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Recruitment Rates (recruitment + rate)

Distribution by Scientific Domains

Life Sciences	65%
Medical Sciences	13%
Earth and Environmental Science	13%
2 Other Domains	9%

Selected Abstracts

Within-sex density dependence and population dynamics of red squirrels Sciurus vulgaris

JOURNAL OF ANIMAL ECOLOGY, Issue 1 2004
Luc A. Wauters
Summary 1Social organization and dispersal of red squirrels (Sciurus vulgaris L.) differ between sexes, and intrasexual competition is intense. Therefore, we predicted that demographic parameters should be gender-specific: that is density-dependent factors will be more strongly related to density of the same sex than to density of the opposite sex. We studied the relative importance of within- and between-sex density-dependent factors and of density-independent factors (habitat type, food abundance, winter temperature) on different demographic parameters, in two populations in northern Belgium. 2Spring density of males was positively correlated with tree-seed abundance in the previous year, but this was not the case for females. None of the population parameters we measured differed between habitats, indicating that the same density-dependent and density-independent mechanisms prevailed in coniferous and deciduous habitat. 3Within each sex, we found several demographic parameters that were dependent on the densities of the same sex; however, none of these parameters was found to be dependent on the density of the opposite sex. 4Reproductive rate increased with food abundance and decreased with female density. Adult survival of females decreased with female density in autumn,winter, while survival of adult males in spring,summer increased with the size of the previous year's seed crop. 5Immigration rate of males was higher in spring than in autumn, and spring immigration increased with food abundance. Male recruitment rate, in both seasons, increased with food abundance, but was male density dependent. However, spring,summer loss rates also increased when food supplies were good, suggesting that despite high food availability, emigration of juvenile and subadult males increased when intrasexual competition was intense. Recruitment rate of females decreased with increasing female density. After a good seed crop, more subadult females dispersed, but their settlement success (recruitment) was lower at high female density. 6Seed crop size positively affected red squirrel densities through increased reproduction, immigration and adult survival of males, but density-dependent reproduction and within-sex density-dependent recruitment of locally born juveniles and dispersing subadults limit the fluctuations in numbers and regulate densities in winter,early spring, as well as in summer. [source]

False Uniqueness: the Self-Perception of New Entrants to Higher Education in the UK and Its Implications for Access , a Pilot Study1

HIGHER EDUCATION QUARTERLY, Issue 1 2007
Andy Thorpe
A central tenet of contemporary education policy relates to the desire to extend higher education (HE) provision to less advantaged groups (,widening participation'). Our paper contends that a key behavioural obstacle to widening participation lies in the erroneous belief that persists among potential entrants from disadvantaged backgrounds as to their capabilities of succeeding within the HE environment , a perception that serves to deflate application/recruitment rates from such groupings. We test this ,false uniqueness' thesis using a sample of 127 new UK undergraduates, finding that students drawn from lower social class backgrounds consistently underestimated their abilities vis-à-vis the overall cohort. [source]

