Department of Watershed Sciences and the Ecology Center, Utah State University, Logan, Utah, USA.
Native Fish Ecology and Conservation Program, Division of Science and Resource Management, Grand Canyon National Park, National Park Service, Flagstaff, Arizona, USA.
Ecol Appl. 2022 Sep;32(6):e2635. doi: 10.1002/eap.2635. Epub 2022 Jun 13.
Understanding the relative strengths of intrinsic and extrinsic factors regulating populations is a long-standing focus of ecology and critical to advancing conservation programs for imperiled species. Conservation could benefit from an increased understanding of factors influencing vital rates (somatic growth, recruitment, survival) in small, translocated populations, which is lacking owing to difficulties in long-term monitoring of rare species. Translocations, here defined as the transfer of wild-captured individuals from source populations to new habitats, are widely used for species conservation, but outcomes are often minimally monitored, and translocations that are monitored often fail. To improve our understanding of how translocated populations respond to environmental variation, we developed and tested hypotheses related to intrinsic (density dependent) and extrinsic (introduced rainbow trout Oncorhynchus mykiss, stream flow and temperature regime) causes of vital rate variation in endangered humpback chub (Gila cypha) populations translocated to Colorado River tributaries in the Grand Canyon (GC), USA. Using biannual recapture data from translocated populations over 10 years, we tested hypotheses related to seasonal somatic growth, and recruitment and population growth rates with linear mixed-effects models and temporal symmetry mark-recapture models. We combined data from recaptures and resights of dispersed fish (both physical captures and continuously recorded antenna detections) from throughout GC to test survival hypotheses, while accounting for site fidelity, using joint live-recapture/live-resight models. While recruitment only occurred in one site, which also drove population growth (relative to survival), evidence supported hypotheses related to density dependence in growth, survival, and recruitment, and somatic growth and recruitment were further limited by introduced trout. Mixed-effects models explained between 67% and 86% of the variation in somatic growth, which showed increased growth rates with greater flood-pulse frequency during monsoon season. Monthly survival was 0.56-0.99 and 0.80-0.99 in the two populations, with lower survival during periods of higher intraspecific abundance and low flood frequency. Our results suggest translocations can contribute toward the recovery of large-river fishes, but continued suppression of invasive fishes to enhance recruitment may be required to ensure population resilience. Furthermore, we demonstrate the importance of flooding to population demographics in food-depauperate, dynamic, invaded systems.
了解调节种群的内在和外在因素的相对强度是生态学的长期关注点，对于推进濒危物种的保护计划至关重要。由于难以对稀有物种进行长期监测，因此对于影响小种群（躯体生长、补充、存活）关键生活史特征的因素的了解相对较少，这对保护工作不利。这里将从源种群转移到新栖息地的野生捕获个体的转移定义为转移，广泛用于物种保护，但结果往往很少受到监测，而且受到监测的转移通常也会失败。为了提高我们对迁移种群如何响应环境变化的理解，我们提出并测试了与内在（密度依赖）和外在（引入虹鳟鱼 Oncorhynchus mykiss、溪流流量和温度模式）因素相关的假说，这些因素导致濒危驼背大麻哈鱼（Gila cypha）种群的关键生活史特征发生变化，这些种群被转移到美国大峡谷（GC）的科罗拉多河支流。使用 10 年来从迁移种群中获得的两年一次的重捕数据，我们使用线性混合效应模型和时间对称标记重捕模型测试了与季节性躯体生长、补充和种群增长率相关的假说。我们结合了来自整个 GC 的分散鱼类（包括物理捕获和连续记录的天线检测）的重捕和再发现数据来测试生存假说，同时使用联合活捕获/活再发现模型来解释对地点的忠诚度。虽然仅在一个地点发生了补充，这也推动了种群的增长（相对于生存而言），但有证据支持与生长、生存和补充的密度依赖性相关的假说，并且引入的鳟鱼进一步限制了躯体生长和补充。混合效应模型解释了躯体生长的 67%至 86%的变异，在季风季节洪峰频率更高时，生长速度更快。两个种群的每月生存率为 0.56-0.99 和 0.80-0.99，在同种个体丰度较高和洪水频率较低的时期生存率较低。我们的研究结果表明，迁移可以促进大河鱼类的恢复，但为了确保种群的恢复力，可能需要继续抑制入侵鱼类以提高补充量。此外，我们证明了洪水对食物匮乏、动态、入侵系统中种群动态的重要性。
