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Zone
Kinds of Zone Terms modified by Zone Selected AbstractsINCIPIENT SPECIATION DESPITE LITTLE ASSORTATIVE MATING: THE YELLOW-RUMPED WARBLER HYBRID ZONEEVOLUTION, Issue 12 2009Alan Brelsford Hybrid zones between recently diverged taxa are natural laboratories for speciation research, allowing us to determine whether there is reproductive isolation between divergent forms and the causes of that isolation. We present a study of a classic avian hybrid zone in North America between two subspecies of the yellow-rumped warbler (Dendroica coronata). Although previous work has shown very little differentiation in mitochondrial DNA across this hybrid zone, we identified two nuclear loci (one sex-linked and one autosomal) that show fixed differences across the hybrid zone, in a close concordance with patterns of plumage variation. Temporal stability and limited width of the hybrid zone, along with substantial linkage disequilibrium between these two diagnostic markers in the center of the zone, indicate that there is moderate reproductive isolation between these populations, with an estimated strength of selection maintaining the zone of 18%. Pairing data indicate that assortative mating is either very weak or absent, suggesting that this reproductive isolation is largely due to postmating barriers. Thus, despite extensive hybridization the two forms are distinct evolutionary groups carrying genes for divergent adaptive peaks, and this situation appears relatively stable. [source] GENETIC ANALYSIS OF A CHROMOSOMAL HYBRID ZONE IN THE AUSTRALIAN MORABINE GRASSHOPPERS (VANDIEMENELLA, VIATICA SPECIES GROUP)EVOLUTION, Issue 1 2009Takeshi Kawakami Whether chromosomal rearrangements promote speciation by providing barriers to gene exchange between populations is one of the long-standing debates in evolutionary biology. This question can be addressed by studying patterns of gene flow and selection in hybrid zones between chromosomally diverse taxa. Here we present results of the first study of the genetic structure of a hybrid zone between chromosomal races of morabine grasshoppers Vandiemenella viatica, P24(XY) and viatica17, on Kangaroo Island, Australia. Chromosomal and 11 nuclear markers revealed a narrow hybrid zone with strong linkage disequilibrium and heterozygote deficits, most likely maintained by a balance between dispersal and selection. Widths and positions of clines for these markers are concordant and coincident, suggesting that selection is unlikely to be concentrated on a few chromosomes. In contrast, a mitochondrial marker showed a significantly wider cline with centre offset toward the P24(XY) side. We argue that the discordance between the mitochondrial and nuclear/chromosomal clines and overall asymmetry of the clines suggest a secondary origin of the contact zone and potential movement of the zone after contact. Genome-wide scans using many genetic markers and chromosomal mapping of these markers are needed to investigate whether chromosomal differences directly reduce gene flow after secondary contact. [source] ECOLOGICAL DIFFERENTIATION AND DIPLOID SUPERIORITY ACROSS A MOVING PLOIDY CONTACT ZONEEVOLUTION, Issue 1 2007Richard J. A. Buggs Plant polyploid complexes provide useful model systems for distinguishing between adaptive and nonadaptive causes of parapatric distributions in closely related lineages. Polyploidy often gives rise to morphological and physiological changes, which may be adaptive to different environments, but separate distributions may also be maintained by reproductive interference caused by postzygotic reproductive isolation. Here, we test the hypothesis that diploid and descendent polyploid races of the wind-pollinated herb Mercurialis annua, which are found in parapatry over an environmental gradient in northeast Spain, are differentiated in their ecophysiology and life history. We also ask whether any such differences represent adaptations to their different natural environments. On the basis of a series of reciprocal transplant experiments in the field, and experiments under controlled conditions, we found that diploid and polyploid populations of M. annua are ecologically differentiated, but that they do not show local adaptation; rather, the diploids have higher fitness than the polyploids across both diploid- and polyploid-occupied regions. In fact, diploids are currently displacing polyploids by advancing south on two separate fronts in Spain, and previous work has shown that this displacement is being driven to a large extent by asymmetrical pollen swamping. Our results here suggest that ecophysiological superiority of the diploids may also be contributing to their expansion. [source] RELATIVE ABUNDANCE AND THE SPECIES-SPECIFIC REINFORCEMENT OF MALE MATING PREFERENCE IN THE CHRYSOCHUS (COLEOPTERA: CHRYSOMELIDAE) HYBRID ZONEEVOLUTION, Issue 12 2005Merrill A. Peterson Abstract Most studies of reinforcement have focused on the evolution of either female choice or male mating cues, following the long-held view in sexual selection theory that mating mastakes are typically more costly for females than for males. However, factors such as conspecific sperm precedence can buffer females against the cost of mating mistakes, suggesting that in some hybrid zones mating mistakes may be more costly for males than for females. Thus, the historical bias in reinforcement research may underestimate its frequency. In this study, we present evidence that reinforcement has driven the evolution of male choice in a hybrid zone between teh highly promiscuous lealf beetles chyrsochus cobaltinus and C. auratus, the hybrids of which have extremely low fitness. In addition, there is evidence for male choice in these beetles and that male mating mistakes may be costly, due to reduced opportunities to mate with conspecific females. The present study combines laboratory and field methods to quantify the strenght of sexual isolation, test the hypothesis of reproductive