Impact of Forest Fragmentation on Understory Plant Species Richness in Amazonia

CONSERVATION BIOLOGY, Issue 2 2003
Julieta Benítez-Malvido
In Central Amazonia, 9 to 19 years after fragmentation, we recorded species richness and net seedling recruitment rate in forest fragments of 1, 10, and 100 ha and in continuous forest. In 1991 all seedlings 5,100 cm tall within permanent 1-m2 plots in fragments and continuous forest were counted and grouped into tree, liana, palm, and herb life-form classes. In 1993 we manually removed all seedlings that were <1 m tall from the permanent plots. Six years and 5 months later ( 1999 ), all new seedlings recruited into the plots were counted, grouped into different life forms, and classified into distinct morphospecies. The species richness of recruited tree, liana, herb, and palm seedlings was lower in forest fragments than in continuous forest, with the 1-ha fragment having the poorest species richness. The total number of recruited individuals was 40% less than that previously present for all life forms, except lianas. Liana recruitment was 7% to 500% higher than the original abundance in the forest fragments and continuous forest. In general, species similarity was higher among fragments than between fragments and continuous forest, with the 1-ha fragment being less similar. Species rank/abundance curves showed that continuous forest species in all life forms tended to disappear in forest fragments, whereas common species in forest fragments were absent from continuous forest. Overall, our results suggest that the life-form composition and structure of the regenerative plant pool in fragments were shifting toward a species-poor seedling community. Losses of understory species diversity, but especially of tree seedlings, threaten the maintenance of rainforest biodiversity and compromise future forest regeneration. Resumen: La fragmentación de las selvas tropicales afecta severamente a a los árboles de gran porte, sin embargo, su efecto sobre otros estadíos y formas de vida de las plantas es poco conocido. En la Amazonia central, de 9 a 19 años después de la fragmentación, se registró la riqueza de especies y la tasa neta de reclutamiento de plántulas en fragmentos de selva de 1, 10, y 100 ha y en selva contínua. En 1991, todas las plántulas de 5,100 cm de altura dentro de cuadrantes permanentes de 1-m2 en los fragmentos y en la selva contínua, fueron contadas y agrupadas en diferentes formas de vida: árboles, lianas, palmas y hierbas. En 1993 se removieron manualmente todas las plántulas <1 m de altura dentro de los cuadrantes. Seis años y cinco meses más tarde (1999) se contaron todas las plántulas reclutadas dentro de los cuadrantes, se agruparon en diferentes formas de vida v se clasificaron en morfoespecies distintivas. La riqueza de especies de plántulas reclutadas en todas las formas de vida fue menor en los fragmentos que en la selva contínua, con el fragmento de 1 ha presentando la menor riqueza de especies. El número total de individuos reclutados fue 40% menor que los previamente presentes para todas las formas de vida, excepto lianas. El reclutamiento de lianas fué de 7 a 500% mayor que la abundancia original en los fragmentos y en la selva contínua. En general la similitud de especies fué mayor entre fragmentos que entre fragmentos y selva contínua, con el fragmento de 1-ha siendo el menos similar. Las curvas de rango/abundancia de especies, mostraron que las especies de selva contínua en todas las formas de vida tendieron a desaparecer de los fragmentos, mientras que las especies comunes en los fragmentos estuvieron ausentes en la selva contínua. En general, nuestros resultados sugieren que la composición de formas de vida y la estructura del banco regenerativo en fragmentos tienden a convertirse en una comunidad de plántulas pobre en especies. La pérdida de diversidad de especies del sotobosque, pero especialmente de plántulas de árboles, amenaza el mantenimiento de la biodiversidad y pone en peligro la regeneración futura de la selva. [source]

Sequential methods and group sequential designs for comparative clinical trials

FUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 5 2003
Véronique Sébille
Abstract Comparative clinical trials are performed to assess whether a new treatment has superior efficacy than a placebo or a standard treatment (one-sided formulation) or whether two active treatments have different efficacies (two-sided formulation) in a given population. The reference approach is the single-stage design and the statistical test is performed after inclusion and evaluation of a predetermined sample size. In practice, the single-stage design is sometimes difficult to implement because of ethical concerns and/or economic reasons. Thus, specific early termination procedures have been developed to allow repeated statistical analyses to be performed on accumulating data and stop the trial as soon as the information is sufficient to conclude. Two main different approaches can be used. The first one is derived from strictly sequential methods and includes the sequential probability ratio test and the triangular test. The second one is derived from group sequential designs and includes Peto, Pocock, and O'Brien and Fleming methods, , and , spending functions, and one-parameter boundaries. We review all these methods and describe the bases on which they rely as well as their statistical properties. We also compare these methods and comment on their advantages and drawbacks. We present software packages which are available for the planning, monitoring and analysis of comparative clinical trials with these methods and discuss the practical problems encountered when using them. The latest versions of all these methods can offer substantial sample size reductions when compared with the single-stage design not only in the case of clear efficacy but also in the case of complete lack of efficacy of the new treatment. The software packages make their use quite simple. However, it has to be stressed that using these methods requires efficient logistics with real-time data monitoring and, apart from survival studies or long-term clinical trials with censored endpoints, is most appropriate when the endpoint is obtained quickly when compared with the recruitment rate. [source]

The use of size,frequency diagrams to characterize prehistoric fish catches and to assess human impact on inshore fisheries

INTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 1-2 2001
Foss Leach
Abstract Archaeological collections of fish bones from previously excavated sites in New Zealand are being re-examined and selected bones measured in order to estimate original fish size, reconstruct prehistoric fish catches and assess human impact on the fishery over the course of about 800 years of New Zealand prehistory. Several problems hamper this research, such as small sample sizes, lack of significant stratigraphy at many sites, inconsistent field collection strategies and failure to retain all of the material after initial analysis. Although some common fish species show a significant decline in mean size between pre-European and early historic samples on the one hand, and modern populations on the other, we have found little support for the common belief that there was a decline in mean fish size during the pre-European period. We have observed increases over time in the mean size of snapper (Pagrus auratus), blue cod (Parapercis colias) and undifferentiated species of Labridae from several sites scattered throughout New Zealand. Distinguishing between changes in fish population structures owing to natural processes, such as surface sea water changes, and those which are the result of human over-fishing is not simple, because both processes can operate simultaneously. We draw on modern fish quota management models to separate these processes. Important factors for each species are inshore biomass and the recruitment rate at different temperature regimes. In the case of blue cod, we find that there are signs in the catch diagrams of changes in fishing technology, and that 30,80% of catches are undersized fish in terms of modern management criteria. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Within-sex density dependence and population dynamics of red squirrels Sciurus vulgaris

Reducing the density of breeding gulls influences the pattern of recruitment of immature Atlantic puffins Fratercula arctica to a breeding colony

JOURNAL OF APPLIED ECOLOGY, Issue 3 2003
S. K. Finney
Summary 1By acting as both competitors and predators, gulls (Larus spp.) are generally considered to reduce significantly the attractiveness of potential breeding sites for other birds. This perceived threat posed by gulls to other breeding birds has led to the implementation of gull control procedures at many seabird colonies. However, the extent to which reducing gull numbers benefits other species has received little rigorous scientific investigation. 2During a gull control programme (1972,89), gull nest density on the Isle of May, south-east Scotland, was reduced by between 30% and 100% in different sections of the island. Following termination of the original programme in 1989, several sections were maintained as gull-free by repeated removal of nests. 3We used data collected over a 23-year period to determine the extent to which the spatial variation in puffin Fratercula arctica recruitment was influenced by changes in the density and spatial distribution of breeding gulls resulting from the control programme. 4The presence of breeding gulls significantly affected the pattern of recruitment of puffins to the colony. Puffin recruitment rate was highest in the sections of the island where gull nest density was low. Gull density explained 21% of the variation in puffin recruitment rate. 5These results suggest that the reduction in the number of breeding gulls substantially increased the attractiveness of areas of the colony as breeding sites for puffins, and is thus likely to have played an important role in the pattern of expansion of the puffin population on the island. 6Synthesis and applications. Following a recent increase in the conservation status of both herring L. argentatus and lesser black-backed gulls L. fuscus, there has been a move to make management decisions more objective. This has highlighted the need for studies such as this, aimed at assessing the impact of gulls and their removal on other breeding birds, to ensure that any future control programmes are both necessary and effective. [source]

Recruiting Teen Smokers in Shopping Malls to a Smoking-Cessation Program Using the Foot-in-the-Door Technique

JOURNAL OF APPLIED SOCIAL PSYCHOLOGY, Issue 5 2006
Paul N. Bloom
Persuading teen smokers to volunteer for smoking-cessation programs is a challenging yet understudied problem. As a method of dealing with this problem, we used and tested a foot-in-the-door (FITD) approach. Teen smokers were intercepted at malls and were assigned randomly to request compliance with a small behavior request of either (a) answering a few questions (light FITD) or (b) answering the same questions and a few additional ones, plus watching a short video about the effects of nicotine (heavy FITD). Participants were then called back by telephone several weeks later and asked to comply with a large behavior request of joining a cessation program that involved the use of self-help materials and telephone counseling. Although no differences were found in responses from the light and heavy groups, consent to enter the program was obtained from 12% of the pooled qualified intercepts and their parents (for those under 18 years). This recruitment rate was considered good, given that this is one of the only reported studies that recruited teen smokers from the general population to cessation programs. [source]

