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Browsing by Author "Smith, David R."

Now showing 1 - 6 of 6
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    Bayesian Hierarchical Methods and the Use of Ecological Thresholds and Changepoints for Habitat Selection Models
    Pooler, Penelope S. (Virginia Tech, 2005-12-02)
    Modeling the complex relationships between habitat characteristics and a species' habitat preferences pose many difficult problems for ecological researchers. These problems are complicated further when information is collected over a range of time or space. Additionally, the variety of factors affecting these choices is difficult to understand and even more difficult to accurately collect information about. In light of these concerns, we evaluate the performance of current standard habitat preference models that are based on Bayesian methods and then present some extensions and supplements to those methods that prove to be very useful. More specifically, we demonstrate the value of extending the standard Bayesian hierarchical model using finite mixture model methods. Additionally, we demonstrate that an extension of the Bayesian hierarchical changepoint model to allow for estimating multiple changepoints simultaneously can be very informative when applied to data about multiple habitat locations or species. These models allow the researcher to compare the sites or species with respect to a very specific ecological question and consequently provide definitive answers that are often not available with more commonly used models containing many explanatory factors. Throughout our work we use a complex data set containing information about horseshoe crab spawning habitat preferences in the Delaware Bay over a five-year period. These data epitomize some of the difficult issues inherent to studying habitat preferences. The data are collected over time at many sites, have missing observations, and include explanatory variables that, at best, only provide surrogate information for what researchers feel is important in explaining spawning preferences throughout the bay. We also looked at a smaller data set of freshwater mussel habitat selection preferences in relation to bridge construction on the Kennerdell River in Western Pennsylvania. Together, these two data sets provided us with insight in developing and refining the methods we present. They also help illustrate the strengths and weaknesses of the methods we discuss by assessing their performance in real situations where data are inevitably complex and relationships are difficult to discern.
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    Bowen Ratio Energy Balance Measurement of Carbon Dioxide (CO2) Fluxes of No-Till and Conventional Tillage Agriculture in Lesotho
    O'Dell, Deb; Sauer, Thomas J.; Hicks, Bruce B.; Lambert, Dayton M.; Smith, David R.; Bruns, Wendy A.; Basson, August; Marake, Makoala V.; Walker, Forbes; Wilcox, Michael D.; Eash, Neal S. (Open Journal of Soil Science, 2014)
    Global food demand requires that soils be used intensively for agriculture, but how these soils are managed greatly impacts soil fluxes of carbon dioxide (CO2). Soil management practices can cause carbon to be either sequestered or emitted, with corresponding uncertain influence on atmospheric CO2 concentrations. The situation is further complicated by the lack of CO2 flux measurements for African subsistence farms. For widespread application in remote areas, a simple experimental methodology is desired. As a first step, the present study investigated the use of Bowen Ratio Energy Balance (BREB) instrumentation to measure the energy balance and CO2 fluxes of two contrasting crop management systems, till and no-till, in the lowlands within the mountains of Lesotho. Two BREB micrometeorological systems were established on 100-m by 100-m sites, both planted with maize (Zea mays) but under either conventional (plow, disk-disk) or no-till soil management systems. The results demonstrate that with careful maintenance of the instruments by appropriately trained local personnel, the BREB approach offers substantial benefits in measuring real time changes in agroecosystem CO2 flux. The periods where the two treatments could be compared indicated greater CO2 sequestration over the no-till treatments during both the growing and non-growing seasons.