character displacement, and assess the link between relative abundance and the strenght of selection against hybridization. We document that, while sexual isolation is weak, it is sufficient to produce positive assortative mating. In addtion, reproductive character displacement was only detected in the relatively rare species. The strong postzygotic barriers in this system are sufficient to generate the bimodality that characterizes this hybrid zone, but the weak sexual isolation is not, calling into question whether strong prezygotic isolation is necessary for the maintenance of bimodality. Growing evidence that the cost of mating mistakes is sufficient to shape the evolution of male mate choice suggests that the reinforecement of male mate choice may prove to be a widespread occurrence. [source] DIFFERENTIAL PATTERNS OF INTROGRESSION ACROSS THE X CHROMOSOME IN A HYBRID ZONE BETWEEN TWO SPECIES OF HOUSE MICEEVOLUTION, Issue 9 2004Bret A. Payseur Abstract A complete understanding of the speciation process requires the identification of genomic regions and genes that confer reproductive barriers between species. Empirical and theoretical research has revealed two important patterns in the evolution of reproductive isolation in animals: isolation typically arises as a result of disrupted epistatic interactions between multiple loci and these disruptions map disproportionately to the X chromosome. These patterns suggest that a targeted examination of natural gene flow between closely related species at X-linked markers with known positions would provide insight into the genetic basis of speciation. We take advantage of the existence of genomic data and a well-documented European zone of hybridization between two species of house mice, Mus domesticus and M. musculus, to conduct such a survey. We evaluate patterns of introgression across the hybrid zone for 13 diagnostic X-linked loci with known chromosomal positions using a maximum likelihood model. Interlocus comparisons clearly identify one locus with reduced introgression across the center of the hybrid zone, pinpointing a candidate region for reproductive isolation. Results also reveal one locus with high frequencies of M. domesticus alleles in populations on the M. musculus side of the zone, suggesting the possibility that positive selection may act to drive the spread of alleles from one species on to the genomic background of the other species. Finally, cline width and cline center are strongly positively correlated across the X chromosome, indicating that gene flow of the X chromosome may be asymmetrical. This study highlights the utility of natural populations of hybrids for mapping speciation genes and suggests that the middle of the X chromosome may be important for reproductive isolation between species of house mice. [source] WHEN VICARS MEET: A NARROW CONTACT ZONE BETWEEN MORPHOLOGICALLY CRYPTIC PHYLOGEOGRAPHIC LINEAGES OF THE RAINFOREST SKINK, CARLIA RUBRIGULARISEVOLUTION, Issue 7 2004Ben L. Phillips Abstract Phylogeographic analyses of the fauna of the Australian wet tropics rainforest have provided strong evidence for long-term isolation of populations among allopatric refugia, yet typically there is no corresponding divergence in morphology. This system provides an opportunity to examine the consequences of geographic isolation, independent of morphological divergence, and thus to assess the broader significance of historical subdivisions revealed through mitochondrial DNA phylogeography. We have located and characterized a zone of secondary contact between two long isolated (mtDNA divergence > 15%) lineages of the skink Carlia rubrigularis using one mitochondrial and eight nuclear (two intron, six microsatellite) markers. This revealed a remarkably narrow (width<3 km) hybrid zone with substantial linkage disequilibrium and strong deficits of heterozygotes at two of three nuclear loci with diagnostic alleles. Cline centers were coincident across loci. Using a novel form of likelihood analysis, we were unable to distinguish between sigmoidal and stepped cline shapes except at one nuclear locus for which the latter was inferred. Given estimated dispersal rates of 90,133 m X gen,1/2 and assuming equilibrium, the observed cline widths suggest effective selection against heterozygotes of at least 22,49% and possibly as high as 70%. These observations reveal substantial postmating isolation, although the absence of consistent deviations from Hardy-Weinberg equilibrium at diagnostic loci suggests that there is little accompanying premating isolation. The tight geographic correspondence between transitions in mtDNA and those for nuclear genes and corresponding evidence for selection against hybrids indicates that these morphologically cryptic phylogroups could be considered as incipient species. Nonetheless, we caution against the use of mtDNA phylogeography as a sole criterion for defining species boundaries. [source] ENVIRONMENT-DEPENDENT ADMIXTURE DYNAMICS IN A TIGER SALAMANDER HYBRID ZONEEVOLUTION, Issue 6 2004Benjamin M. Fitzpatrick Abstract After an estimated five million years of independent evolution, the barred tiger salamander (Ambystoma tigrinum mavortium) was introduced by bait dealers into the native range of the California tiger salamander (A. californiense). Hybridization and backcrossing have been occurring in central California for 50,xs60 years, or an estimated 15,30 generations. We studied genetic and ecological factors influencing admixture of these two divergent gene pools by analyzing frequencies of hybrid genotypes in three kinds of breeding habitats: natural vernal pools, ephemeral man-made cattle ponds, and perennial man-made ponds. Perennial ponds tended to have higher frequencies of nonnative alleles than either type of seasonal pond, even in cases where perennial and seasonal ponds are within a few hundred meters. Thus, the hybrid zone has a mosaic structure that depends on pond hydrology or ecology. The presence of some broadly acting constraints on