			Home About us Contact

Edge Effects (edge + effects)

Distribution by Scientific Domains

Life Sciences	66%
Medical Sciences	9%
Earth and Environmental Science	9%
Humanities and Social Sciences	6%
2 Other Domains	10%

Distribution within Life Sciences

Conservation Science	45%
Ecology & Organismal Biology	18%
Entomology	13%

Selected Abstracts

Landscape Context Moderates Edge Effects: Nesting Success of Wood Thrushes in Central New York

CONSERVATION BIOLOGY, Issue 5 2004
MELANIE J. L. DRISCOLL
We studied abundance and nesting success in Wood Thrushes (Hylocichla mustelina) breeding across a heterogeneous landscape in central New York from 1998 to 2000 to test the hypothesis that edge effects on nesting passerines are stronger in fragmented than contiguous landscapes. We monitored nests to estimate nesting success in edge and interior habitats in both fragmented and contiguously forested landscapes. In contiguous landscapes, daily survival rate did not differ between edge nests (0.963) and interior nests (0.968) (,2= 0.19, p = 0.66). In contrast, in fragmented landscapes, daily survival estimates were higher in interior (0.971) than edge (0.953) nests (,2= 3.1, p = 0.08). Our study supports the hypothesis that landscape composition moderates edge effects on actual nests of birds but does not determine the mechanisms causing these patterns. Resumen:,No obstante dos décadas de investigación sobre fragmentación de hábitat y efecto de borde sobre aves anidantes, aun se carece de información sobre el efecto de borde sobre el éxito de nidos naturales de aves migratorias neotropicales que se reproducen en pasajes heterogéneos. Estudiamos la abundancia y éxito de anidación de Hylocichla mustelina en un paisaje heterogéneo en el centro de New York de 1998 , 2000 para probar la hipótesis de que el efecto de borde sobre paserinas anidantes eran mayores en paisajes fragmentados que en continuos. Monitoreamos nidos para estimar el éxito en hábitats de borde y de interior en paisajes tanto con bosques continuos como discontinuos. En paisajes continuos, la tasa de supervivencia diaria no difirió entre nidos de borde (0.963) y nidos de interior (0.968) (,2= 0.19, p = 0.66). En contraste, en paisajes fragmentados, las estimaciones de supervivencia diaria fueron mayores en nidos del interior (0.971) que del borde (0.953) (,2= 3.1, p = 0.08). Nuestro estudio soporta la hipótesis de que la composición del paisaje modera los efectos de borde sobre nidos de aves, pero no determina los mecanismos que causan estos patrones. [source]

Edge Effects on ERA,Sandwiches

PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 2 2006
Manfred Held
Abstract The momentum transfer of thick flying plates of an ERA sandwich and iterative disturbances of shaped charge jets by thin flying plates are shortly described. [source]

Edge Effects and Seedling Bank Depletion: The Role Played by the Early Successional Palm Attalea oleifera (Arecaceae) in the Atlantic Forest

BIOTROPICA, Issue 2 2010
Antônio Venceslau Aguiar
ABSTRACT In this study, we examined the impacts of Attalea oleifera on the structure of seedling bank and discuss potential mechanisms of palm influence. Seed rain, seedling bank, and palm leaf fall were assessed beneath the canopy and in the vicinity of 16 adult palms across the edges of a large fragment (3500 ha) of the Atlantic forest. Moreover, we examined A. oleifera impacts on seed germination and seedling mortality by experimentally submitting seeds and seedlings to prolonged palm-leaf covering. As expected, seedling bank beneath the adults exhibited reduced abundance and species richness at local and habitat scale. Small to large seeds (3.1,30 mm) were underrepresented in the seed rain below adults palms, while experimental leaf covering drastically reduced both seed germination and seedling survivorship. A. oleifera leaf fall occurred over the whole year (3.6±2.7 leaves/individual/yr), which resulted in deep leaf litter mounds (10.7±9.2 cm). Finally, adult palm density (21.6±11.9 individuals/ha) correlated negatively with seedling density across Attalea clusters. Our results suggest that A. oleifera exerts negative effects on the seedling bank by reducing seedling abundance and richness as a consequence of two complementary mechanisms: impoverished and size-biased seed rain plus reduced seed germination and increased seedling mortality due to prolonged covering by fallen leaves. Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp [source]

