Large-scale biodiversity databases have great potential for quantifying long-term trends of species, but they also bring many methodological challenges. Spatial bias of species occurrence records is well recognized. Yet, the dynamic nature of this spatial bias – how spatial bias has changed over time – has been largely overlooked. We examined the spatial bias of species occurrence records within multiple biodiversity databases in Germany and tested whether spatial bias in relation to land cover or land use (urban and protected areas) has changed over time. We focused our analyses on urban and protected areas as these represent two well-known correlates of sampling bias in biodiversity datasets. We found that the proportion of annual records from urban areas has increased over time while the proportion of annual records within protected areas has not consistently changed. Using simulations, we examined the implications of this changing sampling bias for estimation of long-term trends of species' distributions. When assessing biodiversity change, our findings suggest that the effects of spatial bias depend on how it affects sampling of the underlying land-use change drivers affecting species. Oversampling of regions undergoing the greatest degree of change, for instance near human settlements, might lead to overestimation of the trends of specialist species. For robust estimation of the long-term trends in species' distributions, analyses using species occurrence records may need to consider not only spatial bias, but also changes in the spatial bias through time.

中文翻译：

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物种发生记录空间偏差的时间趋势

大型生物多样性数据库在量化物种长期趋势方面具有巨大潜力，但它们也带来了许多方法学挑战。物种出现记录的空间偏差是公认的。然而，这种空间偏差的动态性质——空间偏差如何随时间变化——在很大程度上被忽视了。我们检查了德国多个生物多样性数据库中物种出现记录的空间偏差，并测试了与土地覆盖或土地利用（城市和保护区）相关的空间偏差是否随时间而变化。我们将分析重点放在城市和保护区，因为它们代表了生物多样性数据集中采样偏差的两个众所周知的相关性。我们发现，城市地区的年度记录比例随着时间的推移而增加，而保护区内的年度记录比例并没有持续变化。通过模拟，我们研究了这种不断变化的抽样偏差对估计物种分布长期趋势的影响。在评估生物多样性变化时，我们的研究结果表明，空间偏差的影响取决于它如何影响对影响物种的潜在土地利用变化驱动因素的抽样。对变化最大的地区进行过度采样，例如人类住区附近，可能会导致高估专业物种的趋势。为了对物种分布的长期趋势进行稳健估计，使用物种出现记录的分析可能不仅需要考虑空间偏差，