Demographic and life-history correlates for Amazonian trees

JOURNAL OF VEGETATION SCIENCE, Issue 6 2005
Henrique E.M. Nascimento
Abstract Questions: Which demographic and life-history differences are found among 95 sympatric tree species? Are there correlations among demographic parameters within this assemblage? Location: Central Amazonian rain forest. Methods: Using long-term data from 24 1,ha permanent plots, eight characteristics were estimated for each species: wood density, annual mortality rate, annual recruitment rate, mean stem diameter, maximum stem diameter, mean stem-growth rate, maximum stem-growth rate, population density. Results: An ordination analysis revealed that tree characteristics varied along two major axes of variation, the major gradient expressing light requirements and successional status, and the second gradient related to tree size. Along these gradients, four relatively discrete tree guilds could be distinguished: fast-growing pioneer species, shade-tolerant sub-canopy species, canopy trees, and emergent species. Pioneers were uncommon and most trees were canopy or emergent species, which frequently had low mortality and recruitment. Wood density was negatively associated with tree mortality, recruitment, and growth rates when all species were considered. Growth rates varied markedly among and within species, with pioneers exhibiting far faster and less variable growth rates than did the other species. Slow growth in subcanopy species relative to canopy and emergent trees was not a simple consequence of mean tree size, but apparently resulted from physiological constraints imposed by low-light and other conditions in the forest understorey. Conclusions: Trees of Amazonian rain forests could be classified with some success into four relatively distinctive guilds. However, several demographic and life-history traits, such as those that distinguish early and late successional species, probably vary along a continuum, rather than being naturally grouped into relatively discrete categories. [source]

Changes in body condition and body size affect breeding and recruitment in fluctuating house mouse populations in south-eastern Australia

AUSTRAL ECOLOGY, Issue 3 2009
GREGORY J. MUTZE
Abstract Changes in body condition and body size in field populations of house mice, Mus domesticus, were examined to investigate why mouse populations do not increase rapidly in some years when favourable environmental and demographic conditions indicate they might. Mice had repeated seasonal patterns each year in breeding, growth rates and body condition that reflected the seasonal availability of food, but mean levels for each parameter varied among years. In most years mice lost body condition during summer, breeding declined and population growth slowed. Rapid population growth occurred when body condition was generally high and was maintained throughout summer. Female mice with large body length were more likely to breed than smaller mice, at all times, but changes in body condition accounted for most of the variability in female breeding activity between years and between habitats, and for the seasonal changes in the importance of body length. During rapid population growth, the recruitment rate of juveniles relative to the number of breeding females was 150,300% higher than in other years but adult survival rates were not higher. The data indicate that the ability of mice to maintain body condition, particularly when subject to moisture stress in summer, affects the proportion of females breeding, the number of juveniles weaned and their body condition at weaning, and is promoted by foraging conditions that favour maintenance of juvenile body condition after weaning. These factors, in turn, greatly affect juvenile recruitment rates and eventual population density of mice. Low juvenile survival is suggested as a reason that numbers of house mice in southern Australian cereal-growing areas do not increase rapidly in some years when other parameters are favourable. Similar processes are likely to play a role in regulating other rodent populations. [source]

Features and preliminary results of the Dutch centre of the ERSPC (Rotterdam, the Netherlands)

