Fish populations at the fringe of their geographic range often inhabit marginal habitats and are vulnerable to ecological disturbances, such as species invasion, land cover conversion, and climate change. The Driftless Area of northeastern Iowa, USA represents the southwestern edge of the native range of Brook Trout Salvelinus fontinalis, where endemic populations have been greatly reduced due to habitat degradation and introduced Brown Trout Salmo trutta. Therefore, documenting Brook Trout occurrence patterns at the southern tip of their range may prove useful for the conservation of peripheral populations. We fitted single-species occupancy models at multiple spatial scales to estimate the relative effects of biotic (e.g., Brown Trout density) and habitat (instream, riparian, and watershed) variables on Brook and Brown Trout occupancy to predict their current distribution in the Iowa Driftless Area. Species occurrence and physical habitat data were collected at 138 stream segments of the Upper Iowa, Yellow, and Little Maquoketa River watersheds (8-digit hydrologic unit codes) during May–September in 2018 and 2019. Brook Trout occupancy was low (19 of 138 sites) and affected by local (instream and riparian) habitat covariates, particularly August–September stream temperatures, but no adverse effects of Brown Trout density were detected. Brown Trout occupied 54% of streams (74 of 138 sites), and occupancy was influenced by a combination of local-scale (mean stream velocity, percentage of run macrohabitat, and August–September stream temperatures) and catchment-scale (percent forested land cover and upstream catchment area) habitat variables. Our results provide evidence that instream thermal conditions are a critical determinant of Brook Trout distribution, while Brown Trout exhibit plasticity in habitat suitability and increased colonization in areas where they are introduced. Given the dependence of Brook Trout on cold stream temperatures, the projected loss of thermally suitable habitats due to climate change may facilitate their replacement by naturalized Brown Trout at the southwestern extent of their range.

中文翻译：

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爱荷华州无漂移地区的本地鳟鱼和棕鳟的发现和分布的相关因素

处于其地理范围边缘的鱼类种群通常居住在边缘生境中，并且容易受到生态干扰，例如物种入侵，土地覆盖转换和气候变化。东北爱荷华Driftless地区，USA表示布鲁克鳟鱼的天然范围的西南边缘溪红点鲑，其中特有种群已由于大大减少了对栖息地退化和引入鳟褐鳟。因此，在其范围的最南端记录布鲁克鳟鱼的发生模式可能对保护外围种群很有帮助。我们在多个空间尺度上拟合了单物种占用模型，以估计生物（例如，鳟鱼密度）和栖息地（河内，河岸和流域）变量对布鲁克和褐鳟种群的相对影响，以预测它们在爱荷华州的当前分布无漂移区。在2018年5月至9月的爱荷华州上，爱荷华州和黄河和小马奎克塔河流域138个河流流域（8位水文单位代码）收集了物种发生和物理栖息地数据。布鲁克鳟鱼的占用率较低（138个中的19个）地点），并受当地（河流和河岸）栖息地协变量的影响，尤其是8月至9月的溪流温度，但未检测到褐鳟密度的不利影响。褐鳟鱼占据了54％的溪流（138个站点中的74个），其占用受到局部尺度（平均溪流速度，运行的大型栖息地的百分比以及8月至9月的溪流温度）和流域尺度（林地百分比）的共同影响覆盖和上游集水区）生境变量。我们的结果提供了证据，表明内流热条件是布鲁克鳟鱼分布的关键决定因素，而褐鳟在栖息地适应性上表现出可塑性，并在引入它们的地区增加了定居。考虑到布鲁克鳟鱼对寒冷溪流温度的依赖，预计气候变化导致的热适宜生境的丧失可能会促进其在西南范围内被天然鳟鱼替代。