underpasses to reduce mortality of black bears may be enhanced if mitigation includes continuous fencing between crossing structures. For small, isolated populations of threatened or endangered large mammals, the potential demographic impacts of highways are an essential consideration in the transportation planning process. Control of mortality factors and maintaining demographic connectivity are particularly important. © 2012 The Wildlife Society.

中文翻译：

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四车道高速公路对北卡罗莱纳州东部的美国黑熊的短期影响

在对陆地景观的众多人为影响中，不断扩大的运输网络是全球野生动植物保护的主要挑战之一。由于通常密度低，繁殖率低和运动频繁，因此较大的哺乳动物可能特别容易受到伤害。尽管已进行了大量研究来记录道路网络对野生动植物的影响，但由于实验设计的局限性，推理一直受到限制。在过去十年中，北卡罗来纳州交通运输部（NCDOT）将位于罗利和外滩之间的美国64号高速公路的路段改道并升级为4车道，分开的高速公路。为华盛顿县24.1公里的路段选择了一条新路线。美洲熊）。我们评估了新高速公路对黑熊的空间生态，种群规模，生存，占用和基因流的短期影响。我们使用前后对照（BACI）研究设计检验了我们的研究假设。我们在高速公路项目区域和附近的控制区域（每个约11,000公顷）中收集了2000-2001年（建设前阶段）和2006-2007年（建设后阶段）的数据，得出了4组数据（即建设前或建设后）研究阶段，治疗或控制区域）。我们捕获并放射领了57只熊，每小时收集了5,775个位置，每天收集了4,998个位置。使用方差和logistic回归的混合模型分析，我们在两个研究阶段之间未发现房屋范围，运动特征，与高速公路路线的接近程度或栖息地使用情况的差异，尽管几项测试的最小可检测效果量很大。但是，新高速公路建成后，与高速公路管制区的熊相比，早上交通繁忙的熊在治疗区的活动减少了（F _1，43  = 6.05，P = 0.018）。我们使用头发样本中的DNA来确定高速公路建设后人口规模和站点占用率是否降低。对于每个研究阶段，我们在每周7个采样周期内从每个研究区域的70个网罗中收集了黑熊的头发，并使用10个微卫星基因座生成了基因型。我们使用多基因座基因型获得了226种不同熊的捕获历史，并使用捕获标记捕获模型来估计种群数量。根据模型平均估计的人口规模，治疗区的面积从建造前的87.7只熊减少到建造后的31.6只（减少64％），而控制区的种群数量则从163.6头减少到108.2只（减少34％）。排列程序表明，对于治疗区域，这种减少成比例地更大（P = 0.086）。我们还应用了空间显式捕获-捕获技术来检验我们的研究假设。具有最大支持的模型表明，与对照区域（减少24％）相比，治疗区域的密度变化更大（减少了69％）。我们没有观察到基于放射性领熊生存的治疗效果。我们用熊访问网罗作为多季节占用模型的检测结果，发现治疗区域的占用率下降幅度更大（施工前：Ψ= 0.84；施工后：Ψ= 0.44；下降48％）比对照区（施工前：Ψ = 0.91；施工后：Ψ= 0.81；下降11％），主要是治疗区域（ε= 0.57）比控制区域（ε= 0.17）更大的部位灭绝概率（ε）。最后，基于个体和人群的当代基因流分析并未表明高速公路是运动的障碍。黑熊很少使用3个野生动物地下通道（基于远程摄像头，跟踪调查和遥测的17个经过验证的穿越）。在高速公路附近有8只熊的家中，只有4只熊在高速公路上穿越（ñ = 36个路口），其中2人在车祸中丧生。在我们完成现场工作之后，从2007年5月至2008年11月，还有6头熊在车祸中丧生。收获数据表明，仅狩猎死亡率就可以解释控制地区人口的减少。然而，在治疗地区，狩猎死亡率仅导致人口下降约40％。我们观察到的另外30％的下降可能是由其他死亡率引起的。我们推测车辆碰撞是主要原因。我们得出的结论是，新公路对居民黑熊的影响发生在人口水平上，而不是在个人或遗传水平上，但影响小于收获死亡率。当交通流量较低时，剩余熊的活动增加，表明行为可塑性。熊对地下通道的利用似乎足以维持新高速公路南北之间的基因流动。如果缓解措施包括在交叉结构之间持续围墙，则可以提高野生动物地下通道降低黑熊死亡率的有效性。对于受威胁或濒临灭绝的大型哺乳动物的小而孤立的种群，高速公路的潜在人口影响是交通运输规划过程中的重要考虑因素。控制死亡率因素和保持人口统计联系特别重要。©2012野生动物协会。对于受威胁或濒临灭绝的大型哺乳动物的小而孤立的种群，高速公路的潜在人口影响是交通运输规划过程中的重要考虑因素。控制死亡率因素和保持人口统计联系特别重要。©2012野生动物协会。对于受威胁或濒临灭绝的大型哺乳动物的小而孤立的种群，高速公路的潜在人口影响是交通运输规划过程中的重要考虑因素。控制死亡率因素和保持人口统计联系特别重要。©2012野生动物协会。