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Search Results: 1 - 10 of 201947 matches for " Andy P Dobson "
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Yellowstone Wolves and the Forces That Structure Natural Systems
Andy P. Dobson
PLOS Biology , 2014, DOI: 10.1371/journal.pbio.1002025
Abstract: Since their introduction in 1995 and 1996, wolves have had effects on Yellowstone that ripple across the entire structure of the food web that defines biodiversity in the Northern Rockies ecosystem. Ecological interpretations of the wolves have generated a significant amount of debate about the relative strength of top-down versus bottom-up forces in determining herbivore and vegetation abundance in Yellowstone. Debates such as this are central to the resolution of broader debates about the role of natural enemies and climate as forces that structure food webs and modify ecosystem function. Ecologists need to significantly raise the profile of these discussions; understanding the forces that structure food webs and determine species abundance and the supply of ecosystem services is one of the central scientific questions for this century; its complexity will require new minds, new mathematics, and significant, consistent funding.
Natural History, a Master Class
Andy Dobson
PLOS Biology , 2013, DOI: 10.1371/journal.pbio.1001496
Abstract:
Spatial Guilds in the Serengeti Food Web Revealed by a Bayesian Group Model
Edward B. Baskerville ,Andy P. Dobson,Trevor Bedford,Stefano Allesina,T. Michael Anderson,Mercedes Pascual
PLOS Computational Biology , 2011, DOI: 10.1371/journal.pcbi.1002321
Abstract: Food webs, networks of feeding relationships in an ecosystem, provide fundamental insights into mechanisms that determine ecosystem stability and persistence. A standard approach in food-web analysis, and network analysis in general, has been to identify compartments, or modules, defined by many links within compartments and few links between them. This approach can identify large habitat boundaries in the network but may fail to identify other important structures. Empirical analyses of food webs have been further limited by low-resolution data for primary producers. In this paper, we present a Bayesian computational method for identifying group structure using a flexible definition that can describe both functional trophic roles and standard compartments. We apply this method to a newly compiled plant-mammal food web from the Serengeti ecosystem that includes high taxonomic resolution at the plant level, allowing a simultaneous examination of the signature of both habitat and trophic roles in network structure. We find that groups at the plant level reflect habitat structure, coupled at higher trophic levels by groups of herbivores, which are in turn coupled by carnivore groups. Thus the group structure of the Serengeti web represents a mixture of trophic guild structure and spatial pattern, in contrast to the standard compartments typically identified. The network topology supports recent ideas on spatial coupling and energy channels in ecosystems that have been proposed as important for persistence. Furthermore, our Bayesian approach provides a powerful, flexible framework for the study of network structure, and we believe it will prove instrumental in a variety of biological contexts.
Climate forcing and desert malaria: the effect of irrigation
Andres Baeza, Menno J Bouma, Andy P Dobson, Ramesh Dhiman, Harish C Srivastava, Mercedes Pascual
Malaria Journal , 2011, DOI: 10.1186/1475-2875-10-190
Abstract: Remote sensing data for the Normalized Difference Vegetation Index (NDVI) are used as an integrated measure of rainfall to examine correlation maps within the districts and at regional scales. The analyses specifically address whether irrigation has decreased the coupling between malaria incidence and climate variability, and whether this reflects (1) a breakdown of NDVI as a useful indicator of risk, (2) a weakening of rainfall forcing and a concomitant decrease in epidemic risk, or (3) an increase in the control of malaria transmission. The predictive power of NDVI is compared against that of rainfall, using simple linear models and wavelet analysis to study the association of NDVI and malaria variability in the time and in the frequency domain respectively.The results show that irrigation dampens the influence of climate forcing on the magnitude and frequency of malaria epidemics and, therefore, reduces their predictability. At low irrigation levels, this decoupling reflects a breakdown of local but not regional NDVI as an indicator of rainfall forcing. At higher levels of irrigation, the weakened role of climate variability may be compounded by increased levels of control; nevertheless this leads to no significant decrease in the actual risk of disease. This implies that irrigation can lead to more endemic conditions for malaria, creating the potential for unexpectedly large epidemics in response to excess rainfall if these climatic events coincide with a relaxation of control over time. The implications of our findings for control policies of epidemic malaria in arid regions are discussed.The response of epidemic malaria to large-scale change in land-use practices related to irrigation and agriculture in arid regions remains poorly understood [1]. In the last three decades, for example, the expansion of a large network of irrigation canals has supplied an important source of freshwater for agriculture in many arid regions of India; in so doing, it has also cont
Assessing the burden of pregnancy-associated malaria under changing transmission settings
Mario Recker, Menno J Bouma, Paul Bamford, Sunetra Gupta, Andy P Dobson
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-245
Abstract: Here, by re-examining historical data, it is demonstrated how excess female mortality can be used to evaluate the burden of PAM. A simple mathematical model is then developed to highlight the contrasting signatures of PAM within the endemicity spectrum and to show how PAM is influenced by the intensity and stability of transmission.Both the data and the model show that maternal malaria has a huge impact on the female population. This is particularly pronounced in low-transmission settings during epidemic outbreaks where excess female mortality/morbidity can by far exceed that of a similar endemic setting.The results presented here call for active intervention measures not only in highly endemic regions but also, or in particular, in areas where malaria transmission is low and seasonal.Malaria during pregnancy poses a significant threat to both the mother and unborn child. For the mother, it increases the risk of illness, severe anaemia and death; for the unborn child it increases the risk of intra-uterine growth retardation and low birth weight, spontaneous abortion and stillbirth (reviewed in [1]). Numerous epidemiological studies have highlighted the various aspects of malaria during pregnancy both in highly endemic regions (mostly from sub-Saharan Africa) and in regions where malaria transmission is low and sporadic (mainly from Asia) (see e.g. [1-4]), and it has become clear that the pathology of malaria during pregnancy and its evaluation are highly dependent on the particular epidemiological setting, due to differences in acquired immunity in women reaching child-bearing age.Acquired immunity to Plasmodium falciparum, the most virulent agent of human malaria, is a gradual process by which individuals build up a repertoire of protective immune responses over years of repeated exposure. Although sterilizing immunity might never be attained, people living in malaria endemic areas seem to acquire protection against clinical malaria after a certain period of exposu
Seasonal Patterns of Infectious Diseases
Mercedes Pascual ,Andy Dobson
PLOS Medicine , 2005, DOI: 10.1371/journal.pmed.0020005
Abstract:
The surface structure of gold
P. J. Dobson
Gold Bulletin , 1974, DOI: 10.1007/BF03215028
Abstract: The anomalous nature of the first two or three atomic layers of a gold surface has an important effect in a number of technical fields, including catalysis and the bonding to semiconductors, and could be responsible for its resistance to oxidation. This paper reviews our present knowledge of the single crystal surfaces of gold and attempts to reconcile some conflicting ideas that have been put forward on the origin of the anomalous structure observed on the cube face.
