Life Sciences Commons^™

Predicting Invasion Risk Of Non-Native Plants Using A Modified I-Rank Assessment, Justin B. Williams

School of Natural Resources: Dissertations, Theses, and Student Research

Biological invasions are a global problem responsible for native species declines worldwide. Understanding the invasion risk from non-native species is important in establishing management goals and making decisions for managing native ecosystems. Useful modeling methods for quantifying or predicting invasion risk should consider research needs, data availability, and operate at an appropriate scale. I evaluated risk assessment methods towards answering a specific research question; which plant species pose the greatest risk of becoming invasive or having the greatest negative impact in Nebraska? I selected the I-Rank assessment method, which consists of 20 questions grouped into four risk categories or Subranks: …

A Population Model For Walleye In Nebraska Irrigation Reservoirs, Robert A. Kill

School of Natural Resources: Dissertations, Theses, and Student Research

Understanding how and why fish population size changes between years is a central theme in fisheries ecology. Fishery agencies have limited time and financial resources, thus there is a need for a quantitative way to direct the limited time and financial resources so agencies can manage fisheries more efficiently. I developed a tool for fishery managers that synthesizes common population indices and evaluated the relative importance of those indices given varying uncertainty in age-0 walleye Sander vitreus survival. Under most circumstances, I determined that resources are best utilized in reducing age-0 survival uncertainty when understanding walleye population growth. I applied …

Determining Scaphirhynchus Sturgeon Population Demographics And Dynamics: Implications For Range-Wide Management, Recovery, And Conservation, Martin J. Hamel

School of Natural Resources: Dissertations, Theses, and Student Research

Sturgeons (Acipenseridae) have experienced world-wide declines as a result of anthropogenic effects such as over-harvest, habitat degradation, altered flow regimes, and pollution. Nearly all European and Asian sturgeon species have experienced population declines and have subsequently been classified as either threatened or endangered. North American sturgeons have experienced a similar plight in that all eight native sturgeon species are listed as endangered, threatened, or of special concern. Direct linkages between North American sturgeon declines and anthropogenic effects are difficult to assess due to scale considerations, fluctuating environmental conditions, difficulty in capture, and the interaction of all these effects. To recover, …

Anoxia Tolerance Of Forensically Important Calliphorids, Melissa M. Lein

School of Natural Resources: Dissertations, Theses, and Student Research

Forensically important blow flies, Diptera: Calliphoridae, are among the first organisms to colonize carrion. After eggs hatch, the larvae of most blow fly species feed in an aggregation or “mass.” While in this mass larvae may experience periods of no oxygen (anoxia), little oxygen (hypoxia), or normal oxygen (normoxia), but the tolerance of blow fly larvae to severe hypoxic conditions is not known. I tested the anoxia tolerance of four species of calliphorids (Calliphora vicina, Cochliomyia macellaria, Lucilia sericata, and Phormia regina), using third stage larvae across five temperatures. Experiments were conducted by exposing larvae to pure nitrogen …

Walleye And White Bass Recruitment In Southwest Nebraska Irrigation Reservoirs, Jason Andrew Deboer

School of Natural Resources: Dissertations, Theses, and Student Research

Walleye Sander vitreus and white bass Morone chrysops are among the most popular sportfish in the reservoirs of the Great Plains. Despite considerable effort by the Nebraska Game and Parks Commission stocking walleye and managing reservoirs for walleye and white bass, populations of walleye and white bass in southwest Nebraska reservoirs are dynamic, as erratic recruitment has led to “boom and bust” fisheries for these two species. We investigated 1) factors regulating walleye and white bass recruitment during an 18-year period at five reservoirs, and 2) walleye spawning ecology at two reservoirs that differ in their degree of environmental variability. …

Shovelnose Sturgeon Reproductive Ecology In The Lower Platte River, Nebraska, Mathew L. Rugg

School of Natural Resources: Dissertations, Theses, and Student Research

Biodiversity and abundance of freshwater organisms are experiencing drastic declines. Anthropogenic disturbances have altered the natural flow regimes of large rivers, and have led to declines in species that rely on elements of natural flow. Similarly, shovelnose sturgeon distribution has diminished in the last 100 years due to habitat alteration, overharvest, and water contamination. To fully understand the status and viability of a fish population, basic knowledge of a fish’s reproductive strategy is needed. Aspects of reproduction that should be understood to manage for sustainability include maturation, fecundity, and spawning dynamics. There is currently little published information on age/size of …

Exploitation Of Channel Catfish In Nebraska Flood-Control Reservoirs, Christopher Lee Wiley

School of Natural Resources: Dissertations, Theses, and Student Research

Channel catfish Ictalurus punctatus, is a popular sportfish in North America, and is the third most-sought fish species in Nebraska. Exploitation rates of channel catfish populations have been estimated to be substantial in states neighboring Nebraska. Despite the popularity of channel catfish, little is known about the exploitation of channel catfish populations in Nebraska. The objectives of this study were to estimate the exploitation rates of channel catfish populations, identify the length bias of angling for channel catfish, and identify the self-imposed length limits for channel catfish at flood-control reservoirs of Nebraska. The software package Program Mark was used to …

Remote Sensing Of Green Leaf Area Index In Maize And Soybean: From Close-Range To Satellite, Anthony L. Nguy-Robertson

