Monitoring wildlife population trends with sample counts: A case study on the Alpine ibex (Capra ibex)

Monitoring population dynamics is of fundamental importance in
conservation but assessing trends in abundance can be costly, especially
in large and rough areas. Obtaining trend estimations from counts
performed in only a portion of the total area (sample counts) can be a
cost-effective method to improve the monitoring and conservation of
species difficult to count. We tested the effectiveness of sample counts
in monitoring population trends of wild animals, using as a model
population the Alpine ibex (Capra ibex) in the Gran Paradiso National Park
(Italy), both with computer simulations and using historical count data
collected over the last 65 years. Despite sample counts failed to
correctly estimate the true population abundance, sampling half of the
target area could reliably monitor the trend of the target population. In
case of strong changes in abundance, an even lower proportion of the total
area could be sufficient to identify the direction of the population
trend. However, when there is a high yearly trend variability, the
required number of samples increases and even counting in the entire area
can be ineffective to detect population trends. The effect of other
parameters, such as which portion of the area is sampled and
detectability, was lower, but these should be tested case by case. Sample
counts could therefore constitute a viable alternative to assess
population trends, allowing for important, cost-effective improvements in
the monitoring of wild animals of conservation interest.

种群动态监测在物种保护领域具有核心重要性，但评估种群丰度趋势往往成本高昂，在广袤且地形崎岖的区域更是如此。仅对研究区域的部分区域开展计数（抽样计数（sample counts））以获取种群趋势估计值，是提升难以直接计数物种监测与保护工作效率的经济可行方案。本研究以意大利格兰帕拉迪索国家公园内的阿尔卑斯羱羊（Capra ibex）为模式种群，结合计算机模拟与过去65年收集的历史计数数据，验证了抽样计数在野生动物种群趋势监测中的有效性。尽管抽样计数无法准确估算种群实际丰度，但仅抽样目标区域的一半面积，即可可靠监测目标种群的变化趋势。当种群丰度发生剧烈变化时，仅需更低比例的抽样区域，即可准确识别种群趋势的走向。但当年际趋势变异程度较高时，所需的抽样数量会增加，甚至全域计数都可能无法有效检测种群趋势。其他参数（如抽样区域的选取位置与物种可检测性）的影响相对较小，但仍需针对具体案例开展逐一验证。因此，抽样计数可作为评估种群趋势的可行替代方案，为具有保护价值的野生动物监测工作带来重要且经济高效的提升空间。