Edge effects as the principal cause of area effects on birds in fragmented secondary forest

OIKOS, Issue 6 2010
Cristina Banks-Leite
Bird communities in tropical forests are strongly affected by both patch area and habitat edges. The fact that both effects are intrinsically confounded in space raises questions about how these two widely reported ecological patterns interact, and whether they are independent or simply different spatial manifestations of the same phenomenon. Moreover, do small patches of secondary forest, in landscapes where the most sensitive species have gone locally extinct, exhibit similar patterns to those previously observed in fragmented and continuous primary forests? We addressed these questions by testing edge-related differences in vegetation structure and bird community composition at 31 sites in fragmented and continuous landscapes in the imperilled Atlantic forest of Brazil. Over a two-year period, birds were captured with mist nets to a standardized effort of 680 net-hours at each site (,22 000 net-hours resulting in 3381 captures from 114 species). We found that the bird community in patches of secondary forest was degraded in species composition compared to primary continuous forest, but still exhibited a strong response to edge effects. In fragmented secondary forests, edge and area effects also interacted, such that the magnitude of edge to interior differences on bird community composition declined markedly with patch size. The change in bird species composition between forest interiors and edges was similar to the change in community composition between large and small patches (because species had congruent responses to edge and area), but after controlling for edge effects community composition was no longer affected by patch area. Our results show that although secondary forests hold an impoverished bird community, ecological patterns such as area and edge effects are similar to those reported for primary forests. Our data provide further evidence that edge effects are the main drivers of area effects in fragmented landscapes. [source]

Edge effects and the impact of non-protected areas in carnivore conservation: leopards in the Phinda,Mkhuze Complex, South Africa

ANIMAL CONSERVATION, Issue 3 2010
G. A. Balme
Abstract Although high rates of anthropogenic mortality are often reported for carnivores near reserve borders, the resulting edge effects are rarely quantified, and the consequences on conservation goals are usually unknown. Here, we assess the extent and impact of edge effects on a protected leopard Panthera pardus population in the Phinda-Mkhuze Complex (PMC), South Africa. We compared the spatial and demographic characteristics of leopards in two areas of the PMC, one closer to the border than the other. Leopard density declined from the core of the reserve (11.11 ± 1.31 leopards 100 km,2) to the border (7.17 ± 1.12 leopards 100 km,2), and was the lowest in non-protected areas adjoining the PMC (2.49 ± 0.87 leopards 100 km,2), but was not related to prey abundance or interspecific competition. Radiotelemetry showed that leopards near the border spent a greater proportion of their time outside the reserve and suffered higher annual mortality rates (0.358 ± 0.075) than those closer to the core (0.122 ± 0.065). A Cox proportional hazards model further demonstrated the negative effect of time spent outside the reserve on the survival probability of leopards. Despite an increased risk of mortality, leopards did not avoid non-protected areas, which may have functioned as an ecological trap for predators. Although the overall conservation outcome of the reserve was positive, edge effects clearly weakened the potential of the PMC to protect leopards. Our findings show that high mortality rates of carnivores in areas bordering reserves can extend to protected populations. Management approaches that control human activities on both sides of administrative borders are therefore essential if reserves are to conserve large carnivores effectively. [source]

Domestic dogs as an edge effect in the Brasília National Park, Brazil: interactions with native mammals

