1. Determining the factors driving population dynamics of stream salmonids across broad landscapes is important for understanding stream ecosystem functioning and for the management and conservation of the populations of such fish. A few studies have described the determinants of the early life history of salmonids across catchments, but none of them have examined how this spatial variation develops temporally.
2. We hypothesised that: (1) spatiotemporal dynamics of young‐of‐the‐year (YoY) trout populations vary within the catchment, with loss rates (emigration plus mortality) being higher in lower elevation, downstream reaches than in higher elevation, upstream ones; and (2) loss rate would be density dependent, leading to reduced intra‐ and inter‐cohort competition and supporting establishment of resident populations.
3. We tested the first hypothesis by examining relationships between geomorphic characteristics of spawning streams and temporal dynamics of YoY brown trout density, loss rate and biological traits through an austral summer across the catchment of New Zealand's fourth‐longest river, the Taieri River. To test the second hypothesis, we examined whether initial YoY density in spring and other biotic determinants affected loss rate and cohort structure dynamics, resulting in density‐dependent self‐thinning of YoY fish to avoid resource limitation.
4. Spring YoY density and subsequent loss rate was higher in low elevation sites, corresponding to stream accessibility to migratory spawners. These significant correlations of YoY density and related biotic variables with elevation disappeared later in the season, indicating that regardless of their origin, brown trout YoY tend to form stream resident populations with multicohort structure and densities low enough to limit intraspecific competition.
5. Our findings provide evidence that geomorphological features of the landscape affect temporal dynamics of YoY trout populations driven by density‐dependent self‐regulatory mechanisms that can control the abundance of growing fish.

中文翻译：

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地貌特征驱动新西兰大流域年幼褐鳟鳟的时空动态

1. 确定驱动跨大溪流鲑鱼种群动态的因素对于理解河流生态系统功能以及管理和养护这类鱼类至关重要。一些研究描述了跨流域鲑鱼早期生活史的决定因素，但没有一个研究过这种空间变化如何随时间变化。
2. 我们假设：（1）流域内年幼鳟鱼种群的时空动态变化，流失率（移徙加死亡率）在低海拔地区，下游河段高于高海拔地区，上游河段。 ; （2）损失率将取决于密度，从而导致内部和内部同类竞争减少，并支持居民的建立。
3. 我们通过检查产卵流的地貌特征与南极鳟鳟鱼密度，流失率和整个夏天的季节性特征之间的关系来检验第一个假说，该季节贯穿了新西兰第四长河泰耶里河的汇水区。为了检验第二个假设，我们检查了春季的初始YoY密度和其他生物决定因素是否会影响损失率和队列结构动态，从而导致YoY鱼的密度依赖性自我稀疏以避免资源限制。
4. 在低海拔地区，春季YoY密度和随后的损失率较高，这与stream游产卵场的河道可及性相对应。这些YoY密度和相关生物变量与海拔高度之间的显着相关性在本季节后期消失了，这表明鳟鱼YoY不论其起源如何，都倾向于形成具有多队列结构和低密度以限制种内竞争的常住种群。
5. 我们的发现提供了证据，表明景观的地貌特征会影响到鳟鱼种群的时间动态，这些种群是由密度依赖性自我调节机制驱动的，该机制可以控制鱼类的生长。