The effect of habitat structure on trophic level transfer efficiency and adaptive tradeoffs by juvenile salmonids

自然生境结构是影响基础系统生产力和能量向更高营养水平转移的关键生态系统属性。在河流和小溪中尤其如此，在那里，不同种类的幼鲑鱼似乎已经进化出了不同的适应自然栖息地极端的环境梯度，这些梯度与河流的坡度、流速和基质大小有关。尽管对鲑鱼幼鱼的栖息地关系进行了广泛的研究，但栖息地结构限制漂食性鱼类适应和生产的机制仍然知之甚少。目前常用的流量和生境对溪流生产能力的影响评估模型是基于相关的生境适宜性曲线关系，其预测能力有限，需要一种更机械的方法来模拟溪流中的鱼类生产。我们提出了一系列实验，以严格评估物理栖息地对i)漂食鱼类的适应性约束，ii)沿着纵向下游梯度向鱼类营养水平的能量转移效率，以及iii)栖息地结构通过增加无脊椎动物猎物的产量对鱼类产量的自下而上影响。将在天然和人工河道进行研究，并可评估不同生境结构影响漂食鱼类生产的基本机制。这些实验的数据将用于开发和参数化一个通用的生物能量模型，该模型将在河流渔业生态学中广泛应用，作为一种新的研究/管理工具，用于预测栖息地、温度、流量和猎物丰度变化对幼年鲑鱼生产能力的影响。总的来说，这些信息将用于在面对人类发展的情况下为河流生境管理和保护活动提供信息，并指导和优化退化河流的恢复。

Physical habitat structure is a key ecosystem attribute that influences both basal system productivity and the transfer of energy to higher trophic levels. This is especially true in rivers and streams, where different species of juvenile salmon appear to have evolved divergent adaptations to physical habitat extremes along environmental gradients related to stream slope, velocity, and substrate size. Despite extensive research on juvenile salmon habitat relationships, the mechanisms whereby habitat structure constrains adaptations and production of drift-feeding fish remain poorly understood. Most commonly used models for assessing the effects of flow and habitat on productive capacity in streams are based on correlative Habitat Suitability Curve relationships, which are limited in their predictive ability, and there is a need for a more mechanistic approach to modeling fish production in streams. We propose a series of experiments that will rigorously evaluate the effects of physical habitat on i) adaptive constraints for drift-feeding fish, ii) transfer efficiency of energy to the fish trophic level along a longitudinal downstream gradient, and iii) bottom-up effects of habitat structure on fish production mediated through increased production of invertebrate prey. Research will be carried out in both natural and artificial stream channels, and will permit assessment of the underlying mechanisms whereby different habitat configurations affect production of drift-feeding fish. Data from these experiments will be used to develop and parameterize a general bioenergetic model that will have broad application in stream fisheries ecology as a novel research/management tool for predicting the effects of changes in habitat, temperature, flows, and prey abundance on juvenile salmon productive capacity. Collectively, this information will be used to inform stream habitat management and conservation activities in the face of human development, and to guide and optimize restoration of degraded streams.