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Distribution by Scientific Domains

Life Sciences	37%
Medical Sciences	18%
Business, Economics, Finance and Accounting	12%

Selected Abstracts

An Experimental Investigation of Landscape Resistance of Forest versus Old-Field Habitats to Emigrating Juvenile Amphibians

CONSERVATION BIOLOGY, Issue 5 2002
Betsie B. Rothermel
Larval amphibians,spotted salamander (Ambystoma maculatum), small-mouthed salamander (A. texanum), and American toad ( Bufo americanus ),were added to artificial pools in four dispersal arrays on forest edges. Each array consisted of a pool surrounded by a circular drift fence with pitfall traps and two 2.5 × 50 m enclosures (runs) extending into forest and old-field habitat. Juveniles captured at the circular fences were individually marked and released into either field or forest runs. We determined initial distance, initial rate, total distance, and net distance moved by juveniles in the field versus forest from recaptures in the runs. We also conducted 24-hour dehydration trials to compare the rates of evaporative water loss by spotted and small-mouthed salamanders in field and forest. Initial orientation of spotted salamanders and toads was significantly biased toward forest. Orientation of small-mouthed salamanders did not differ significantly from random expectations. The avoidance of open-canopy habitat by juvenile American toads in particular indicates that predictions of dispersal behavior based on adult habitat use may be misleading. Spotted salamanders moved almost four times farther and toads more than three times farther into the forest than into the field, and recapture rates of both species were much lower in the field. We attribute the lower recapture rates and shorter distances moved in the field to higher mortality due to desiccation or an abundance of predators. Juvenile spotted and small-mouthed salamanders experienced greater evaporative water loss in the field. Our data on movement behavior and dehydration rates suggest that old-field habitats offer greater landscape resistance to dispersing juveniles of some species. Thus, forest fragmentation is likely to reduce dispersal rates between local populations of these three species, with potentially negative consequences for population persistence in altered landscapes. Resumen: Utilizamos un enfoque experimental para investigar los efectos de la composición del paisaje sobre el éxito inicial de dispersión de anfibios juveniles. Colcamos larvas de anfibios (salamandras manchadas [Ambystoma maculatum] y A. texanum y sapo americano [Bufo americanus] ) en estanques artificiales en cuatro secuencias de dispersión en bordes de bosque. Cada secuencia consistió de un estanque rodeado por un cerco circular con trampas de fosa y dos encierros (corridas) de 2.5 × 50 m que se extendían hacia el hábitat de bosque y de campo viejo. Los juveniles capturados en los cercos circulares fueron marcados individualmente y liberados en las corridas de bosque o de campo. A partir de recapturas en las corridas, determinamos la distancia inicial, la tasa inicial, las distancia total y la distancia neta recorrida por juveniles en el campo versus el bosque. También realizamos pruebas de deshidratación de 24 horas para comparar las tasas de pérdida de agua por evaporación en salamandras en el campo y el bosque. La orientación inicial de Ambystoma maculatum y Bufo americanus estuvo significativamente sesgada hacia el bosque. La orientación inicial de A. texanum no fue significativamente diferente de las expectativas aleatorias. La evasión del hábitat abierto en particular por juveniles de sapo americano indica que las predicciones del comportamiento de dispersión basadas en el uso del hábitat por adultos pueden llevar a conclusiones erróneas. Las salamandras manchadas se movieron cuatro veces mas lejos y los sapos más de tres veces más lejos dentro del bosque que dentro del campo, y las tasas de recaptura de ambas especies fueron mucho menores en el campo. Atribuimos las bajas tasas de recaptura y las distancias menores a la mayor mortalidad debido a la desecación o a la abundancia de depredadores. Los juveniles de las dos especies de salamandras experimentaron mayor pérdida de agua por evaporación en los campos. Nuestros datos del comportamiento de movimiento y las tasas de deshidratación sugieren que los hábitats de campo viejo ofrecen mayor resistencia de paisaje para los juveniles dispersantes de algunas especies. Por tanto, es probable que la fragmentación de bosques reduce las tasas de dispersión entre poblaciones locales de estas tres especies, con consecuencias potencialmente negativas para la persistencia de la población en paisajes alterados. [source]

