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Long-term Persistence (long-term + persistence)
Selected AbstractsLong-term outcome of pediatric obsessive,compulsive disorder: a meta-analysis and qualitative review of the literatureACTA PSYCHIATRICA SCANDINAVICA, Issue 1 2004S. E. Stewart Objective:, To review the extant literature on the long-term outcome of child/adolescent-onset obsessive,compulsive disorder (OCD). Method:, Medline and Psychlit databases were systematically searched for articles regarding long-term outcomes of child/adolescent-onset OCD. Meta-analysis regression was applied to evaluate predictors and persistence of OCD. Results:, Sixteen study samples (n = 6,132; total = 521 participants) in 22 studies had follow-up periods ranging between 1 and 15.6 years. Pooled mean persistence rates were 41% for full OCD and 60% for full or subthreshold OCD. Earlier age of OCD onset (z = ,3.26, P = 0.001), increased OCD duration (z = 2.22, P = 0.027) and in-patient vs. out-patient status (z = 2.94, P = 0.003) predicted greater persistence. Comorbid psychiatric illness and poor initial treatment response were poor prognostic factors. Although psychosocial function was frequently compromised, most studies lacked comprehensive outcome measures. Conclusion:, Long-term persistence of pediatric OCD may be lower than believed. Future studies should include broader measures of outcome including symptomatic persistence and functional impairment in multiple domains. [source] P27 Long-term persistence of A098G RT mutation after cessation of non-nucleoside (NNRTI) therapy: a marker of NNRTI exposureHIV MEDICINE, Issue 3 2000A Pozniak [source] Modelling the efficacy of entomopathogenic nematodes in the regulation of invertebrate pests in glasshouse cropsJOURNAL OF APPLIED ECOLOGY, Issue 2 2000A. Fenton Summary 1. ,Entomopathogenic nematodes belonging to the families Heterorhabditidae and Steinernematidae are lethal obligate parasites of a wide range of invertebrate species. These nematodes exhibit many characteristics that make them ideal candidates as biological control agents of insect pests (rapid host death, high reproductive rates, easily mass-reared in vitro, easy application techniques). 2. ,However, at present, the number of pest species to which these nematodes are applied successfully is small. Clearly, there is a need to develop existing knowledge of the nematode into a more complete understanding of the nematode,pest system as a whole. 3. ,To consider the potential of entomopathogenic nematodes as biological control agents, we adopted a generalized analytical modelling approach and, using realistic parameter estimates, determined the conditions under which these nematodes can regulate a pest population. 4. ,Stability analyses suggested that entomopathogenic nematodes may not be capable of regulating a host population to a stable equilibrium. Long-term persistence of the host and nematode population is unlikely, due to the highly destabilizing effects of the parasite,host relationship. As such, these nematodes may be better suited to short-term control through inundative application techniques rather than long-term regulation. 5. ,This preliminary generalized model highlights areas where further work is needed. This includes estimation of the probability of nematode infection in the field, the effect of host size on the transmission cycle and the influence of spatial heterogeneity on stability. [source] Area-Based Refinement for Selection of Reserve Sites with the Benefit-Function ApproachCONSERVATION BIOLOGY, Issue 2 2007ANNI ARPONEN algoritmo de selección de sitios; persistencia; peso de especies; relaciones especies-área; selección de reservas Abstract:,Optimization of resource use is necessary for efficient conservation planning. Many reserve-selection algorithms aim to identify representative but inexpensive networks, which may lead to selecting small sites due to their lower costs and collectively higher species richness. Nevertheless, larger sites would be preferable regarding species' long-term persistence. An area-based refinement can be used to overcome this problem. We used a reserve-planning framework in which continuous benefit functions valued representation (numbers of populations), and differential species weights were based on a species' local rarity and threatened status. We introduced a refinement based on the species-area relationship that provides relatively higher values for larger sites. We applied the proposed method to rich fen vegetation in southern Finland. The species-area refinement resulted in a network of significantly larger sites with minor trade-offs with representation (numbers of populations). Giving endangered species higher weights ensured that the trade-off occurred mostly between site size and representation of low-priority species. We recommend using a species-area refinement for practical, maximum-coverage conservation planning. Resumen:,La optimización del uso de recursos es necesaria para la planificación eficiente de la conservación. Muchos algoritmos para la selección de reservas tratan de identificar redes representativas pero poco costosas, que pueden conducir a la selección de sitios pequeños debido a sus costos menores y mayor riqueza de especies colectiva. Sin embargo, los sitios grandes serían preferibles para la persistencia de las especies a largo plazo. Para sobreponerse a este problema se puede utilizar un refinamiento basado en el área. Utilizamos un marco de referencia para la planificación de reservas en el que las funciones de beneficio continuas valoraron la representación (número de poblaciones), y los pesos diferenciales de las especies se basaron en la rareza local de una especie y en su estatus de amenaza. Introdujimos un refinamiento basado en la relación especies-área que proporciona valores relativamente mayores a los sitios grandes. Aplicamos el método propuesto a la rica vegetación de ciénegas en el sur de Finlandia. El refinamiento de las especies-área resultó en una red de sitios significativamente más grandes con desequilibrios menores en la representación (número de poblaciones). La asignación de valores más altos a las especies en peligro aseguró que el desequilibrio ocurriera principalmente entre el tamaño del sitio y la representación de especies de prioridad baja. Recomendamos la utilización de de un refinamiento de especies-área para una planificación de la conservación de cobertura máxima. [source] Remarkable Amphibian Biomass and Abundance in an Isolated Wetland: Implications for Wetland ConservationCONSERVATION BIOLOGY, Issue 5 2006J. WHITFIELD GIBBONS biodiversidad; declinación de anfibios; recuperación de humedales sequía; uso de suelo Abstract:,Despite the continuing loss of wetland habitats and associated declines in amphibian populations, attempts to translate wetland losses into measurable losses to ecosystems have been lacking. We estimated the potential productivity from the amphibian community that would be compromised by the loss of a single isolated wetland that has been protected from most industrial, agricultural, and urban impacts for the past 54 years. We used a continuous drift fence at Ellenton Bay, a 10-ha freshwater wetland on the Savannah River Site, near Aiken, South Carolina (U.S.A.), to sample all amphibians for 1 year following a prolonged drought. Despite intensive agricultural use of the land surrounding Ellenton Bay prior to 1951, we documented 24 species and remarkably high numbers and biomass of juvenile amphibians (>360,000 individuals; >1,400 kg) produced during one breeding season. Anurans (17 species) were more abundant than salamanders (7 species), comprising 96.4% of individual captures. Most (95.9%) of the amphibian biomass came from 232095 individuals of a single species of anuran (southern leopard frog[Rana sphenocephala]). Our results revealed the resilience of an amphibian community to natural stressors and historical habitat alteration