Population Niche Research Articles

Stealth and Opportunism: Alternative Lifestyles of Species in the Fungal GenusPneumocystis

Pneumocystis species are ascomycetous fungi that obligatorily dwell with no apparent ill effect in the lungs of normal mammals, but they become pathogenic when host defenses are compromised. Identified more than 100 years ago, these atypical fungi manifest characteristics that are unique within the Fungi, such as the lack of ergosterol, genetic complexity of surface antigens, and antigenic variation. Thought to be confined to the severely immunocompromised host, Pneumocystis spp. are being associated with new population niches owing to the advent of immunomodulatory therapies and increased numbers of patients suffering from chronic diseases. The inability to grow Pneumocystis spp. outside the mammalian lung has thwarted progress toward understanding their basic biology, but via the use of new genetic tools and other strategies, researchers are beginning to uncover their biological and genetic characteristics including a biphasic life cycle, significant metabolic capacities, and modulation of lifestyles.

Contrasting patterns of individual specialization and trophic coupling in two marine apex predators

1. Apex predators are often assumed to be dietary generalists and, by feeding on prey from multiple basal nutrient sources, serve to couple discrete food webs. But there is increasing evidence that individual level dietary specialization may be common in many species, and this has not been investigated for many marine apex predators. 2. Because of their position at or near the top of many marine food webs, and the possibility that they can affect populations of their prey and induce trophic cascades, it is important to understand patterns of dietary specialization in shark populations. 3. Stable isotope values from body tissues with different turnover rates were used to quantify patterns of individual specialization in two species of 'generalist' sharks (bull sharks, Carcharhinus leucas, and tiger sharks, Galeocerdo cuvier). 4. Despite wide population-level isotopic niche breadths in both species, isotopic values of individual tiger sharks varied across tissues with different turnover rates. The population niche breadth was explained mostly by variation within individuals suggesting tiger sharks are true generalists. In contrast, isotope values of individual bull sharks were stable through time and their wide population level niche breadth was explained by variation among specialist individuals. 5. Relative resource abundance and spatial variation in food-predation risk tradeoffs may explain the differences in patterns of specialization between shark species. 6. The differences in individual dietary specialization between tiger sharks and bull sharks results in different functional roles in coupling or compartmentalizing distinct food webs. 7. Individual specialization may be an important feature of trophic dynamics of highly mobile marine top predators and should be explicitly considered in studies of marine food webs and the ecological role of top predators.

Dendritic cell vaccines for the immunocompromised patient: prevention of influenza virus infection

Prophylactic vaccination of cancer patients and recipients of hematopoietic stem cell transplant is generally a simple, efficient and cost-effective manner by which to prevent unnecessary infection and enhance overall clinical outcomes. However, some neoplastic conditions, particularly B-cell malignancies, impart a degree of immunosuppression that complicates traditional prophylactic approaches. Here, we make the case that the application of dendritic cell (DC) immunotherapy for the prophylaxis of infectious disease is both appropriate and cost effective for certain niche populations who are at risk of increased morbidity and who respond poorly to traditional vaccination, particularly influenza vaccination. Here we review the full spectrum of our preclinical work in this area, results demonstrating that DCs loaded with subunit recombinant hemagglutinin can generate robust hemagglutinin-specific immune responses both in vitro and in vivo. In vivo data indicated that a single injection of hemagglutinin-loaded DC was sufficient to generate high-titer antibody responses that could mediate protective immunity to lethal influenza virus challenge. The results suggest that DC immunotherapy for influenza prophylaxis is safe and feasible and that clinical studies might be warranted.

