Studies of stream macroinvertebrates traditionally use sampling methods that target benthic habitats. These methods could underestimate biodiversity if important assemblage components exist outside of the benthic zone. To test the efficacy of different sampling methods, we collected paired reach-wide benthic and edge samples from up to 10 study reaches in nine basins spanning an aridity gradient across the United States. Edge sampling targeted riparian-adjacent microhabitats not typically sampled, including submerged vegetation, roots, and overhanging banks. We compared observed richness, asymptotic richness, and assemblage dissimilarity between benthic samples alone and different combinations of benthic and edge samples to determine the magnitude of increased diversity and assemblage dissimilarity values with the addition of edge sampling. We also examined how differences in richness and assemblage composition varied across an aridity gradient. The addition of edge sampling significantly increased observed richness (median increase = 29%) and asymptotic richness (median increase = 173%). Similarly, median Bray–Curtis dissimilarity values increased by as much as 0.178 when benthic and edge samples were combined. Differences in richness metrics were generally higher in arid basins, but assemblage dissimilarity either increased or decreased across the aridity gradient depending on how benthic and edge samples were combined. Our results suggest that studies that do not sample stream edges may significantly underestimate reach diversity and misrepresent assemblage compositions, with effects that can vary across climates. We urge researchers to carefully consider sampling methods in field studies spanning climatic zones and the comparability of existing data sets when conducting data synthesis studies.

中文翻译：

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与沿干旱梯度单独进行底栖采样相比，结合底栖和河流边缘采样可以更好地代表大型无脊椎动物组合

对河流大型无脊椎动物的研究传统上使用针对底栖栖息地的采样方法。如果重要的组合成分存在于底栖区之外，这些方法可能会低估生物多样性。为了测试不同采样方法的有效性，我们从跨越美国干旱梯度的 9 个盆地的多达 10 个研究河段采集了配对的河段底栖和边缘样本。边缘采样针对的是通常不采样的邻近河岸的微生境，包括水下植被、树根和悬垂的河岸。我们比较了单独的底栖样本以及底栖样本和边缘样本的不同组合之间观察到的丰富度、渐近丰富度和组合相异性，以确定添加边缘采样后多样性和组合相异性值增加的幅度。我们还研究了丰富度和组合组成的差异如何随着干旱梯度的变化而变化。添加边缘采样显着增加了观察到的丰富度（中值增加 = 29%）和渐近丰富度（中值增加 = 173%）。同样，当海底样本和边缘样本合并时，Bray-Curtis 差异值中位数增加了 0.178。在干旱盆地中，丰富度指标的差异通常较高，但在干旱梯度上，组合差异会增加或减少，具体取决于底栖和边缘样本的组合方式。我们的结果表明，不对河流边缘进行采样的研究可能会严重低估河段多样性并歪曲组合成分，其影响可能因气候而异。我们敦促研究人员在进行数据综合研究时仔细考虑跨气候带实地研究的采样方法以及现有数据集的可比性。