Tropical dry forests (TDFs) are one of the most threatened ecosystems worldwide. Two hypotheses have been proposed to explain the origin of TDFs in South America: the Amazonian TDF hypothesis and the Pleistocene Arc hypothesis (PAH). There is a need to evaluate the distribution patterns of different organisms across the TDF distribution. We tested the following hypotheses: the species composition is determined by historical-evolutionary events, and therefore, the TDFs have a similar species composition as predicted by the PAH. Alternatively, the species composition is determined by recent ecological processes, and therefore, the TDFs have a sharing of species to their respective adjacent dominant habitat, with no support for the PAH. We expect that climatic factors drive the species richness, abundance and species dissimilarity (β-diversity) between TDFs and adjacent habitats across the latitudinal gradient. We sampled dung beetles across six Brazilian states in TDF fragments and adjacent dominant habitats and obtained the climatic conditions across the gradient. We used the β-diversity partition and generalised linear models to test our hypotheses. We sampled 8,625 dung beetles representing 102 species. Sorensen dissimilarity was higher among TDFs than between TDFs and adjacent habitats and was mostly due to the substitution of species. Annual mean temperature had a positive effect on abundance in TDFs but did not affect species richness. Species substitution (Podani’s approach) between TDFs and adjacent habitats decreased with mean diurnal range of temperature, while nestedness patterns (Baselga’s approach) increased with annual precipitation. Depending on the approach used (Baselga’s vs. Podani’s), we can obtain different results across the latitudinal gradient. The composition and structure of dung beetle assemblages in TDFs are mostly determined by more recent regional-to-local ecological processes since each TDF has a unique evolutionary history and a different dung beetle species composition. Our results do not support the Pleistocene Arc hypothesis.

中文翻译：

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巴西热带干旱森林中的蜣螂β多样性不支持更新世弧假说

热带干旱森林 (TDF) 是全球受威胁最严重的生态系统之一。已经提出了两个假说来解释南美洲 TDF 的起源：亚马逊 TDF 假说和更新世弧假说 (PAH)。有必要评估 TDF 分布中不同生物的分布模式。我们测试了以下假设：物种组成由历史进化事件决定，因此，TDF 具有与 PAH 预测的相似的物种组成。或者，物种组成是由最近的生态过程决定的，因此，TDF 与其各自相邻的主要栖息地共享物种，而不支持 PAH。我们预计气候因素会推动物种丰富度，跨纬度梯度的 TDF 和相邻栖息地之间的丰度和物种差异（β-多样性）。我们在巴西六个州的 TDF 碎片和邻近的主要栖息地对粪甲虫进行了采样，并获得了整个梯度的气候条件。我们使用β-多样性分区和广义线性模型来检验我们的假设。我们采样了代表 102 个物种的 8,625 只粪甲虫。TDF 之间的 Sorensen 差异高于 TDF 和相邻生境之间的差异，主要是由于物种的替代。年平均温度对 TDF 的丰度有积极影响，但不影响物种丰富度。TDFs 和相邻栖息地之间的物种替代（Podani 方法）随着平均昼夜温度范围而减少，而嵌套模式（巴塞尔加的方法）随着年降水量的增加而增加。根据使用的方法（Baselga's vs. Podani's），我们可以在纬度梯度上获得不同的结果。TDF 中蜣螂组合的组成和结构主要由最近的区域到地方的生态过程决定，因为每个 TDF 都有独特的进化历史和不同的蜣螂物种组成。我们的结果不支持更新世弧假说。TDF 中蜣螂组合的组成和结构主要由最近的区域到地方的生态过程决定，因为每个 TDF 都有独特的进化历史和不同的蜣螂物种组成。我们的结果不支持更新世弧假说。TDF 中蜣螂组合的组成和结构主要由最近的区域到地方的生态过程决定，因为每个 TDF 都有独特的进化历史和不同的蜣螂物种组成。我们的结果不支持更新世弧假说。