School of Natural Resources: Dissertations, Theses, and Student Research

This dissertation seeks to explore alternative methodologies for estimating green leaf area index (LAI) and crop developmental stages. Specifically this research [1] developed an approach for creating a Moderate Resolution Imaging Spectroradiometer (MODIS) high spatial resolution product for estimating green LAI on the base of data collected using two different close-range sensors. It was determined that the vegetation indices (VIs) Wide Dynamic Range Vegetation Index (WDRVI) and Enhanced Vegetation Index 2 (EVI2) were capable of accurate estimation of green LAI from MODIS 250 m data using models developed from hyperspectral (RMSE < 0.69 m² m^-2; CV < 33%) or multispectral sensors (RMSE < 0.69 m² m^-2; …

Changes In Avian Vocalization Occurrence And Frequency Range During The Winter, Amy I. Oden

School of Natural Resources: Dissertations, Theses, and Student Research

Human population expansion has led to an increase in vehicle traffic and therefore vehicle noise. Traffic and traffic noise has been shown to affect avian abundance, breeding success, density and species diversity on the landscape. Documented changes in avian vocalizations due to traffic noise include shifts in amplitude, frequency, rate, timing, and duration of vocalizations along with a number of behavioral adaptations. During the winters of 2011–2012 and 2012–2013, we recorded and measured the “chick-a-dee” vocalization of Black-capped Chickadees (Poecile atricapillus) and the “po-ta-to-chip” vocalization of American Goldfinches (Spinus tristis) to determine …

Decomposition And Nutrient Release Of Different Cover Crops In Organic Farm Systems, Jianru Shi

School of Natural Resources: Dissertations, Theses, and Student Research

Cover crops act as green manure adding organic matter to agricultural-soils. For legume green manures to be an effective nitrogen (N) source for organic farming systems, their N release must be in synchrony with crop N demand. The objectives of this study were 1) determine the decomposition rates of three common cover crops (white clover, (Trifolium repens,L ) red clover (Trifolium pratense L.) and soybean (Glycine max L) in order to determine when most N was released and its synchrony with subsequent corn crop uptake; 2) we focused on the effect of cover crops on soil …

Amphibian Occupancy And Functional Connectivity Of Restored Wetlands In The Missouri River Floodplain, Michelle L. Hellman

School of Natural Resources: Dissertations, Theses, and Student Research

Wetland decline may threaten many taxa including shorebirds, amphibians, and fish. As agencies increase restoration of wetland habitat, monitoring is crucial to inform the process. Permeable skin sensitive to water quality and biphasic life histories requiring both terrestrial and aquatic habitat make amphibians good indicators of wetland health. I modeled amphibian occupancy in restored Missouri River bends to determine habitat characteristics associated with the presence of amphibians.

Occupancy modeling acknowledges imperfect detection and allows the inclusion of detection covariates. To assess detection I examined two methods currently used to assess anuran occupancy in wetlands, aural anuran surveys and tadpole dip-netting. …

Assessment Of Tillage Practices Using Landsat-Tm 5 In Nebraska., Sonisa Sharma

School of Natural Resources: Dissertations, Theses, and Student Research

Tillage management practices are an important component to crop production and to federal and state conservation efforts and crop subsidy programs. Crop residue created by conservation tillage reduces soil erosion and reduce evaporation from exposed soil. Agro-hydrological models require information on tillage practices to estimate their impacts on soil-water-holding capacity, total evapotranspiration, carbon sequestration, water runoff and water and wind erosion for agricultural lands. Classification of tillage practices using remote sensing offers promise for the rapid collection of tillage information on individual fields over large areas. Using satellite imagery proves to be challenging due to the similarity in spectral signatures …

Building Upon Common-Pool Resource Theory To Explore Success In Transitioning Water Management Institutions, Christina M. Hoffman

School of Natural Resources: Dissertations, Theses, and Student Research

Nebraska, like many regions around the world, is faced with the challenge of adapting to a new era in water management. Increasing demands for water resources, mounting concerns over threatened and endangered species, and obligations to abide by interstate water allocation agreements have motivated Nebraska to revisit traditional water management approaches. However, although Nebraska’s water management institutions have undergone much change, little research exists on the influence these changes have had on the ability of water institutions to successfully manage water allocations. This research (1) qualitatively explores the perspectives and experiences of stakeholders in the overappropriated region of the Platte …

The Influence Of Sea-Water Inundation On Coupled Iron And Sulfur Cycling In A Coastal Freshwater Wetland, Valerie Anne Schoepfer

School of Natural Resources: Dissertations, Theses, and Student Research

Coastal freshwater wetland chemistry is rapidly changing due to increased frequency of saltwater inundation, a consequence of global change. Seasonal salt water inundation introduces sulfate, which biologically reduces to sulfide via microbial metabolism. Sulfide binds with reduced iron producing iron sulfide (FeS), recognizable in wetland soils by its characteristic black color. The objective of this study is to document rates of iron and sulfate reduction, as well as product formation (acid volatile and chromium reducible sulfide, AVS and CRS) in a coastal freshwater wetland undergoing seasonal salt water inundation. Understanding iron and sulfur cycling, as well as their reduction products …