admixture is suggested by linkage disequilibria between physically unlinked molecular markers within ponds. In addition, we found several marker-specific deviations from Hardy-Weinberg equilibrium. One marker showed a consistent deficit of heterozygotes across pond types. Another showed heterozygote deficits only in vernal pools. A third was more likely to have heterozygote excess in ephemeral cattle ponds. These patterns indicate that admixture is influenced by complex genotype-by-environment interactions. [source] EVOLUTION OF SUBTERRANEAN DIVING BEETLES (COLEOPTERA: DYTISCIDAE HYDROPORINI, BIDESSINI) IN THE ARID ZONE OF AUSTRALIAEVOLUTION, Issue 12 2003Remko Leys Abstract Calcrete aquifers in arid inland Australia have recently been found to contain the world's most diverse assemblage of subterranean diving beetles (Coleoptera: Dytiscidae). In this study we test whether the adaptive shift hypothesis (ASH) or the climatic relict hypothesis (CRH) is the most likely mode of evolution for the Australian subterranean diving beetles by using a phylogeny based on two sequenced fragments of mitochondrial genes (CO1 and 16S-tRNA-ND1) and linearized using a relaxed molecular clock method. Most individual calcrete aquifers contain an assemblage of diving beetle species of distantly related lineages and/or a single pair of sister species that significantly differ in size and morphology. Evolutionary transitions from surface to subterranean life took place in a relatively small time frame between nine and four million years ago. Most of the variation in divergence times of the sympatric sister species is explained by the variation in latitude of the localities, which correlates with the onset of aridity from the north to the south and with an aridity maximum in the Early Pliocene (five mya). We conclude that individual calcrete aquifers were colonized by several distantly related diving beetle lineages. Several lines of evidence from molecular clock analyses support the CRH, indicating that all evolutionary transitions took place during the Late Miocene and Early Pliocene as a result of aridification. [source] EVIDENCE FOR HISTORICAL INTROGRESSION ALONG A CONTACT ZONE BETWEEN TWO SPECIES OF CHAR (PISCES: SALMONIDAE) IN NORTHWESTERN NORTH AMERICAEVOLUTION, Issue 5 2002Z. Redenbach Abstract Phylogeographic analyses can yield valuable insights into the geographic and historical contexts of contact and hybridization between taxa. Two species of char (Salmonidae), Dolly Varden (Salvelinus malma) and bull trout (S. confluentus) have largely parapatric distributions in watersheds of northwestern North America. They are, however, sympatric in several localities and hybridization and some introgression occurs across a broad area of contact. We conducted a comparative phylogenetic analysis of Dolly Varden and bull trout to gain a historical perspective of hybridization between these species and to test for footprints of historical introgression. We resolved two major Dolly Varden mitochondrial DNA (mtDNA) clades (with 1.4,2.2% sequence divergence between haplotypes) that had different geographical distributions. Clade N is distributed across most of the range of Dolly Varden, from southern British Columbia through to the Kuril Islands in Asia. Clade S had a much more limited distribution, from Washington state, at the southern limit of the Dolly Varden range, to the middle of Vancouver Island. The distribution and inferred ages of the mtDNA clades suggested that Dolly Varden survived the Wisconsinan glaciation in a previously unsuspected refuge south of the ice sheet, and that Dolly Varden and bull trout were probably in continuous contact over most of the last 100,000 years. When bull trout were included in the phylogenetic analysis, however, the mtDNA of neither species was monophyletic: Clade S Dolly Varden clustered within the bull trout mtDNA clade. This pattern was discordant with two nuclear phylogenies produced (growth hormone 2 and rRNA internal transcribed sequence 1), in which Dolly Varden and bull trout were reciprocally monophyletic. This discordance between mtDNA- and nDNA-based phylogenies indicates that historical introgression of bull trout mtDNA into Dolly Varden occurred. Percent sequence divergence within these introgressed Dolly Varden (clade S) was 0.2,0.6%, implying that the introgression occurred prior to the most recent glaciation. Our analysis and other evidence of contact between divergent lineages in northwestern North America strongly suggests that the area may be the site of previously unsuspected suture zones of aquatic biotas. [source] VARYING EFFECT OF FERTILITY DETERMINANTS AMONG MIGRANT AND INDIGENOUS FEMALES IN THE TRANSITIONAL AGRO-ECOLOGICAL ZONE OF GHANAGEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 1 2007Samuel Nii Ardey Codjoe ABSTRACT. The transitional agro-ecological zone of Ghana, located between the richly endowed south and the impoverished north, has attracted seasonal and permanent farm migrants, mainly from northern Ghana, who now live side by side with the indigenous people. While migrants have higher numbers of Muslims, indigenous people are mainly Christians. Although the majority of the migrants live in migrant quarters with less favourable socio-economic conditions, they are more successful farmers and therefore wealthier. The objectives are to examine the varying effect of fertility determinants among migrants and indigenous females. This paper uses data collected in 2002 among 194 females aged 15 to 49 years. Multiple regression models are used to assess fertility determinants. Results show that although migrant households were wealthier, migrant females were more traditional. They had more children living in foster care, and a lower proportion of them approved of men participating in household activities. In addition, they were less well educated, recorded higher infant mortality, gave birth earlier and used less contraception. Furthermore, while a female's migration status is