BJU INTERNATIONAL, Issue 2003
M.J. Roobol
OBJECTIVE To describe the preliminary results of the Dutch section of a large multicentre study of screening for prostate cancer, the European Randomized study of Screening for Prostate Cancer (ERSPC), initiated in the Netherlands and Belgium in 1991. MATERIALS AND METHODS After a series of five pilot studies which started in 1991, full-capacity screening started in 1994 with the use of a serum prostate-specific antigen (PSA) determination, a digital rectal examination (DRE) and transrectal ultrasonography (TRUS) as screening tests. Depending on the results and the screening protocol used, men were referred for further examination by sextant biopsies (extended with a seventh biopsy if TRUS showed abnormality). The protocols used, efficiency of the different screening tests, number of cancers detected in the pilot studies, initial screening round and preliminary results of the second screening round are described. RESULTS After the pilot studies it became clear that a study of prostate cancer screening was feasible in the Rotterdam area. The screening protocol was workable and the recruitment rate acceptable (39.5%). An inventory of the population registries of Rotterdam and surrounding municipalities, and the known recruitment rate, made it clear that a contribution of 40 000 men (aged 55,74 years) from the Dutch centre to the ERSPC was feasible. The initial screening round started in December 1993 and lasted until December 1999 (protocol 5,10). In all, 42 376 men were randomized and 1014 cancers detected (5.1%). During this screening the protocol was simplified. After evaluating the different screening tests abnormal results of the DRE and TRUS were omitted as an indication for a sextant biopsy. Only a serum PSA level of , 3.0 ng/mL is now used as the indication. The second screening round started in December 1997 and continues. To December 2002, 9920 men were screened for the second time, 4 years after their initial screening visit. To date 446 cancers have been detected (4.5%); this round will last to December 2003. Further evaluation of the screening regimen and characteristics of the cancers detected are constantly assessed within the Dutch ERSPC. Meanwhile a third screening round has also been initiated, which will last to December 2007. CONCLUSION A prostate cancer screening study of the projected magnitude is feasible in Rotterdam; the recruitment rate is acceptable and the screening tests well tolerated. The study has generated many scientific publications and will be of great value in determining whether prostate cancer screening should be part of general healthcare. [source]

Climate warming and the evolution of morphotypes in a reptile

GLOBAL CHANGE BIOLOGY, Issue 2 2009
VIRGINIE LEPETZ
Abstract Climate warming is known to have effects on population dynamics through variations in survival, fecundity and density. However, the impacts of climate change on population composition are still poorly documented. Morphotypes are powerful markers to track changes in population composition. In the common lizard, Lacerta vivipara, individuals display two types of dorsal patterns: reticulated (R individuals) and linear (L individuals). We examined how local warming affected intrapopulation frequencies of these morphotypes across 11 years. We observed changes in morph frequency of dorsal patterns across years, paralleling the rise of spring temperatures. The proportion of R individuals increased with June temperatures in juveniles, yearlings, and adult males and females. Three mechanisms could explain these changes: phenotypic plasticity, microevolution and/or dispersal between populations. We investigated the ontogenetic determinism, fitness and recruitment rates associated with dorsal morphotypes. Dorsal pattern ontogeny showed temperature dependence but this relationship was not associated with the warming trend during this study. We found variation by morphotype in survival and clutch size, but these factors did not explain R frequency increases. Among all the parameters considered in this study, only a decrease of immigration, which was more pronounced in the L morphotype, could explain the change in population composition. To our knowledge, this provides the first evidence of the impact of climate warming on population composition due to its effects on immigration. [source]

Early life history of the Mediterranean gorgonian Paramuricea clavata: implications for population dynamics

INVERTEBRATE BIOLOGY, Issue 1 2008
Cristina Linares
Abstract. Knowledge about early stages of marine sessile invertebrates dispersing by means of free-swimming propagules is fundamental toward understanding their population biology. In this study, we describe and quantify survivorship of early stages of the gorgonian Paramuricea clavata to contribute to the understanding of their implications on population dynamics of this emblematic species of the Mediterranean hard-bottom communities. Spawning was recorded in June for the 3 years studied (2001,2003). High levels of fertilization rate were observed during the main spawning in 2001 and 2002 (62,69%). This appears to be related to the surface brooding mode of development, synchronous spawning, and high fecundity of the species. The timing of development of the blastulae was ,24 h and the planulae appeared after 48,72 h. In the laboratory, metamorphosis into polyp started between 8 and 25 d, but this timing may have been delayed by lack of unknown appropriate cues for settlement. The behavior of first developed planulae exhibited a marked negative phototaxis that may be a strategy to avoid competition with fast-growing algae on photophilous habitats. Despite the high fertilization rate in P. clavata, laboratory and field experiences indicate that survivorship through the planulae and polyp stages was very low, given that none of the settled polyps survived for >7 months in both experimental years. The low survival of the early stages may help explain the low recruitment rates observed in the field in addition to indicating major limitations for colonization of new areas and for persistence of the local population under disturbances. [source]

