Browsing by Author "Michels, Noland"

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    Comparison Of Multi-Piscivore Foraging Success On Native And Invasive Prey Fish Under Variable Light Intensities
    (2020-05) Michels, Noland
    The majority of fish predator-prey studies have focused on interactions using a single predator. We explored the complexity of foraging at different times of the day by examining the interactions of paired native predators (Burbot Lota lota or Smallmouth Bass Micropterus dolomieu) with either native (Mottled Sculpin Cottus bairdii) or invasive (Round Goby Neogobius melanostomus) benthic prey (n=20). The study allowed the comparison of a pursuit (Smallmouth Bass) and ambush (Burbot) predator. Trials were performed under natural relevant lighting conditions with downwelling light intensity and emission spectrum matched to the irradiance at 10 m depth found in the St. Louis River estuary during summer at night, civil twilight, sunrise, and midmorning. Smallmouth Bass were more active than burbot and initiated 1,510 reactions that resulted in the successful capture of 61 Round Goby and 103 Mottled Sculpin (10.9% success rate overall) whereas Burbot initiated 475 reactions resulting in 24 successful retentions including 9 Round Goby and 15 Mottled Sculpin (5.0% success rate overall). The percentage of successful retentions was greater for Smallmouth Bass at 10.9% compared to only 5.0% for Burbot. Reaction probabilities to each prey differed significantly which resulted in a two-fold increase in attacks on Mottled Sculpin compared to Round Gobies within the same time period. Reaction distances for both predator species did not differ in regard to prey species, but Smallmouth Bass reacted farther than Burbot (max. reaction distances of 159 and 98 cm, respectively). Greater success of native predators on native prey likely cause predators to expend more energy capturing invasive prey and cause higher mortality on native prey populations due to greater predator success.
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    Prey Behavior to Predator Growth: The Influence of Light Intensity on Predator-Prey Interactions in North Temperate Lakes and Rivers
    (2024-08) Michels, Noland
    Abiotic and biotic conditions interact to influence fish behavior, which can scale up temporally to affect growth and population dynamics. My dissertation includes four unique studies that improve our knowledge of how predator-prey interactions change across species and diel periods, and the translation of individual interactions into effects on long-term growth rate. My first study tested the predator avoidance behaviors of invasive (round goby; Neogobius melanostomus) and native (mottled sculpin; Cottus bairdii) prey fishes from active (smallmouth bass, Micropterus dolomieu) and ambush (burbot; Lota lota) predators at multiple light intensities. Round goby were more successful at avoiding predators as they have an increased flight initiation distance, flee at angles closer to their theoretical optimal, and made more turns during an escape. Next, I examined the scotopic spectral sensitivity of adult walleye (Sander vitreus) and then observed age-0 walleye foraging behavior under their optimal wavelength. I found that walleye were most sensitive to 500-550 nm light. Under 525 nm light, age-0 walleye had the most reactions and attacks on prey from 1.58 × 1011 - 3.16 × 1013 photons m-2 s-1 (nautical-civil twilight). To test whether individual interactions translated to effects on growth, as well as the effect of light intensity, I tested the growth rates of age-0 walleye under 525 nm light at three intensities and three staining levels. I observed a higher growth rate in darker, heavily stained water and lowest growth rates were in bright, clear conditions. Lastly, I combined information from the previous chapters into an individual-based model on walleye foraging and tested whether light intensity, temperature, and prey density affected growth rates of a walleye population. Growth rate was greatly affected by temperature and prey density independently, but light intensity did not influence growth rate. Light intensity had a large influence on predator and prey behavior, but extrapolating these behavioral effects over time as measured by growth rate showed light intensity had limited effects.