Early adolescents show enhanced acute cocaine-induced locomotor activity in comparison to late adolescent and adult rats

DEVELOPMENTAL PSYCHOBIOLOGY, Issue 2 2008
Kimberly A. Badanich
Abstract Initiation of drug use during adolescence is associated with an increased probability to develop a drug addiction. The present study examined dose,response effects of cocaine (0, 5, 10, or 20 mg/kg, i.p.) on locomotor activity in early adolescent (postnatal day (PND) 35), late adolescent (PND 45), and young adults (PND 60) by measuring total distance moved (TDM) and frequency of start,stops. In response to 20 mg/kg cocaine, early adolescents showed the greatest cocaine-induced increase in TDM in comparison to late adolescent and adult rats. At this same dose, early adolescents showed the greatest cocaine-induced attenuation of start,stops relative to older rats. Results suggest that early adolescents engage in more cocaine-induced locomotor activity and less stationary behavior indicating that early adolescents are more sensitive to locomotor activating effects of high dose cocaine than older rats. © 2008 Wiley Periodicals, Inc. Dev Psychobiol 50: 127,133, 2008. [source]

Arboreal substrates influence foraging in tropical ants

ECOLOGICAL ENTOMOLOGY, Issue 4 2010
NATALIE A. CLAY
1. Physically complex substrates impart significant costs on cursorial central-place foragers in terms of time spent outside the nest and total distance travelled. Ants foraging in trees navigate varied surfaces to access patchy resources, thus providing an appropriate model system for examining interactions between foraging efficiency and substrates. 2. We expected that the speed of recruitment, body size distribution and species richness of foraging arboreal ants would differ predictably among common substrate types occurring on tropical tree trunks. We measured changes in ant abundance and species composition over time at baits placed on bare tree bark, moss-covered bark, and vine-like vegetation appressed to bark. We also measured average body size and body size frequency on the three substrate types. Ants discovered baits sooner and accumulated at baits relatively faster when using vine substrates as the primary foraging trail. Average body size was smaller on vine substrates than on bark. Experimental removal of vine and moss substrates nullified these differences. Contrary to our predictions, species richness and body size distributions did not differ among the three substrate types, due in part to the frequent presence of a few common ground-nesting species at baits on bare bark. 3. Our results collectively indicate that linear substrates facilitate access of foraging ants to patchy resources. Ant use of vine-like substrates appears to be opportunistic; vine use is not confined to certain species nor constrained by body size. [source]

Evaluation of relative distance as new descriptor of yellow European eel spatial distribution

ECOLOGY OF FRESHWATER FISH, Issue 4 2008
H. Imbert
Abstract,,, The spatial distribution of yellow European eel (Anguilla anguilla) smaller than 300 mm was analysed during the upstream colonisation process. A 9-year electric-fishing programme in the Gironde catchment (France) provided eel occurrence data in 256 sites and eel abundance data in 23 sites. Generalized linear models showed that small eel spatial distribution decreased with river slope, dam number and with downstream-upstream distance, estimated using either the distance from the tidal limit, called ,tidal distance', or the ,relative distance', calculated as the fish's position relative to the total distance between tidal limit and river source. This new descriptor should be considered in future eel distribution studies as it reveals fractal dimension in eel spatial distribution and may provide a standardised method to compare directly freshwater eel assessment between streams and catchments of different lengths. If the relevancy of this descriptor is subsequently confirmed, it may have important implications for the management of eel population conservation. [source]

Is food availability limiting African Penguins Spheniscus demersus at Boulders?