ANIMAL CONSERVATION, Issue 5 2009
A. C. R. Lacerda
Abstract Edge effects are a well-known result of habitat fragmentation. However, little has been published on fragmentation, isolation and the intrusive influence from the surrounding matrix at the landscape level. The objectives of the present study are to evaluate the presence of dogs in the Brasília National Park (BNP) in relation to habitat type and the influence from the surrounding matrix. In addition, this study examines the response of the native mammal fauna to the presence of dogs. Track stations were built along dirt roads in the BNP and subsequently examined for the presence or absence of tracks. We used a stepwise logistic regression to model the occurrence of five mammal species relative to habitat variables, with an ,=0.05 to determine whether to enter and retain a variable in the model. A simulation of each species occurrence probability was conducted using a combination of selected habitat variables in a resource selection probability function. Results indicate a negative relationship between distance from the BNP edge and the probability of dog occurrences. From an ecological perspective, the presence of dogs inside the BNP indicates an edge effect. The occurrence of the maned wolf was positively associated with distance from a garbage dump site and negatively associated with the presence of dog tracks. The maned wolf and giant anteater seem to avoid areas near the garbage dump as well as areas with dog tracks. There is no support for the possible existence of a feral dog population inside the BNP, but the effects of free-ranging dogs on the wildlife population in such an isolated protected area must not be neglected. Domestic dog Canis familiaris populations and disease control programs should be established in the urban, sub-urban and rural areas surrounding the BNP, along with the complete removal of the garbage dump from the BNP surroundings. [source]

Edge effects on avian nest predation: the quest for a conceptual framework

ANIMAL CONSERVATION, Issue 4 2009
T. Spanhove
No abstract is available for this article. [source]

Response of ground-dwelling beetles across logging coupe edges into streamside reserves

AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 3 2009
Susan C Baker
Abstract Streamside reserves can provide important habitat reservation in forest landscapes subject to logging. Depending on the width of streamside reserves, edge effects have the potential to compromise their effectiveness for terrestrial conservation, yet edge effects into riparian environments have rarely been assessed. It would be unwise to assume that edge effects act in the same way at streamside reserves as at the non-riparian edges of logging coupes, as interactions with riparian influences on beetles along the stream-upslope gradient might create unique edge conditions. In this study, we assess edge effects on ground dwelling beetles at four sites, using transects of pitfall traps across logging coupe edges into streamside reserves that have only been affected by logging on one side of the stream. Edge effects were found to extend further into streamside reserves in this study than into upslope habitat at the same sites from a concurrent study. Edge effects were site specific and appeared to extend as far as the stream in most cases (23,65 m). Comparison of beetle assemblage composition with adjacent unlogged streams supported the conclusion that beetles within 10 m of streams in streamside reserves were still responding to edge effects. These results suggest that streamside reserves might not contain habitat comparable with riparian areas away from the influences of nearby clearfelling, and wider reserves are recommended to maintain core habitat not compromised by edge effects. [source]

Landscape Context Moderates Edge Effects: Nesting Success of Wood Thrushes in Central New York

Effects of experimental small-scale grassland fragmentation on spatial distribution, density, and persistence of ant nests

ECOLOGICAL ENTOMOLOGY, Issue 6 2003
Brigitte Braschler
Abstract., 1.,Grassland fragmentation is expected to influence the abundance of different invertebrate species to a different extent. Fragmentation-related effects are of particular importance in species that interact with many other species. 2.,The density and spatial distribution of nests of 15 ant species in experimentally fragmented calcareous grasslands at three sites in the Northern Swiss Jura mountains were examined. Fragments of different size (0.25 m2, 2.25 m2, and 20.25 m2) were isolated by a 5-m wide strip of frequently mown vegetation. Control plots of corresponding size were situated in adjacent undisturbed grassland. 3.,Three years after initiation of the experiment, ant nest density did not differ between fragments and control plots. Six years after initiation of the experiment, however, ant nest density and forager abundance were higher in large fragments than in large control plots. Ant nests tended to occur more frequently along the edge of fragments than in the core area. Persistence time of nests of the most abundant species, Lasius paralienus, tended to be shorter in fragments than in control plots. Furthermore, persistence time was longer in nests situated close to the fragment edge than in nests in the core area. 4.,Effects on nest density, edge effects on the spatial distribution of nests, and the relationships between nest density and environmental factors were more pronounced when only nests of L. paralienus were considered. The implications of these findings for plant and other invertebrate species are discussed. [source]

Spillover edge effects: the dispersal of agriculturally subsidized insect natural enemies into adjacent natural habitats