statistically significant so far as non-proximate determinants of fertility are concerned, the same variable is not significant with respect to proximate determinants. In addition, a married female migrant would on average have almost one more child compared to her indigenous counterpart, and migrant females who had experienced the loss of a child would on average have 2.5 more children compared to their indigenous counterparts. Finally, more affluent migrant females have 0.08 fewer children compared to their indigenous counterpart. [source] IMMEDIATE LOADING OF IMPLANTS IN THE ESTHETIC ZONEJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 5 2005Saj Jivraj DDS The predictability of dental implants using the traditional Branemark protocol has been well documented. Since its inception, this protocol has been progressively challenged to decrease treatment time, minimize the number of surgical procedures, and maximize esthetic outcomes. Today, in specific clinical situations, implants may be placed and immediately loaded with provisional restorations. Immediate loading in the edentulous mandible has been well documented. There are also good data to show that immediate loading of the edentulous maxilla is also feasible if bone quality is suitable. The focus now has shifted toward immediate loading of implants placed in the esthetic zone. Clinicians have recognized that the challenge of providing anterior tooth replacements is in preserving the hard and soft tissue components that exist around natural teeth. The advantages of immediate restoration are obvious; however, the application of immediate or early load may pose an increased risk of implant failure in single-tooth situations. The prerequisites for achieving and maintaining acceptable results are not fully known. This review examines some of the literature concerning the reliability of early or immediate loading of implants placed in the esthetic zone. [source] PATERNAL LEAKAGE OF MITOCHONDRIAL DNA IN A FUCUS (PHAEOPHYCEAE) HYBRID ZONE,JOURNAL OF PHYCOLOGY, Issue 3 2009Galice Hoarau Eukaryotic mitochondria are mostly uniparentally (maternally) inherited, although mtDNA heteroplasmy has been reported in all major lineages. Heteroplasmy, the presence of more than one mitochondrial genome in an individual, can arise from recombination, point mutations, or by occasional transmission of the paternal mtDNA (=paternal leakage). Here, we report the first evidence of mtDNA paternal leakage in brown algae. In Denmark, where Fucus serratus L. and Fucus evanescens C. Agardh have hybridized for years, we found eight introgressed individuals that possessed the very distinct haplotypes of each parental species. The finding of heteroplasmy in individuals resulting from several generations of backcrosses suggests that paternal leakage occurred in earlier generations and has persisted through several meiotic bottlenecks. [source] PSYCHIATRY IN A BATTLE ZONEBIOETHICS, Issue 6 2010IZET PAJEVI ABSTRACT The authors describe the arrival and treatment of 164 severe chronic psychiatric patients who were displaced from the Serbian army-controlled Jakes psychiatric hospital and off-loaded on the afternoon of 28th of May, 1992 at the gates of the Psychiatry Clinic in Tuzla. Through analysis of their incomplete medical records, which arrived with the patients in Tuzla, and analysis of their activities during and after the war, they found that 83 of the patients (50%) were males and 147 (89.6%) were admitted to the Psychiatry Clinic in Tuzla. Of the patients, 86 (58.5%) were found to be Serbs. The majority of them were incapable of independent living and required ongoing medical and social care. They were from all regions of Bosnia-Herzegovina, 81.6% had schizophrenia and 70 (47.6%) were over 50 years of age. For its humanitarian work, its contribution to peace and for the maintenance of the multi-ethnic Bosnia-Herzegovina, the Psychiatry Clinic in Tuzla received the Golden Award for Peace from the International Legion of Humanists in May 1998. [source] COMMENTARY ON PSYCHIATRY IN A BATTLE ZONEBIOETHICS, Issue 6 2010STEVEN H. MILES No abstract is available for this article. [source] LEADING: OUT OF THE COMFORT ZONEBUSINESS STRATEGY REVIEW, Issue 3 2010Stuart Crainer No abstract is available for this article. [source] DO SUTURE ZONES EXIST?EVOLUTION, Issue 11 2004Nathan G. Swenson Abstract Remington (1968) argued that 13 suture zones exist in North America. Remington defined a suture zone as, "a band of geographic overlap between major biotic assemblages, including some pairs of species or semispecies which hybridize in the zone" (p. 322). Although initially controversial, the idea that suture zones exist has picked up momentum over the past decade, due largely to the phylogeographic work of Hewitt, Avise, and their colleagues. Nevertheless, the reality of suture zones has not yet been subjected to rigorous analysis using statistical and geographic information system (GIS) approaches. To test for the existence of Remington's suture zones, we first identified 117 terrestrial hybrid zones in Canada and the United States through a literature search for the key words "cline,""contact zone,""hybrid zone," and "hybridization" in articles published between 1970 and 2002. The 117 hybrid zones were mapped using a GIS approach and compared with a digitized version of Remington's original suture zone map. Overall, there does appear to be an association between hybrid zones and suture zones, but this association is largely attributable to clustering of hybrid zones in only two of the 13 suture zones recognized by Remington. The results suggest that evolutionary biologists should retain some skepticism toward Remington's suture zones. [source] A COMPARISON OF FIVE HYBRID ZONES OF THE WETA HEMIDEINA THORACICA (ORTHOPTERA: ANOSTOSTOMATIDAE): DEGREE OF CYTOGENETIC DIFFERENTIATION FAILS TO PREDICT ZONE WIDTHEVOLUTION, Issue 4 2003Mary Morgan-Richards Abstract Tension zones are maintained by the interaction between selection