Browsing by Subject "food webs"

Now showing 1 - 3 of 3
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    A brown-world cascade in the dung decomposer food web of an alpine meadow: effects of predator interactions and warming
    (2011) Wu, Xinwei; Duffy, J. Emmett; Reich, Peter B; Sun, Shucun
    Top-down control has been extensively documented in food webs based on living plants, where predator limitation of herbivores can cascade to facilitate plant growth (the green-world hypothesis), particularly in grasslands and aquatic systems. Yet the ecosystem role of predators in detrital food webs is less explored, as is the potential effect of climate warming on detritus-based communities. We here show that predators have a “brown-world” role in decomposer communities via a cascading top-down control on plant growth, based on the results of an experiment that factorially manipulated presence and size of two predator species as well as temperature (warmed vs. unwarmed). The inclusion of predatory beetles significantly decreased abundance of coprophagous beetles and thus the rate of dung decomposition and productivity of plants growing surrounding the dung. Moreover, the magnitude of these decreases differed between predator species and, for dung loss, was temperature dependent. At ambient temperature, the larger predators tended to more strongly influence the dung loss rate than did the smaller predators; when both predators were present, the dung loss rate was higher relative to the treatments with the smaller predators but comparable to those with the larger ones, suggesting an antagonistic effect of predator interaction. However, warming substantially reduced dung decomposition rates and eliminated the effects of predation on dung decomposition. Although warming substantially decreased dung loss rates, warming only modestly reduced primary productivity. Consistent with these results, a second experiment exploring the influence of the two predator species and warming on dung loss over time revealed that predatory beetles significantly decreased the abundance of coprophagous beetles, which was positively correlated with dung loss rates. Moreover, experimental warming decreased the water content of dung and hence the survival of coprophagous beetles. These results confirm that the “brown-world” effect of predator beetles was due to cascading top-down control through coprophagous beetles to nutrient cycling and primary productivity. Our results also highlight potentially counterintuitive effects of climate warming. For example, global warming might significantly decrease animal-mediated decomposition of organic matter and recycling of nutrients in a future warmed world.
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    Characterization of streams and rivers in the Minnesota River Basin Critical Observatory: water chemistry and biological field collections, 2013-2016
    (2017-09-06) Dolph, Christine, L.; Hansen, Amy, T.; Kemmitt, Katie, L.; Janke, Ben; Rorer, Michelle; Winikoff, Sarah; Baker, Anna; Boardman, Evelyn; Finlay, Jacques, C.; dolph008@umn.edu; Dolph, Christine, L.
    This dataset was collected to inform the Water, Sustainability and Climate Minnesota River Basin Observatory, and was supported by the National Science Foundation under Grant No. 1209402 Water, Sustainability and Climate (WSC) – Category 2, Collaborative: Climate and human dynamics as amplifiers of natural change: a framework for vulnerability assessment and mitigation planning. The dataset contains point locations, watershed areas and water quality information for 231 ditch, stream, river and wetland sites located in the Le Sueur River, Chippewa River, Cottonwood River, Cannon River, Wantonwan River and Blue Earth River basins of Minnesota. Study sites ranged in size from 1st order ditches and streams to an 8th order river. Each of these sites was sampled at least once between 2013-2016 (most sites were sampled multiple times) for one or more of the following parameters: 1) water chemistry (total dissolved nitrogen, nitrate-N, nitrite-N, ammonium-N, particulate nitrogen, soluble reactive phosphorus, total dissolved phosphorus, particulate phosphorus, total phosphorus, dissolved organic carbon, dissolved inorganic carbon, particulate carbon, chlorophyll a, total suspended solids, volatile suspended solids, delta-H-2 and delta-O-18 stable isotopes of site water, specific UV absorbance (SUVA) of site water, fluorescence index (FI) of site water); 2) stable isotopes (delta-C-13, delta-N-15, delta-H-2) of invertebrate consumers, particulate carbon and potential food sources; 3) denitrification rates and characteristics of benthic sediment in agricultural drainage ditches; and 4) stream discharge. This dataset also includes spatial data files containing study site locations and watershed areas delineated for each site.
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    Mercury concentration and aquatic food web alterations associated with zebra mussel invasion in Minnesota lakes
    (2023-08) Link, Denver
    Zebra mussels (Dreissena polymorpha) are an invasive species documented in 299Minnesota lakes, with 231 of those lakes managed as walleye fisheries. Many ecological changes are associated with zebra mussel invasion, including increased water clarity, depleted pelagic energy resources, expanded littoral zones, deposition of benthic organic matter causing anoxic sediments, and increased benthic energy reliance of food webs. However, the effects of zebra mussels vary among lakes, and few opportunities exist to examine lake ecosystems and food webs pre- and post- zebra mussel invasion. Furthermore, recent evidence has suggested that Dreissenid mussels may impact contaminant bioaccumulation in higher trophic levels, but these effects have not been well-studied in inland lakes. I took two distinct approaches to understanding zebra mussel impacts on food webs and contaminants in fishes. I combined historic Minnesota statewide mercury monitoring data from 1997-2021 coupled with stable isotope data to provide insight into food web dynamics and mercury concentration alterations with zebra mussel invasion. I found the probability of exceeding the Minnesota safe threshold for safe eating of average sized northern pike (Esox Lucius) and walleye (Sander vitreus) ranged from 60%-70%, with zebra mussel lakes having an increased chance. Specifically, mercury concentrations analyzed using Before-After Control-Impact (BACI) study design increased by 8.2% in northern pike and 15.4% in walleye for invaded lakes, while uninvaded systems were stagnant or decreased. To quantify resource use and community structure, food webs in Leech Lake were analyzed pre- and post- invasion using stable isotope analysis of δ13C and δ15N. Fish community response to zebra mussel invasion varied spatially in Leech Lake. Bays on the western shoreline of Leech Lake with heterogeneous habitat increased niche size by 39.81% and fish in those areas relied more heavily on benthic resources following invasion. In contrast to the western bays and to hypothesized effects of zebra mussels, fish from the main basin of Leech Lake, containing mostly homogenous pelagic resources, decreased in niche size by 32.26% and relied more heavily on offshore resources. Taken together, high mercury concentrations in Minnesota northern pike and walleye are exacerbated in zebra mussel lakes. Food web dynamics are variable within the same lake, suggesting preexisting food web structure and access to benthic resources are important to community resilience with zebra mussel invasion.