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    Long-term population dynamics of dreissenid mussels (Dreissena polymorpha and D. rostriformis): a cross-system analysis
    Strayer, David L.; Adamovich, Boris, V.; Adrian, Rita; Aldridge, David C.; Balogh, Csilla; Burlakova, Lyubov E.; FriedPetersen, Hannah B.; G-Toth, Laszlo; Hetherington, Amy L.; Jones, Thomas S.; Karatayev, Alexander Y.; Madill, Jacqueline B.; Makarevich, Oleg A.; Marsden, J. Ellen; Martel, Andre L.; Minchin, Dan; Nalepa, Thomas F.; Noordhuis, Ruurd; Robinson, Timothy J.; Rudstam, Lars G.; Schwalb, Astrid N.; Smith, David R.; Steinman, Alan D.; Jeschke, Jonathan M. (Ecological Society of America, 2019-04)
    Dreissenid mussels (including the zebra mussel Dreissena polymorpha and the quagga mussel D. rostriformis) are among the world's most notorious invasive species, with large and widespread ecological and economic effects. However, their long-term population dynamics are poorly known, even though these dynamics are critical to determining impacts and effective management. We gathered and analyzed 67 long-term (>10 yr) data sets on dreissenid populations from lakes and rivers across Europe and North America. We addressed five questions: (1) How do Dreissena populations change through time? (2) Specifi- cally, do Dreissena populations decline substantially after an initial outbreak phase? (3) Do different measures of population performance (biomass or density of settled animals, veliger density, recruitment of young) follow the same patterns through time? (4) How do the numbers or biomass of zebra mussels or of both species combined change after the quagga mussel arrives? (5) How does body size change over time? We also considered whether current data on long-term dynamics of Dreissena populations are adequate for science and management. Individual Dreissena populations showed a wide range of temporal dynamics, but we could detect only two general patterns that applied across many populations: (1) Populations of both species increased rapidly in the first 1-2 yr after appearance, and (2) quagga mussels appeared later than zebra mussels and usually quickly caused large dedines in zebra mussel populations. We found little evidence that combined Dreissena populations declined over the long term. Different measures of population performance were not congruent; the temporal dynamics of one life stage or population attribute cannot generally be accurately inferred from the dynamics of another. We found no consistent patterns in the long-term dynamics of body size. The long-term dynamics of Dreissena populations probably are driven by the ecological characteristics (e.g., predation, nutrient inputs, water temperature) and their temporal changes at individual sites rather than following a generalized time course that applies across many sites. Existing long-term data sets on dreissenid populations, although dearly valuable, are inadequate to meet research and management needs. Data sets could be improved by standardizing sampling designs and methods, routinely collecting more variables, and increasing support.
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    Runoff and pollution abatement characteristics of concrete grid pavements
    Day, Gary E.; Smith, David R.; Bowers, John (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1981)
    Problems of water quaIity and quantity have forced many communities to redefine their approaches to local stormwater management. New approaches--alternatives to the conventional means of piping a problem downstream--focus on maintaining predevelopment runoff levels by increasing opportunities for runoff infiltration, by controlling runoff velocities and volumes, and by reducing nonpoint pollutants. Concrete grid pavements have potential as a technology capable of performing these functions, but they have not yet been evaluated to the satisfaction of officials who must endorse or implement stormwater management strategies. This research measured, in a laboratory setting, runoff volume and pollutant load reductions associated with three types of grid pavements. A concrete slab was used as a control. Reductions in pollutant concentration and mass in water that percolated through the grids in the pavements were also measured. Runoff from the surface of the pavements and from water within the soils beneath the pavements was analyzed for phosphorus, nitrogen, organic carbon, chromium, lead, and zinc. Results show that the grid pavements greatly reduced runoff volume, as compared to the concrete slab. The masses of 10 pollutants found in the runoff from this slab were much greater than those in the runoff from the grid pavements. The soils beneath the grid pavements acted effectively in removing significant quantities of pollutants from the water that infiltrated into them.
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    A stormwater management analysis of Blacksburg, Virginia
    Smith, David R. (Virginia Polytechnic Institute and State University, 1982)
    Many aspects of managing stormwater runoff were investigated for the Town of Blacksburg, Virginia, that would minimize the costly installation and environmentally damaging impacts of storm sewers as the town urbanizes. These aspects included the technical, political, financial, legal, and administrative approaches for controlling runoff at present levels, and for promoting the restoration of streams and preservation of natural drainage ways. The study used a computer model of the town's drainage system to assess the potential of technical approaches for runoff control and stream restoration. The financial and legal ramifications of a storm drainage user fee were explored in depth as a means to finance drainage improvements that rely on natural means for controlling runoff. Recommendations were presented on how to implement these technical, legal, and financial approaches through the town administration and citizen groups.