Genetic and ecological differentiation in the endemic avifauna of Tiburón Island

Tiburón Island is a land‐bridge island in the Gulf of California, separated from mainland Sonora by 3 km. The shallow channel (13 m) separating the island and mainland is thought to have formed 10 000 years ago. Although the majority of avian resident species are not taxonomically differentiated, six species are represented by endemic subspecies (cactus wren, gila woodpecker, black‐tailed gnatcatcher, Gambel's quail, canyon towhee, northern cardinal), of which all but one (black‐tailed gnatcatcher) possess a pallid, ash‐gray coloration compared to those on the mainland. We compared mtDNA sequences of five of the endemic subspecies (we lacked samples of northern cardinal) and one more widespread subspecies (verdin) present on the island from sequences previously published for mainland populations. For most populations, we discovered no genetic differentiation between the island and the mainland, thus questioning the taxonomic validity of the endemic subspecies. The canyon towhee and the verdin showed significant mitochondrial DNA differentiation, although neither was reciprocally monophyletic. We modeled the ecological niche for the mainland populations of the study species (plus the curve‐billed thrasher, which was studied earlier) and determined if species’ occurrence on the island was predicted. We found no ecological differences for the four species that showed no genetic differences and one of the species that did (verdin). In contrast, some ecological differentiation was detected for the canyon towhee and the curve‐billed thrasher. We conclude that the ecological differences leading to paler plumages in Tiburón Island endemics are sufficiently subtle as to not be discovered in our ecological models, although they are likely influenced by variation in rainfall, temperature and the vegetation. In addition, the black‐tailed gnatcatcher is not paler, and therefore might respond to different ecological variables. We simulated sequence data and showed that if the populations on Tiburón Island have been isolated for 10 000 years, there ought to be greater differences than we observed for black‐tailed gnatcatcher, Gambel's quail, cactus wren, and gila woodpecker, suggesting that there has been gene flow connecting the mainland and island populations. If so, then the paler coloration of these Tiburón Island subspecies (excluding black‐tailed gnatcatcher) has been maintained by natural selection despite gene flow. In any case, the pale coloration apparently evolved within the past 10 000 years.

Consequent Effects of Parasitism on Population Dynamics, Food Webs, and Human Health Under Climate Change

Consequent Effects of Parasitism on Population Dynamics, Food Webs, and Human Health Under Climate Change

Seasonal diet and feeding habits of juvenile fishes foraging along a subtropical marine ecotone

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 9:279-290 (2010) - DOI: https://doi.org/10.3354/ab00251 Seasonal diet and feeding habits of juvenile fishes foraging along a subtropical marine ecotone Neil Hammerschlag1,2,*, Dan Ovando1,4, Joseph E. Serafy1,3 1Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA 2Leonard and Jayne Abess Center for Ecosystem Science and Policy, University of Miami, PO Box 248203, Coral Gables, Florida 33124, USA 3National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southeast Fisheries Science Center, 75 Virginia Beach Drive, Miami, Florida 33149, USA 4Present address: Donald Bren School of Environmental Science and Management, University of California Santa Barbara, 2400 Bren Hall, Santa Barbara, California 93106-5131, USA *Email: nhammerschlag@rsmas.miami.edu ABSTRACT: Few studies have examined seasonal diet variation and trophic relationships among fishes in shallow subtropical waters. We sampled consecutive wet and dry seasons within Biscayne Bay, Florida, USA, to examine seasonal diet and feeding habit variation in juvenile gray snapper Lutjanus griseus (GS), bluestriped grunt Haemulon sciurus (BSG), seabream Archosargus rhomboidalis (SB) and great barracuda Sphyraena barracuda (GB). We found significantly lower feeding intensity during the dry season compared to the wet, which is likely related to lower water temperatures during the former season. GS fed on a variety of fishes and crustaceans, while BSG fed primarily on caridean shrimps. SB fed on vegetation and GB was piscivorous. Seasonal shifts in major food resources generally did not correspond with changes in relative abundance of food supply. Seasonal population niche breadth differences were evident for GS, GB and BSG, but for SB niche breadth was similar between seasons. Based on seasonal food supply, population niche breadth values did not match basic foraging theory predictions, which state that niche breadth should expand as preferred food items become scarce. In GS, BSG and GB, individuals fed on a narrow subset of prey consumed by the population, revealing the existence of individual specialization. For these species, seasonal expansion in population niche breadth did not correspond to increased individual specialization, but rather via increased within-individual variation in resource use. Given the seasonal differences in feeding habits, it is important to incorporate seasonal variation when modeling trophodynamics of shallow subtropical systems or characterizing them as essential fish habitats. KEY WORDS: Diet · Niche breadth · Resource use · Habitat use · Snapper · Grunt · Barracuda · Food availability · Feeding intensity · Individual specialization Full text in pdf format PreviousNextCite this article as: Hammerschlag N, Ovando D, Serafy JE (2010) Seasonal diet and feeding habits of juvenile fishes foraging along a subtropical marine ecotone. Aquat Biol 9:279-290. https://doi.org/10.3354/ab00251Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 9, No. 3. Online publication date: June 10, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.

Drug resistance in community-acquired respiratory tract infections: role for an emerging antibacterial.

