| Habitat suitability influences the distribution and abundance of natural populations. Although suitable habitat is composed of a core collection of features, food availability is among the most critical. For central place foraging animals, food and space are interconnected as individuals must maintain access to sufficient space to capture food. One group of animals proposed to experience co-occurring food and space limitation are drift-feeding fishes such as stream salmonids. While food and space are thought to limit productivity in salmonid populations, questions remain regarding the interconnection between physical habitat structure and the energetic quality of habitat, how prey availability influence foraging rates, and the range and extent of prey availability in lotic ecosystems. The aim of my dissertation research was to address these topics. I conducted three research projects to investigate the connection between food and space for stream salmonids. In my first study, I conducted a field experiment to evaluate how increasing space through the addition of pool habitat, influences habitat quality, population abundance, and growth of cutthroat trout. I found that pool additions increased the availability of energetically favorable habitat, juvenile fish abundance, and cutthroat trout growth. My second project was an observational study where I examined how physical features at foraging stations were related to body size and how food availability influenced foraging rates in cutthroat trout. I found that habitat conditions associated with higher prey encounter rates were positively correlated with body size, and that cutthroat trout increased their foraging rates with higher prey availability but foraging rates plateaued at high prey densities. In the third study, I conducted a literature review to determine the range and extent of prey availability and foraging rates in drift-feeding fishes and examined if climatic factors influenced drift abundance. Here, food abundance and foraging rates tended to be low and drift density was best predicted by latitude, elevation, and precipitation. Overall, my results indicate that density and biomass of stream-salmonid populations are often restricted through co-occurring food and space limitation. |