ECOLOGY LETTERS, Issue 5 2006
Tatyana A. Rand
Abstract The cross-edge spillover of subsidized predators from anthropogenic to natural habitats is an important process affecting wildlife, especially bird, populations in fragmented landscapes. However, the importance of the spillover of insect natural enemies from agricultural to natural habitats is unknown, despite the abundance of studies examining movement in the opposite direction. Here, we synthesize studies from various ecological sub-disciplines to suggest that spillover of agriculturally subsidized insect natural enemies may be an important process affecting prey populations in natural habitat fragments. This contention is based on (1) the ubiquity of agricultural,natural edges in human dominated landscapes; (2) the substantial literature illustrating that crop and natural habitats share important insect predators; and (3) the clear importance of the landscape matrix, specifically distance to ecological edges, in influencing predator impacts in agroecosystems. Further support emerges from theory on the importance of cross-boundary subsidies for within site consumer,resource dynamics. In particular, high productivity and temporally variable resource abundance in agricultural systems are predicted to result in strong spillover effects. More empirical work examining the prevalence and significance of such natural enemy spillover will be critical to a broader understanding of fragmentation impacts on insect predator,prey interactions. [source]

Analysing soil variation in two dimensions with the discrete wavelet transform

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2004
R. M. Lark
Summary Complex spatial variation in soil can be analysed by wavelets into contributions at several scales or resolutions. The first applications were to data recorded at regular intervals in one dimension, i.e. on transects. The theory extends readily to two dimensions, but the application to small sets of gridded data such as one is likely to have from a soil survey requires special adaptation. This paper describes the extension of wavelet theory to two dimensions. The adaptation of the wavelet filters near the limits of a region that was successful in one dimension proved unsuitable in two dimensions. We therefore had to pad the data out symmetrically beyond the limits to minimize edge effects. With the above modifications and Daubechies's wavelet with two vanishing moments the analysis is applied to soil thickness, slope gradient, and direct solar beam radiation at the land surface recorded at 100-m intervals on a 60 × 101 square grid in south-west England. The analysis revealed contributions to the variance at several scales and for different directions and correlations between the variables that were not evident in maps of the original data. In particular, it showed how the thickness of the soil increasingly matches the geological structure with increasing dilation of the wavelet, this relationship being local to the strongly aligned outcrops. The analysis reveals a similar pattern in slope gradient, and a negative correlation with soil thickness, most clearly evident at the coarser scales. The solar beam radiation integrates slope gradient and azimuth, and the analysis emphasizes the relations with topography at the various spatial scales and reveals additional effects of aspect on soil thickness. [source]

Managing Environmental Impacts of Recreation and Tourism in Rainforests of the Wet Tropics of Queensland World Heritage Area

GEOGRAPHICAL RESEARCH, Issue 2 2005
Stephen M. Turton
Abstract This paper describes environmental impacts of tourism and recreation activities in the world heritage listed rainforests of northeast Australia and presents management strategies for sustainable visitor use of the protected area. Tropical rainforests are characterised by their low resistance and moderate to high resilience to impacts associated with human visitation. Visitor use in the World Heritage Area is mostly associated with walking tracks, camping areas, day use areas and off-road vehicle use of old forestry roads and tracks. Adverse environmental impacts range from vegetation trampling, soil compaction, water contamination and soil erosion at the local scale through to spread of weeds, feral animals and soil pathogens along extensive networks of old forestry roads and tracks at the regional scale. Concentration of visitor use is the most desirable management strategy for controlling adverse impacts at most World Heritage Area visitor nodes and sites, and includes methods such as site hardening and shielding to contain impacts. For dispersed visitor activities, such as off-road vehicle driving and long-distance walking, application of best practice methods by the tourist industry and recreational users such as removal of mud and soils from vehicle tyres and hiking boots before entering pathogen-free catchments, together with seasonal closure of roads and tracks, are the preferred management strategies. Retention of canopy cover at camping areas and day use areas, as well as along walking tracks and forestry roads is a simple, yet effective, management strategy for reduction of a range of adverse impacts, including dispersal of weeds and feral animals, edge effects, soil erosion and nutrient loss, road kill and linear barrier effects on rainforest fauna. [source]