and the potential magnitude of biomass and energy transfer from isolated wetlands to surrounding terrestrial habitat. We attributed the postdrought success of amphibians to a combination of adult longevity (often >5 years), a reduction in predator abundance, and an abundance of larval food resources. Likewise, the increase of forest cover around Ellenton Bay from <20% in 1951 to >60% in 2001 probably contributed to the long-term persistence of amphibians at this site. Our findings provide an optimistic counterpoint to the issue of the global decline of biological diversity by demonstrating that conservation efforts can mitigate historical habitat degradation. Resumen:,A pesar de la pérdida de hábitats de humedales y las declinaciones asociadas de poblaciones de anfibios, se han realizado pocos intentos para traducir las pérdidas de humedales en pérdidas mensurables en los ecosistemas. Estimamos la productividad potencial de la comunidad de anfibios que se afectaría por la pérdida de un humedal aislado que ha estado protegido de los impactos industriales, agrícolas y urbanos durante los últimos 54 años. Utilizamos un cerco de desvío en la Bahía Ellentonn, un humedal dulceacuícola de 10 ha en el Río Savannah, cerca de Aiken, Carolina del Sur (E.U.A.), para muestrear todos los anfibios durante 1 año después de una sequía prolongada. A pesar del intensivo uso agrícola del suelo alrededor de la Bahía Ellenton antes de 1951, documentamos 24 especies y números y biomasa de anfibios juveniles notablemente altos (>360,000 individuos; >1,400 kg) en una temporada reproductiva. Los anuros (17 especies) fueron más abundantes que las salamandras (7 especies), y comprendieron 96.4% de las capturas individuales. La mayor parte (95.9%) de la biomasa provino de 232095 individuos de una sola especie de anuro (Rana sphenocephala). Nuestros resultados revelaron que la resiliencia de la comunidad de anfibios a los estresantes naturales y a la alteración histórica del hábitat y la magnitud potencial de la transferencia de biomasa y energía desde los humedales aislados hacia el hábitat terrestre circundante. Atribuimos el éxito post-sequía de los anfibios a una combinación de longevidad de adultos (a menudo > 5 años), la reducción de la abundancia de depredadores y la abundancia de recursos alimenticios para las larvas. Asimismo, el incremento de la cobertura forestal alrededor de la Bahía Ellerton de < 20% en 1951 a > 60% en 2001 probablemente contribuyó a la persistencia de los anfibios a largo plazo en este sitio. Nuestros hallazgos proporcionan un contrapunto optimista al tema de la declinación global de la diversidad biológica al demostrar que los esfuerzos de conservación pueden mitigar a la degradación histórica del hábitat. [source] Wilderness and future conservation priorities in AustraliaDIVERSITY AND DISTRIBUTIONS, Issue 6 2009James E.M. Watson Abstract Aim, Most approaches to conservation prioritization are focused on biodiversity features that are already threatened. While this is necessary in the face of accelerating anthropogenic threats, there have been calls to conserve large intact landscapes, often termed ,wilderness', to ensure the long-term persistence of biodiversity. In this study, we examine the consequences of directing conservation expenditure using a threat-based framework for wilderness conservation. Location, The Australian continent. Methods, We measured the degree of congruence between the extent of wilderness and the Australian protected area network in 2000 and 2006, which was established using a threat-based systematic planning framework. We also assessed priority areas for future reserve acquisitions identified by the Australian government under the current framework. Results, In 2000, 14% of Australia's wilderness was under formal protection, while the protected area network covered only 8.5% of the continent, suggesting a historical bias towards wilderness protection. However, the expansion of the reserve system from 2000 to 2006 was biased towards non-wilderness areas. Moreover, 90% of the wilderness that was protected over this period comprised areas not primarily designated for biodiversity conservation. We found a significant (P < 0.05) negative relationship between bioregions considered to be a priority for future reserve prioritization and the amount of wilderness they contain. Main conclusions, While there is an urgent need to overcome past biases in reserve network design so as to better protect poorly represented species and habitats, prioritization approaches should not become so reactive as to ignore the role that large, intact landscapes play in conserving biodiversity, especially in a time of human-induced climate change. This can be achieved by using current or future threats rather than past threats to prioritize areas, and by incorporating key ecological processes and costs of acquisition and management within the planning framework. [source] Conversion of sagebrush shrublands to exotic annual grasslands negatively impacts small mammal communitiesDIVERSITY AND DISTRIBUTIONS, Issue 5 2009Steven M. Ostoja Abstract Aim, The exotic annual cheatgrass (Bromus tectorum) is fast replacing sagebrush (Artemisia tridentata) communities throughout the Great Basin Desert and nearby regions in the Western United States, impacting native plant communities and altering fire regimes, which contributes to the long-term persistence of this weedy species. The effect of this conversion on native faunal communities remains largely unexamined. We assess the impact of conversion from native perennial to exotic annual plant communities on desert rodent communities. Location, Wyoming big sagebrush shrublands and nearby sites previously converted to cheatgrass-dominated annual grasslands in the Great Basin Desert, Utah, USA. Methods, At two sites in Tooele County, Utah, USA, we investigated with Sherman live trapping whether intact sagebrush vegetation and nearby converted Bromus tectorum -dominated vegetation differed in rodent abundance, diversity and community composition. Results, Rodent abundance and species richness were considerably greater in sagebrush plots than in cheatgrass-dominated plots. Nine species were captured in sagebrush plots; five of these were also trapped in cheatgrass plots, all at lower abundances than in the sagebrush. In contrast, cheatgrass-dominated plots had no species that were not found in sagebrush. In addition, the site that had been converted to cheatgrass longer had lower abundances of rodents than the site more recently converted to cheatgrass-dominated plots. Despite large differences in abundances and species richness, Simpson's D diversity and Shannon-Wiener diversity and Brillouin evenness indices did not differ between sagebrush and cheatgrass-dominated plots. Main conclusions, This survey of rodent communities in native sagebrush and in converted cheatgrass-dominated vegetation suggests that the abundances and community composition of rodents may be shifting, potentially at the larger spatial scale of the entire Great Basin, where cheatgrass continues to invade and dominate more landscape at a rapid rate. [source] Functional dentate gyrus neurogenesis in a rapid kindling seizure modelEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2006Paul D. Smith Abstract Neurogenesis in the adult mammalian hippocampus resulting in long-term persistence of new neurons with features of capacity for functional activation is recognized. Many stimuli are capable of increasing the rate of neurogenesis, including seizure activity. Whether these insults result in an increased number of new functionally active neurons over and above the baseline rate of neurogenesis is not known. The rapid electrical amygdala kindling (REAK) model of seizures isolates the effects of seizures alone in the absence of neuronal death and the resulting seizures induce expression of c-Fos in the vast majority of dentate gyrus (DG) granule cells. C57BL/6 mice were