against hybrids and dispersal of individuals. Investigating multiple hybrid zones within a single species provides the opportunity to examine differences in zone structure on a background of differences in extrinsic factors (e.g., age of the zone, ecology) or intrinsic factors (e.g., chromosomes). The New Zealand tree weta Hemideina thoracica comprises at least eight distinct chromosomal races with diploid numbers ranging from 2n = 11 (XO) to 2n = 23 (XO). Five independent hybrid zones were located that involve races differing from one another by a variety of chromosomal rearrangements. The predicted negative correlation between extent of karyotypic differentiation (measured in terms of both percent of genome and number of rearrangements) and zone width was not found. Conversely, the widest zones were those characterized by two chromosome rearrangements involving up to 35% of the genome. The narrowest zone occurred where the two races differ by a single chromosome rearrangement involving approximately 2% of the genome. The five estimates of chromosomal cline width ranged from 0.5 km to 47 km. A comparative investigation of cline width for both chromosomal and mitochondrial markers revealed a complex pattern of zone characteristics. Three of the five zones in this study showed cline concordance for the nuclear and cytoplasmic markers, and at two of the zones the clines were also coincident. Zones with the widest chromosomal clines had the widest mitochondrial DNA clines. It appears that, even within a single species, the extent of karyotypic differentiation between pairs of races is not a good predictor of the level of disadvantage suffered by hybrids. [source] ORIGINAL AND SECONDARY HIGH-FREQUENCY SANDSTORM ZONES IN THE LOESS PLATEAU REGION, CHINAGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2007JIONGXIN XU ABSTRACT. A study of sandstorms in the Loess Plateau and neighbouring areas is based on observations of sandstorms and precipitation. Through analysis of the relationship between the mean annual number of sandstorms and the mean annual precipitation, an original sandstorm zone and a secondary high-frequency zone of sandstorms have been defined. The latter is mainly formed as a result of human activities, such as vegetation destruction and waste-land cultivation, and not because of climatic change. The secondary sandstorm zone is located 350,500 km away from the original sandstorm zone, reflecting the fact that the sandstorm zone in the Loess Plateau area has shifted 350,500 km to the southeast, in response to human impact. Some abrupt change has been found in the area where the mean annual precipitation is 270 mm, where the original sandstorm zone ends and a secondary zone of high-frequency sandstorms begins. This transition area can be regarded as an abnormally unstable area. This study shows that destruction of the vegetation can cause changes in the environment similar to those attributed to climatic change. [source] CHALLENGES IN MODELING HYDROLOGIC AND WATER QUALITY PROCESSES IN RIPARIAN ZONES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2006Shreeram Inamdar ABSTRACT: This paper presents key challenges in modeling water quality processes of riparian ecosystems: How can the spatial and temporal extent of water and solute mixing in the riparian zone be modeled? What level of model complexity is justified? How can processes at the riparian scale be quantified? How can the impact of riparian ecosystems be determined at the watershed scale? Flexible models need to be introduced that can simulate varying levels of hillslope-riparian mixing dictated by topography, upland and riparian depths, and moisture conditions. Model simulations need to account for storm event peak flow conditions when upland solute loadings may either bypass or overwhelm the riparian zone. Model complexity should be dictated by the level of detail in measured data. Model algorithms need to be developed using new macro-scale and meso-scale experiments that capture process dynamics at the hillslope or landscape scales. Monte Carlo simulations should be an integral part of model simulations and rigorous tests that go beyond simple time series, and point-output comparisons need to be introduced. The impact of riparian zones on watershed-scale water quality can be assessed by performing simulations for representative hillsloperiparian scenarios. [source] SEDIMENT TRAPPING WITHIN FORESTRY STREAMSIDE MANAGEMENT ZONES: GEORGIA PIEDMONT, USA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2004Jason M. Ward ABSTRACT: The effectiveness of streamside management zones (SMZs) was assessed for reducing sediment transport from concentrated overland flow draining two Georgia Piedmont clearcuts that had undergone mechanical and chemical site preparation and planting. Silt fences were used to trap sediment transport from zero-order ephemeral swales at the edge of and within SMZs. Four control swales and nine treatment swales were studied. A double mass curve approach was used to graphically compare sediment accumulation rates at the edge of SMZs to accumulation rates within the SMZs at a distance consistent with current recommendations for SMZ width in Georgia. SMZ efficiencies for trapping sediment transported by concentrated flow ranged from 71 to 99 percent. No statistical model was found to explain how SMZ efficiencies varied with SMZ and contributing area characteristics. Measured sediment accumulations at the SMZ boundary were compared to Revised Universal Soil Loss Equation (RUSLE) predictions of up- slope erosion, and a delivery ratio of 0.25 was calculated. SMZs had a quantifiable and substantial ameliorating effect on sediment transport from concentrated overland flow on the clearcut study sites. [source] LANDSCAPE ATTRIBUTES AS CONTROLS ON GROITHD WATER NITRATE REMOVAL CAPACITY OF RIPARIAN ZONES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2001Arthur J. Gold ABSTRACT: Inherent site factors can generate substantial variation in the ground