Fish resource use and habitat coupling in lake ecosystems

Thesis (Master's)--University of Washington, 2021Mobile consumers frequently acquire and use resources from differing habitats. This habitat coupling can influence ecosystem function, stability, and structure. Mobile consumers such as freshwater lacustrine fish are known to couple littoral-benthic, pelagic, and terrestrial ecosystems. Studies have shown that some freshwater fish are strong couplers, while others remain relative resource specialists with studies demonstrating the relative use of terrestrial, littoral-benthic, and pelagic resources varying widely. This research leans into this variability and seeks to identify abiotic and biotic factors that control resource use and habitat coupling. The overarching questions woven through this research are: 1) What are the spatial patterns in resource use and habitat coupling by fish in lake ecosystems? 2) What are the abiotic (environmental) and biotic (consumer traits or community context) determinants of resource use and habitat coupling? In chapter 1, from a local perspective leveraging the simple food webs of stocked mountain lakes in the Cascade Range of western North America I address how different population sizes, along with the relative availability of illuminated benthic habitat and terrestrial influence, determine resource use by rainbow trout. After collecting data and samples 16 lakes, I used stable isotope mixing models to quantify proportional use of basal resources for each trout, then compositional regression analysis to identify how interactions between relative habitat availability and population abundance influence Rainbow Trout use of basal resources. My findings from this first study highlighted the importance of environmental and biological interactions as drivers of relative resource use in lake ecosystems. In chapter 2, with a global perspective, I considered the influence of environmental factors (mean annual temp, elevation, area, average depth, shoreline index), relative 15N:14N increase, and fish community species richness on habitat coupling by fishes worldwide. I also explored how morphological traits influence habitat coupling. Using dataset consisting of fish 13C:12C and 15N:14N I developed an index of habitat coupling for fish populations in lake communities around the world. Using Bayesian hierarchical and non-hierarchical beta regressions I estimated the effects of environmental context and morphological traits on habitat coupling by fishes. These results demonstrate high rates of habitat coupling among fishes globally and show increases in relative habitat coupling is slightly associated with decreases in mean annual temp and elevation, while other environmental context factors had little or no relationship to habitat coupling. Last, I found relative habitat coupling was associated with morphological traits, in particular traits related to locomotion. Overall, these studies highlight the prevalence of multiple resources supporting fish populations and the importance of studying, conserving, and protecting littoral habitat