Murphy Sean M, Augustine Ben C, Ulrey Wade A, Guthrie Joseph M, Scheick Brian K, McCown J Walter, Cox John J
Department of Forestry, University of Kentucky, Lexington, Kentucky, United States of America.
Department of Fish and Wildlife Conservation, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States of America.
PLoS One. 2017 Jul 24;12(7):e0181849. doi: 10.1371/journal.pone.0181849. eCollection 2017.
Loss and fragmentation of natural habitats caused by human land uses have subdivided several formerly contiguous large carnivore populations into multiple small and often isolated subpopulations, which can reduce genetic variation and lead to precipitous population declines. Substantial habitat loss and fragmentation from urban development and agriculture expansion relegated the Highlands-Glades subpopulation (HGS) of Florida, USA, black bears (Ursus americanus floridanus) to prolonged isolation; increasing human land development is projected to cause ≥ 50% loss of remaining natural habitats occupied by the HGS in coming decades. We conducted a noninvasive genetic spatial capture-recapture study to quantitatively describe the degree of contemporary habitat fragmentation and investigate the consequences of habitat fragmentation on population density and genetics of the HGS. Remaining natural habitats sustaining the HGS were significantly more fragmented and patchier than those supporting Florida's largest black bear subpopulation. Genetic diversity was low (AR = 3.57; HE = 0.49) and effective population size was small (NE = 25 bears), both of which remained unchanged over a period spanning one bear generation despite evidence of some immigration. Subpopulation density (0.054 bear/km2) was among the lowest reported for black bears, was significantly female-biased, and corresponded to a subpopulation size of 98 bears in available habitat. Conserving remaining natural habitats in the area occupied by the small, genetically depauperate HGS, possibly through conservation easements and government land acquisition, is likely the most important immediate step to ensuring continued persistence of bears in this area. Our study also provides evidence that preferentially placing detectors (e.g., hair traps or cameras) primarily in quality habitat across fragmented landscapes poses a challenge to estimating density-habitat covariate relationships using spatial capture-recapture models. Because habitat fragmentation and loss are likely to increase in severity globally, further investigation of the influence of habitat fragmentation and detector placement on estimation of this relationship is warranted.
人类土地利用导致的自然栖息地丧失和破碎化，已将几个原本连续的大型食肉动物种群分割成多个小型且往往孤立的亚种群，这会减少遗传变异并导致种群数量急剧下降。城市发展和农业扩张造成的大量栖息地丧失和破碎化，使美国佛罗里达州高地 - 沼泽地黑熊（美洲黑熊佛罗里达亚种，Ursus americanus floridanus）的亚种群长期处于隔离状态；预计在未来几十年，人类土地开发的增加将导致高地 - 沼泽地亚种群（HGS）所占据的剩余自然栖息地丧失≥50%。我们开展了一项非侵入性遗传空间捕获 - 重捕研究，以定量描述当代栖息地破碎化程度，并调查栖息地破碎化对高地 - 沼泽地亚种群的种群密度和遗传学的影响。维持高地 - 沼泽地亚种群的剩余自然栖息地比支撑佛罗里达州最大黑熊亚种群的栖息地破碎化程度更高、斑块更零散。遗传多样性较低（等位基因丰富度AR = 3.57；期望杂合度HE = 0.49），有效种群规模较小（有效种群数量NE = 25只熊），尽管有一些迁入的证据，但在跨越一代熊的时间段内，这两个指标均保持不变。亚种群密度（0.054只熊/平方公里）是黑熊报道中最低的之一，显著偏向雌性，对应于可利用栖息地中98只熊的亚种群规模。通过保护地役权和政府土地收购等方式，保护小型、遗传多样性匮乏的高地 - 沼泽地亚种群所占据区域内的剩余自然栖息地，可能是确保该地区黑熊持续生存的最重要的直接措施。我们的研究还提供了证据，表明在破碎景观中主要将探测器（如毛发陷阱或相机）放置在优质栖息地，对使用空间捕获 - 重捕模型估计密度 - 栖息地协变量关系构成挑战。由于全球范围内栖息地破碎化和丧失的严重程度可能会增加，因此有必要进一步研究栖息地破碎化和探测器放置对这种关系估计的影响。