exposed to REAK then injected with bromodeoxyuridine (BrDU) to label dividing cells, then re-exposed to REAK after a delay period to allow detection of functional activation in new neurons by measurement c-Fos expression in response to seizures. Adult subgranular zone cells migrated into the DG granule cell layer (GCL), assumed a neuronal phenotype and demonstrated seizure-dependent responsiveness. Larger absolute numbers of new neurons demonstrating seizure-dependent activation were found in the GCL of previously kindled mice. Seizures are capable of increasing the number of new neurons with the capacity for functional activation laid down in the postseizure period and incorporated into seizure-activated circuitry. [source] PHYLOGENETIC ANALYSIS OF ECOMORPHOLOGICAL DIVERGENCE, COMMUNITY STRUCTURE, AND DIVERSIFICATION RATES IN DUSKY SALAMANDERS (PLETHODONTIDAE: DESMOGNATHUS)EVOLUTION, Issue 9 2005Kenneth H. Kozak Abstract An important dimension of adaptive radiation is the degree to which diversification rates fluctuate or remain constant through time. Focusing on plethodontid salamanders of the genus Desmognathus, we present a novel synthetic analysis of phylogeographic history, rates of ecomorphological evolution and species accumulation, and community assembly in an adaptive radiation. Dusky salamanders are highly variable in life history, body size, and ecology, with many endemic lineages in the southern Appalachian Highlands of eastern North America. Our results show that lifehistory evolution had important consequences for the buildup of plethodontid-salamander species richness and phenotypic disparity in eastern North America, a global hot spot of salamander biodiversity. The origin of Desmognathus species with aquatic larvae was followed by a high rate of lineage accumulation, which then gradually decreased toward the present time. The peak period of lineage accumulation in the group coincides with evolutionary partitioning of lineages with aquatic larvae into seepage, stream-edge, and stream microhabitats. Phylogenetic simulations demonstrate a strong correlation between morphology and microhabitat ecology independent of phylogenetic effects and suggest that ecomorphological changes are concentrated early in the radiation of Desmognathus. Deep phylogeographic fragmentation within many codistributed ecomorph clades suggests long-term persistence of ecomorphological features and stability of endemic lineages and communities through multiple climatic cycles. Phylogenetic analyses of community structure show that ecomorphological divergence promotes the coexistence of lineages and that repeated, independent evolution of microhabitat-associated ecomorphs has a limited role in the evolutionary assembly of Desmognathus communities. Comparing and contrasting our results to other adaptive radiations having different biogeographic histories, our results suggest that rates of diversification during adaptive radiation are intimately linked to the degree to which community structure persists over evolutionary time. [source] Factors affecting habitat selection by a small spawning charr population, bull trout, Salvelinus confluentus: implications for recovery of an endangered speciesFISHERIES MANAGEMENT & ECOLOGY, Issue 1 2004R. C. Wissmar Abstract Bull trout, Salvelinus confluentus (Suckley), populations are declining in many streams of North America and are listed under the Endangered Species Act in the United States. Many small populations are isolated in fragmented habitats where spawning conditions and success are not well understood. Factors affecting habitats selected for redds by spawning bull trout and redd habitat characteristics within Gold Creek, a headwater stream in the Yakima River within the Columbia River basin, Washington State, USA, were evaluated. Most spawning (>80% of the redds) occurred in upstream habitats after dewatering of downstream channels isolated fish. Habitats were selected or avoided in proportions different to their availability. For example, most bull trout selected pools and glides and avoided riffles despite the latter being more readily available. Although preferences suggest influences of prolonged fish entrapment, site fidelity could be important. A habitat with redds commonly contained abundant cover, gravel substratum and higher stream flows. The major factors influencing habitat selection by spawning fish and their persistence in streams of the Yakima and Columbia River regions include entrapment of fish by dewatering of channels and geographical isolation by dams. The goal of the US Government's recovery plan is ,to ensure the long-term persistence of self-sustaining bull trout populations'. Recovery plans linked to provisions for protecting and conserving bull trout populations and their habitats were recommended. Landscape approaches are needed that provide networks of refuge habitats and greater connectivity between populations. Concurrent recovery efforts are encouraged to focus on protecting small populations and minimizing dangers of hybridization. [source] In vivo studies on the long-term persistence of volatiles in the breathFLAVOUR AND FRAGRANCE JOURNAL, Issue 6 2004M. Hodgson Abstract The long-term persistence of ,ve volatiles in the breath was studied to determine the effects of respiration and the physical properties of each of the volatiles. The long-term persistence of each of the volatiles in the breath was modelled successfully and used to show that the breath volatile concentration 1 min after consuming the solution was greater when panelists exhaled at a slower rate. The air,water partition coef,cient (Kaw) was in,uential in controlling the initial stages of persistence; compounds with a higher Kaw were found to decay at a much faster rate than compounds with a low Kaw. The decay rate during the later stages was constant for all the volatiles, which indicates that the rate-limiting factor during the later stages of persistence does not depend on the individual properties of the volatiles. Copyright © 2004 John Wiley & Sons, Ltd. [source] Association of Sphaeropsis sapinea with insect-damaged red pine shoots and conesFOREST PATHOLOGY, Issue 1 2003E. Feci Summary The association of the shoot blight and canker pathogen Sphaeropsis sapinea with red pine (Pinus resinosa) shoots and cones damaged by insects (especially Dioryctria sp.) was investigated. Samples from a single plantation approximately 35 years old, in Sauk Co., Wisconsin and also from three plantations, between approximately 40 and 50 years old, located in an area of pine shoot moth activity in the preceding year in Adams Co., Wisconsin were visually examined. Samples were arbitrarily collected from trees felled in the first plantation in May. Pycnidia of S. sapinea and insect damage were observed on 56 of 91 (62%) of closed cones and 17 of 165 (7%) of previous year's shoots. In the absence of insect damage, pycnidia of the pathogen were identified only on eight of 91 (9%) closed cones and never on previous year's shoots. In each of the other three plantations, 10 trees were located at intervals along transects in mid-June; one branch from the lower half of the crown per tree was pruned off, and both current and previous year's shoots were examined. Insect damage and S. sapinea pycnidia were too rare on current year's shoots to draw any conclusions. Insect damage occurred on 20,40% of over 2000 previous year's shoots that were examined, but pycnidia of the pathogen were identified on only about 5%. Although infrequent, S. sapinea was identified in association with insect-damaged previous year's shoots from these three plantations three times more frequently than those without insect damage. Random amplified polymorphic DNA (RAPD) markers from eight randomly selected isolates were consistent with the A group of S. sapinea, which can be aggressive on red pine. This ability to exploit insect-damaged shoots may facilitate long-term persistence of S. sapinea