The nasopharynx is the ecological niche where evolution towards resistance occurs in respiratory tract isolates. Dynamics of different bacterial populations in antibiotic-free multibacterial niches are the baseline that antibiotic treatments can alter by shifting the competitive balance in favor of resistant populations. For this reason, antibiotic resistance is increasingly being considered to be an ecological problem. Traditionally, resistance has implied the need for development of new antibiotics for which basic efficacy and safety data are required prior to licensing. Antibiotic development is mainly focused on demonstrating clinical efficacy and setting susceptibility breakpoints for efficacy prediction. However, additional information on pharmacodynamic data predicting absence of selection of resistance and of resistant subpopulations, and specific surveillance on resistance to core antibiotics (to detect emerging resistances and its link with antibiotic consumption in the community) are valuable data in defining the role of a new antibiotic, not only from the perspective of its therapeutic potential but also from the ecologic perspective (countering resistances to core antibiotics in the community). The documented information on cefditoren gleaned from published studies in recent years is an example of the role for an emerging oral antibacterial facing current antibiotic resistance in community-acquired respiratory tract infections.

Change in population niche during vegetation community succession in the Yellow River Delta

对黄河三角洲天然湿地陆生植被和水生植被两种演替序列的种群生态位宽度和生态位重叠进行了调查研究。结果表明: 陆生植被经过翅碱蓬群落、碱蓬柽柳群落、柽柳群落、白茅群落的演替过程, 每个阶段优势种的生态位宽度都较大。翅碱蓬群落阶段优势种翅碱蓬的生态位宽度达9.99, 碱蓬柽柳群落阶段碱蓬的生态位宽度为9.72, 柽柳群落阶段柽柳的生态位宽度为9.20, 白茅群落阶段白茅的生态位宽度为9.31。水生植被的演替序列为眼子菜金鱼藻群落(沉水植物)阶段、浮萍水鳖群落(浮水植物)阶段、芦苇水烛群落(挺水植物)阶段和杞柳芦苇群落(湿生植物)阶段, 沉水植物阶段优势种眼子菜的生态位宽度为8.62, 浮水植物阶段优势种浮萍生态位宽度为9.23, 挺水植物阶段优势种芦苇的生态位宽度为8.59, 湿生植物阶段优势种杞柳生态位宽度为7.45。生态位宽度计测结果较好地对应着各种群在群落中的地位和作用, 生态位宽度在演替系列中的动态也较好地反映了种群在群落演替过程的数量动态。各演替阶段生态位重叠计算结果表明, 各阶段种群间的生态位重叠值低, 每一阶段内种群间有较高的生态位重叠

Change in population niche during vegetation community succession in the Yellow River Delta

对黄河三角洲天然湿地陆生植被和水生植被两种演替序列的种群生态位宽度和生态位重叠进行了调查研究。结果表明: 陆生植被经过翅碱蓬群落、碱蓬柽柳群落、柽柳群落、白茅群落的演替过程, 每个阶段优势种的生态位宽度都较大。翅碱蓬群落阶段优势种翅碱蓬的生态位宽度达9.99, 碱蓬柽柳群落阶段碱蓬的生态位宽度为9.72, 柽柳群落阶段柽柳的生态位宽度为9.20, 白茅群落阶段白茅的生态位宽度为9.31。水生植被的演替序列为眼子菜金鱼藻群落(沉水植物)阶段、浮萍水鳖群落(浮水植物)阶段、芦苇水烛群落(挺水植物)阶段和杞柳芦苇群落(湿生植物)阶段, 沉水植物阶段优势种眼子菜的生态位宽度为8.62, 浮水植物阶段优势种浮萍生态位宽度为9.23, 挺水植物阶段优势种芦苇的生态位宽度为8.59, 湿生植物阶段优势种杞柳生态位宽度为7.45。生态位宽度计测结果较好地对应着各种群在群落中的地位和作用, 生态位宽度在演替系列中的动态也较好地反映了种群在群落演替过程的数量动态。各演替阶段生态位重叠计算结果表明, 各阶段种群间的生态位重叠值低, 每一阶段内种群间有较高的生态位重叠

