Lafferty Diana J R, Kumar Alexander V, Whitcher Sarah, Hackländer Klaus, Mills L Scott
Fisheries, Wildlife, and Conservation Biology Program, Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695, USA.
Wildlife Biology Program, University of Montana, Missoula, MT 59812, USA.
Conserv Physiol. 2017 Dec 8;5(1):cox068. doi: 10.1093/conphys/cox068. eCollection 2017.
Faecal glucocorticoid metabolite (FGM) concentrations are used increasingly as a non-invasive measure to index physiological stress experienced by diverse taxa. However, FGM may not be evenly distributed throughout a faecal mass or faecal pellet group. Moreover, within-sample variation in FGM measurements associated with different sampling and/or processing techniques is rarely reported despite potentially having important implications for inferring stress levels in free-ranging wildlife. Using a captive collection of snowshoe hares (), we (i) assessed repeatability of FGM measurements (i.e. precision) from two processing techniques (measurements derived from dividing whole pellet groups into equal proportions prior to processing [G1], measurements from subsamples derived from thoroughly homogenized whole pellet groups [G2]) and (ii) conducted a power analysis to estimate sample-size requirements for detecting statistically significant differences in FGM concentrations at a population level. Our results indicate that the mean percent coefficient of variation (%CV) for within-sample FGM variation was slightly higher for G1 (%CV = 35, range 13.45-65.37) than for G2 (%CV = 23, range 7.26-47.94), though not statistically significant (two sample -test, = 8, = 1.57, = 0.16). Thus, FGM is relatively evenly distributed within snowshoe hare faecal pellet groups. However, subsampling from homogenized whole pellet groups may be more appropriate when the sampling time frame is less controlled (e.g. multiple defecation events) because a subsample derived from a homogenized whole pellet group might be more representative of the animal's 'average' physiological state compared to FGM concentrations derived from a few haphazardly selected faecal pellets. Power analysis results demonstrated the importance of consideration of sample sizes. Relatively small effect sizes (e.g. <20%) may require sampling that is logistically and/or cost prohibitive. Yet for many situations of ecological or conservation interest, treatment effects may be substantial (>25%) and thus moderate sample sizes may be sufficient for testing research hypotheses regarding changes FGM concentrations.
粪便糖皮质激素代谢物（FGM）浓度越来越多地被用作一种非侵入性测量方法，以衡量不同分类群所经历的生理应激。然而，FGM可能不会在整个粪便团块或粪便颗粒组中均匀分布。此外，尽管与不同采样和/或处理技术相关的FGM测量中的样本内变异可能对推断自由放养野生动物的应激水平具有重要意义，但很少有报道。我们利用圈养的雪兔群体，（i）评估了两种处理技术（处理前将整个粪便颗粒组分成相等比例得出的测量值[G1]，来自完全均质化的整个粪便颗粒组的子样本的测量值[G2]）的FGM测量的重复性（即精密度），以及（ii）进行了功效分析，以估计在种群水平上检测FGM浓度的统计学显著差异所需的样本量。我们的结果表明，G1的样本内FGM变异的平均变异系数百分比（%CV）略高于G2（G1的%CV = 35，范围为13.45 - 65.37；G2的%CV = 23，范围为7.26 - 47.94），尽管差异无统计学意义（双样本t检验，df = 8，t = 1.57，p = 0.16）。因此，FGM在雪兔粪便颗粒组内相对均匀分布。然而，当采样时间框架控制较少时（例如多次排便事件），从均质化的整个粪便颗粒组中抽取子样本可能更合适，因为与从一些随机选择的粪便颗粒得出的FGM浓度相比，来自均质化的整个粪便颗粒组的子样本可能更能代表动物的“平均”生理状态。功效分析结果证明了考虑样本量的重要性。相对较小的效应量（例如<20%）可能需要在后勤和/或成本上令人望而却步的采样。然而，对于许多具有生态或保护意义的情况，处理效应可能很大（>25%），因此适度的样本量可能足以检验关于FGM浓度变化的研究假设。