at low disease incidence and severity. The potential role of insect wounds as infection courts and insects as vectors of this important pathogen of pines deserves further study. Résumé L'étude a porté sur l'association entre le parasite de pousses et agent de chancre Sphaeropsis sapinea, et les pousses et cônes de Pinus resinosa endommagés par des insectes (surtout Dioryctria sp.). Des échantillons ont été examinés visuellement; ils provenaient d'une plantation d'environ 35 ans à Sauk Co., Wisconsin, et de trois plantations âgées d'environ 40 et 50 ans situées dans une zone où les insectes des pousses avaient été actifs l'année précédente à Adams Co., Wisconsin. Dans la première plantation, les échantillons ont été prélevés arbitrairement sur des arbres abattus en mai. Des pycnides de S. sapinea et des dégâts d'insectes ont été observés sur 56/91 (62%) des cônes fermés et sur 17/165 (7%) des pousses de l'année précédente. En l'absence de dégâts d'insectes, les pycnides n'ont été trouvées que sur 8/91 (9%) des cônes fermés, et jamais sur les pousses de l'année précédente. Dans chacune des trois autres plantations, 10 arbres ont été choisis à la mi-juin le long de transects ; sur chaque arbre une branche a été coupée dans la moitié inférieure de la couronne, et les pousses de l'année en cours et de l'année précédente ont été examinées. Sur les pousses de l'année, les dégâts d'insectes et les pycnides de S. sapineaétaient trop rares pour pouvoir en tirer des conclusions. Parmi plus de 2000 pousses de l'année précédente examinées, les dégâts d'insectes étaient présents sur 20,40% des pousses, mais les pycnides n'ont été trouvées que sur environ 5% d'entre elles. Bien que peu fréquent chez ces trois plantations, S. sapinea a été trouvé associé aux pousses de l'année précédente, 3 fois plus fréquemment chez celles endommagées par les insectes que chez les non endommagées. Pour huit isolats pris au hasard, les marqueurs RAPD ont indiqué leur appartenance au groupe A de S. sapinea qui peut être agressif sur P. resinosa. Cette aptitude de S. sapineaà utiliser les pousses endommagées par les insects peut faciliter sa persistance à long terme à des niveaux bas d'abondance et de dégâts. Le rôle potentiel des blessures d'insectes comme voies d'infection, et des insectes comme vecteurs du champignon parasite mérite d'être étudié. Zusammenfassung Es wurde die Assoziation zwischen Sphaeropsis sapinea (Erreger von Triebsterben und Rindennekrosen) und Schädigung an Trieben und Zapfen von Pinus resinosa untersucht, durch Insekten (vorwiegend Dioryctria sp.) untersucht. Proben von einer ca. 35 Jahre alten Plantage in Sauk Co., Wisconsin und von drei 40-50jährigen Plantagen mit Dioryctria -Befall im Vorjahr in Adams Co., Wisconsin wurden makroskopisch untersucht. Die Proben am ersten Standort wurden von Bäumen entnommen, die im Mai gefällt wurden (willkürliche Auswahl). Pyknidien und Schädigung durch Insekten wurden an 56/91 (62%) der geschlossenen Zapfen und an 17/165 (7%) der vorjährigen Triebe beobachtet. An Organen ohne Schädigung durch Insekten wurden die Pyknidien des Pathogens nur bei 8/91 (9%) der geschlossenen Zapfen und in keinem Fall an den vorjährigen Trieben nachgewiesen. In den anderen drei Plantagen wurden Mitte Juni je 10 Bäume entlang von Transekten untersucht; pro Baum wurde aus dem unteren Kronenbereich ein Ast abgeschnitten und sowohl die diesjährigen als auch die vorjährigen Triebe wurden untersucht. An den diesjährigen Triebabschnitten waren sowohl Schädigungen durch Insekten als auch Pyknidien von S. sapinea zu selten, um daraus Schlüsse zu ziehen. An den vorjährigen Triebabschnitten kamen Insektenschäden an 20,40% von über 2,000 untersuchten Objekten vor, aber Pyknidien des Pathogens wurden nur in 5% der Fälle nachgewiesen. Trotz des geringen Vorkommens wurde S. sapinea auf den vorjährigen und von Insekten beschädigten Trieben dreimal häufiger nachgewiesen als an Trieben ohne Beschädigung. Acht zufällig ausgewählte Isolate wurden anhand von RAPD Markern der Gruppe A von S. sapinea zugeordnet, die auf P. resinosa agressiv sein kann. Die Fähigkeit von S. sapinea, durch Insekten beschädigte Triebe zu nutzen, kann das Überdauern des Pilzes auf einem niedrigen Befallsniveau erleichtern. Die Bedeutung von Wunden, die durch Insekten verursacht werden, als Infektionspforten und die mögliche Rolle von Insekten als Vektoren dieses wichigen Pathogens sollte in weiteren Untersuchungen geklärt werden. [source] Photo-induced Charge Transfer and Relaxation of Persistent Charge Carriers in Polymer/Nanocrystal Composites for Applications in Hybrid Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Marc Daniel Heinemann Abstract The photo-induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3-hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc-CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and [6,6]-phenyl C61 -butyric acid methyl ester (PCBM) are studied as well. The light-induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo-induced absorption (PIA) and light-induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo-excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long-term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc-CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed. [source] Persistence and the four-factor model in the Australian funds market: a noteACCOUNTING & FINANCE, Issue 1 2010Jacquelyn E. Humphrey G11; G23 Abstract We investigate whether Australian fund managers are able to deliver persistent performance using Carhart's (1997) four-factor model. Short- and long-term persistence is examined and the sample is also divided into unit trusts and superannuation funds. We do not find evidence of persistence in any sample of funds. We find that winner (loser) funds tend to hold past winner (loser) stocks. Winner and loser unit trusts both appear to have positive exposure to small stocks. [source] Reconstructing the demise of Tethyan plants: climate-driven range dynamics of Laurus since the PlioceneGLOBAL ECOLOGY, Issue 6 2008Francisco Rodríguez-Sánchez ABSTRACT Aim Climate changes are thought to be responsible for the retreat and eventual extinction of subtropical lauroid species that covered much of Europe and North Africa during the Palaeogene and early Neogene; little is known, however, of the spatial and temporal patterns of this demise. Herein we calibrate ecological niche models to assess the climatic requirements of Laurus L. (Lauraceae), an emblematic relic from the Tethyan subtropical flora, subsequently using these models to infer how the range dynamics of Laurus were affected by Plio-Pleistocene climate changes. We also provide predictions of likely range changes resulting from future climatic scenarios. Location The Mediterranean Basin and Macaronesian islands (Canaries, Madeira, Azores). Methods We used a maximum-entropy algorithm (Maxent) to model the relationship between climate and Laurus distribution over time. The models were fitted both to the present and to the middle Pliocene, based on fossil records. We employed climatic reconstructions for the mid-Pliocene (3 Ma), the Last Glacial Maximum (21 ka) and a CO2 -doubling future scenario to project putative species distribution in each period. We validated the model projections with Laurus fossil and present occurrences. Results Laurus preferentially occupied warm and moist areas with low seasonality, showing a marked stasis of its climatic niche. Models fitted to Pliocene conditions successfully predicted the current species distribution. Large suitable areas existed during the Pliocene, which were strongly reduced during the Pleistocene, but humid refugia within the Mediterranean Basin and Macaronesian islands enabled long-term persistence. Future climate conditions are likely to re-open areas suitable for colonization north of the current range. Main conclusions The climatic requirements of Laurus remained virtually unchanged over the last 3 Myr. This marked niche