IBIS, Issue 1 2006
A comparison of foraging effort at mainland, island colonies
The African Penguin Spheniscus demersus (Vulnerable) formed three new colonies during the 1980s, two on the South African mainland (Stony Point and Boulders) and one on Robben Island. One of the mainland colonies, at Boulders, Simon's Town, is in a suburban area, resulting in conflict with humans. Growth of the Boulders colony was initially rapid, largely through immigration, but has since slowed, possibly as a result of density-dependent effects either on land (where there has been active management to limit the spread of the colony) or at sea. We test the latter hypothesis by comparing the foraging effort of Penguins feeding small chicks at island and mainland sites, and relate this to the foraging area available to birds. Three-dimensional foraging paths of African Penguins were reconstructed using GPS and time,depth loggers. There were no intercolony differences in the rate at which birds dived during the day (33 dives/h), in diving depths (mean 17 m, max. 69 m) or in travelling speeds. The maximum speed recorded was 2.85 m/s, with birds travelling faster when commuting (average 1.18 m/s) than when foraging (0.93 m/s) or resting at sea (0.66 m/s during the day, 0.41 m/s at night). There were strong correlations between foraging trip duration, foraging range and total distance travelled. Foraging effort was correlated with chick age at Robben Island, but not at Boulders. Contrary to Ashmole's hypothesis, birds from Boulders (c. 1000 pairs) travelled further (46,53 km) and foraged for longer (13.2 h) than did birds from Robben Island (c. 7000 pairs) and Dassen Island (c. 21 000 pairs) (33 km, 10.3 h). The mean foraging range also differed significantly between mainland (18,20 km) and island colonies (9 km). The area available to central-place-foraging seabirds breeding on the mainland is typically less than that for seabirds breeding on islands, but the greater foraging range of Boulders birds results in an absolute foraging area roughly twice that of island colonies, and the area per pair is an order of magnitude greater for the relatively small Boulders colony. Ashmole's hypothesis assumes relatively uniform prey availability among colonies, but our results suggest this does not apply in this case. The greater foraging effort of Boulders birds probably reflects reduced prey availability in False Bay, and thus the recent slowing in growth at the colony may be the result of differential immigration rather than management actions to limit the spatial growth of the colony. [source]

Local-scale synchrony and variability in mast seed production patterns of Picea glauca

JOURNAL OF ECOLOGY, Issue 5 2007
JALENE M. LAMONTAGNE
Summary 1Mast seeding is the synchronous and highly variable production of seed by a population of plants. Mast seeding results from the behaviour of individuals; however, little is known about the synchrony of individuals at local scales. 2We address two primary questions at a within-population (17,36 ha study plots) and individual level: (i) How variable is seed production between and within years? (ii) How synchronized is seed production between individuals? 3We monitored annual cone production of 356 Picea glauca (white spruce) from 1990 to 2005 within four plots spanning a total distance of 5.3 km in the Yukon Territory, Canada. 4Spearman correlations (rs) were conducted to test for synchrony. Overall, the trees were moderately synchronous (mean rs (± SE) of 0.52 ± 0.14), and synchrony was statistically detectable (rs > 0) over all distances. Individuals < 75 m apart were highly synchronous (0.64 ± 0.18), and correlations dropped to 0.33 ± 0.07 for trees > 3 km apart. There was considerable variation in cone production patterns among pairs of individuals. 5The number of mast years per plot varied from one to three. During a mast year, many individuals within plots produced large cone crops, with more variability between individuals in low mean cone years. Individual trees had dominant endogenous cycles varying from none to 1,5 years. Forty-four per cent of trees had no significant lag, 23% a negative 1-year lag, and 20% a positive 3-year lag. Basal area did not influence lags, but trees with higher mean cone production throughout the study were more likely to have a 3-year lag compared with no lag. 6The scale of highest synchrony coincided with the scale at which the dominant seed predator in the area, the territorial red squirrel (Tamiasciurus hudsonicus), operates. This may be the scale at which selection for synchrony occurs. 7Based on high synchrony locally, high synchrony within a mast year, and multiple lags in cone production by individuals, both available resources and strong weather cues appear to play roles in the observed patterns. [source]

Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
N. F. Martin
ABSTRACT We present the discovery of three faint dwarf galaxies and a globular cluster in the halo of the Andromeda galaxy (M31), found in our MegaCam survey that spans the southern quadrant of M31, from a projected distance of ,50 to ,150 kpc. Though the survey covers 57 deg2, the four satellites lie within 2° of one another. From the tip of the red giant branch (RGB), we estimate that the globular cluster lies at a distance of 631 ± 58 kpc from the Milky Way and along with a ,100 kpc projected distance from M31 we derive a total distance of 175 ± 55 kpc from its host, making it the farthest M31 globular cluster known. It also shows the typical characteristics of a bright globular cluster, with a half-light radius of 2.3 ± 0.2 pc and an absolute magnitude in the V band of MV,0=,8.5 ± 0.3. Isochrone fitting reveals that it is dominated by a very old population with a metallicity of [Fe/H],,1.3. The three dwarf galaxies are revealed as overdensities of stars that are aligned along the RGB tracks in their colour,magnitude diagrams. These satellites are all very faint, with absolute magnitudes in the range ,7.3 ,MV,0,,6.4, and show strikingly similar characteristics with metallicities of [Fe/H],,1.4 and half-light radii of ,120 ± 45 pc, making these dwarf galaxies two to three times smaller than the smallest previously known satellites of M31. Given their faintness, their distance is difficult to constrain, but we estimate them to be between 740 and 955 kpc which places them well within the virial radius of the host galaxy. The panoramic view of the MegaCam survey can provide an unbiased view of the satellite distribution of the Andromeda galaxy and, extrapolating from its coverage of the halo, we estimate that up to 45 ± 20 satellites brighter than MV,,6.5 should be orbiting M31. Hence faint dwarf galaxies cannot alone account for the missing satellites that are predicted by , cold dark matter models, unless they reside in dark matter minihaloes that are more massive than the typical masses of 107 M, currently inferred from their central radial velocity dispersion. [source]

A branch-and-price-based large neighborhood search algorithm for the vehicle routing problem with time windows

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2009
Eric Prescott-Gagnon
Abstract Given a fleet of vehicles assigned to a single depot, the vehicle routing problem with time windows (VRPTW) consists of determining a set of feasible vehicle routes to deliver goods to a set of customers while minimizing, first, the number of vehicles used and, second, total distance traveled. A large number of heuristic approaches for the VRPTW have been proposed in the literature. In this article, we present a large neighborhood search algorithm that takes advantage of the power of branch-and-price which is the leading methodology for the exact solution of the VRPTW. To ensure diversification during the search, this approach uses different procedures for defining the neighborhood explored at each iteration. Computational results on the Solomo's and the Gehring and Homberge's benchmark instances are reported. Compared to the best known methods, the proposed algorithm produces better solutions, especially on the largest instances where the number of vehicles used is significantly reduced. © 2009 Wiley Periodicals, Inc. NETWORKS, 2009 [source]

Solving the asymmetric traveling salesman problem with periodic constraints

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 1 2004
Giuseppe Paletta
Abstract In this article we describe a heuristic algorithm to solve the asymmetrical traveling salesman problem with periodic constraints over a given m -day planning horizon. Each city i must be visited ri times within this time horizon, and these visit days are assigned to i by selecting one of the feasible combinations of ri visit days with the objective of minimizing the total distance traveled by the salesman. The proposed algorithm is a heuristic that starts by designing feasible tours, one for each day of the m -day planning horizon, and then employs an improvement procedure that modifies the assigned combination to each of the cities, to improve the objective function. Our heuristic has been tested on a set of test problems purposely generated by slightly modifying known test problems taken from the literature. Computational comparisons on special instances indicate encouraging results. © 2004 Wiley Periodicals, Inc. NETWORKS, Vol. 44(1), 31,37 2004 [source]

Functional Electrical Stimulation-Supported Interval Training Following Sensorimotor-Complete Spinal Cord Injury: A Case Series