Vascular Precursors: Origin, Regulation and Function

Series Editor: Karen K. Hirschi ATVB In Focus Vascular Precursors: Origin, Regulation and Function Articles in this series: •Hirschi KK. Vascular Precursors: Origin, Regulation and Function. Arterioscler Thromb Vasc Biol . 2010;30:1078–1079. •Kumar AHS, Caplice NM. Clinical potential of adult vascular progenitor cells. Arterioscler Thromb Vasc Biol . 2010;30:1080–1087. •Dimmeler S. Regulation of bone marrow-derived vascular progenitor cell mobilization and maintenance. Arterioscler Thromb Vasc Biol . 2010;30:1088–1093. •Yoder MC. Is endothelium the origin of endothelial progenitor cells? Arterioscler Thromb Vasc Biol . 2010;30:1094–1103. •Corselli M, Chen C-W, Crisan M, Lazzari L, Peault B. Perivascular ancestors of adult multipotent stem cells. Arterioscler Thromb Vasc Biol . 2010;30:1104–1109. •Iacobas I, Vats A, Hirschi KK. Vascular potential of human pluripotent stem cells. Arterioscler Thromb Vasc Biol . 2010;30:1110–1117. In this miniseries, we discuss the phenotype, origin, and specialized microenvironment (niche) of distinct populations of stem and progenitor cells that exhibit vascular potential. Their usefulness and effectiveness for clinical therapies are also described. We have learned a great deal about postnatal vascular …

Niche partitioning and densities of Albertine Rift endemics and their congeners in Bwindi Impenetrable Forest, Uganda

Biogeographical theory predicts that restricted-range species should typically occur at lower densities than ecologically similar, but geographically widespread species. Exceptions may arise where endemics occupy distinctive habitats, in which they are capable of reaching higher densities than their more widespread competitors. This paper describes the habitat requirements and abundance of a sample of insectivores in Bwindi Impenetrable Forest, part of the Albertine Rift mountains Endemic Bird Area. The altitude ranges, habitat preferences, foraging niches and densities of five Albertine Rift endemics from the genera Phylloscopus, Apalis, Batis and Parus were compared with those of their congeners, or with ecologically similar species. The five endemics were associated with ridgetop forest, steeply sloping ground and a sparse understorey or field layer. They foraged within a narrower height range and used a wider range of substrates than their partner species, but showed no significant differences with regard to altitude range, the number of habitat features with which they were associated, foraging niche width or population density. Two endemic apalises were among the most abundant of their genus, achieving densities at least seven times that of the least abundant apalis at Bwindi. These findings are broadly consistent with results from studies of other montane bird communities in Africa, which suggest that bird species endemic to Afromontane forests often achieve densities comparable with those of widespread, ecologically similar species, and may thus avoid the ‘double jeopardy’ of small range size and low population density.

Rho Kinase Inhibitor Y27632 Alters the Balance Between Pluripotency and Early Differentiation Events in Human Embryonic Stem Cells

Human embryonic stem cells (hESC) differentiate spontaneously in culture and develop a complex microenvironment comprising of autologously derived niche that in turn supports their pluripotency. The basic hypothesis that we deal with is that hESCs undergoing differentiation, sequentially generate trophectoderm and endoderm lineages and thereafter influence further events through the production of growth factors. These factors control the fate of hESCs either by promoting or retarding the recruitment of new cells in the differentiation program. This scenario therefore represents an analog of the in vivo situation in which extra-embryonic tissues influence the behavior of the inner cell mass (ICM). The premise of the paper is the Rho kinase inhibitor Y27632 that can spatiotemporally alter this balance between pluripotency and differentiation. To evaluate the composition and inclination of lineage specification during spontaneous differentiation, we have studied the hESC colonies and their surrounding niche as interdependent entities. We show that the population of fibroblastic niche that surrounds hESC colonies co-expresses trophectoderm and niche cell markers including SSEA1, hCG, progesterone, HAND1, pSmad1 and FGFR1 as early as day 4. A sudden increase in the expression of GATA4 and AFP secretion indicated putative endoderm formation on day 6 in both control and Y27632 treated cultures. On day 6, 20 microM of Y27632 supplementation significantly reduced the trophectoderm-like niche population without affecting endoderm formation, enhanced the average size and number of hESC colonies, decreased IGF1 secretion thereby improving the pluripotency. Overall our findings support the afore mentioned hypothesis and demonstrate that closely packed epithelial trophectoderm-like cells bordering the hESC colonies present an initial and imminent localized niche which is spatiotemporally regulated. Such advances in understanding the behavior and modulation of hESC and its surrounding niche would facilitate better differentiation protocols for applications in regenerative medicine and drug screening.