water nitrate removal capacity of riparian zones. This paper examines research in the glaciated Northeast to relate variability in ground water nitrate removal to site attributes depicted in readily available spatial databases, such as SSUIRGO. Linking site-specific studies of riparian ground water nitrate removal to spatial data can help target high-value riparian locations for restoration or protection and improve the modeling of watershed nitrogen flux. Site attributes, such as hydric soil status (soil wetness) and geomorphology, affect the interaction of nitrate-enriched ground water with portions of the soil ecosystem possessing elevated biogeochemical transformation rates (i.e., biologically active zones). At our riparian sites, high ground water nitrate-N removal rates were restricted to hydric soils. Geomorphology provided insights into ground water flowpaths. Riparian sites located on outwash and organic/alluvial deposits have high potential for nitrate-enriched ground water to interact with biologically active zones. In till deposits, ground water nitrate removal capacity may be limited by the high occurrence of surface seeps that markedly reduce the time available for biological transformations to occur within the riparian zone. To fully realize the value of riparian zones for nitrate retention, landscape controls of riparian nitrate removal in different climatic and physiographic regions must be determined and translated into available spatial databases. [source] "THEY COME IN PEASANTS AND LEAVE CITIZENS": Urban Villages and the Making of Shenzhen, ChinaCULTURAL ANTHROPOLOGY, Issue 3 2010JONATHAN BACH ABSTRACT This essay examines the ongoing process of postsocialist transformation at the intersection of cultural and economic forces in an urban environment through the example of the so-called "urban villages"(chengzhongcun) in Shenzhen, China, a booming southern Chinese city and former Special Economic Zone next to Hong Kong. This essay ethnographically examines the role of former rural collectives encircled by a city that has exploded from farmland to an export-driven city of over 14 million people in little over one generation. These villages form an internal other that is both the antithesis and the condition of possibility for Shenzhen city. By co-opting the market economy in ways that weave them into the fabric of the contemporary global city, the villages become as much an experiment as the Special Economic Zone itself. This essay analyzes the urban,rural divide as complicit in each other's continued production and effacement and explores how village and city exploit the ambiguities of their juxtaposition in the making of Shenzhen. [source] Coastal conglomerates around the Hadjer el Khamis inselbergs (western Chad, central Africa): new evidence for Lake Mega-Chad episodesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2003Mathieu Schuster Abstract This paper reports on a study dealing with the rhyolitic inselbergs of Hadjer el Khamis that formed palaeoislands during Lake Mega-Chad events. Field observations have shown that: (1) conglomeratic patches of immature to mature clasts are preserved at the feet of the Hadjer el Khamis inselbergs; (2) in cross-section, their pro,le reveals a well de,ned cliff,platform junction at a constant elevation (325 m). The monolithological clasts show all degrees of roundness, from angular cobbles to well rounded pebbles. This wide range of maturity suggests a coastal origin for these cobbles. The system was permanently fed with angular clasts, which were progressively worn by waves. Cobbles that were wave-worked for the longest time are the best rounded. The cliff,platform junction is the result of erosion by waves, which attacked and undercut the inselberg cliffs during Lake Mega-Chad events. Asymmetrical erosion pro,les moreover suggest a wind regime dominated by SW to NE oriented winds. These interpretations have two implications. The elevation of the cliff,platform junction is an indication of the highest water level of Lake Mega-Chad at 320,325 m, which is in agreement with other observations elsewhere in the basin. The SW to NE oriented winds show that monsoon-related winds were prevalent during Lake Mega-Chad events, suggesting the Inter-Tropical Convergence Zone was located higher in latitude than today. Copyright © 2003 John Wiley & Sons, Ltd. [source] Discontinuity in fish assemblages across an elevation gradient in a southern Appalachian watershed, USAECOLOGY OF FRESHWATER FISH, Issue 1 2005J. L. Robinson This region is noted for extreme topographical relief, high cumulative annual rainfall and many rare and endemic plants and animals. The study area encompasses a portion of the Blue Ridge Escarpment and the associated Brevard Fault Zone. We hypothesise that major waterfalls and cascade complexes have acted to limit invasion and colonisation by fishes from downstream. This hypothesis is supported by longitudinal fish assemblage patterns in our study streams. Fish species richness in Toxaway River increased from 4 to 23 between Lake Toxaway and Lake Jocassee, a distance of 10 river km. We found similar discontinuities in neighbouring Horsepasture River and Bearwallow Creek. We found no instances of species replacement along this elevation gradient, and the trend in increased diversity downstream showed discontinuities coincident with sharp elevation breaks. With regard to theories posited to explain community formation in headwater stream fish communities (especially in those characterised by high topographical relief), we suggest coloniser ,access' may be more important than other factors including competitive interactions. Resumen 1. En este estudio examinamos patrones en los ensamblajes de peces de los ríos Toxaway y Horsepasture, dos ríos de elevada altitud de Carolina del Norte (USA). Esta región se caracteriza por rupturas topografías extremas, gran cantidad de lluvia anual y numerosos endemismos animales y vegetales. El estudio incluye una porción de la región del Blue Ridge Escarpment y la zona asociada de Brevard Fault. 