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Search Results: 1 - 10 of 118812 matches for " Colleen T. Webb "
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Transmission Shifts Underlie Variability in Population Responses to Yersinia pestis Infection
Michael G. Buhnerkempe,Rebecca J. Eisen,Brandon Goodell,Kenneth L. Gage,Michael F. Antolin,Colleen T. Webb
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0022498
Abstract: Host populations for the plague bacterium, Yersinia pestis, are highly variable in their response to plague ranging from near deterministic extinction (i.e., epizootic dynamics) to a low probability of extinction despite persistent infection (i.e., enzootic dynamics). Much of the work to understand this variability has focused on specific host characteristics, such as population size and resistance, and their role in determining plague dynamics. Here, however, we advance the idea that the relative importance of alternative transmission routes may vary causing shifts from epizootic to enzootic dynamics. We present a model that incorporates host and flea ecology with multiple transmission hypotheses to study how transmission shifts determine population responses to plague. Our results suggest enzootic persistence relies on infection of an off-host flea reservoir and epizootics rely on transiently maintained flea infection loads through repeated infectious feeds by fleas. In either case, early-phase transmission by fleas (i.e., transmission immediately following an infected blood meal) has been observed in laboratory studies, and we show that it is capable of driving plague dynamics at the population level. Sensitivity analysis of model parameters revealed that host characteristics (e.g., population size and resistance) vary in importance depending on transmission dynamics, suggesting that host ecology may scale differently through different transmission routes enabling prediction of population responses in a more robust way than using either host characteristics or transmission shifts alone.
Environmental and Demographic Determinants of Avian Influenza Viruses in Waterfowl across the Contiguous United States
Matthew L. Farnsworth, Ryan S. Miller, Kerri Pedersen, Mark W. Lutman, Seth R. Swafford, Philip D. Riggs, Colleen T. Webb
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032729
Abstract: Outbreaks of avian influenza in North American poultry have been linked to wild waterfowl. A first step towards understanding where and when avian influenza viruses might emerge from North American waterfowl is to identify environmental and demographic determinants of infection in their populations. Laboratory studies indicate water temperature as one determinant of environmental viral persistence and we explored this hypothesis at the landscape scale. We also hypothesized that the interval apparent prevalence in ducks within a local watershed during the overwintering season would influence infection probabilities during the following breeding season within the same local watershed. Using avian influenza virus surveillance data collected from 19,965 wild waterfowl across the contiguous United States between October 2006 and September 2009 We fit Logistic regression models relating the infection status of individual birds sampled on their breeding grounds to demographic characteristics, temperature, and interval apparent prevalence during the preceding overwintering season at the local watershed scale. We found strong support for sex, age, and species differences in the probability an individual duck tested positive for avian influenza virus. In addition, we found that for every seven days the local minimum temperature fell below zero, the chance an individual would test positive for avian influenza virus increased by 5.9 percent. We also found a twelve percent increase in the chance an individual would test positive during the breeding season for every ten percent increase in the interval apparent prevalence during the prior overwintering season. These results suggest that viral deposition in water and sub-freezing temperatures during the overwintering season may act as determinants of individual level infection risk during the subsequent breeding season. Our findings have implications for future surveillance activities in waterfowl and domestic poultry populations. Further study is needed to identify how these drivers might interact with other host-specific infection determinants, such as species phylogeny, immunological status, and behavioral characteristics.
A Bayesian Approach for Modeling Cattle Movements in the United States: Scaling up a Partially Observed Network
Tom Lindstr?m, Daniel A. Grear, Michael Buhnerkempe, Colleen T. Webb, Ryan S. Miller, Katie Portacci, Uno Wennergren
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0053432
Abstract: Networks are rarely completely observed and prediction of unobserved edges is an important problem, especially in disease spread modeling where networks are used to represent the pattern of contacts. We focus on a partially observed cattle movement network in the U.S. and present a method for scaling up to a full network based on Bayesian inference, with the aim of informing epidemic disease spread models in the United States. The observed network is a 10% state stratified sample of Interstate Certificates of Veterinary Inspection that are required for interstate movement; describing approximately 20,000 movements from 47 of the contiguous states, with origins and destinations aggregated at the county level. We address how to scale up the 10% sample and predict unobserved intrastate movements based on observed movement distances. Edge prediction based on a distance kernel is not straightforward because the probability of movement does not always decline monotonically with distance due to underlying industry infrastructure. Hence, we propose a spatially explicit model where the probability of movement depends on distance, number of premises per county and historical imports of animals. Our model performs well in recapturing overall metrics of the observed network at the node level (U.S. counties), including degree centrality and betweenness; and performs better compared to randomized networks. Kernel generated movement networks also recapture observed global network metrics, including network size, transitivity, reciprocity, and assortativity better than randomized networks. In addition, predicted movements are similar to observed when aggregated at the state level (a broader geographic level relevant for policy) and are concentrated around states where key infrastructures, such as feedlots, are common. We conclude that the method generally performs well in predicting both coarse geographical patterns and network structure and is a promising method to generate full networks that incorporate the uncertainty of sampled and unobserved contacts.
