1. Vertebrate communities in headwater streams are assumed to be regulated through competitive and predatory interactions. Although documented predation is rare, studies regularly report competitive dominance by fish that, as larger competitors reliant on aquatic habitat, exclude semi‐aquatic salamanders to marginal stream habitat. However, it is unclear whether fish interact with stream‐breeding salamanders through indirect effects such as competition for resources (e.g. food or cover) or fear (i.e. threat of predation) nor is it known whether these interactions are consistent through time.
2. This study used a novel caging approach to determine if competitive outcomes between a headwater fish and salamanders were regulated primarily through resource depletion (exploitative competition) or behavioural avoidance (interference competition).
3. We paired banded sculpin (Cottus carolinae) and larval red salamanders (Pseudotriton ruber) of similar body size in independent flow through mesocosms with intra‐ and inter‐specific pairs allowed to interact physically or non‐physically. The experiment was repeated in the autumn and in the spring when stream salamander larvae begin to transform into terrestrial juveniles.
4. Banded sculpin negatively influenced growth of red salamanders regardless of whether they were allowed to physically interact, suggesting interference competition and behavioural avoidance. This asymmetrical effect was strongest in the spring when salamanders underwent metamorphosis at higher rates in the presence of fish. However, in the autumn, the effects were more balanced between the two species with salamanders impacting fish through exploitative competition.
5. By studying the temporal relationships between two competitors and using a caging method novel to competition studies, we established that the outcomes of competition are dependent on season and may vary in type relative to the timing of life‐history events. For this community, these results suggest that outcomes of competition are highly dependent on season and could indicate a biotic mechanism maintaining headwater salamander distributions through source–sink dynamics. Our results also suggest that, in this species interaction, it may be unwarranted to assume that the outcomes of competition at one time represent the complex relationships regulating community interactions.

中文翻译：

---

上游源流捕食者之间干扰竞争强度的季节性变化

1. 假定上游水域中的脊椎动物群落是通过竞争性和掠夺性相互作用进行调控的。尽管有记录的捕食是罕见的，但研究定期报告鱼类的竞争优势，因为较大的竞争者依赖水生生境，因此将半水生am排除在边际河生境中。但是，尚不清楚鱼类是否通过诸如争夺资源（例如食物或掩盖物）或恐惧（即掠食的威胁）等间接影响与stream繁殖的interact相互作用，也不清楚这些相互作用在时间上是否一致。
2. 这项研究使用一种新颖的笼养方法来确定源头鱼类和sal之间的竞争结果是否主要通过资源消耗（剥削性竞争）或行为避免（干扰竞争）来调节。
3. 我们将体型相似的带状（Cottus carolinae）和幼虫红sal（Pseudotriton ruber）配对成独立流经中膜，并通过种内和种间对进行物理或非物理相互作用。当stream流幼虫开始转化为陆生幼体时，在秋季和春季重复了该实验。
4. 无论是否允许其进行身体互动，带状子都会对红色sal的生长产生负面影响，这表明干扰竞争和行为规避。当sal在有鱼的情况下以较高的发生率变态时，这种不对称作用在春季最强。然而，在秋天，这两种物种之间的影响更加平衡，sal通过剥削竞争影响了鱼类。
5. 通过研究两个竞争者之间的时间关系，并使用竞争研究中的新颖方法，我们确定了竞争的结果取决于季节，并且相对于生活史事件的时间可能会有所不同。对于这个社区，这些结果表明竞争的结果高度依赖季节，并可能表明通过源-汇动态来维持源头sal分布的生物机制。我们的结果还表明，在这种物种相互作用中，假设竞争结果一次代表调节社区相互作用的复杂关系可能是不必要的。