Browsing by Author "Wenger, Seth J."

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    Distinctive Connectivities of Near-Stream and Watershed-Wide Land Uses Differentially Degrade Rural Aquatic Ecosystems
    Jackson, C. Rhett; Cecala, Kristen K.; Wenger, Seth J.; Kirsch, Joseph E.; Webster, Jackson R.; Leigh, David S.; Sanders, Jennifer M.; Love, Jason P.; Knoepp, Jennifer D.; Fraterrigo, Jennifer M.; Rosemond, Amy D. (Oxford University Press, 2022-02-03)
    The water-quality effects of low-density rural land-use activities are understudied but important because of large rural land coverage. We review and synthesize spatially extensive studies of oligotrophic mountain streams in the rural Southern Appalachian Mountains, concluding that rural land-use activities significantly degrade water quality through altered and mostly enhanced landscape-stream connections, despite high forest retention. Some connections (insolation, organic inputs, root-channel interactions, stream-field connectivity, individual landowner discharges) are controlled by near-stream land-use activities, whereas others (reduced nitrogen uptake and cycling, enhanced biological nitrogen fixation, nutrient subsidy, runoff from compacted soils, road runoff delivery) are controlled by basin-wide land use. These connections merge to alter basal resources and shift fish, salamander, and invertebrate assemblages toward species tolerant of higher turbidity and summer temperatures and those more competitive in mesotrophic systems. Rural water quality problems could be mitigated substantially with well-known best management practices, raising socioecological governance questions about best management practice adoption.
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    Simple statistical models can be sufficient for testing hypotheses with population time-series data
    Wenger, Seth J.; Stowe, Edward S.; Gido, Keith B.; Freeman, Mary C.; Kanno, Yoichiro; Franssen, Nathan R.; Olden, Julian D.; Poff, N. LeRoy; Walters, Annika W.; Bumpers, Phillip M.; Mims, Meryl C.; Hooten, Mevin B.; Lu, Xinyi (Wiley, 2022-09)
    Time-series data offer wide-ranging opportunities to test hypotheses about the physical and biological factors that influence species abundances. Although sophisticated models have been developed and applied to analyze abundance time series, they require information about species detectability that is often unavailable. We propose that in many cases, simpler models are adequate for testing hypotheses. We consider three relatively simple regression models for time series, using simulated and empirical (fish and mammal) datasets. Model A is a conventional generalized linear model of abundance, model B adds a temporal autoregressive term, and model C uses an estimate of population growth rate as a response variable, with the option of including a term for density dependence. All models can be fit using Bayesian and non-Bayesian methods. Simulation results demonstrated that model C tended to have greater support for long-lived, lower-fecundity organisms (K life-history strategists), while model A, the simplest, tended to be supported for shorter-lived, high-fecundity organisms (r life-history strategists). Analysis of real-world fish and mammal datasets found that models A, B, and C each enjoyed support for at least some species, but sometimes yielded different insights. In particular, model C indicated effects of predictor variables that were not evident in analyses with models A and B. Bayesian and frequentist models yielded similar parameter estimates and performance. We conclude that relatively simple models are useful for testing hypotheses about the factors that influence abundance in time-series data, and can be appropriate choices for datasets that lack the information needed to fit more complicated models. When feasible, we advise fitting datasets with multiple models because they can provide complementary information.