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    Testing a global standard for quantifying species recovery and assessing conservation impact
    Grace, Molly K.; Akcakaya, H. Resit; Bennett, Elizabeth L.; Brooks, Thomas M.; Heath, Anna; Hedges, Simon; Hilton-Taylor, Craig; Hoffmann, Michael; Hochkirch, Axel; Jenkins, Richard; Keith, David A.; Long, Barney; Mallon, David P.; Meijaard, Erik; Milner-Gulland, E. J.; Paul Rodriguez, Jon; Stephenson, P. J.; Stuart, Simon N.; Young, Richard P.; Acebes, Pablo; Alfaro-Shigueto, Joanna; Alvarez-Clare, Silvia; Andriantsimanarilafy, Raphali Rodlis; Arbetman, Marina; Azat, Claudio; Bacchetta, Gianluigi; Badola, Ruchi; Barcelos, Luis MD D.; Barreiros, Joao Pedro; Basak, Sayanti; Berger, Danielle J.; Bhattacharyya, Sabuj; Bino, Gilad; Borges, Paulo A.; Boughton, Raoul K.; Brockmann, H. Jane; Buckley, Hannah L.; Burfield, Ian J.; Burton, James; Camacho-Badani, Teresa; Santiago Cano-Alonso, Luis; Carmichael, Ruth H.; Carrero, Christina; P Carroll, John; Catsadorakis, Giorgos; Chapple, David G.; Chapron, Guillaume; Chowdhury, Gawsia Wahidunnessa; Claassens, Louw; Cogoni, Donatella; Constantine, Rochelle; Craig, Christie Anne; Cunningham, Andrew A.; Dahal, Nishma; Daltry, Jennifer C.; Das, Goura Chandra; Dasgupta, Niladri; Davey, Alexandra; Davies, Katharine; Develey, Pedro; Elangovan, Vanitha; Fairclough, David; Di Febbraro, Mirko; Fenu, Giuseppe; Fernandes, Fernando Moreira; Fernandez, Eduardo Pinheiro; Finucci, Brittany; Foldesi, Rita; Foley, Catherine M.; Ford, Matthew; Forstner, Michael RJ J.; Garcia, Nestor; Garcia-Sandoval, Ricardo; Gardner, Penny C.; Garibay-Orijel, Roberto; Gatan-Balbas, Marites; Gauto, Irene; Ghazi, Mirza Ghazanfar Ullah; Godfrey, Stephanie S.; Gollock, Matthew; Gonzalez, Benito A.; Grant, Tandora D.; Gray, Thomas; Gregory, Andrew J.; van Grunsven, Roy HA A.; Gryzenhout, Marieka; Guernsey, Noelle C.; Gupta, Garima; Hagen, Christian A.; Hagen, Christian A.; Hall, Madison B.; Hallerman, Eric M.; Hare, Kelly; Hart, Tom; Hartdegen, Ruston; Harvey-Brown, Yvette; Hatfield, Richard; Hawke, Tahneal; Hermes, Claudia; Hitchmough, Rod; Hoffmann, Pablo Melo; Howarth, Charlie; Hudson, Michael A.; Hussain, Syed Ainul; Huveneers, Charlie; Jacques, Helene; Jorgensen, Dennis; Katdare, Suyash; Katsis, Lydia KD D.; Kaul, Rahul; Kaunda-Arara, Boaz; Keith-Diagne, Lucy; Kraus, Daniel T.; de Lima, Thales Moreira; Lindeman, Ken; Linsky, Jean; Louis, Edward; Loy, Anna; Lughadha, Eimear Nic; Mangel, Jeffrey C.; Marinari, Paul E.; Martin, Gabriel M.; Martinelli, Gustavo; McGowan, Philip JK K.; McInnes, Alistair; Mendes, Eduardo Teles Barbosa; Millard, Michael J.; Mirande, Claire; Money, Daniel; Monks, Joanne M.; Laura Morales, Carolina; Mumu, Nazia Naoreen; Negrao, Raquel; Anh, Ha Nguyen; Niloy, Md Nazmul Hasan; Norbury, Grant Leslie; Nordmeyer, Cale; Norris, Darren; O'Brien, Mark; Oda, Gabriela Akemi; Orsenigo, Simone; Outerbridge, Mark Evan; Pasachnik, Stesha; Perez-Jimenez, Juan Carlos; Pike, Charlotte; Pilkington, Fred; Plumb, Glenn; Portela, Rita de Cassia Quitete D. C. Q.; Prohaska, Ana; Quintana, Manuel G.; Rakotondrasoa, Eddie Fanantenana; Ranglack, Dustin H.; Rankou, Hassan; Rawat, Ajay Prakash; Reardon, James Thomas; Rheingantz, Marcelo Lopes; Richter, Stephen C.; Rivers, Malin C.; Rogers, Luke Rollie; da