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High Connectivity (high + connectivity)
Selected AbstractsEffect of Small-World Networks on Epidemic Propagation and InterventionGEOGRAPHICAL ANALYSIS, Issue 3 2009Zengwang Xu The small-world network, characterized by special structural properties of high connectivity and clustering, is one of the highlights in recent advances in network science and has the potential to model a variety of social contact networks. In an attempt to better understand how these structural properties of small-world networks affect epidemic propagation and intervention, this article uses an agent-based approach to investigate the interplay between an epidemic process and its underlying network structure. Small-world networks are derived from a network "rewiring" process, which readjusts edges in a completely regular two-dimensional network by different rewiring probabilities (0,1) to produce a spectrum of modified networks on which an agent-based simulation of epidemic propagation can be conducted. A comparison of simulated epidemics discloses the effect of small-world networks on epidemic propagation as well as the effectiveness of different intervention strategies, including mass vaccination, acquaintance vaccination, targeted vaccination, and contact tracing. Epidemics taking place on small-world networks tend to reach large-scale epidemic peaks within a short time period. Among the four intervention strategies tested, only one strategy,the targeted vaccination,proves to be effective for containing epidemics, a finding supported by a simulation of the severe acute respiratory syndrome epidemic in a large-scale realistic social contact network in Portland, OR. Las redes de mundo de pequeño (,small-world networks'), caracterizadas por sus propiedades estructurales especiales de alta conectividad y aglomeración (,clustering') son uno de los ejemplos más destacados de los avances más recientes de la ciencia de redes, y tiene el potencial de modelar una gran variedad de redes sociales de contacto. En un intento de comprender mejor como estas propiedades estructurales de redes ,small-world' afectan la propagación e intervención de epidemias, el estudio presente emplea un enfoque basado en modelos multi-agente (,agent based') para investigar la interacción entre el proceso epidémico y la estructura de redes en la que estan integrados. Las redes de mundo pequeño se derivan del proceso de recableado (,rewiring') el cual reajusta los límites en una red 2-D de acuerdo a varias probabilidades de reconexión (0-1) para producir un abanico de posibles de redes modificadas sobre los cuales se condujo una simulación multi-agente de la propagación de la epidemia. El efecto de las redes ,small world' y de las diferentes estrategias de intervención (por ejemplo, diferentes estrategias de vacunación) son evidenciadas mediante la comparación entre varias simulaciones de la epidemia. Las epidemias que ocurren en redes de tipo ,small-world' tienden a alcanzar picos de gran escala epidémica en un corto periodo de tiempo. Entre las estrategias evaluadas, sólo una ,vacunación dirigida a una población objetivo (,targeted vaccination')- demostró ser efectiva en la contención de la epidemia. Dicho resultado se obtuvo vía la simulación de la epidemia de SRAS (Síndrome Respiratorio Agudo Severo ,SARS') realiada en Portland, Oregon (EEUU). [source] Surrogacy and persistence in reserve selection: landscape prioritization for multiple taxa in BritainJOURNAL OF APPLIED ECOLOGY, Issue 1 2009Aldina M. A. Franco Summary 1A principal goal of protected-area networks is to maintain viable populations of as many species as possible, particularly those that are vulnerable to environmental change outside reserves. Ideally, one wants to be able to protect all biodiversity when selecting priority areas for conservation. 2Using the area-prioritization algorithm ZONATION, we identified the locations where UK Biodiversity Action Plan (BAP) species of mammals, birds, herptiles, butterflies and plants occur in concentrated populations with high connectivity. Both these features are likely to be correlated with population persistence. The analyses were successful in maintaining a high proportion of the connectivity of narrow-range species, and large total amounts of the connectivity of wider-range species over 10% of the land surface of Great Britain. 3Biodiversity Action Plan (BAP , high priority) species of one taxonomic group were not particularly good surrogates (indicators) for BAP species of other taxonomic groups. Hence, maintaining population concentrations of one taxonomic group did not guarantee doing likewise for other taxa. 4Species with narrow geographic ranges were most effective at predicting conservation success for other species, probably because they represent the range of environmental conditions required by other species. 