Use of stable isotopes to quantify seasonal changes of trophic niche and levels of population and individual specialisation in seabirds

Niche variation is a widespread phenomenon that has important implications for ecolog- ical interactions and conservation biology, but few studies have quantified the trophic niche width (TNW) and its within- and between-individual components. We used stable isotopes of body feathers to investigate (1) seasonal isotopic niche changes of 4 southern procellariiforms and, (2) the level to which individuals are specialised relative to their population within each season. (1) δ 13 C and δ 15 N values of chicks and adults indicated a well-defined trophic segregation within the seabird assem- blage during both the breeding and poorly known moulting (inter-nesting) periods, and they under- lined marked species-specific seasonal changes. One species (light-mantled sooty albatross) remained within the Southern Ocean both during breeding and body feather moult, while the 3 others migrated either to oceanic subtropical waters (wandering and sooty albatrosses) or high isotopic marine areas (e.g. productive neritic waters; white-chinned petrel) during the moulting period. (2) Isotopic vari- ances and TNW were generally low, indicating that birds belong to isotopic specialist populations within a given period. Variances and TNW were larger for white-chinned petrel chicks and light-man- tled sooty albatross adults, respectively, indicating isotopic generalist populations and revealing 2 new foraging behaviours. Individual white-chinned petrel chicks segregated by their feather iso- topic signatures, thus indicating individual/pair specialisation of parent birds during the chick-rearing period. The light-mantled sooty albatross population included mostly isotopic generalist individuals during the moulting period, with individuals using different habitats and diets. The study highlights the utility of feather isotopic signature for determining TNW and points out the necessity to develop such new approaches to better depict niche variations at both population and individual levels.

Ecological release from interspecific competition leads to decoupled changes in population and individual niche width.

A species's niche width reflects a balance between the diversifying effects of intraspecific competition and the constraining effects of interspecific competition. This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced. The resulting ecological release permits population niche expansion, via increased individual niche widths and/or increased among-individual variation. We report an experimental test of the theory of ecological release in three-spine stickleback (Gasterosteus aculeatus). We factorially manipulated the presence or absence of two interspecific competitors: juvenile cut-throat trout (Oncorhynchus clarki) and prickly sculpin (Cottus asper). Consistent with the classic niche variation hypothesis, release from trout competition increased stickleback population niche width via increased among-individual variation, while individual niche widths remained unchanged. In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation. Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales. Importantly, we find that changes in population niche width are decoupled from changes in the niche widths of individuals within the population.

Evolutionary diversification, coevolution between populations and their antagonists, and the filling of niche space

The population component of a species’ niche corresponds to the distribution of individuals across environments within a region. As evolutionary clades of species diversify, they presumably fill niche space, and, consequently, the rate of increase in species numbers slows. Total niche space and species numbers appear to be relatively stable over long periods, and so an increase in the species richness of one clade must be balanced by decrease in others. However, in several analyses, the total population niche space occupied per clade is independent of the number of species, suggesting that species in more diverse clades overlap more in niche space. This overlap appears to be accommodated by variation in the populations of each species, including their absence, within suitable niche space. I suggest that the uneven filling of niche space results from localized outcomes of the dynamic coevolutionary interactions of populations with their pathogens or other antagonists. Furthermore, I speculate that relationships with pathogens might constrain diversification if pathogen diversity increased with host diversity and resulted in more frequent host switching and emergent disease. Many indirect observations are consistent with these scenarios. However, the postulated influence of pathogens on the filling of niche space and diversification of clades primarily highlights our lack of knowledge concerning the space and time dimensions of coevolutionary interactions and their influence on population distribution and species diversification.

Cancer stem cells of multiple myeloma:recent progress

Cancer stem cells(CSCs) are a small proportion of tumor cells with the property of stem cells in the tumor tissue;they are capable of self-renewal,multi-lineage differentiation and serve as the source of tumor cells and tumor tissues.The discovery of multiple myeloma CSCs and the study on its relationship with side population cells and niche provide a new interpretation on the pathogenesis of multiple myeloma.