Anticipating the Prevalence of Avian Influenza Subtypes H9 and H5 in Live-Bird Markets
Kim M. Pepin, Jia Wang, Colleen T. Webb, Jennifer A. Hoeting, Mary Poss, Peter J. Hudson, Wenshan Hong, Huachen Zhu, Yi Guan, Steven Riley
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056157
Abstract: An ability to forecast the prevalence of specific subtypes of avian influenza viruses (AIV) in live-bird markets would facilitate greatly the implementation of preventative measures designed to minimize poultry losses and human exposure. The minimum requirement for developing predictive quantitative tools is surveillance data of AIV prevalence sampled frequently over several years. Recently, a 4-year time series of monthly sampling of hemagglutinin subtypes 1–13 in ducks, chickens and quail in live-bird markets in southern China has become available. We used these data to investigate whether a simple statistical model, based solely on historical data (variables such as the number of positive samples in host X of subtype Y time t months ago), could accurately predict prevalence of H5 and H9 subtypes in chickens. We also examined the role of ducks and quail in predicting prevalence in chickens within the market setting because between-species transmission is thought to occur within markets but has not been measured. Our best statistical models performed remarkably well at predicting future prevalence (pseudo-R2 = 0.57 for H9 and 0.49 for H5), especially considering the multi-host, multi-subtype nature of AIVs. We did not find prevalence of H5/H9 in ducks or quail to be predictors of prevalence in chickens within the Chinese markets. Our results suggest surveillance protocols that could enable more accurate and timely predictive statistical models. We also discuss which data should be collected to allow the development of mechanistic models.
Scaling from traits to ecosystems: Developing a general Trait Driver Theory via integrating trait-based and metabolic scaling theories
Brian J. Enquist,Jon Norberg,Stephen P. Bonser,Cyrille Violle,Colleen T. Webb,Amanda Henderson,Lindsey L. Sloat,Van M. Savage
Quantitative Biology , 2015,
Abstract: The rise of trait-based ecology has led to an increased focus on the distribution and dynamics of traits in communities. However, a general theory of trait-based ecology, that can apply across different scales (e.g., species that differ in size) and gradients (e.g., temperature), has yet to be formulated. While research focused on metabolic and allometric scaling theory provides the basis for such a theory it does not explicitly account for differences traits within and across taxa, such as variation in the optimal temperature for growth. Here we synthesize trait-based and metabolic scaling approaches into a framework that we term Trait Drivers Theory or TDT. It shows that the shape and dynamics of trait distributions can be uniquely linked to fundamental drivers of community assembly and how the community will respond to future drivers. To assess predictions and assumptions of TDT, we review several theoretical studies, recent empirical studies spanning local and biogeographic gradients. Further, we analyze how the shift in trait distributions influences ecosystem productivity across an elevational gradient and a 140-year long ecological experiment. We argue that our general TDT provides a baseline for (i) recasting the predictions of ecological theories based on species richness in terms of the shape of trait distributions; and (ii) integrating how specific traits, including body size, and functional diversity scale up to influence the dynamics of species assemblages across climatic gradients and how shifts in functional composition influences ecosystem functioning. Further, it offers a novel framework to integrate trait, metabolic/allometric, and species-richness based approaches in order to build a more predictive functional biogeography to show how assemblages of species have and will respond to climate change.
Programmable Ligand Detection System in Plants through a Synthetic Signal Transduction Pathway
Mauricio S. Antunes,Kevin J. Morey,J. Jeff Smith,Kirk D. Albrecht,Tessa A. Bowen,Jeffrey K. Zdunek,Jared F. Troupe,Matthew J. Cuneo,Colleen T. Webb,Homme W. Hellinga,June I. Medford
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0016292
Abstract: There is an unmet need to monitor human and natural environments for substances that are intentionally or unintentionally introduced. A long-sought goal is to adapt plants to sense and respond to specific substances for use as environmental monitors. Computationally re-designed periplasmic binding proteins (PBPs) provide a means to design highly sensitive and specific ligand sensing capabilities in receptors. Input from these proteins can be linked to gene expression through histidine kinase (HK) mediated signaling. Components of HK signaling systems are evolutionarily conserved between bacteria and plants. We previously reported that in response to cytokinin-mediated HK activation in plants, the bacterial response regulator PhoB translocates to the nucleus and activates transcription. Also, we previously described a plant visual response system, the de-greening circuit, a threshold sensitive reporter system that produces a visual response which is remotely detectable and quantifiable.