Numerical fluctuations in the northern short-tailed shrew: evidence of non-linear feedback signatures on population dynamics and demography

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2002
Mauricio Lima
Summary 1,We studied a fluctuating population of the northern short-tailed shrew (Blarina brevicauda) in the Appalachian Plateau Province of Pennsylvania, USA, spanning 21 years of monitoring. We analysed the pattern of annual temporal variation fitting both time-series models and capture,mark,recapture (CMR) statistical models for survival and recruitment rates. 2,We determined that non-linear first-order models explain almost 80% of the variation in annual per capita population growth rates. In particular, a non-linear self-excited threshold autoregressive (SETAR) model describes the time-series data well. Average snowfall showed positive and non-linear effects on population dynamics. 3,The CMR statistical models showed that a non-linear threshold model with strong effects of population density was the best one to describe temporal variation in survival rates. On the other hand, population density or climatic variables did not explain temporal variation in recruitment rates. Survival rates were high during the study period. Weekly changes in population size attributable to new recruits entering in the population fluctuate between 21% and 0%, while the changes in population size related to survival fluctuate between 79% and 100%. 4,Two important results arise from this study. First, non-linear models with first-order feedback appear to capture the essential features of northern short-tailed shrew dynamics and demography. Secondly, climate effects represented by snowfall appear to be small and non-linear on this insectivore. The population dynamics of this shrew in the Appalachian Plateau are determined apparently by a strong non-linear first-order feedback process, which is related to survival rates. 5,This study links population dynamics and demography by detecting the underlying demographic mechanisms driving population dynamics. The feedback structure of this shrew suggests the existence of population dynamics dominated by intraspecific competitive interactions, such as aggression, solitary nesting, non-overlapping home ranges and territoriality. [source]

Patterns of reproductive effort and success in birds: path analyses of long-term data from European ducks

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2002
Peter Blums
Summary 1We tested ecological hypotheses about timing of breeding and reproductive effort in birds, by analysing > 15-year data sets for individually marked females in three species of Latvian ducks (northern shoveler, tufted duck, common pochard). 2Duckling survival and recruitment declined with advancing hatch date in pochard and tufted duck, after controlling for effects of female age and other factors with path analysis, a novel finding which indicates that fitness advantages associated with early hatching extended beyond the prefledging period. Logistic regression analysis suggested further that individual duckling prefledging survival was moderate in the earliest phase of the breeding season, greatest in mid-season and lowest later on. 3However, selection acting against early hatched ducklings was surpassed by strong directional selection favouring recruitment of the earliest hatching females. The absolute and relative numbers of female recruits produced by a breeding female declined sharply with advancing hatch date in all species. 4Unlike previous studies, an hypothesized intraspecific trade-off between duckling mass and brood size was detected, being very robust in two of three species. 5Unexpectedly, female age effects on recruitment were manifested only indirectly by several pathways, the most important being the earlier hatching dates of older females. Size-adjusted body mass (i.e. condition index) was positively related to reproductive success, and was 2,8-fold more influential than female size (indexed by wing length). 6Overall, fecundity-independent variables (e.g. hatching date, weather, indices of duckling production and habitat quality) generally had 2,10 times greater influence on recruitment rates than did fecundity-dependent variables such as female size or condition, duckling mass and brood size, suggesting a critical role for external environmental factors vs. individual female-specific traits in the recruitment process. [source]

Forest canopy and community dynamics in a temperate old-growth evergreen broad-leaved forest, south-western Japan: a 7-year study of a 4-ha plot