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    Stream fish colonization but not persistence varies regionally across a large North American river basin
    Wheeler, Kit; Wenger, Seth J.; Walsh, Stephen J.; Martin, Zachary P.; Jelks, Howard L.; Freeman, Mary C. (2018-07)
    Many species have distributions that span distinctly different physiographic regions, and effective conservation of such taxa will require a full accounting of all factors that potentially influence populations. Ecologists recognize effects of physiographic differences in topography, geology and climate on local habitat configurations, and thus the relevance of landscape heterogeneity to species distributions and abundances. However, research is lacking that examines how physiography affects the processes underlying metapopulation dynamics. We used data describing occupancy dynamics of stream fishes to evaluate evidence that physiography influences rates at which individual taxa persist in or colonize stream reaches under different flow conditions. Using periodic survey data from a stream fish assemblage in a large river basin that encompasses multiple physiographic regions, we fit multi-species dynamic occupancy models. Our modeling results suggested that stream fish colonization but not persistence was strongly governed by physiography, with estimated colonization rates considerably higher in Coastal Plain streams than in Piedmont and Blue Ridge systems. Like colonization, persistence was positively related to an index of stream flow magnitude, but the relationship between flow and persistence did not depend on physiography. Understanding the relative importance of colonization and persistence, and how one or both processes may change across the landscape, is critical information for the conservation of broadly distributed taxa, and conservation strategies explicitly accounting for spatial variation in these processes are likely to be more successful for such taxa.
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    Toward Improved Understanding of Streamflow Effects on Freshwater Fishes
    Freeman, Mary C.; Bestgen, Kevin R.; Carlisle, Daren; Frimpong, Emmanuel A.; Franssen, Nathan R.; Gido, Keith B.; Irwin, Elise; Kanno, Yoichiro; Luce, Charles; Kyle McKay, S.; Mims, Meryl C.; Olden, Julian D.; LeRoy Poff, N.; Propst, David L.; Rack, Laura; Roy, Alliso H.; Stowe, Edward S.; Walters, Annika; Wenger, Seth J. (Wiley, 2022-07)
    Understanding the effects of hydrology on fish populations is essential to managing for native fish conservation. However, despite decades of research illustrating streamflow influences on fish habitat, reproduction, and survival, biologists remain challenged when tasked with predicting how fish populations will respond to changes in flow regimes. This uncertainty stems from insufficient understanding of the context-dependent mechanisms underlying fish responses to, for example, periods of reduced flow or altered frequency of high-flow events. We aim to address this gap by drawing on previous research to hypothesize mechanisms by which low and high flows influence fish populations and communities, identifying challenges that stem from data limitations and ecological complexity, and outlining research directions that can advance an empirical basis for prediction. Focusing flow ecology research on testing and refining mechanistic hypotheses can help narrow management uncertainties and better support species conservation in changing flow regimes.
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    Twenty-six key research questions in urban stream ecology: an assessment of the state of the science
    Wenger, Seth J.; Roy, Allison H.; Jackson, C. Rhett; Bernhardt, Emily S.; Carter, Timothy L.; Filoso, Solange; Gibson, Catherine A.; Hession, W. Cully; Kaushal, Sujay S.; Marti, Eugenia; Meyer, Judy L.; Palmer, Margaret A.; Paul, Michael J.; Purcell, Alison H.; Ramirez, Alonso; Rosemond, Amy D.; Schofield, Kate A.; Sudduth, Elizabeth B.; Walsh, Christopher J. (The North American Benthological Society, 2009-10-27)
    Urban streams have been the focus of much research in recent years, but many questions about the mechanisms driving the urban stream syndrome remain unanswered. Identification of key research questions is an important step toward effective, efficient management of urban streams to meet societal goals. We developed a list of priority research questions by: 1) soliciting input from interested scientists via a listserv and online survey, 2) holding an open discussion on the questions at the Second Symposium on Urbanization and Stream Ecology, and 3) reviewing the literature in the preparation of this paper. We present the resulting list of 26 questions in the context of a review and summary of the present understanding of urban effects on streams. The key questions address major gaps in our understanding of ecosystem structure and function responses (e.g., what are the sublethal impacts of urbanization on biota?), characteristics of urban stream stressors (e.g., can we identify clusters of covarying stressors?), and management strategies (e.g., what are appropriate indicators of ecosystem structure and function to use as management targets?). The identified research needs highlight our limited understanding of mechanisms driving the urban stream syndrome and the variability in characteristics of the effects of urbanization across different biogeoclimatic conditions, stages of development, government policies, and cultural norms. We discuss how to proceed with appropriate management activities given our current incomplete understanding of the urban stream syndrome.