The Impact of Movements and Animal Density on Continental Scale Cattle Disease Outbreaks in the United States
Michael G. Buhnerkempe, Michael J. Tildesley, Tom Lindstr?m, Daniel A. Grear, Katie Portacci, Ryan S. Miller, Jason E. Lombard, Marleen Werkman, Matt J. Keeling, Uno Wennergren, Colleen T. Webb
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0091724
Abstract: Globalization has increased the potential for the introduction and spread of novel pathogens over large spatial scales necessitating continental-scale disease models to guide emergency preparedness. Livestock disease spread models, such as those for the 2001 foot-and-mouth disease (FMD) epidemic in the United Kingdom, represent some of the best case studies of large-scale disease spread. However, generalization of these models to explore disease outcomes in other systems, such as the United States’s cattle industry, has been hampered by differences in system size and complexity and the absence of suitable livestock movement data. Here, a unique database of US cattle shipments allows estimation of synthetic movement networks that inform a near-continental scale disease model of a potential FMD-like (i.e., rapidly spreading) epidemic in US cattle. The largest epidemics may affect over one-third of the US and 120,000 cattle premises, but cattle movement restrictions from infected counties, as opposed to national movement moratoriums, are found to effectively contain outbreaks. Slow detection or weak compliance may necessitate more severe state-level bans for similar control. Such results highlight the role of large-scale disease models in emergency preparedness, particularly for systems lacking comprehensive movement and outbreak data, and the need to rapidly implement multi-scale contingency plans during a potential US outbreak.
Abundance of the endangered Cape parrot, Poicephalus robustus in South Africa: implications for its survival
Colleen T. Downs
African Zoology , 2011,
Abstract: Factors affecting the decline of the endangered Cape parrot, which is endemic to South Africa, are presented. Its abundance and status were investigated during annual intensive national surveys. The merits of such a census are reported. Presence of birds was unpredictable at forest patches throughout its range. Present distributions in forest fragments reflect past distribution in a larger mosaic of forest patches. Numbers are low and the best estimate of numbers is 300–350 birds in the Eastern Cape, 170–220 in KwaZulu-Natal, and 50–60 in Limpopo Province. This suggests less than 1000 Cape parrots remain in the wild. About 20% of the entire population of the Cape parrot resident within the forest mosaic of southern KwaZulu-Natal roosts in one particular forest, which consequently needs urgent conservation protection.
Survival, persistence, and regeneration of the reindeer lichens, Cladina stellaris, C. rangiferina, and C. mitis following clearcut logging and forest fire in northwestern Ontario
Elizabeth T. Webb
Rangifer , 1998,
Abstract: The responses of the reindeer lichens (Cladina stellaris, C. rangiferina, and C. mitis) to logging and fire were compared in lichen-rich forest stands in northwestern Ontario. In the summer of 1992, reindeer lichen cover, in total and by species, was visually estimated and detailed notes were taken on reindeer lichen conditions, modes of reproduction, and substrate use on 34 undisturbed, burned, or logged sites. While virtually no reindeer lichens survived forest fire, much of the reindeer lichen cover remained after logging. Reindeer lichen cover increased with time since fire. Total reindeer lichen cover was not correlated with time since logging. Fragment growth was found to be an important mode of reproduction on logged sites, and occurred with greater frequency on logged sites than on burned sites. Colonization of organic substrates by reindeer lichens was observed on both logged and burned sites.
Abundance and home ranges of feral cats in an urban conservancy where there is supplemental feeding: a case study from South Africa
Jaclyn Tennent,Colleen T. Downs
African Zoology , 2011,
Abstract: There is much debate surrounding the impact of feral cats (Felis catus) on wildlife. Conservancies are usually areas where indigenous flora and fauna are protected and aliens excluded or managed. The University of KwaZulu-Natal’s Howard College campus (HCC) is an urban conservancy containing feral cats that are presently not managed, and little is known about their ecology and behaviour. Consequently a feral cat population census was conducted, and their home range investigated. Estimates of the overall campus feral cat population numbers ranged between 23.4–40.0 cats/km2 with a minimum of 55 identified as resident. They were not randomly distributed in the study area, with spacing patterns being related to resource availability. Home range area and core distribution of eight radio-collared cats were determined over 13 months. Total home range areas were relatively small, with considerable overlap between them. Home ranges were clustered in areas with permanent feeding stations and these were also within the cats’ core ranges. Supp
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