2. Nuestra hipótesis es que los complejos sistemas de cataratas han limitado la invasión y la colonización de los peces desde las localidades aguas abajo. Los patrones longitudinales de los ensamblajes de peces fueron consistentes con esta hipótesis. La riqueza de las especies de peces en el río Toxaway incrementó desde 4 a 23 especies en una distancia de 10 Km de río, entre los lagos Taxoway y Jocasee. Encontramos discontinuidades similares en los vecinos ríos Horsepasture y Bearwallow. No encontramos ningún caso de re-emplazamiento de especies a lo largo del gradiente de altitud y la tendencia a incrementar la diversidad aguas abajo mostró discontinuidades que coincidieron con rupturas de altitudes. 3. Al considerar teorías que explican la formación de comunidades en zonas altas de ríos (especialmente en regiones caracterizadas por rupturas topografías), sugerimos que el acceso para los colonizadores puede ser más importante que otros factores incluyendo interacciones competitivas. [source] Pesticide residues in the aquatic environment of banana plantation areas in the North Atlantic Zone of Costa RicaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2000Luisa E. Castillo Abstract A study of pesticide residues in surface waters and sediments was undertaken in the Suerte River Basin, Costa Rica, that drains into the Tortuguero conservation area. Samples were collected in streams, packing plants, and the Suerte River. The most frequently measured compounds in surface water samples were the fungicides thiabendazole, propiconazole, and imazalil; the nematicides terbufos and cadusafos; and the insecticide chlorpyrifos. At the conservation area, propiconazole was detected in 43% of the samples at concentrations ranging from 0.05 to 1.0 ,g/L. In 25% of the samples collected at this site, a nematicide (cadusafos, carbofuran, or ethoprophos) was detected (0.06,6.2 ,g/L). According to this study, most of the insecticide-nematicides analyzed pose a risk for acute or chronic toxicity to aquatic organisms based on the exposure levels and toxicity values from the literature. Ametryn, imazalil, and thiabendazole also exceeded the calculated chronic risk ratio. The most frequently detected compounds in sediments were thiabendazole, chlorpyrifos, imazalil, and propiconazole. The occurrence was higher in the packing plants and streams. Pesticides in waters and sediments of Tortuguero conservation area could pose a threat to this wetland and an additional stress to the endangered species that inhabit this area. More information is needed regarding the distribution and stability of pesticides in the lagoon system as well as of the effects of mixtures of low levels of pesticides and their degradation products on representative species of the Tortuguero ecosystem. Meanwhile, all measures to reduce the emissions of pesticides from the banana plantations and the packing plants should be taken. [source] Subtraction SPECT Coregistered to MRI in Focal Malformations of Cortical Development: Localization of the Epileptogenic Zone in Epilepsy Surgery CandidatesEPILEPSIA, Issue 4 2004Terence J. O'Brien Summary: Purpose: To determine the extent to which periictal subtraction single-photon emission computed tomography (SPECT) may improve detection and definition of the epileptogenic zone in patients with focal malformations of cortical development (MCDs). Methods: Subtraction SPECT coregistered to magnetic resonance (MR) images (SISCOM) were constructed for 22 consecutive patients with focal MCDs who underwent periictal SPECT injection (18 ictal and four postictal). In the 17 patients who had epilepsy surgery, concordance between the site of SISCOM localization and site of surgical resection was determined by coregistration of SISCOM images with postoperative MRIs. Results: SISCOM images were localizing in 19 (86%) patients, including eight of the 10 with nonlocalizing MRI. Concordance of SISCOM localization was 91% with MRI localization, 93% with scalp ictal EEG localization, and 100% with intracranial EEG localization. Eight patients whose SISCOM localization was concordant with the surgical resection site had lower postoperative seizure frequency scores (SFSs; p = 0.04) and greater postoperative improvement in SFSs (p = 0.05) than the nine patients whose SISCOM was either nonconcordant or nonlocalizing. On multiple regression analysis, a model combining SISCOM concordance with surgical resection site and extent of MRI lesion resection was predictive of postoperative SFS (R2= 0.47; p = 0.03). Conclusions: Periictal subtraction SPECT using the SISCOM technique provides useful information for seizure localization in patients with focal MCDs, even when MRI is nonlocalizing. [source] Movement and behaviour of large southern bluefin tuna (Thunnus maccoyii) in the Australian region determined using pop-up satellite archival tagsFISHERIES OCEANOGRAPHY, Issue 5 2008TOBY A. PATTERSON Abstract Pop-up satellite archival tags (PSATs) were deployed on 52 large (156,200 cm length to caudal fork) southern bluefin tuna (Thunnus maccoyii) in the western Tasman Sea during the austral winters of 2001,2005. Southern bluefin tuna (SBT) were resident in the Tasman Sea for up to 6 months with movements away from the tagging area occurring at highly variable rates. The data indicated a general tendency for SBT to move south from the tagging area in the Western Tasman Sea. Four individuals migrated west along the southern continental margin of Australia and into the Indian Ocean. Three individuals moved east into the central Tasman Sea, with one individual reaching New Zealand. We also describe the first observed migration of an SBT from the Tasman Sea to the Indian Ocean spawning grounds south of Indonesia. Individuals spent most of their time relatively close to the Australian coast, with an estimated 84% of time spent in the Australian Fishing Zone. SBT favored temperatures between 19 and 21°C, adjusting their depth