JOURNAL OF ECOLOGY, Issue 5 2001
Masahiro Miura
Summary 1Forest canopy gap and community dynamics were studied in a 4-ha permanent plot of an old-growth evergreen broad-leaved forest dominated by Castanopsis cuspidata var. sieboldii and Distylium racemosum in the Tatera Forest Reserve, Tsushima Islands, south-western Japan. The forest was affected by a powerful typhoon in 1987 and was monitored from 1990 to 1997. 2In 1990, all woody stems , 5 cm diameter at breast height (d.b.h.) in the plot were identified, mapped and marked, and the state of 1600 5 m × 5 m contiguous quadrats used to locate canopy gaps. Gaps occupied 17.1% of the plot, which contained 4494 tree and shrub stems (total basal area 63.48 m2 ha,1). Gaps were re-censused in 1997 and both marked and newly recruited (, 5 cm d.b.h.) stems were recorded in 1992 and 1997. 3Over 7 years the rates of canopy gap formation and closure were 0.72% year,1 and 1.61% year,1, respectively, mortality and recruitment rates were 0.97% year,1 and 0.99% year,1, and the rates of loss and gain in basal area were 0.95% year,1 and 0.83% year,1. 4The mortality of stems was size-dependent, with those in middle size classes having the lowest rates. Mortality of stems was lower in canopy and higher in the understorey, while the proportion of stems killed by disturbances increased with height. 5Stems that died during the 7 years were predominantly located in newly created gaps, whereas stems were recruited into both established and new gaps. Deciduous broad-leaved species were largely restricted to gaps that remained open throughout the study. 6Both composition and structure of the forest changed in response to disturbance-related effects on canopy dynamics. [source]

Population dynamics and stage structure in a haploid-diploid red seaweed, Gracilaria gracilis

JOURNAL OF ECOLOGY, Issue 3 2001
Carolyn Engel
Summary 1,Many red seaweeds are characterized by a haploid-diploid life cycle in which populations consist of dioecious haploid (gametophyte) and diploid (tetrasporophyte) individuals as well as an additional diploid zygote-derived sporangium (carposporophyte) stage. A demographic analysis of Gracilaria gracilis populations was carried out to explore and evaluate the population dynamics and stage structure of a typical haploid-diploid red seaweed. 2,Four G. gracilis populations were studied at two sites on the French coast of the Strait of Dover. Survival, reproduction and recruitment rates were measured in each population for up to 4 years. Eight two-sex stage-based population projection matrices were built to describe their demography. 3,All four populations were characterized by high survival and low recruitment rates. Population growth rates (,) were similar between populations and between years and ranged from 1.03 to 1.17. In addition, generation times were found to be as long as 42 years. 4,Sex and ploidy ratios were variable across populations and over time. Female frequencies ranged from 0.31 to 0.59 and tetrasporophyte frequencies from 0.44 to 0.63. However, in most cases, the observed population structures were not significantly different from the calculated stage distributions. 5,Eigenvalue elasticity analysis showed that , was most sensitive to changes in matrix transitions that corresponded to survival of the gametophyte and tetrasporophyte stages. In contrast, the contribution of the fertility elements to , was small. Eigenvector elasticity analysis also showed that survival elements had the greatest impact on sex and ploidy ratios. [source]

Seed Dynamics in Relation to Gaps in a Tropical Montane Rainforest of Hainan Island, South China: (II) Seed Bank

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 5 2008
Run-Guo Zang
Abstract Spatial and temporal patterns of seed bank dynamics in relation to gaps in an old growth tropical montane rainforest of Hainan Island, South China, were studied over two consecutive years. From June 2001 to June 2003, soil seed bank sampling blocks were taken near each of the four sides of each seed trap and immediately put into a nursery for observation of seedling emergence dynamics in four seasons (each experiment in each season). The abundances of seedlings that emerged from seed banks showed the trend of vine functional group (VFG) > shrub functional group (SFG) > tree functional group (TFG) > herb functional group (HFG), but the trend in species richness of seedlings that emerged from the soil seed banks was TFG > VFG > SFG > HFG. The abundances of seedlings that emerged from seed banks in the three gap zones showed no significant differences, but significant differences did exist for the species richness. The time of sampling or seasons of experiments had significant influences on both the species richness and seedling abundances. The seedling emergence processes of each experiment all revealed the unimodal patterns. Few emergences occurred 1 year after each experiment. Compared with those under closed canopies, the recruitment rates from seed to seedlings and from seedlings to saplings in gaps were higher, but the mortality rates from saplings to big trees were also higher in the gaps. [source]

A long-term study of neighbour-regulated demography during a decline in forest species diversity