NEUROMODULATION, Issue 3 2009
Jack Crosbie PhD
ABSTRACT Objective.,To investigate the effect of interval training supported by Functional Electrical Stimulation (FES) on ambulation ability in complete spinal cord injury (SCI). Methods.,We trained four men with sensorimotor-complete (ASIA A) SCI, who achieved gait through FES of the quadriceps femoris, gluteus maximus, and common peroneal nerve on each side on a motorized treadmill. Training involved progressive interval walking exercise, consisting of periods of activity followed by equal periods of rest, repeated until muscle fatigue. We used time to muscle fatigue during continuous treadmill ambulation as the primary outcome measure. We also recorded the patterns of incremental stimulation for all training and testing sessions. Results.,All subjects increased their ambulation capacity; however, the responses varied from subject to subject. Some subjects increased the total distance walked by as much as 300% with progressive improvement over the entire training period; however, others made more modest gains and appeared to reach a performance plateau within a few training sessions. Conclusions.,FES-supported interval training offers a useful and effective strategy for strength-endurance improvement in the large muscle groups of the lower limb in motor-complete SCI. We believe that this training protocol offers a viable alternative to that of continuous walking training in people with SCI using FES to aid ambulation. [source]

Intraspecific variation in movement patterns: modeling individual behaviour in a large marine predator

OIKOS, Issue 1 2004
Deborah Austin
In large marine predators, foraging entails movement. Quantitative models reveal how behaviours can mediate individual movement, such that deviations from a random pattern may reveal specific search tactics or behaviour. Using locations for 52 grey seals fitted with satellite-linked recorders on Sable Island; we modeled movement as a correlated random walk (CRW) for individual animals, at two temporal scales. Mean move length, turning angle, and net squared displacement (R2n: the rate of change in area over time) at successive moves over 3 to 10 months were calculated. The distribution of move lengths of individual animals was compared to a Lévy distribution to determine if grey seals use a Lévy flight search tactic. Grey seals exhibited three types of movement as determined by CRW model fit: directed movers , animals displaying directed long distance travel that were significantly underpredicted by the CRW (23% of animals); residents , animals remaining in the area surrounding Sable Island that were overpredicted by the model (29% of animals); and correlated random walkers , those (48% of animals) in which movement was predicted by the CRW model. Kernel home range size differed significantly among all three movement types, as did travel speed, mean move length, mean R2n and total distance traveled. Sex and season of deployment were significant predictors of movement type, with directed movers more likely to be male and residents more likely to be female. Only 30% of grey seals fit a Lévy distribution, which suggests that food patches used by the majority of seals are not randomly distributed. Intraspecific variation in movement behaviour is an important characteristic in grey seal foraging ecology, underscoring the need to account for such variability in developing models of habitat use and predation. [source]

Meta analysis of the treatment-related factors of external apical root resorption

ORTHODONTICS & CRANIOFACIAL RESEARCH, Issue 2 2004
GR Segal
Structured Abstract Authors , Segal GR, Schiffman PH, Tuncay OC Objective , To elucidate possible treatment-related etiological factors , such as, duration of treatment and apical displacement , for external root resorption. Design , Meta-analysis of the available English-language literature. Inclusion & Exclusion Criteria , Papers with a sample size >10, fixed appliances, pre- and post-operative radiographs, and apical displacement recorded were included. History of trauma, prior root resorption and endodontic treatment were excluded. Appropriateness of these selections was tested with a ,funnel plot' analysis. Outcome Measure , Correlations between root resorption, apical displacement, and treatment duration. Results , Mean apical root resorption was strongly correlated with total apical displacement (r = 0.822) and treatment duration (r = 0.852). Conclusion , The treatment-related causes of root resorption appear to be the total distance the apex had moved and the time it took. [source]

Physical Activity: Patterns of active transport in 11,12 year old Australian children

AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 2 2004
Nathan Marten
Objectives: To describe the habitual transport patterns of 11 to 12-year-old children in Australia, to determine the personal and environmental factors associated with active transport (AT), and to quantify how much AT contributes to overall daily energy expenditure (EE). Methods: The participants in this study were 136 children aged 11,12 year olds from eight randomly chosen primary schools in Adelaide, South Australia. Each child recalled their trips on two school days and a non-school day. Mass and stature were measured, and children completed a computerised activity recall and a neighbourhood satisfaction questionnaire. Trips were categorised according to their destination, child and parent dissatisfaction with the neighbourhood, and the gender, socio-economic status (SES), BMI and activity levels of the children undertaking them. These categories, along with the distance to the destination, were used as independent variables in a logistic regression model, with trip mode (passive versus active) as the dependent variable. Results: Children made an average of 1.0 active trips per day, with a median trip length of 0.63 km, while the median total distance covered actively per child per day was 0.61 km. Twenty-six per cent of children did no AT over the three days, and 67% did no AT on a weekend day. Distance was by far the strongest predictor of the likelihood that a trip would be active. Trips made by girls were less likely to be active compared with boys. Trips to the shops were less likely to be active than trips to school. Children's AT accounted for 1.3% of their daily EE. Conclusions and Implications: The active transport levels of children were very low. Interventions should focus on making neighbourhoods safer and more accessible to children and should promote bicycle use. [source]