5Synthesis and applications. This study identifies landscape-scale priority areas for conservation of priority species from several taxonomic groups, using the Zonation software. ,Indicator groups' were only partially successful as predictors of priority areas for other taxonomic groups, and therefore, the identification of priority areas for biodiversity conservation should include information from all taxonomic groups available. Larger areas should be protected to account for species not included in the analyses. Conservation solutions based on data for many different species, and particularly those species with narrowly defined ranges, appear to be most effective at protecting other rare taxa. [source] Connectivity and binding-site recognition: Applications relevant to drug designJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2010Christopher J. R. Illingworth Abstract Here, we describe a family of methods based on residue,residue connectivity for characterizing binding sites and apply variants of the method to various types of protein,ligand complexes including proteases, allosteric-binding sites, correctly and incorrectly docked poses, and inhibitors of protein,protein interactions. Residues within ligand-binding sites have about 25% more contact neighbors than surface residues in general; high-connectivity residues are found in contact with the ligand in 84% of all complexes studied. In addition, a k-means algorithm was developed that may be useful for identifying potential binding sites with no obvious geometric or connectivity features. The analysis was primarily carried out on 61 protein,ligand structures from the MEROPS protease database, 250 protein,ligand structures from the PDBSelect (25%), and 30 protein,protein complexes. Analysis of four proteases with crystal structures for multiple bound ligands has shown that residues with high connectivity tend to have less variable side-chain conformation. The relevance to drug design is discussed in terms of identifying allosteric-binding sites, distinguishing between alternative docked poses and designing protein interface inhibitors. Taken together, this data indicate that residue,residue connectivity is highly relevant to medicinal chemistry. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Interactions between habitat quality and connectivity affect immigration but not abundance or population growth of the butterfly, Parnassius smintheusOIKOS, Issue 10 2009Stephen F. Matter Habitat geometry has been a primary focus in studies of spatially structured systems. Recent studies have indicated that a more comprehensive approach including habitat quality may be needed, however most previous studies have neglected potential interactions between quality and geometry. We investigated the effects of habitat quality for the butterfly Parnassius smintheus among a series of 17 sub-populations. Specifically, we examined how habitat connectivity and local nectar flower density affect dispersal, and local population abundance and growth. We first determined which flower species were potentially important by examining nectar flower electivity and then quantified nectar flower density in meadows over a five year period (2003,2007). These data along with meadow connectivity were compared to local population statistics derived from mark,recapture over the same time period. The number of immigrants to a meadow increased as meadow connectivity increased, but showed no direct relationship with nectar flower density; however, there was a significant interaction between meadow connectivity and nectar flower density such that meadows with high connectivity and a high density of nectar flowers received the greatest number of immigrants. The number of emigrants from a meadow increased with increasing habitat quality and connectivity, but showed no interactive effect. The abundance of butterflies increased with meadow connectivity, but showed no relationship with habitat quality or any interactive effect. Separate experiments showed that access to nectar flowers significantly increased female reproductive output, but not lifespan. Despite the effects on immigration and reproductive output, local population growth rates also showed no relationship to nectar flower density. Our results indicate that habitat quality can be important for immigration in spatially structured populations; however, effects of habitat quality may not necessarily translate into higher abundance or population growth. Additionally, habitat quality should not be considered independently from habitat isolation, particularly if it directly affects dispersal. Preserving or augmenting habitat quality will do little to bolster immigration or colonization without adequate connectivity. [source] The importance of ecosystem-based management for conserving aquatic migratory pathways on tropical high islands: a case study from FijiAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2010Aaron P. Jenkins Abstract 1.Tropical, high islands of the Pacific have developed unique freshwater fish faunas that are currently threatened by a range of human activities. This paper documents distinct differences in life history strategies from fish communities found in streams of Fiji compared with fish assemblages in freshwater systems on larger continental land masses. While river systems of northern Australia and Papua New Guinea have a high proportion of freshwater residents, the Fiji fauna is dominated by amphidromous gobiids that migrate across a broad range of habitats throughout their life cycle. 