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Browsing by Subject "Foraging"

Now showing 1 - 4 of 4
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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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    Environmental contributions to value computations and population dynamics in ventromedial prefrontal cortex
    (2021-06) Mehta, Priyanka
    On a hot summer day, there’s nothing nicer than giving a kid on the roadside a dollar in exchange for an ice cold cup of lemonade. That is, unless you just turned down a fifty-cent cup of lemonade. From a traditional perspective, the disappointment you feel when you pay the full dollar for that cup of lemonade is quantifiable: you’ve missed out on an offer that was twice as good as the one you ended up with. However, our brains did not evolve in a world of mathematical equations.The early primate brain had access to no lemonade stands; no dollar values were attributed to its food sources. Instead, early humans then (and other primates now), obtained food a slightly different way: they foraged. Foraging theory is an approach to studying decision making where we assume that because the brain evolved in a naturalistic environment, it is built to make decisions in naturalistic situations. Many foraging studies claim the ventromedial prefrontal cortex (vmPFC)- a brain region strongly associated with value (local) encoding - does not participate in foraging-related (environmental) computations. However, we posit here that the vmPFC contributes to the foraging process by encoding not just local value but also environmental variables. To this end, we designed a novel diet-search task, for monkeys to complete while we record neural activity in their vmPFC First, we sought out the contribution of local and environmental factors to vmPFC neurons’ processing of value. Specifically, we found relationships between several environmental variables and the animal’s threshold for accepting an offer, as well as encoding in vmPFC in response to the variable. Next, we were interested in examining vmPFC neurons as a population in the same context of foraging-based decision making..Here, we examined how the population of vmpfc neurons moves through stages of the foraging process. Specifically, we determined that distinct computations involving the reward rate occur during travel time versus foraging. Taken together, our results suggest that when we limit ourselves to only looking at how local value is encoded in the brain, we miss out on a valuable slice of cognition. Ultimately, the power of the foraging framework is that it takes everything that is generally a pesky impediment to clear science - uncontrollable, outside variables - and turns it into an advantage.
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    Foraging mechanisms of siscowet Lake Trout (Salvelinus namaycush siscowet) on pelagic prey
    (2014-12) Keyler, Trevor Daniel
    Little is known about the foraging mechanisms of siscowet (Salvelinus namaycush siscowet), the most abundant piscivore within Lake Superior because they occupy light-limited environments as a result of diel vertical migration. The reaction distance, angle of attack, and foraging success were determined for siscowet during laboratory trials under lighting conditions that approximated downwelling spectral irradiance and intensity (0-10 lx) at daytime depths. Siscowet reaction distance in response to golden shiners (Notemigonus crysoleucas) was directly correlated with increasing light intensity until saturation at 0.01 lx, and afterwards the relationship was asymptotic within our range of tested light intensities. In total darkness, lateral line sensory detection was sufficient to locate prey at 24.9 ± 1.7 cm, while increasing light intensities increased reaction distance up to 58.6 ± 2.3 cm at 10 lx. Larger prey elicited higher reaction distances than smaller prey at all light intensities while moving prey elicited higher reaction distances than stationary prey at the higher light intensities (0.001-10 lx). The capture and consumption of prey similarly increased with increasing light intensity while time to capture decreased with increasing light intensity. The majority of orientations toward prey occurred within 120° of the longitudinal axis of the siscowet's eyes, although reaction distances among 30° increments along the axis were not significantly different. Our predictive model will help determine reaction distances for siscowet in various photic environments and will help identify the mechanisms and behavior that allow for low light intensity foraging within freshwater systems.t>
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    Sandbars managed for least terns within the Missouri River: evaluating the influence of fish, spatial scale and environment on habitat use
    (2012-09) Stucker, Jennifer Hathaway
    Interior Least Terns (Sternula antillarum) nest on barren sandy habitats, typically sandbars and shorelines within large river systems of the central United States. Loss of natural ecosystem processes which create and maintain these habitats is considered the primary reason for population decline and Federal listing of this population. Throughout their range, management for Least Terns focuses on maintenance of breeding habitats, including placement of dredged material specifically as nesting substrate. Wide expanses of barren land are known to attract Least Terns, yet specific small scale habitat features are thought to trigger nest habitat selection. Yet as a plunge-diving piscivore, Least Terns also rely on ready access to appropriately sized slender-bodied fish: <52 mm total length for adults and <34 mm total length for young chicks. It remains unknown whether sandbar construction