conservatism imposed largely deterministic range dynamics driven by climate conditions. This species's relatively high drought tolerance might account for the survival of Laurus in continental Europe throughout the Quaternary whilst other Lauraceae became extinct. Climatic scenarios for the end of this century would favour an expansion of the species's range towards northern latitudes, while severely limiting southern populations due to increased water stress. [source] Pharmaceuticals and Other Organic Waste Water Contaminants Within a Leachate Plume Downgradient of a Municipal LandfillGROUND WATER MONITORING & REMEDIATION, Issue 2 2004Kimberlee K. Barnes Ground water samples collected from the Norman Landfill research site in central Oklahoma were analyzed as part of the U.S. Geological Survey (USGS) Toxic Substances Hydrology Program's national reconnaissance of pharmaceuticals and other organic waste water contaminants (OWCs) in ground water. Five sites, four of which are located downgradient of the landfill, were sampled in 2000 and analyzed for 76 OWCs using four research methods developed by the USGS. OWCs were detected in water samples from all of the sites sampled, with 22 of the 76 OWCs being detected at least once. Cholesterol (a plant and animal steroid), was detected at all five sites and was the only compound detected in a well upgradient of the landfill. N,N-diethyltoluamide (DEBT used in insect repellent) and tri(2-chloroethyl) phosphate (fire-retardant) were detected in water samples from all four sites located within the landfill-derived leachate plume. The sites closest to the landfill had more detections and greater concentrations of each of the detected compounds than sites located farther away. Detection of multiple OWCs occurred in the four sites located within the leachate plume, with a minimum of four and a maximum of 17 OWCs detected. Because the landfill was established in the 1920s and closed in 1985, many compounds detected in the leachate plume were likely disposed of decades ago. These results indicate the potential for long-term persistence and transport of some OWCs in ground water. [source] Trends in timing of low stream flows in Canada: impact of autocorrelation and long-term persistenceHYDROLOGICAL PROCESSES, Issue 8 2010Eghbal Ehsanzadeh Abstract The annual timing of river flows might indicate changes that are climate related. In this study, trends in timing of low flows for the Reference Hydrometric Basin Network were investigated under three different hypotheses namely: independence, short-term persistence (STP) and long-term persistence (LTP). Both summer and winter time series were characterized with scaling behaviour providing strong evidence of LTP. The Mann,Kendall trend test was modified to account for STP and LTP, and used to detect trends in timing of low flows. It was found that considering STP and LTP resulted in a significant decrease in the number of detected trends. Numerical analysis showed that the timing of summer 7-day low flows exhibited significant trends in 16, 9 and 7% of stations under independence, STP and LTP assumptions, respectively. Timing of summer low flow shifted toward later dates in western Canada, whereas the majority of stations in the east half of the country (except Atlantic Provinces) experienced a shift toward earlier dates. Timing of winter low flow experienced significant trends in 20, 12, and 6% of stations under independence, STP and LTP assumptions, respectively. Shift in timing of winter low flow toward earlier dates was dominant all over the country where it shifted toward earlier dates in up to 3/4 of time series with significant trends. There are local patterns of upward significant/insignificant trends in southeast, southwest and northern Canada. This study shows that timing of low flows in Canada is time dependent; however, addressing the full complexity of memory properties (i.e. short term vs long term) of a natural process is beyond the scope of this study. Copyright © 2009 John Wiley & Sons, Ltd. [source] Using habitat distribution models to evaluate large-scale landscape priorities for spatially dynamic speciesJOURNAL OF APPLIED ECOLOGY, Issue 1 2008Regan Early Summary 1Large-scale conservation planning requires the identification of priority areas in which species have a high likelihood of long-term persistence. This typically requires high spatial resolution data on species and their habitat. Such data are rarely available at a large geographical scale, so distribution modelling is often required to identify the locations of priority areas. However, distribution modelling may be difficult when a species is either not recorded, or not present, at many of the locations that are actually suitable for it. This is an inherent problem for species that exhibit metapopulation dynamics. 2Rather than basing species distribution models on species locations, we investigated the consequences of predicting the distribution of suitable habitat, and thus inferring species presence/absence. We used habitat surveys to define a vegetation category which is suitable for a threatened species that has spatially dynamic populations (the butterfly Euphydryas aurinia), and used this as the response variable in distribution models. Thus, we developed a practical strategy to obtain high resolution (1 ha) large scale conservation solutions for E. aurinia in Wales, UK. 3Habitat-based distribution models had high discriminatory power. They could generalize over a large spatial extent and on average predicted 86% of the current distribution of E. aurinia in Wales. Models based on species locations had lower discriminatory power and were poorer at generalizing throughout Wales. 4Surfaces depicting the connectivity of each grid cell were calculated for the predicted distribution of E. aurinia habitat. Connectivity surfaces provided a distance-weighted measure of the concentration of habitat in the surrounding landscape, and helped identify areas where the persistence of E. aurinia populations is expected to be highest. These identified successfully known areas of high conservation priority for E. aurinia. These connectivity surfaces allow conservation planning to take into account long-term spatial population dynamics, which would be impossible without being able to predict the species' distribution over a large spatial extent. 5Synthesis and applications. Where species location data are unsuitable for building high resolution predictive habitat distribution models, habitat data of sufficient quality can be easier to collect. We show that they can perform as well as or better than species data as a response variable. When coupled with a technique to translate distribution model predictions into landscape priority (such as connectivity calculations), we believe this approach will be a powerful tool for large-scale conservation planning. [source] Validity of methyl mercury hair analysis: mercury monitoring in human scalp/nude mouse modelJOURNAL OF APPLIED TOXICOLOGY, Issue 4 2008Grazyna Zareba Abstract Objective. The grafting of human scalp hair was used as a new application of this method to explore methyl mercury incorporation into human hair and to validate this model for mercury monitoring in hair. Methods. Human scalp grafts were transplanted to athymic BALB/c nude mice. The animals were exposed to methyl mercury either as a single dose i.p. or continuously for 4 months, using ALZET osmotic pumps. The mercury concentration in hair was determined using x-ray fluorescence (XRF) spectrometry by segmental (2 mm) analysis of a single strand, and tissue concentrations were measured by cold vapor atomic absorption analysis. Results. Human scalp hair grown in nude mice showed long-term persistence of human features including the expression of histocompatibility antigens (KAB 3, W 6/32, SF 1-1.1.1) and normal hair morphometry. The disposition of methyl mercury in nude mice followed a one-compartment model with a