Faculty Research
Permanent URI for this collection
Browse
Recent Submissions
Item Arctic Sea Ice Surface Roughness Estimated from Multi-Angular Reflectance Satellite Imagery(2019) Nolin, Anne W.; Mar, EugeneSea ice surface roughness affects ice-atmosphere interactions, serves as an indicator of ice age, shows patterns of ice convergence and divergence, affects the spatial extent of summer meltponds, and affects ice albedo. We have developed a method for mapping sea ice surface roughness using angular reflectance data from the Multi-angle Imaging SpectroRadiometer (MISR) and lidar-derived roughness measurements from the Airborne Topographic Mapper (ATM). Using an empirical data modeling approach, we derived estimates of Arctic sea ice roughness ranging from centimeters to decimeters within the MISR 275-m pixel size. Using independent ATM data for validation, we find that histograms of lidar and multi-angular roughness values were nearly identical for areas with a roughness < 20 cm, but for rougher regions, the MISR-estimated roughness had a narrower range of values than the ATM data. The algorithm was able to accurately identify areas that transition between smooth and rough ice. Because of its coarser spatial scale, MISR-estimated roughness data have a variance about half that of ATM roughness data.Item Complex immune responses and molecular reactions to pathogens and disease in a desert reptile (Gopherus agassizii)(2019) Drake, K. Kristina; Aiello, Christina M.; Bowen, Lizabeth; Lewison, Rebecca L.; Esque, Todd C.; Nussear, Kenneth E.; Waters, Shannon C.; Hudson, Peter J.Immune function plays an important role in an animal's defense against infectious disease. In reptiles, immune responses may be complex and counterintuitive, and diagnostic tools used to identify infection, such as induced antibody responses are limited. Recent studies using gene transcription profiling in tortoises have proven useful in identifying immune responses to various intrinsic and extrinsic stressors. As part of a larger experiment with Mojave desert tortoises (Gopherus agassizii), we facilitated the transmission of the pathogenic bacteria, Mycoplasma agassizii (Myag), to naive adults and measured innate and induced immune reactions over time. Specifically, we evaluated clinical condition, presence of Myag in the nasal/oral cavity, induced antibody responses specific to Myag, and measured molecular reactions (gene transcript profiles) in 15 captive tortoises classified as naive, exposed, or infected and 14 wild tortoises for comparison. Myag was confirmed inside the nasal/oral cavity in exposed tortoises within 30-60 days of introduction to infected animals, yet we did not detect Myag specific induced antibody responses in these individuals until 420-595 days post exposure. Surprisingly, we found no overall differences in the gene transcript profiles between our experimental treatment groups throughout this study. This work highlights the complexities in assessing immune function and diagnosing pathogen related infections in tortoises and other reptiles.Item Modeling spatiotemporal abundance of mobile wildlife in highly variable environments using boosted GAMLSS hurdle models(2019) Smith, Adam; Hofner, Benjamin; Lamb, Juliet S.; Osenkowski, Jason; Allison, Taber; Sadoti, Giancarlo; McWilliams, Scott R.; Paton, PeterModeling organism distributions from survey data involves numerous statistical challenges, including accounting for zero-inflation, overdispersion, and selection and incorporation of environmental covariates. In environments with high spatial and temporal variability, addressing these challenges often requires numerous assumptions regarding organism distributions and their relationships to biophysical features. These assumptions may limit the resolution or accuracy of predictions resulting from survey-based distribution models. We propose an iterative modeling approach that incorporates a negative binomial hurdle, followed by modeling of the relationship of organism distribution and abundance to environmental covariates using generalized additive models (GAM) and generalized additive models for location, scale, and shape (GAMLSS). Our approach accounts for key features of survey data by separating binary (presence-absence) from count (abundance) data, separately modeling the mean and dispersion of count data, and incorporating selection of appropriate covariates and response functions from a suite of potential covariates while avoiding overfitting. We apply our modeling approach to surveys of sea duck abundance and distribution in Nantucket Sound (Massachusetts, USA), which has been proposed as a location for offshore wind energy development. Our model results highlight the importance of spatiotemporal variation in this system, as well as identifying key habitat features including distance to shore, sediment grain size, and seafloor topographic variation. Our work provides a powerful, flexible, and highly repeatable modeling framework with minimal assumptions that can be broadly applied to the modeling of survey data with high spatiotemporal variability. Applying GAMLSS models to the count portion of survey data allows us to incorporate potential overdispersion, which can dramatically affect model results in highly dynamic systems. Our approach is particularly relevant to systems in which little a priori knowledge is available regarding relationships between organism distributions and biophysical features, since it incorporates simultaneous selection of