is a benefit or a detriment to forage abundance for Least Terns. Lastly, the relationship between availability of nesting habitats and required foraging habitats remains ambiguous. This information is needed to refine understanding of Least Tern habitat needs from a foraging ecology perspective, and contribute to knowledge and potential value of habitat restoration efforts. This study evaluates 1) the shallow water (<1.5 m) fish community near river and mechanically created emergent sandbars during three nesting seasons (2006-2008), 2) nest-scale habitat selection to determine if nest habitats differ between constructed and natural sandbars, and it evaluates the consequences of this selection on nest success, and 3) the potential associations between specific habitat features, at differing spatial scales, associated with airborne and foraging Least Terns. The research effort focused on the 95 kilometers of Gavins Point Reach of the Missouri River, between Yankton, SD and Ponca, NE during the Least Tern nesting season in 2006-2008. We sampled fish within 15-16 areas every two weeks from late May - July to document the relative abundance, species richness, and size classes of fish. Using systematic surveys on sandbars every 2-3 days, we detected and tracked 869 Least Tern nests until eggs hatched or failed, on constructed and natural sandbars in the Missouri River examining them for evidence of microhabitat selection at the nest and 3 m from nest. Least Terns successful foraging sites (N=416) were compared to a paired nearby random location to evaluate evidence of habitat selection during successful foraging in 2007-2008. We used systematic surveys every two weeks from late May - July in each year to identify Least Tern airborne (foraging or flying) locations within the river corridor (2006:966 sites, 2007:2940 sites, 2008:2003 sites), recording them using spot mapping. We modeled the probability that an observation (random and bird) as an airborne tern using logistic regression and habitat variables derived from remote sensing. Lastly, to refine our understanding of behavior in specifying habitat use, we modeled the probability of a location as a foraging site. Fish relative abundance was negatively related to depth. Catches were dominated by schooling species, including emerald shiner, sand shiner, spotfin shiner, and bigmouth buffalo. Significant inter-annual differences in relative abundance were observed, with generally increasing trends in intra-seasonal relative abundance of shiners and the smallest size classes of fish (<34 mm). Significant differences in the fish communities between the sandbar types were not detected in this study. These results suggest that mechanical sandbar habitats host comparable fish communities at similar levels of relative abundance. Among nests, significant differences were observed in substrates, amount of debris, and measures of vegetation between natural and created habitats, and between microhabitat at nests and the surrounding area. In general, Least Tern nest sites had coarser and larger substrate materials at the nest, more debris, and shorter and less vegetation compared to areas within the 3 m surrounding area. Nests in constructed habitats had a greater proportion of coarse substrates and less vegetation or debris than naturally created habitats. Observed nest success among constructed sandbars was 1.8x greater than that recorded among nests on natural sandbars, but a greater proportion of nests on natural bars were in or adjoining moist habitats where they were frequently destroyed. The best supported model predicting nest success on constructed and natural sandbars each included positive associations with percentage of pebble substrate, but inclusion of additional habitat predictors differed by sandbar type. Selection of microhabitat characteristics at the nest and vicinity constrains this species to barren water and wind scoured habitats. Historically, scoured habitats and the comparative abundance of debris within sites may have been a cue indicating safe habitats as river stage decreased. Water management regimes during this study favored survival of nests on higher elevation sandbars which included limited areas of wet substrates, typical of mechanically constructed sandbars. Among the micro-site habitat assessments for foraging birds, differences were not observed in water depth availability between natural or mechanically created habitats. Based on AIC relative importance scores, the variables water depth and microhabitat characteristics were most critical among micro-site characteristics of successful foraging locations; turbidity and larger scale aquatic features were comparatively of less importance. Within the greater landscape, Least Tern airborne locations within the river corridor were best explained by multi-scale logistic regressions; birds concentrated in areas with higher proportions of sandbar and wet sand habitats (200 m radius), while avoiding trees (50 m radius). When applied to a reserved sample of random locations, results suggest that in any given year, 40-97% of river corridor habitats were likely unsuitable for airborne terns. Furthermore, habitat use differed by behavior; foraging birds approached nearer to wet sand patches and in areas with less emergent sandbar habitat than flying birds, with some habitat relationships differing by year. Despite the surficial visual uniformity of many aquatic habitats on the Missouri River, successful foraging by Least Terns was associated with shallow, slack-water microhabitats adjacent to emergent sandbars and within areas with a greater proportion of sandbar habitat. This study demonstrates the importance of incorporating both spatial scale and behavior into ecological assessments of Least Tern foraging habitats.