whole body elimination half-life of 6.7 days (elimination constant, k = 0.1/day). Autoradiographic studies revealed that methyl mercury was rapidly incorporated into areas of the hair follicle undergoing active keratinization. Methyl mercury concentrations in human hair transplanted onto nude mice were two orders of magnitude higher than in blood and attained a mean hair: blood ratio of 217 : 1, similar to ratios reported only in human studies. Conclusions. This study demonstrated that human hair grown on nude mice can record the level of exposure to methyl mercury and can serve as a valuable research tool to study mercury incorporation into human hair. Copyright © 2007 John Wiley & Sons, Ltd. [source] Phylogeography of the world's tallest angiosperm, Eucalyptus regnans: evidence for multiple isolated Quaternary refugiaJOURNAL OF BIOGEOGRAPHY, Issue 1 2010Paul G. Nevill Abstract Aim, There is a need for more Southern Hemisphere phylogeography studies, particularly in Australia, where, unlike much of Europe and North America, ice sheet cover was not extensive during the Last Glacial Maximum (LGM). This study examines the phylogeography of the south-east Australian montane tree species Eucalyptus regnans. The work aimed to identify any major evolutionary divergences or disjunctions across the species' range and to examine genetic signatures of past range contraction and expansion events. Location, South-eastern mainland Australia and the large island of Tasmania. Methods, We determined the chloroplast DNA haplotypes of 410 E. regnans individuals (41 locations) based on five chloroplast microsatellites. Genetic structure was examined using analysis of molecular variance (AMOVA), and a statistical parsimony tree was constructed showing the number of nucleotide differences between haplotypes. Geographic structure in population genetic diversity was examined with the calculation of diversity parameters for the mainland and Tasmania, and for 10 regions. Regional analysis was conducted to test hypotheses that some areas within the species' current distribution were refugia during the LGM and that other areas have been recolonized by E. regnans since the LGM. Results, Among the 410 E. regnans individuals analysed, 31 haplotypes were identified. The statistical parsimony tree shows that haplotypes divided into two distinct groups corresponding to mainland Australia and Tasmania. The distribution of haplotypes across the range of E. regnans shows strong geographic patterns, with many populations and even certain regions in which a particular haplotype is fixed. Many locations had unique haplotypes, particularly those in East Gippsland in south-eastern mainland Australia, north-eastern Tasmania and south-eastern Tasmania. Higher haplotype diversity was found in putative refugia, and lower haplotype diversity in areas likely to have been recolonized since the LGM. Main conclusions, The data are consistent with the long-term persistence of E. regnans in many regions and the recent recolonization of other regions, such as the Central Highlands of south-eastern mainland Australia. This suggests that, in spite of the narrow ecological tolerances of the species and the harsh environmental conditions during the LGM, E. regnans was able to persist locally or contracted to many near-coastal refugia, maintaining a diverse genetic structure. [source] Tertiary relict trees in a Mediterranean climate: abiotic constraints on the persistence of Prunus lusitanica at the eroding edge of its rangeJOURNAL OF BIOGEOGRAPHY, Issue 8 2008Fernando Pulido Abstract Aim, To investigate the ecophysiological traits allowing persistence of a subtropical relict tree (Prunus lusitanica L.) under a dry Mediterranean climate at the eroding edge of its range. Location, A glasshouse for the study under controlled conditions and two marginal populations located in riparian forests of central Spain and exposed to summer drought, in contrast to subtropical populations that grow in mountain cloud forests. Methods, Two experiments were conducted to assess tolerance to the abiotic conditions found in riparian habitats. In a glasshouse experiment, gas-exchange and light-use parameters were measured to evaluate seedling responses to a factorial combination of irradiance (60%, 10%, 2% and 0.5% full sun) and moisture (well watered control and drought stress). In a parallel field experiment, irradiance and soil moisture were measured as predictors of seedling survival at two sites in which half the seedlings were subjected to a threefold increase in summer precipitation by adding water every 10 days. Results Soil moisture strongly determined survival both in the glasshouse and in the two field sites. In the field, periodic addition of water failed to increase survival. Water-use efficiency (WUE) increased with drought. Seedlings did not tolerate deep shade (2,0.5%) and their performance and survival were better when exposed to moderate (10%) or high (60%) irradiance. The effect of water stress on seedling performance was stronger at moderate irradiance, moderate at high irradiance and negligible at very low light. Seedling size (height and number of leaves) attained after 1 month of experimental treatments had a positive effect on survival at the end of the summer, hence greater survival was not achieved at the expense of vertical growth. Main conclusions, While studies in Macaronesia have shown that P. lusitanica occupies a wide range of moisture conditions along mountain slopes, it behaves as an obligate riparian species in dry peripheral populations. Intolerance to deep shade and tolerance to moderate and high irradiance allow the species to grow in small and moist gaps, or in treeless river sections. Despite the species' low range filling in marginal, drought-prone regions, long-term persistence might have been achieved through shifts to riparian habitats serving as local refuges. [source] Species richness, rarity and endemicity on Italian offshore islands: complementary signals from island-focused and species-focused analysesJOURNAL OF BIOGEOGRAPHY, Issue 4 2008Leonardo Dapporto Abstract Aims, To investigate the relative explanatory power of source faunas and geographical variables for butterfly incidence, frequency, richness, rarity, and endemicity on offshore islands. Location, The western Italian offshore islands (Italy and Malta). Methods, Thirty-one islands were examined. Data were taken from our own field surveys and from the literature. Two approaches were undertaken, described as island-focused and species-focused, respectively. Offshore islands were allocated to their neighbouring source landmasses (Italian Peninsula, Sicily and Sardinia,Corsica) and compared with each other for faunal attributes, source and island geography. Generalized linear and stepwise multiple regression models were then used to determine the relationships of island species richness, rarity and endemicity with potential geographical predictors and source richness, rarity, and endemicity (island-focused). Species frequency and incidence were assessed in relation to geographical and source predictors using stepwise linear and logistic regression, and inter-island associations were examined using K-Means clustering and non-metric scaling (species-focused). Results, The analysis reveals firm evidence for the influence of the nearest large landmass sources on island species assemblages, richness, rarity and endemicity. A clear distinction in faunal affinities occurs between the Sardinian islands and islands lying offshore from the Italian mainland and Sicily. Islands neighbouring these three distinct sources differ significantly in richness, rarity and endemicity. Source richness, rarity, and endemicity have explanatory power for island richness, rarity, and endemicity, respectively, and together with island geography account for a substantial part of the variation in island faunas (richness 59%, rarity 60% and endemicity 64%). Source dominates