to the vertical temperature distribution. Distinct diurnal diving patterns were observed and adjustment of depth to maintain constant ambient light levels over a 24-h period. The findings of this study are a significant advance toward greater understanding of the spatial dynamics of large SBT and understanding the connectivity between distant regions of their distribution. [source] Spatial distribution of the Japanese common squid, Todarodes pacificus, during its northward migration in the western North Pacific OceanFISHERIES OCEANOGRAPHY, Issue 2 2006ATSUSHI KAWABATA Abstract The spatial distribution of Todarodes pacificus in and near the Kuroshio/Oyashio Transition Zone during its northward migration was examined by comparative surveys using two types of mid-water trawl net and supplementary squid jigging from June to July 2000. The vertical and horizontal distribution patterns varied for different body sizes in relation to the oceanographic structure. Todarodes pacificus of 1,20 cm dorsal mantle length (ML) were widely distributed from the coastal waters of Japan to near 162°E longitude, probably due to transport by the Kuroshio Extension (KE). Todarodes pacificus smaller than 10 cm ML were mainly distributed in temperate surface layers at sea surface temperatures (SSTs) >15°C near the KE meander probably because of their poor tolerance to lower temperatures and limited swimming ability. Squid of 10,15 cm ML were distributed in the offshore waters of 10,15°C SST and in the coastal waters of northern Honshu, and underwent diel vertical migrations between the sea surface at night and deeper layers during the daytime. Squid larger than 15 cm ML were distributed in the coastal feeding grounds of northern Honshu and Hokkaido until they began their southward spawning migration. They also underwent diel vertical migrations, but remained deeper at night than the squid of 10,15 cm ML; this migration pattern closely matched that of their main prey such as euphausiids. We concluded that as T. pacificus grow, they shift their distribution range from the temperate surface layer around the KE toward the colder deeper layers, above 5°C, in the Oyashio and coastal areas. [source] Modeling the influence of oceanic-climatic changes on the dynamics of Pacific saury in the northwestern Pacific using a life cycle modelFISHERIES OCEANOGRAPHY, Issue 2004YONGJUN TIAN Abstract A life cycle model for Pacific saury (Cololabis saira) was developed to clarify the possible causes of interannual and decadal variability in its abundance. In the model, the population of saury is composed of two spawning cohorts: one spawned in the Kuroshio region during autumn,winter and the other spawned in the Kuroshio-Oyashio Transition Zone during winter,spring. The life cycle of saury was divided into six stages: namely egg, larval, juvenile, young, immature and adult stages. The life cycle model combines growth, survival, fishing and reproductive processes, in which the effects of sea surface temperature (SST) in the Kuroshio region and El Niño-Southern Oscillation (ENSO) events on the winter-spawning cohorts, the effects of SST in the Oyashio region on the spring-spawning cohorts, and the effects of fishing on the two spawning cohorts are taken into account. Results of basic modeling, in which environments are assumed stable and the stock is affected by fishing only, shows that the interannual fluctuations in the abundance are small and could hardly explain the observed large annual changes in abundance. On the contrary, results of modeling incorporating the effects of oceanic-climatic changes corresponded well with actual interannual-decadal variations in abundance. These results suggest the following environmental effects: (1) SST in the Kuroshio region affects decadal changes in abundance; (2) ENSO events influence the survival of the winter spawning cohort and result in large interannual variations in the abundance. It is concluded that large-scale climatic and oceanic changes strongly affect the abundance of saury. [source] Differing body size between the autumn and the winter,spring cohorts of neon flying squid (Ommastrephes bartramii) related to the oceanographic regime in the North Pacific: a hypothesisFISHERIES OCEANOGRAPHY, Issue 5 2004Taro Ichii Abstract The neon flying squid (Ommastrephes bartramii), which is the target of an important North Pacific fishery, is comprised of an autumn and winter,spring cohort. During summer, there is a clear separation of mantle length (ML) between the autumn (ML range: 38,46 cm) and the winter,spring cohorts (ML range: 16,28 cm) despite their apparently contiguous hatching periods. We examined oceanic conditions associated with spawning/nursery and northward migration habitats of the two different-sized cohorts. The seasonal meridional movement of the sea surface temperature (SST) range at which spawning is thought to occur (21,25°C) indicates that the spawning ground occurs farther north during autumn (28,34°N) than winter,spring (20,28°N). The autumn spawning ground coincides with the Subtropical Frontal Zone (STFZ), characterized by enhanced productivity in winter because of its close proximity to the Transition Zone Chlorophyll Front (TZCF), which move south to the STFZ from the Subarctic Boundary. Hence this area is thought to become a food-rich nursery ground in winter. The winter,spring spawning ground, on the other hand, coincides with the Subtropical Domain, which is less productive throughout the year. Furthermore, as the TZCF and SST front migrate northward in spring and summer, the autumn cohort has the advantage of being in the SST front and productive area north of the chlorophyll front, whereas the winter,spring cohort remains to the south in a less productive area. Thus, the autumn cohort can utilize a food-rich habitat from winter through summer, which, we hypothesize, causes its members to grow larger than those in the winter,spring cohort in summer. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||