ABSTRACT

The classic Wallace’s riverine barrier hypothesis (RBH) has been widely invoked to explain species distribution and evolutionary divergence throughout Amazonia. Dispersal and gene flow limited by the inability to cross a river restricts geographic distribution to an interfluvial zone, which causes different assemblage compositions between opposite river banks. In this study, we sampled frogs and Squamata reptiles along the Jari River, a tributary of the lower Amazon River, to test the RBH at assemblage level. We used non-metric multidimensional scaling based on species abundance to compare assemblage composition between river banks. We found that 63.6% of the frogs sampled are absent or occur in low abundances on one of the river banks, which resulted in distinct assemblages between banks. This finding supported the barrier-effect as a predictor of the regional frog diversity, which is remarkable, since the Jari River is considerably narrower than all the Amazonian rivers for which RHB has been supported. However, although some reptile species were restricted to one of the river banks, assemblage composition did not differ between banks. This finding suggests that the barrier-effect should not be extrapolated to other groups of organisms, since good dispersers can homogenize assemblages between river banks.

摘要

经典的华莱士河流屏障假说 (RBH) 已被广泛用于解释整个亚马逊流域的物种分布和进化差异。由于无法穿越河流而限制的扩散和基因流动将地理分布限制在河流间带，这导致相对河岸之间的组合组成不同。在这项研究中，我们在亚马孙河下游支流贾里河沿岸对青蛙和有鳞爬行动物进行了采样，以在组合水平上测试 RBH。我们使用基于物种丰度的非度量多维尺度来比较河岸之间的组合组成。我们发现 63.6% 的抽样青蛙在其中一条河岸上不存在或以低丰度出现，这导致两岸之间出现明显的组合。这一发现支持屏障效应作为区域青蛙多样性的预测因子，这是值得注意的，因为贾里河比支持 RHB 的所有亚马逊河流窄得多。然而，尽管一些爬行动物物种仅限于其中一个河岸，但河岸之间的组合组成没有差异。这一发现表明，不应将屏障效应外推到其他生物群，因为良好的分散器可以使河岸之间的组合均质化。