Rosa, Patricia; Rose, Paul; Royer, Emily; Ryan, Catherine; de Mitcheson, Yvonne J. Sadovy; Salmon, Lily; Salvador, Carlos Henrique; Samways, Michael J.; Sanjuan, Tatiana; Dos Santos, Amanda Souza; Sasaki, Hiroshi; Schutz, Emmanuel; Scott, Heather Ann; Scott, Robert Michael; Serena, Fabrizio; Sharma, Surya P.; Shuey, John A.; Silva, Carlos Julio Polo; Simaika, John P.; Smith, David R.; Spaet, Julia LY Y.; Sultana, Shanjida; Talukdar, Bibhab Kumar; Tatayah, Vikash; Thomas, Philip; Tringali, Angela; Hoang, Trinh-Dinh; Tuboi, Chongpi; Usmani, Aftab Alam; Vasco-Palacios, Aida M.; Vie, Jean-Christophe; Virens, Jo; Walker, Alan; Wallace, Bryan; Waller, Lauren J.; Wang, Hongfeng; Wearn, Oliver R.; van Weerd, Merlijn; Weigmann, Simon; Willcox, Daniel; Woinarski, John; Yong, Jean WH H.; Young, Stuart (Wiley, 2021-07-21)
    Recognizing the imperative to evaluate species recovery and conservation impact, in 2012 the International Union for Conservation of Nature (IUCN) called for development of a “Green List of Species” (now the IUCN Green Status of Species). A draft Green Status framework for assessing species’ progress toward recovery, published in 2018, proposed 2 separate but interlinked components: a standardized method (i.e., measurement against benchmarks of species’ viability, functionality, and preimpact distribution) to determine current species recovery status (herein species recovery score) and application of that method to estimate past and potential future impacts of conservation based on 4 metrics (conservation legacy, conservation dependence, conservation gain, and recovery potential). We tested the framework with 181 species representing diverse taxa, life histories, biomes, and IUCN Red List categories (extinction risk). Based on the observed distribution of species’ recovery scores, we propose the following species recovery categories: fully recovered, slightly depleted, moderately depleted, largely depleted, critically depleted, extinct in the wild, and indeterminate. Fifty-nine percent of tested species were considered largely or critically depleted. Although there was a negative relationship between extinction risk and species recovery score, variation was considerable. Some species in lower risk categories were assessed as farther from recovery than those at higher risk. This emphasizes that species recovery is conceptually different from extinction risk and reinforces the utility of the IUCN Green Status of Species to more fully understand species conservation status. Although extinction risk did not predict conservation legacy, conservation dependence, or conservation gain, it was positively correlated with recovery potential. Only 1.7% of tested species were categorized as zero across all 4 of these conservation impact metrics, indicating that conservation has, or will, play a role in improving or maintaining species status for the vast majority of these species. Based on our results, we devised an updated assessment framework that introduces the option of using a dynamic baseline to assess future impacts of conservation over the short term to avoid misleading results which were generated in a small number of cases, and redefines short term as 10 years to better align with conservation planning. These changes are reflected in the IUCN Green Status of Species Standard.