Linking Spatial Pattern and Ecological Responses in Human-Modified Landscapes: The Effects of Deforestation and Forest Fragmentation on Biodiversity

GEOGRAPHY COMPASS (ELECTRONIC), Issue 4 2009
John A. Kupfer
Studies of forest loss and fragmentation provide clear examples of the linkages between ecological pattern and process. Reductions in forest area lead to higher within-patch extinction rates, the eventual loss of area-sensitive species, and declines in species richness and diversity. Forest loss also results in increased isolation of remnants, lower among-patch immigration rates, and less ,rescue' from surrounding populations. Specific responses, however, are sometimes counterintuitive because they depend on life-history tradeoffs that influence population dynamics and species co-existence in heterogeneous landscapes, not just forest remnants. Thus, while fragmentation generally favours r-selected, generalist strategies, such as high dispersal and a wide niche breadth, ecological outcomes may be confounded by species-specific responses to conditions in the human-dominated matrix and the ways in which forest edges shape cross-landscape movements. Given that pressures on global forestlands continue to intensify due to growing population sizes, economic pressures, and needs for space and resources, successfully maintaining or restoring species will necessitate a combination of short- and long-term actions that address both habitat protection and restoration. Doing so will require an interdisciplinary approach that gives adequate attention to the manners by which forest loss and fragmentation affect population dynamics through changes in forest area, isolation, habitat quality, matrix properties, and edge effects as well as the synergistic interactions of fragmentation with climate change, human-altered disturbance regimes, species interactions and other drivers of species population declines. [source]

Empirical comparison of density estimators for large carnivores

JOURNAL OF APPLIED ECOLOGY, Issue 1 2010
Martyn E. Obbard
Summary 1. Population density is a critical ecological parameter informing effective wildlife management and conservation decisions. Density is often estimated by dividing capture,recapture (C,R) estimates of abundance () by size of the study area, but this relies on the assumption of geographic closure , a situation rarely achieved in studies of large carnivores. For geographically open populations is overestimated relative to the size of the study area because animals with only part of their home range on the study area are available for capture. This bias (,edge effect') is more severe when animals such as large carnivores range widely. To compensate for edge effect, a boundary strip around the trap array is commonly included when estimating the effective trap area (). Various methods for estimating the width of the boundary strip are proposed, but / estimates of large carnivore density are generally mistrusted unless concurrent telemetry data are available to define. Remote sampling by cameras or hair snags may reduce study costs and duration, yet without telemetry data inflated density estimates remain problematic. 2. We evaluated recently developed spatially explicit capture,recapture (SECR) models using data from a common large carnivore, the American black bear Ursus americanus, obtained by remote sampling of 11 geographically open populations. These models permit direct estimation of population density from C,R data without assuming geographic closure. We compared estimates derived using this approach to those derived using conventional approaches that estimate density as /. 3. Spatially explicit C,R estimates were 20,200% lower than densities estimated as /. AICc supported individual heterogeneity in capture probabilities and home range sizes. Variable home range size could not be accounted for when estimating density as /. 4.Synthesis and applications. We conclude that the higher densities estimated as / compared to estimates from SECR models are consistent with positive bias due to edge effects in the former. Inflated density estimates could lead to management decisions placing threatened or endangered large carnivores at greater risk. Such decisions could be avoided by estimating density by SECR when bias due to geographic closure violation cannot be minimized by study design. [source]

Breeding bird species diversity in the Negev: effects of scrub fragmentation by planted forests

