Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR, USA.
Columbia River Inter-Tribal Fish Commission, Portland, OR, USA.
J Anim Ecol. 2021 Jul;90(7):1727-1741. doi: 10.1111/1365-2656.13491. Epub 2021 Apr 21.
Changes in biophysical conditions through time generate spatial and temporal variability in habitat quality across landscapes. For river ecosystems, researchers are increasingly able to characterize spatial and temporal patterns in habitat conditions, referred to as shifting habitat mosaics, yet rarely demonstrate how this translates into corresponding biological processes such as organism growth and production. We assessed spatial patterns and processes determining seasonal changes in juvenile Chinook Salmon Oncorhynchus tshawytscha size, growth and production over 30-40 km in two NE Oregon subbasins. We quantified seasonal patterns of growth by combining estimated emergence dates and body size distributions in July and September. We then used analysis of bioenergetics, empirical fish diets and spatial models incorporating temperature, habitat and population density to evaluate mechanisms driving spatiotemporal patterns of growth. Lastly, we quantified seasonal contributions to individual fish growth and to total production as a function of position within the stream network. Spatial heterogeneity in incubation temperatures corresponded to later estimated emergence timing with distance upstream in both subbasins. During spring, estimated growth rates decreased with distance upstream, and coupled with emergence patterns, resulted in pronounced longitudinal gradients in body size by July. During summer, spatial patterns of growth reversed, with greater diet ration sizes and growth efficiencies upstream than downstream. These opposing spatiotemporal patterns of emergence timing and seasonal growth rates produced longitudinal gradients in the proportion of fish growth achieved in spring versus summer, with up to 80% of an individual's growth occurring in spring at downstream sites but as low as 10% at upstream sites. Coupling longitudinal patterns of fish density and growth revealed that in one subbasin the majority (65%) of total production occurred in spring, while in the other, in which fish were concentrated in headwaters, the majority (60%) of production occurred in summer. While recent work has emphasized inter-annual shifts in fish production across large spatial scales, this study demonstrates that longitudinal gradients of fish growth and production can reverse across seasons, and reveals important contributions of warmer, downstream habitats to overall production that occurred during cooler times of the year.
随着时间的推移，生物物理条件的变化会导致景观中栖息地质量的空间和时间变化。对于河流生态系统，研究人员越来越能够描述栖息地条件的时空模式，这些模式被称为不断变化的栖息地镶嵌体，但很少有研究表明这如何转化为相应的生物过程，如生物生长和繁殖。我们评估了决定 30-40 公里范围内两个俄勒冈东北部子流域幼年奇努克鲑鱼 Oncorhynchus tshawytscha 大小、生长和繁殖季节性变化的空间模式和过程。我们通过结合 7 月和 9 月的估计出现日期和体型分布来量化生长的季节性模式。然后，我们使用生物能量学分析、经验鱼类饮食和包含温度、栖息地和种群密度的空间模型来评估驱动生长时空模式的机制。最后，我们量化了个体鱼生长和总繁殖作为溪流网络中位置函数的季节性贡献。两个子流域中孵化温度的空间异质性与上游距离对应的估计出现时间有关。在春季，估计的生长速度随上游距离的增加而降低，与出现模式相结合，导致 7 月时体型出现明显的纵向梯度。在夏季，生长的空间模式发生逆转，上游的饮食比例和生长效率高于下游。这种出现时间和季节性生长率的时空模式的相反变化导致了春季与夏季个体生长比例的纵向梯度，在下游地点，个体生长的 80%可能发生在春季，但在上游地点，最低可达 10%。将鱼类密度和生长的纵向模式结合起来表明，在一个子流域中，大部分（65%）的总繁殖发生在春季，而在另一个子流域中，鱼类集中在源头，大部分（60%）的繁殖发生在夏季。虽然最近的研究强调了跨年度鱼类繁殖在大空间尺度上的变化，但本研究表明，鱼类生长和繁殖的纵向梯度可以在季节之间逆转，并揭示了温暖下游栖息地对全年凉爽时期总体繁殖的重要贡献。
