Both decreases in compositional similarity with increasing geographic distances between sites (i.e. distance–decay relationship) and vertical stratification of species composition are key issues in ecology. However, the intersection between these two trends has scarcely been investigated. Here we use identical sampling methods in the canopy and at ground level in a tropical rainforest remnant on the coast of the Gulf of Mexico to evaluate, for the first time, a distance–decay relationship within vertical strata in insect assemblages. We found that the ant assemblage was vertically stratified; ant species richness was higher at ground level than in the canopy, and the species composition differed between the two vertical strata. Moreover, we observed that β-diversity increased with geographic distance at ground level, but not in the canopy strata. However, contrary to our prediction, there was less species turnover (lower β-diversity) between vertical strata than between trees. These findings may reflect differences in the dispersal capacity and nest habit of ants from each vertical stratum, and also habitat heterogeneity on the horizontal scale, e.g. the species of sampled trees. Our results illustrate the importance of sampling more than one vertical stratum to understand the spatial distribution patterns of biological diversity in tropical rainforests.

中文翻译：

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热带雨林中树冠和地面蚂蚁组合之间的距离衰减模式不同

随着站点之间地理距离的增加（即距离衰减关系）和物种组成的垂直分层，组成相似性的降低都是生态学中的关键问题。然而，这两种趋势之间的交叉点几乎没有被研究过。在这里，我们在墨西哥湾沿岸的热带雨林遗迹的树冠和地面上使用相同的采样方法，首次评估昆虫组合中垂直层内的距离衰减关系。我们发现蚂蚁组合是垂直分层的；地面的蚂蚁物种丰富度高于冠层，两个垂直地层的物种组成不同。此外，我们观察到β-多样性在地平面上随着地理距离的增加而增加，但在冠层中却没有。然而，与我们的预测相反，垂直地层之间的物种更替（较低的 β 多样性）比树木之间的要少。这些发现可能反映了每个垂直层的蚂蚁的传播能力和筑巢习惯的差异，以及水平尺度上的栖息地异质性，例如采样树木的种类。我们的结果说明了采样多个垂直层以了解热带雨林生物多样性的空间分布模式的重要性。