covariates and their functional relationships with organism responses.Item North-south dipole in winter hydroclimate in the western United States during the last deglaciation(2019) Hudson, Adam M.; Hatchett, Benjamin J.; Quade, Jay; Boyle, Douglas P.; Bassett, Scott D.; Ali, Guleed; De los Santos, Marie G.During the termination of the last glacial period the western U.S. experienced exceptionally wet conditions, driven by changes in location and strength of the mid-latitude winter storm track. The distribution of modern winter precipitation is frequently characterized by a north-south wet/dry dipole pattern, controlled by interaction of the storm track with ocean-atmosphere conditions over the Pacific and Atlantic Oceans. Here we show that a dipole pattern of similar geographic extent persisted and switched sign during millennial-scale abrupt climate changes of the last deglaciation, based on a new lake level reconstruction for pluvial Lake Chewaucan (northwestern U.S.), and a compilation of regional paleoclimate records. This suggests the dipole pattern is robust, and one mode may be favored for centuries, thereby creating persistent contrasting wet/dry conditions across the western U.S. The TraCE-21k climate model simulation shows an equatorward enhancement of winter storm track activity in the northeastern Pacific, favoring wet conditions in southwestern U.S. during the second half of Heinrich Stadial 1(16.1-14.6 ka) and consistent with paleoclimate evidence. During the Bolling/Allerod (14.6-12.8 ka), the northeastern Pacific storm track contracted poleward, consistent with wetter conditions concentrated poleward toward the northwest U.S.Item Catalyzing Transformations to Sustainability in the World's Mountains(2019) Klein, J. A.; Tucker, C. M.; Nolin, Anne W.; Hopping, K. A.; Reid, R. S.; Steger, C.; Gret-Regamey, A.; Lavorel, S.; Mueller, B.; Yeh, E. T.; Boone, R. B.; Bourgeron, P.; Butsic, V.; Castellanos, E.; Chen, X.; Dong, S. K.; Greenwood, G.; Keiler, M.; Marchant, R.; Seidl, R.; Spies, T.; Thorn, J.; Yager, K.; Abbott, M.; Bowser, G.; Carpenter, C.; Cumming, G. S.; Evangelista, P.; Fernandez-Gimenez, M. E.; Flint, C. G.; Forbes, B. C.; Gerkey, D.; Ghate, R.; Ghorbani, M.; Haider, L. J.; Karna, B.; Leisz, S. J.; Martin-Lopez, B.; Nakileza, B. R.; Price, M. F.; Savchuk, D.; Hribar, M. Smid; Sproles, E.; Suryawanshi, K. R.; Taber, A.; Tappeiner, U.; Tevzadze, G.; Ueno, K.Mountain social-ecological systems (MtSES) are vital to humanity, providing ecosystem services to over half the planet's human population. Despite their importance, there has been no global assessment of threats to MtSES, even as they face unprecedented challenges to their sustainability. With survey data from 57 MtSES sites worldwide, we test a conceptual model of the types and scales of stressors and ecosystem services in MtSES and explore their distinct configurations according to their primary economic orientation and land use. We find that MtSES worldwide are experiencing both gradual and abrupt climatic, economic, and governance changes, with policies made by outsiders as the most ubiquitous challenge. Mountains that support primarily subsistence-oriented livelihoods, especially agropastoral systems, deliver abundant services but are also most at risk. Moreover, transitions from subsistence- to market-oriented economies are often accompanied by increased physical connectedness, reduced diversity of cross-scale ecosystem services, lowered importance of local knowledge, and shifting vulnerabilities to threats. Addressing the complex challenges facing MtSES and catalyzing transformations to MtSES sustainability will require cross-scale partnerships among researchers, stakeholders, and decision makers to jointly identify desired futures and adaptation pathways, assess trade-offs in prioritizing ecosystem services, and share best practices for sustainability. These transdisciplinary approaches will allow local stakeholders, researchers, and practitioners to jointly address MtSES knowledge gaps while simultaneously focusing on critical issues of poverty and food security. Plain Language Summary Mountain ecosystems and the human communities that inhabit them deliver critical resources-such as fresh water and timber-to over half the planet's human population. Despite their importance, there has been no global assessment of threats to mountain systems, even as they face unprecedented challenges to their sustainability. With survey data from 57 mountain sites worldwide, we test our understanding of the types of stresses that are threatening mountain systems as well as the resources and benefits that come from mountains. We find that mountain systems worldwide are experiencing both gradual and abrupt climatic, economic, and governance changes. One of the most ubiquitous challenges facing mountain systems is that policies directly affecting mountain systems are being made by those living outside of the mountains themselves. Mountains that support primarily subsistence-oriented livelihoods in the developing world, especially mixed agriculture and animal husbandry systems, deliver abundant services but are also most at risk. Addressing the complex challenges facing mountain systems will require partnerships among researchers, stakeholders, and decision makers to jointly identify the types of futures they desire and the actions to achieve these. This approach will address knowledge gaps in mountains while simultaneously focusing on critical issues of poverty and food security.