the logistic regression parameters predicting the incidence of island species [13 (38%) of 34 species that could be analysed]; three ecological factors (source frequency, flight period and maximal altitude at which species live) explained 75% of the variation in the occurrence of species on the islands. Species found more frequently on islands occurred more frequently at sources, had longer flight periods, and occurred at lower altitudes at the sources. The incidence of most species on islands (84%) is correctly predicted by the same three variables. Main conclusions, The Italian region of the Mediterranean Sea has a rich butterfly fauna comprising endemics and rare species as well as more cosmopolitan species. Analysis of island records benefited from the use of two distinct approaches, namely island-focused and species-focused, that sift distinct elements in island and source faunas. Clear contemporary signals appear in island,source relationships as well as historical signals. Differences among faunas relating to sources within the same region caution against assuming that contemporary (ecological) and historical (evolutionary) influences affect faunas of islands in different parts of the same region to the same extent. The implications of source,island relationships for the conservation of butterflies within the Italian region are considered, particularly for the long-term persistence of species. [source] Vegetation and disturbance history of a rare dwarf pitch pine community in western New England, USAJOURNAL OF BIOGEOGRAPHY, Issue 10-11 2002Glenn Motzkin Abstract Aim, This study documents the vegetation history and age-structure of a rare, ridgetop dwarf pine,oak community and compares the dynamics of this unusual vegetation with similar dwarf pine communities found elsewhere in the north-eastern United States (US). Location, The study area is located on the summit of Mt Everett in the Taconic Mountains of south-western Berkshire County, Massachusetts, USA (42°06,N 73°26,W). Methods, Vegetation composition, tree age-structure, physical site characteristics, and evidence of fire and other disturbances were determined for twelve 15 × 15 m plots in dwarf pine,oak vegetation and two plots in oak forests on the summit. Age-structure analyses, tree-ring patterns, and historical records of human and natural disturbance were used to investigate the long-term history and dynamics of the summit vegetation. Results, The summit of Mt Everett has been dominated by dwarf pines (1,3 m tall) and ericaceous shrubs similar to the modern vegetation throughout the historical period; there is no evidence that tall-stature forests occurred on the site at any point in the past few centuries. The summit supports uneven-aged stands; pitch pine (Pinus rigida) recruitment began in the 1830s and occurred in every decade since the 1860s. Average pitch pine age is seventy-eight with a range of 12,170 years. Red oak (Quercus rubra) and red maple (Acer rubrum) increased in importance in the twentieth century, with most stems establishing from 1940 to 1980. Pitch pine radial growth rates averaged <0.5 mm year,1 while red oak and red maple averaged 1.0 and 0.8 mm year,1, respectively. In some areas, hardwoods have overtopped pitch pines, apparently resulting in pitch pine mortality. Whereas most dwarf pitch pine communities occur on sites that burn frequently and have a high degree of cone serotiny, we found no evidence of recent fires or cone serotiny. Small amounts of macroscopic charcoal that we documented may have resulted from fires in the pre-European or early historical periods. Conclusions, Harsh edaphic conditions and chronic low-level disturbances on the summit, including frequent winter storms, have apparently contributed to the establishment, long-term persistence, and slow radial growth of dwarf pitch pines on Mt Everett. The ability of dwarf pines to persist on a site in the absence of frequent fire is highly unusual among North-eastern barrens and has not been well-incorporated into previous conceptual ecological models of these communities. Our results suggest that even among North-eastern barrens, the summit of Mt Everett is characterized by highly unusual vegetation and dynamics. The site has long been recognized as regionally significant and should be afforded the strictest conservation protection. With no evident history of human disturbance or recent fire, there is no apparent need for immediate active management of the site. [source] The maintenance of sex: host,parasite coevolution with density-dependent virulenceJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 10 2009C. M. LIVELY Abstract Why don't asexual females replace sexual females in most natural populations of eukaryotes? One promising explanation is that parasites could counter the reproductive advantages of asexual reproduction by exerting frequency-dependent selection against common clones (the Red Queen hypothesis). One apparent limitation of the Red Queen theory, however, is that parasites would seem to be required by theory to be highly virulent. In the present study, I present a population-dynamic view of competition between sexual females and asexual females that interact with co-evolving parasites. The results show that asexual populations have higher carrying capacities, and more unstable population dynamics, than sexual populations. The results also suggest that the spread of a clone into a sexual population could increase the effective parasite virulence as population density increases. This combination of parasite-mediated frequency-dependent selection, and density-dependent virulence, could lead to the coexistence of sexual and asexual reproductive strategies and the long-term persistence of sex. [source] Allochronic differentiation among Daphnia species, hybrids and backcrosses: the importance of sexual reproduction for population dynamics and genetic architectureJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2004T. Jankowski Abstract Seasonal dynamics of the abundance, sexual reproduction and genetic architecture in a Daphnia hyalina-galeata hybrid complex were studied in the large and deep Lake Constance. We found evidence for the occurrence of first and second order hybridization. Our study revealed strong differences between the parental species not only regarding their seasonal dynamics, genetic architecture and diversity, but also their sexual reproductive behaviour. The overwintering D. hyalina showed low genetic diversity, no genetic differentiation during the season, and reproduced sexually in autumn, whereas D. galeata reached higher levels of genetic diversity, reproduced sexually in early summer, and exhibited changes in genetic structure during the season, but was only present from spring to autumn. However, in both species sexual reproduction was a rare event, and daphnids, including hybrids, reproduced predominantly asexually. This allows long-term persistence of hybrids as well without continuing hybridization events. Within all variables studied, F1 and F2 hybrids showed an intermediate pattern, whereas proposed backcross hybrids were more similar to their respective parentals. These differences in phenotype as well as significant differences in pairwise Fst values between parentals suggest that gene flow seems to be relatively low in the Lake Constance hybrid system. We found evidence for unidirectional introgression by backcrossing from D. galeata to D. hyalina and found a decrease in at least one of the proposed introgressed alleles in the hyalina -backcross while the season progressed. Our findings suggest allochronic differentiation within this hybrid population and different microevolutionary trajectories of the parental species, which will be discussed in the light of the ongoing reoligotrophication process of Lake Constance. [source] Intrahepatic long-term persistence of parvovirus B19 and its role in chronic viral hepatitis,JOURNAL OF MEDICAL VIROLOGY, Issue 12 2009Chun Wang Abstract Parvovirus B19 (B19V) has been detected in the liver of Asian patients infected with HBV and may contribute to acute and chronic liver disease. This study aimed to investigate the impact of B19V infection in European patients with viral hepatitis. B19V DNA was detected in 1/91 and 0/50 serum samples from patients with chronic hepatitis C and B, respectively. In contrast, B19V DNA was amplified frequently from explanted end-stage liver tissues (37/50, 74%) and from routine biopsy samples (14/32, 44%) (P,<,0.05). However, there was no significant difference in B19V copy number per cell between these two groups. B19V-specific CD4+ T-cell responses to two dominant MHC-class-restricted epitopes were detected in a similar frequency in healthy anti-B19V-positive individuals (3/19; 16%) and patients with chronic hepatitis C (3/13; 23%). These results indicate that B19V can persist in the liver. However, there is no evidence that B19V is a "hepatitis virus" worsening liver disease in European patients with chronic hepatitis C. J. Med. Virol. 