JOURNAL OF APPLIED ECOLOGY, Issue 5 2001
Eyal Shochat
Summary 1Afforestation of the Northern Negev, Israel, from 1956 resulted in patches of primarily coniferous trees that fragmented large scrubland areas. This alteration in landscape pattern was followed by immigration of mediterranean bird species to the Negev. 2We counted breeding birds, and measured various environmental variables in scrubland and planted forest patches, to test whether bird assemblages were random subsets of the regional species pool, and whether area or habitat structure was the major correlate with species abundance and distribution. 3Of 22 bird species recorded, only three appeared in both scrub and forest, showing that these two habitats were occupied by different species assemblages. In both habitats, species richness increased with area at a rate greater than that expected by random sampling. In the scrub this increase was related to area per se, while in the forest it was related to habitat diversity in terms of stand age and tree type. 4The density of forest species was unaffected by area, but specialist scrubland species declined as area decreased. We suggest that edge effects might reduce species abundance in small scrubland patches. 5Nested subset analysis indicated that, at the community level, species composition was not random. However, at the species level, the distribution of three forest-dwelling species appeared as random, as it was associated with habitat rather than with patch size. 6Our results indicate that increased diversity of breeding birds in the Northern Negev will require scrub patches larger than 50 ha among the increasingly forested landscape. In contrast, increasing forest area would hardly increase species diversity in the whole landscape. Future forest management regimes should also aim to increase habitat diversity by adding foliage layers, especially in the understorey. Exotic coniferous forests support fewer species than deciduous forests in mediterranean zones around the world. The suggested management regime may improve such forests as habitat for species-rich bird communities. [source]

Reactive mold filling in resin transfer molding processes with edge effects

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009
Yanyu Ding
Abstract Reactive mold filling is one of the important stages in resin transfer molding processes, in which resin curing and edge effects are important characteristics. On the basis of previous work, volume-averaging momentum equations involving viscous and inertia terms were adopted to describe the resin flow in fiber preform, and modified governing equations derived from the Navier,Stokes equations are introduced to describe the resin flow in the edge channel. A dual-Arrhenius viscosity model is newly introduced to describe the chemorheological behavior of a modified bismaleimide resin. The influence of the curing reaction and processing parameters on the resin flow patterns was investigated. The results indicate that, under constant-flow velocity conditions, the curing reaction caused an obvious increase in the injection pressure and its influencing degree was greater with increasing resin temperature or preform permeability. Both a small change in the resin viscosity and the alteration of the injection flow velocity hardly affected the resin flow front. However, the variation of the preform permeability caused an obvious shape change in the resin flow front. The simulated results were in agreement with the experimental results. This study was helpful for optimizing the reactive mold-filling conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

What causes the vulnerability of endemic animals?

JOURNAL OF ZOOLOGY, Issue 2 2004
A case study from Sri Lanka
Abstract Around the world, endemic species with restricted ranges seem to be at particular risk of extinction. When range size is controlled, lowland continental species may be especially at risk, more so than island or montane species. Our study aimed to investigate reasons behind the high vulnerability of endemic species. In Sri Lanka, large-scale national surveys and intensive localized fieldwork established that endemic plant and animal species are mostly associated with undisturbed rainforest habitats. On the other hand, non-endemic species used both forest and non-forest habitats almost equally, suggesting they are less likely to suffer from deleterious edge effects. To understand the different distribution of endemic and non-endemic species, our study focused on rats. Compared to the widespread species, the endemic rat species had a larger home range and fed on fewer species of forest fruit, possibly indicating greater specialization. The abundance of the endemic species was also negatively correlated with the abundance of the non-endemic species, to which it was behaviourally subordinate. Greater specialization and competitive inferiority could both contribute to the vulnerability of endemic species. [source]

Evanescent fields,Direct measurement, modeling, and application

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2007
S.T. Huntington
Abstract The evanescent field surrounding an exposed planar waveguide in silica is accurately measured using scanning near field optical microscopy (SNOM) and compared to models of the field distribution. Distortions in the field due to edge effects and the proximity of the mode to the surface are all detected. The characterized field is use to quantitatively explore the difference in collection efficiency between contact mode SNOM and intermittent contact mode SNOM. A strong correlation between tip oscillation amplitude and detection efficiency is determined. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source]