2.The number of amphidromous fish species and the number of all fish species in mid-reaches of Fiji rivers are significantly affected by loss of catchment forest cover and introductions of tilapia (Oreochromis spp.). On average, stream networks with established Oreochromis spp. populations have 11 fewer species of native fish than do intact systems. The fish that disappear are mostly eleotrid and gobiid taxa, which have important dietary and economic value. 3.Based on the strong links between catchment land clearing, non-native species introductions and loss of migratory pathways for freshwater fish, spatial information was compiled on a national scale to identify priority areas for conservation in Fiji with intact connectivity between forests, hydrologic networks and coral reefs. Areas with high connectivity included remote, largely undeveloped regions of Vanua Levu (Kubulau, Wainunu, Dama, Udu Point, Natewa, Qelewara) and Taveuni, as well as smaller mapping units (Naikorokoro, Sawakasa) of Viti Levu with low density of roads and high relative amounts of mangroves and reefs. 4.These priority areas for conservation can only be effectively protected and managed through cross-sectoral collaboration and ecosystem-based approaches. Copyright © 2009 John Wiley & Sons, Ltd. [source] A method to assess longitudinal riverine connectivity in tropical streams dominated by migratory biota,AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2009Kelly E. Crook Abstract 1.One way in which dams affect ecosystem function is by altering the distribution and abundance of aquatic species. 2.Previous studies indicate that migratory shrimps have significant effects on ecosystem processes in Puerto Rican streams, but are vulnerable to impediments to upstream or downstream passage, such as dams and associated water intakes where stream water is withdrawn for human water supplies. Ecological effects of dams and water withdrawals from streams depend on spatial context and temporal variability of flow in relation to the amount of water withdrawn. 3.This paper presents a conceptual model for estimating the probability that an individual shrimp is able to migrate from a stream's headwaters to the estuary as a larva, and then return to the headwaters as a juvenile, given a set of dams and water withdrawals in the stream network. The model is applied to flow and withdrawal data for a set of dams and water withdrawals in the Caribbean National Forest (CNF) in Puerto Rico. 4.The index of longitudinal riverine connectivity (ILRC), is used to classify 17 water intakes in streams draining the CNF as having low, moderate, or high connectivity in terms of shrimp migration in both directions. An in-depth comparison of two streams showed that the stream characterized by higher water withdrawal had low connectivity, even during wet periods. Severity of effects is illustrated by a drought year, where the most downstream intake caused 100% larval shrimp mortality 78% of the year. 5.The ranking system provided by the index can be used as a tool for conservation ecologists and water resource managers to evaluate the relative vulnerability of migratory biota in streams, across different scales (reach-network), to seasonally low flows and extended drought. This information can be used to help evaluate the environmental tradeoffs of future water withdrawals. Copyright © 2009 John Wiley & Sons, Ltd. [source] Short-term differences in animal assemblages in patches formed by loss and growth of habitatAUSTRAL ECOLOGY, Issue 5 2010PETER I. MACREADIE Abstract Ecological theory predicts that habitat growth and loss will have different effects on community structure, even if they produce patches of the same size. Despite this, studies on the effects of patchiness are often performed without prior knowledge of the processes responsible for the patchiness. We manipulated artificial seagrass habitat in temperate Australia to test whether fish and crustacean assemblages differed between habitats that formed via habitat loss and habitat growth. Habitat loss treatments (originally 16 m2) and habitat growth treatments (originally 0 m2) were manipulated over 1 week until each reached a final patch size of 4 m2. At this size, each was compared through time (0,14 days after manipulation) with control patches (4 m2 throughout the experiment). Assemblages differed significantly among treatments at 0 and 1 day after manipulation, with differences between growth and loss treatments contributing to most of the dissimilarity. Immediately after the final manipulation, total abundance in habitat loss treatments was 46% and 62% higher than controls and habitat growth treatments, respectively, which suggests that animals crowded into patches after habitat loss. In contrast to terrestrial systems, crowding effects were brief (,1 day), signifying high connectivity in marine systems. Growth treatments were no different to controls, despite the lower probability of animals encountering patches during the growth phase. Our study shows that habitat growth and loss can cause short-term differences in animal abundance and assemblage structure, even if they produce patches of the same size. [source] | ||||||||||