Niches of plant populations in mangrove reserve of Qi’ao Island, Pearl River Estuary

Thirty-two 10 × 10 m 2 quadrats were set up in four mangrove communities for the study of the niches of nine plants with horizontal and vertical resource sequences in Dawei Bay, Qi’ao Island, Zhuhai City. Generally, species diversities of natural mangroves were higher than those of plantations. The diversities decreased along sequence of substrate layer, shrub layer and tree layer in natural mangroves; and were highest on the shrub layer in plantations. At the horizontal resource sequence, the niche breadth varied 0.132–0.896 ( B ( sw )) and 0.120–0.693 ( B ( L )). The niche breadth of Acanthus ilicifolius and Aegiceras corniculatum were the highest and that of Spartina alterniflora was the lowest. At the vertical resource sequence, the niche breadth varied 0–0.400 ( B ( sw )) and 0.333–0.747 ( B ( L )). All the niche breadth values were the lowest except those of A. ilicifolius and A. corniculatum. The niche similarity of the populations varied 0–0.746 and 0–1.000 at the horizontal and vertical resource sequences, respectively. A. ilicifolius and A. corniculatum had niche overlap with all plants at the horizontal resource sequence, while the introduced Sonneratia caseolaris and Sonneratia apetala had no such overlapping between six and five plants in the community, respectively. At the vertical resource sequence, A. ilicifolius and A. corniculatum had niche overlapping with all the populations. The more niche overlapping existed among the other populations. The results indicated that, currently, the mangrove plantation in Qi’ao Island had a simplex structure and composition of species. The status of plant populations’ niche was determined by the species selected and structure of afforestation. It is suggested to create forest gaps artificially and introduce Kandelia obovata saplings to reverse its current status of lower niche breadth, facilitate natural regeneration and spreading of A. corniculatum and A. ilicifolius, and accelerate the restoration process of natural mangrove. Simultaneously, the species matching and planting methods of mix stands should be emphasized in the future.

Population ecology and niche seeking in the development of gay and lesbian rights groups

This paper explores the formation of groups within the framework of the population ecology literature. Specifically, I argue that newly formed groups’ target membership bases and policy agendas will become more focused as the density of interest groups in a population increases, though groups will not necessarily continue this focused trend once the density of the population has reached its upper limits. To test this theory, I utilize Nownes’ [Nownes, A. J. (2004). The population ecology of interest group formation: Mobilizing for gay and lesbian rights in the United States, 1950–1998. British Journal of Political Science, 34, 49–67] dataset on the population ecology of gay and lesbian rights groups and a typology of groups that Bosso [Bosso, C. J. (2005). Environment, Inc.: From Grassroots to Beltway. Lawrence: University Press of Kansas] used in explaining the focus of environmental rights groups. I find that as the population of gay and lesbian groups became more dense, the groups that formed tended to narrow down their potential membership populations. However, the results were different for a newly formed group's policy agenda. While niche seeking occurred during the rapid growth of groups in the 1970s and the early 1980s, groups that formed after growth leveled off in the mid-1980s balanced their agendas between being too broad and too narrow. This important finding indicates that niche seeking does not always occur in very dense interest populations.

Reurbanization and Housing Markets in the Central and Inner Areas of Liverpool

British cities appear to be moving from a period of counter-urbanization to a period of reurbanization. One reason for this appears to be the growth of residential development in city centres. At the same time as there has been a boom in city centre housing, many cities appear to have experienced housing market failure in parts of the inner urban area. Through a study of Liverpool this article considers the evidence to support the notion that reurbanization is becoming an established trend, and why. What is the relationship between this emerging central area housing market and the surrounding inner urban areas? What are the implications for planning practice? The article concludes that there is evidence of reurbanization, partly driven by the economic revival of the city centre economy. But this emerging housing sector caters only for a niche population and makes a relatively inefficient contribution to housing supply. However, with the exception of student housing, it appears to be segmented from and not adversely impacting upon the inner-area housing market. If the goal is to broaden the appeal of city centre living to a wider social spectrum and to increase the efficiency of its contribution to housing supply, then its provision needs to be more carefully planned in terms of housing mix, local environmental conditions and amenities.

Consumer Typology and Online Travel Websites

This research attempts to investigate differences in past experiences of using internet in repurchasing. In doing so, the authors identify online consumer characteristics, particularly one-time and repeat users comparison across geographical borders of Korean and Taiwanese teenage customers. Results show that there are significant differences in online shopping typologies between Korean and Taiwanese customers. While attitude serves as a distinguishing factor for both data sets along the other two dimensions, trust does not. Since researchers have focused on comparisons between Western cultures and Asian cultures` online purchase behavior or Internet use, the current study provides a valuable comparison for this niche population of young customers at least in a Korean-Taiwanese context. The authors also make a brief argument that these findings can influence marketing practitioners and site developers in their strategies.