Measuring SPIO and Gd contrast agent magnetization using 3,T MRI

NMR IN BIOMEDICINE, Issue 8 2009
Pádraig Cantillon-Murphy
Abstract Traditional methods of measuring magnetization in magnetic fluid samples, such as vibrating sample magnetometry (VSM), are typically limited to maximum field strengths of about 1,T. This work demonstrates the ability of MRI to measure the magnetization associated with two commercial MRI contrast agents at 3,T by comparing analytical solutions to experimental imaging results for the field pattern associated with agents in cylindrical vials. The results of the VSM and fitted MRI data match closely. The method represents an improvement over VSM measurements since results are attainable at imaging field strengths. The agents investigated are Feridex, a superparamagnetic iron oxide suspension used primarily for liver imaging, and Magnevist, a paramagnetic, gadolinium-based compound used for tumors, inflammation and vascular lesions. MR imaging of the agents took place in sealed cylindrical vials in the presence of a surrounding volume of deionized water where the effects of the contrast agents had a measurable effect on the water's magnetization in the vicinity of the compartment of contrast agent. A pair of phase images were used to reconstruct a B0 fieldmap. The resultant B0 maps in the water region, corrected for shimming and container edge effects, were used to predict the agent's magnetization at 3,T. The results were compared with the results from VSM measurements up to 1.2,T and close correlation was observed. The technique should be of interest to those seeking quantification of the magnetization associated with magnetic suspensions beyond the traditional scope of VSM. The magnetization needs to be sufficiently strong (Ms , 50 Am2/kg Fe for Feridex and Xm , 5 × 10,5 m3/kg Gd for Magnevist) for a measurable dipole field in the surrounding water. For this reason, the technique is mostly suitable for undiluted agents. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Disturbance and habitat use: is edge more important than area?

OIKOS, Issue 1 2006
Alissa E. Moenting
In their efforts to maximize fitness while reducing the probability of dying, animals must decide which patches to forage in, when to forage, and how long to forage in each patch. Each decision will be modified by habitat and habitat disturbance. We evaluate the effects of habitat disturbance on foraging behaviour by imagining an initially homogeneous environment that is altered to create patches of different sizes. Disturbance increases predation risk, or otherwise alters patch profitability. Foragers can respond by changing their pattern of foraging, or by reducing their activity. We develop predictions for each scenario. We then test the predictions with data on the abundance and foraging activity of meadow voles (Microtus pennsylvanicus) in and around four sizes of circular disturbed patches. We created the patches by mowing vegetation in an abandoned hay field in northern Ontario, Canada. The treatments had no effect on vole density, and there was no consistent relationship between vole activity and distance from the edge of disturbed patches. Incidental predation of sunflower seeds, our measure of vole foraging behaviour, declined linearly with increasing patch circumference (edge). Seed consumption by meadow voles, and predation by voles on lower food levels, correlates with the length of edge habitat rather than with the area disturbed. Adaptive behaviour can thereby explain edge effects that, under current priorities emphasizing area, would appear at odds with conservation ecology. [source]

The Effect of Ablation Electrode Length and Catheter Tip to Endocardial Orientation on Radiofrequency Lesion Size in the Canine Right Atrium

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1 2002
RODRIGO C. CHAN
CHAN, R.C., et al.: The Effect of Ablation Electrode Length and Catheter Tip to Endocardial Orientation on Radiofrequency Lesion Size in the Canine Right Atrium. Although the determinants of radiofrequency lesion size have been characterized in vitro and in ventricular tissue in situ, the effects of catheter tip length and endocardial surface orientation on lesion generation in atrial tissue have not been studied. Therefore, the dimensions of radiofrequency lesions produced with 4-, 6-, 8-, 10-, and 12-mm distal electrode lengths were characterized in 26 closed-chested dogs. The impact of parallel versus perpendicular catheter tip/endocardial surface orientation, established by biplane fluoroscopy and/or intracardiac echocardiography, on lesion dimensions was also assessed. Radiofrequency voltage was titrated to maintain a steady catheter tip temperature of 75°C for 60 seconds. With a perpendicular catheter tip/tissue orientation, the lesion area increased from 29 ± 7 mm2 with a 4-mm tip to 42 ± 12 mm2 with the 10-mm tip, but decreased to 29 ± 8 mm2 with ablation via a 12-mm tip. With a parallel distal tip/endocardial surface orientation, lesion areas were significantly greater: 54 ± 22 mm2 with a 4-mm tip, 96 ± 28 mm2 with a 10- mm tip and 68 ± 24 mm2 with a 12-mm tip (all P < 0.001 vs perpendicular orientation). Lesion lengths and apparent volumes were larger with parallel, compared to perpendicular tip/tissue orientations, although lesion depth was independent of catheter tip length with both catheter tip/tissue orientations. Electrode edge effects were not observed with any tip length. Direct visualization using intracardiac ultrasound guidance was subjectively helpful in insuring an appropriate catheter tip/tissue interface needed to maximize lesion size. Although atrial lesion size is critically dependent on catheter tip length, it is more influenced by the catheter orientation to the endocardial surface. This information may also be helpful in designing electrode arrays for the creation of continuous linear lesions for the elimination of complex atrial tachyarrhythmias. [source]

