Given the prevalence of invasive species and high rates of habitat homogenisation across the globe, understanding how these drivers interact to influence native species assemblages is crucial. In river networks, confluences create discontinuities in physical conditions, likely creating hotspots of heterogeneity that influence interactions between native and invasive fish. We examined how spatial configuration of confluences affected the outcome of interactions between native galaxiids and non-native salmonids in New Zealand alpine rivers. Electrofishing in mainstem and tributary branches of twelve replicate confluences revealed highly context-dependent distributions, contingent upon interactions between: (a) the combination of flood disturbance history in confluence branches; (b) distance to the confluence; and (c) the direction of flow, either upstream or downstream, of the confluence. Shifts in native–invasive species relative abundance were determined by the preference of large predatory salmonids for more hydrologically stable conditions, which subsequently limited the abundance of young-of-year galaxiids, and meant galaxiids were more abundant in flood-prone conditions. Distance-from-confluence effects were stronger upstream than downstream, suggesting that flow direction had an important influence on dispersal. Tributary flow regimes also predictably influenced downstream physical conditions, thereby affecting predatory salmonid distribution which likely controlled galaxiid distributions. Overall, our results reveal strong spatial context-dependency in fish assemblages in river networks, and demonstrate how flow regime influences are spatially transferred at confluences, thereby creating areas of influential riverscape heterogeneity. Understanding the influence of such heterogeneity enables ecologically significant locations to be identified, particularly for management of native species vulnerable to invaders.

考虑到全球范围内入侵物种的普遍存在和高水平的栖息地同质化，了解这些驱动因素如何相互作用以影响本土物种组合至关重要。在河流网络中，汇流会在物理条件下产生不连续性，可能会产生异质性热点，从而影响本地鱼类和入侵鱼类之间的相互作用。我们研究了汇合的空间构型如何影响新西兰高山河流域中的天然加拉西虫和非天然鲑鱼之间相互作用的结果。在十二个重复汇合的干支流和支流支流中进行电钓，显示出高度依赖于上下文的分布，取决于以下之间的相互作用：（a）汇流支流中洪水干扰历史的结合；（b）到汇合处的距离；（c）流动方向，汇合处的上游或下游。本地入侵物种相对丰度的变化取决于较大的掠食性鲑鱼对水文稳定条件的偏好，这随后限制了年幼的Galaxid的数量，这意味着在洪水易发的条件下Galaxid的含量更高。汇合距离的影响在上游要强于下游，这说明流动方向对扩散有重要影响。支流状态也可预测地影响下游的物理条件，从而影响掠夺性鲑鱼的分布，这很可能控制了Galaxid的分布。总体而言，我们的研究结果揭示了河网中鱼群的强烈的空间背景依赖性，并展示了汇流区的水流影响如何在空间上转移，从而创造出具有影响力的河景异质性区域。了解这种异质性的影响可以确定具有生态学意义的位置，特别是对于易于受到入侵者入侵的本地物种的管理。