Data from: Who escapes detection? Quantifying the causes and consequences of sampling biases in a long-term field study

Inferences drawn from long-term field studies are vulnerable to biases in observability of different classes of individuals, which may lead to biases in the estimates of selection, or fitness. Population surveys that monitor breeding individuals can introduce such biases by not identifying individuals that fail early in their reproductive attempts. Here, we quantify how the standard protocol for detecting breeding females introduces bias in a long-term population study of the great tit, Parus major. We do so by identifying females whose breeding attempts fail before they would normally be censused, and explore whether this early failure can be predicted by a number of intrinsic and extrinsic factors. We investigate the effect of these biases on estimates of reproductive performance and selection. We show that females that go undetected by standard censusing because they fail early in their breeding attempt were less likely to have been previously trapped within our study site and were more likely to breed in poor quality habitats. Furthermore we demonstrate that this bias sampling had lead previous studies on this population to overestimate the reproductive performance of unringed females, which are likely to be immigrants to the population. Finally, we show that these biases in detectability influence estimates of selection on a key life history trait. While these conclusions are specific to this study, we suggest that such effects are likely to be widespread, and that more attention should be given to whether or not methods for surveying natural populations introduce systematic bias that will influence conclusions about ecological and evolutionary processes.

长期野外研究得出的推论极易受到不同类群个体可观测性偏差的影响，此类偏差可能引发自然选择（selection）或适合度（fitness）的估算偏倚。监测繁殖个体的种群调查若未识别出繁殖尝试早期失败的个体，便会引入此类偏倚。本研究以大山雀（Parus major）的长期种群研究为对象，量化了检测繁殖雌性的标准规程如何引入偏倚。我们通过识别常规普查前便已出现繁殖失败的雌性个体完成量化分析，并探究此类早期繁殖失败能否通过多种内在与外在因素进行预测。本研究还分析了此类偏倚对繁殖性能与自然选择估算结果的影响。研究结果显示，因繁殖尝试早期失败而未被常规普查检测到的雌性个体，此前被捕获于研究样地内的概率更低，且更倾向于在低质量生境中繁殖。此外，本研究证实，这种有偏的采样方式使得此前针对该种群的研究高估了未佩戴脚环雌性的繁殖性能——这类个体大概率为种群的迁入者。最后，本研究表明，此类可观测性偏倚会影响关键生活史性状上的自然选择估算结果。尽管本研究的结论仅适用于该研究对象，但我们认为此类偏倚效应可能广泛存在，且学界应更多关注自然种群调查方法是否会引入系统性偏倚，进而影响关于生态与演化过程的研究结论。