81:2079,2088, 2009. © 2009 Wiley-Liss, Inc. [source] Effects of regional climate and small-scale habitat quality on performance in the relict species Ramonda myconiJOURNAL OF VEGETATION SCIENCE, Issue 2 2002M. Riba Bolòs et al. (1993) Abstract. The Mediterranean Basin harbours paleo-endemic species with a highly restricted and fragmented distribution. Many of them might also be of the remnant type, for which the regional dynamics depends on the persistence of extant populations. Therefore, a key issue for the long-term persistence of these species is to assess the variability and effects of ecological factors determining plant performance. We investigated the spatio-temporal variability in plant traits and ecological factors of Ramonda myconi, a preglacial relict species with remnant dynamics, in 5 populations over 4,7 yr. Ecological factors contributing to fecundity showed a high degree of between-year variability. Pre-dispersal fruit predation had a minor influence on total reproductive output, and most of the variability was found among individuals within populations and years. Spatio-temporal variability in growth and survival was rather low but significant, whereas recruitment showed important between-population variability. Among-year variability in fecundity and growth was related to climatic fluctuations on a regional scale, notably rainfall and temperature in a particular period, while the spatial variability in survival and recruitment was explained by within-population (patch) habitat quality. Although R. myconi is able to withstand repeated periods of drought, water availability seems to be the most important factor affecting plant performance in all the study populations. These findings suggest that the long-term persistence of species showing remnant population dynamics in habitats under the influence of Mediterranean climate might be threatened by increased aridity as a result of climate change. [source] Land clearing reduces gene flow in the granite outcrop-dwelling lizard, Ctenophorus ornatusMOLECULAR ECOLOGY, Issue 19 2010ESTHER LEVY Abstract An important question for the conservation of species dwelling in fragmented habitats is whether changes to the intervening landscape create a barrier to gene flow. Here, we make use of the spatial distribution of the granite outcrop-dwelling lizard, Ctenophorus ornatus, to compare inferred levels of gene flow between outcrops in a nature reserve with that between outcrops in the adjacent agricultural land. Genetic variation, relatedness and subdivision were compared within groups of individuals from different outcrops similar in size and distance apart at each site. In the agricultural land, we found significantly lower genetic variation within outcrops and greater genetic differentiation between outcrops than in the reserve. Further, the rate at which genetic divergence between outcrops increased over geographical distance was significantly greater in the agricultural land than in the reserve. We also found that individuals were more closely related within outcrops but more distantly related between outcrops in the cleared land. These effects occur over a small spatial scale with an average distance between outcrops of less than five kilometres. Thus, even though land clearing around the outcrops leaves outcrop size unchanged, it restricts gene flow, reducing genetic variation and increasing population structure, with potentially negative consequences for the long-term persistence of the lizards on these outcrops. [source] Contrasting patterns of mitochondrial and microsatellite population structure in fragmented populations of greater prairie-chickensMOLECULAR ECOLOGY, Issue 12 2003Jeff A. Johnson Abstract Greater prairie-chickens (Tympanuchus cupido pinnatus) were once found throughout the tallgrass prairie of midwestern North America but over the last century these prairies have been lost or fragmented by human land use. As a consequence, many current populations of prairie-chickens have become isolated and small. This fragmentation of populations is expected to lead to reductions in genetic variation as a result of random genetic drift and a decrease in gene flow. As expected, we found that genetic variation at both microsatellite DNA and mitochondrial DNA (mtDNA) markers was reduced in smaller populations, particularly in Wisconsin. There was relatively little range-wide geographical structure (FST) when we examined mtDNA haplotypes but there was a significant positive relationship between genetic (FST) and geographical distance (isolation by distance). In contrast, microsatellite DNA loci revealed significant geographical structure (FST) and a weak effect of isolation by distance throughout the range. These patterns were much stronger when populations with reduced levels of genetic variability (Wisconsin) were removed from the analyses. This suggests that the effects of genetic drift were stronger than gene flow at microsatellite loci, whereas these forces were in range-wide equilibrium at mtDNA markers. These differences between the two molecular markers may be explained by a larger effective population size (Ne) for mtDNA, which is expected in species such as prairie-chickens that have female-biased dispersal and high levels of polygyny. Our results suggest that historic populations of prairie-chickens were once interconnected by gene flow but current populations are now isolated. Thus, maintaining gene flow may be important for the long-term persistence of prairie-chicken populations. [source] Polyploidy, phylogeography and Pleistocene refugia of the rockfern Asplenium ceterach: evidence from chloroplast DNAMOLECULAR ECOLOGY, Issue 10 2002S. A. Trewick Abstract Chloroplast DNA sequences were obtained from 331 Asplenium ceterach plants representing 143 populations from throughout the range of the complex in Europe, plus outlying sites in North Africa and the near East. We identified nine distinct haplotypes from a 900 bp fragment of trnL-trnF gene. Tetraploid populations were encountered throughout Europe and further afield, whereas diploid populations were scarcer and predominated in the Pannonian-Balkan region. Hexaploids were encountered only in southern Mediterranean populations. Four haplotypes were found among diploid populations of the Pannonian-Balkans indicating that this region formed a northern Pleistocene refugium. A separate polyploid complex centred on Greece, comprises diploid, tetraploid and hexaploid populations with two endemic haplotypes and suggests long-term persistence of populations in the southern Mediterranean. Three chloroplast DNA (cpDNA) haplotypes were common among tetraploids in Spain and Italy, with diversity reducing northwards suggesting expansion from the south after the Pleistocene. Our cpDNA and ploidy data indicate at least six independent origins of polyploids. [source] | ||||||||||||||||||||||||||||||||||||||||