Colonisation of grapevine wood by Trichoderma harzianum and Eutypa lata

AUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 1 2008
S. JOHN
Abstract Background and Aims:,Trichoderma species have potential in biocontrol of eutypa dieback; however, little is known about their ability to colonise grapevine wood. The colonisation of vines by Trichoderma harzianum and its effects on colonisation by Eutypa lata were studied. Methods and Results:,T. harzianum colonised canes over a total distance (above and below the inoculation point) of 10 cm or more in 12 weeks after inoculation. Application of T. harzianum to canes prior to E. lata, either at the same inoculation point or at a different point, reduced recovery of the pathogen. In the field, T. harzianum grew 3 cm from the inoculation point in 4 months in all seven of the mature vines treated. The fungus persisted for 20 months in four of the seven vines at 6 cm from the inoculation point and reached the crown of one vine. Prior inoculation of mature vines with Trichodowels, containing T. harzianum, reduced recovery of E. lata 14 months after inoculation. Conclusions:,T. harzianum colonised wood of Chardonnay, Shiraz and Nyora and reduced colonisation by E. lata. T. harzianum persisted in wood of mature vines of Nyora for up to 20 months. Significance of the Study:, The results support the potential of T. harzianum in the biocontrol of eutypa dieback. [source]

Spatial planning, mobilities and culture,Chinese and New Zealand student preferences for Californian travel

INTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 3 2007
Chris Ryan
Abstract Itineraries are under-researched within tourism, which is arguably strange given their potential importance as determinants of visitor expenditure distribution, and how itinerary planning may become a tool of destination management in determining which areas are most affected by visitor flows, whether positively or negatively. This exploratory study required students in New Zealand and the Peoples' Republic of China to draw maps of potential trips to the south-west of the USA in order to assess to what degree differences might exist as to (i) preferred places to visit; (ii) durations of stay; (iii) speeds of dispersion and concentration at the points of embarkation and disembarkation (in this instance Los Angeles); and (iv) total distances travelled. Differences were indeed found, and ethnicity appeared to be the main explanatory variable for the differences. Chinese students were found to travel slightly less, not to become so dispersed overall, but were also found to have higher rates of dispersion and slower rates of concentration at the commencement and at the end of the trip. The itineraries also suggest a further triangular pattern of travel that can be added to the categories identified by Oppermann. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Truck schedule recovery for solid waste collection in Porto Alegre, Brazil

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 5 2008
Jing-Quan Li
Abstract This paper considers a truck schedule recovery problem in the context of solid waste collection in the city of Porto Alegre, Brazil. When a truck on a scheduled trip breaks down, a backup truck needs to be selected to serve the cargo on that trip and other trucks might be rescheduled in order to gain the minimum operating and delay costs. The problem consists of designing, in the case of a severe disruption in a trip, new schedules taking into account the existing trucks in the system and a set of unfinished and not initiated collection trips, on which the trucks collect the solid waste in fixed routes and empty the loads in one of the several operational recycling facilities. The main objective is to minimize the total distances traveled and delay costs, as well as to obtain balanced assignments of truck unloads into the recycling facilities, due to the social benefits of the solid waste program. We modeled the problem as a mixed-integer linear problem and used CPLEX to solve it. Finally, computational experiments are conducted on real-world data. The results show that our approach successfully reduces the distances traveled and delays, simultaneously balancing the number of trucks unloading at each recycling facility, in comparison with the current manual strategy. [source]