Rabies Exposures, Post-Exposure Prophylaxis and Deaths in a Region of Endemic Canine Rabies
Katie Hampson ,Andy Dobson,Magai Kaare ?,Jonathan Dushoff,Matthias Magoto,Emmanuel Sindoya,Sarah Cleaveland
PLOS Neglected Tropical Diseases , 2008, DOI: 10.1371/journal.pntd.0000339
Abstract: Background Thousands of human deaths from rabies occur annually despite the availability of effective vaccines following exposure, and for disease control in the animal reservoir. Our aim was to assess risk factors associated with exposure and to determine why human deaths from endemic canine rabies still occur. Methods and Findings Contact tracing was used to gather data on rabies exposures, post-exposure prophylaxis (PEP) delivered and deaths in two rural districts in northwestern Tanzania from 2002 to 2006. Data on risk factors and the propensity to seek and complete courses of PEP was collected using questionnaires. Exposures varied from 6–141/100,000 per year. Risk of exposure to rabies was greater in an area with agropastoralist communities (and larger domestic dog populations) than an area with pastoralist communities. Children were at greater risk than adults of being exposed to rabies and of developing clinical signs. PEP dramatically reduced the risk of developing rabies (odds ratio [OR] 17.33, 95% confidence interval [CI] 6.39–60.83) and when PEP was not delivered the risks were higher in the pastoralist than the agro-pastoralist area (OR 6.12, 95% CI 2.60–14.58). Low socioeconomic class and distance to medical facilities lengthened delays before PEP delivery. Over 20% of rabies-exposed individuals did not seek medical treatment and were not documented in official records and <65% received PEP. Animal bite injury records were an accurate indicator of rabies exposure incidence. Conclusions Insufficient knowledge about rabies dangers and prevention, particularly prompt PEP, but also wound management, was the main cause of rabies deaths. Education, particularly in poor and marginalized communities, but also for medical and veterinary workers, would prevent future deaths.
Transmission Dynamics and Prospects for the Elimination of Canine Rabies
Katie Hampson,Jonathan Dushoff,Sarah Cleaveland,Daniel T. Haydon,Magai Kaare,Craig Packer,Andy Dobson
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1000053
Abstract: Rabies has been eliminated from domestic dog populations in Western Europe and North America, but continues to kill many thousands of people throughout Africa and Asia every year. A quantitative understanding of transmission dynamics in domestic dog populations provides critical information to assess whether global elimination of canine rabies is possible. We report extensive observations of individual rabid animals in Tanzania and generate a uniquely detailed analysis of transmission biology, which explains important epidemiological features, including the level of variation in epidemic trajectories. We found that the basic reproductive number for rabies, R0, is very low in our study area in rural Africa (~1.2) and throughout its historic global range (<2). This finding provides strong support for the feasibility of controlling endemic canine rabies by vaccination, even near wildlife areas with large wild carnivore populations. However, we show that rapid turnover of domestic dog populations has been a major obstacle to successful control in developing countries, thus regular pulse vaccinations will be required to maintain population-level immunity between campaigns. Nonetheless our analyses suggest that with sustained, international commitment, global elimination of rabies from domestic dog populations, the most dangerous vector to humans, is a realistic goal.
Transmission Dynamics and Prospects for the Elimination of Canine Rabies
Katie Hampson ,Jonathan Dushoff,Sarah Cleaveland,Daniel T Haydon,Magai Kaare ?,Craig Packer,Andy Dobson
PLOS Biology , 2009, DOI: 10.1371/journal.pbio.1000053
Abstract: Rabies has been eliminated from domestic dog populations in Western Europe and North America, but continues to kill many thousands of people throughout Africa and Asia every year. A quantitative understanding of transmission dynamics in domestic dog populations provides critical information to assess whether global elimination of canine rabies is possible. We report extensive observations of individual rabid animals in Tanzania and generate a uniquely detailed analysis of transmission biology, which explains important epidemiological features, including the level of variation in epidemic trajectories. We found that the basic reproductive number for rabies, R0, is very low in our study area in rural Africa (~1.2) and throughout its historic global range (<2). This finding provides strong support for the feasibility of controlling endemic canine rabies by vaccination, even near wildlife areas with large wild carnivore populations. However, we show that rapid turnover of domestic dog populations has been a major obstacle to successful control in developing countries, thus regular pulse vaccinations will be required to maintain population-level immunity between campaigns. Nonetheless our analyses suggest that with sustained, international commitment, global elimination of rabies from domestic dog populations, the most dangerous vector to humans, is a realistic goal.
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