JOURNAL OF VEGETATION SCIENCE, Issue 1 2006
Lin Yi-ching
Abstract Question: Did disturbance, no density-dependence of the dominant species, and negative neighbourhood interactions on rare species affect tree demography during a decline in species diversity associated with the increase of Acer saccharum from 1939,2001? Hypotheses: 1. The rise in dominance of A. saccharum was because of its advantage in disturbances and lack of density-dependence of its demography. 2. Rare species were not favoured by disturbances, including those from Dutch elm disease, and demonstrated negative neighbourhood interactions with A. saccharum. Location: Brownfield Woods in Illinois, USA. Methods: Historical maps of trees (, 7.6 cm DBH) from 1939, 1951, 1988, and 2001 in 16 quadrats (48 m × 68 m) were used to compare demography of eight tree species. Effects of disturbances, density-dependence, and neighbourhood interactions on mortality and recruitment of tree species within a 6-m radius of individual target trees were studied. Results: A. saccharum demonstrated a demographic advantage over rare species. It had lower mortality and higher recruitment rates. Disturbances facilitated recruitment of A. saccharum, but did not enhance rare species. Density-dependence of both mortality and recruitment of A. saccharum occurred, but population projection models indicated that ecological conditions became more favourable for A. saccharum in the past 62 years. Furthermore, negative neighbourhood interactions were detected between rare species and A. saccharum. The increase in neighbouring A. saccharum significantly increased mortality and reduced recruitment of the rare species. Conclusions: The general disturbance regime, enhanced by Dutch elm disease, in Brownfield Woods facilitated the rise of dominance of A. saccharum. Meanwhile, rare species declined as a result of their disadvantage in disturbance and negative neighbourhood interactions with A. saccharum. [source]

WILL THE DILEMMA OF EVIDENCE-BASED SURGERY EVER BE RESOLVED?

ANZ JOURNAL OF SURGERY, Issue 9 2006
Ned S. Abraham
Exponents of evidence-based medicine do not undermine the importance of clinical expertise and skills, but they emphasize that decision-making in medicine should be based on the best available evidence derived from the systematic analysis of observations made in an objective, unbiased and a reproducible fashion. The randomized controlled trial (RCT) is the most scientifically rigorous means of hypothesis testing in epidemiology. Discrepancies between established surgical and other interventions and best available evidence are common. These can be in the form of significant delay in adopting a new intervention despite strong supportive evidence, adopting an intervention before supportive evidence becomes available for reasons of novelty or pear pressure and the lack of supportive evidence for many established common practices. This is compounded further by the paucity of good quality evidence for most surgical procedures. This is arguably because of the inherent difficulties in conducting surgical RCT. The practical, ethical and financial ramifications are complex and the nature of surgical disease often compromise the chances of success or completion of RCT. Carrying out surgical RCT may have more implications on the clinician's authority, autonomy and income and their results are more likely to be influenced by his/her expertise and competence than medical RCT. Furthermore, the success of surgical RCT is often jeopardized by very low recruitment rates. The aim of this study is to discuss the dilemma of producing evidence in surgery. [source]

Changes in body condition and body size affect breeding and recruitment in fluctuating house mouse populations in south-eastern Australia

The Influence of Topography on Tree Growth, Mortality, and Recruitment in a Tropical Montane Forest,

BIOTROPICA, Issue 3 2000
P. J. Bellingham
ABSTRACT To determine if there were consistent differences in growth, mortality, and recruitment on slopes and ridge crests in tropical montane forests, which could explain the (frequent but not universal) low stature of trees in the ridgetop forests, we analyzed data from long-term plots in Jamaica (1990,1994; sixteen 200-m2 plots, six on ridge crests and five each on north and south slopes). Mortality was higher on north slopes, while growth and recruitment rates were not significantly different among positions. Soil pH and effects of recent disturbance by Hurricane Gilbert were positively correlated with growth and recruitment, while slope angle and disturbance effects were the best predictors of mortality. The patterns we found in Jamaica, that growth and recruitment were not higher on ridge crests than slopes, are different than those found by Herwitz and Young in Australia where growth and turnover were greater on a ridge crest. Therefore, it is not possible at present to make simple generalizations about dynamics of ridge crest versus slope forests in the montane tropics. [source]