Edge effects and the impact of non-protected areas in carnivore conservation: leopards in the Phinda,Mkhuze Complex, South Africa

Forest fragmentation relaxes natural nest predation in an Afromontane forest

ANIMAL CONSERVATION, Issue 4 2009
T. Spanhove
Abstract Nest predation is widely regarded as a major driver underlying the population dynamics of small forest birds. Following forest fragmentation and the subsequent invasion by species from non-forested landscape matrices, shifts in predator communities may increase nest predation near forest edges. However, effects of human-driven habitat change on nest predation have mainly been inferred from studies with artificial nests, despite being regarded as poor surrogates for natural ones. We studied variation in predation rates, and relationships with timing of breeding and characteristics of microhabitats and fragments, on natural white-starred robin Pogonocichla stellata nests during three consecutive breeding seasons (2004,2007) in a Kenyan fragmented cloud forest. More than 70% of all initiated nests were predated during each breeding season. Predation rates nearly quadrupled between the earliest and the latest nests within a single breeding season, increased with distance to the forest edge, and decreased with the edge-to-area ratio of forest fragments. These spatial relationships oppose the traditional perception of edge and fragmentation effects on nest predation, but are in line with results from artificial nest experiments in other East African forests. In case of inverse edge and fragmentation effects on nest predation, such as shown in this study, species that tolerate edges for breeding may be affected positively, rather than negatively, by forest fragmentation, while the opposite can be expected for species restricted to the forest interior. The possibility of inverse edge effects, and its conservation implications, should therefore be taken into account when drafting habitat restoration plans. [source]

Does avian species richness in natural patch mosaics follow the forest fragmentation paradigm?

ANIMAL CONSERVATION, Issue 1 2007
D. C. Pavlacky Jr.
Abstract As one approaches the north-eastern limit of pinyon (Pinus spp.) juniper (Juniperus spp.) vegetation on the Colorado Plateau, USA, woodland patches become increasingly disjunct, grading into sagebrush (Artemisia spp.)-dominated landscapes. Patterns of avian species richness in naturally heterogeneous forests may or may not respond to patch discontinuity in the same manner as bird assemblages in fragmented agricultural systems. We used observational data from naturally patchy woodlands and predictions derived from studies of human-modified agricultural forests to estimate the effects of patch area, shape, isolation and distance to contiguous woodland on avian species richness. We predicted that patterns of species richness in naturally patchy juniper woodlands would differ from those observed in fragmented agricultural systems. Our objectives were to (1) estimate the effect of naturally occurring patch structure on avian species richness with respect to habitat affinity and migratory strategy and (2) assess the concordance of the effects to predictions from agricultural forest systems. We used the analogy between populations and communities to estimate species richness, where species are treated as individuals in the application of traditional capture,recapture theory. Information-theoretic model selection showed that overall species richness was explained primarily by the species area relationship. There was some support for a model with greater complexity than the equilibrium theory of island biogeography where the isolation of large patches resulted in greater species richness. Species richness of woodland-dwelling birds was best explained by the equilibrium hypothesis with partial landscape complementation by open-country species in isolated patches. Species richness within specific migratory strategies showed concomitant increases and no shifts in species composition along the patch area gradient. Our results indicate that many patterns of species richness considered to be fragmentation effects may be general consequences of patch discontinuity and are ubiquitous in naturally heterogeneous systems. There was no evidence for the effects of patch shape and distance to contiguous woodland in juniper woodland, suggesting edge effects and dependence upon regional species pools are characteristics of fragmented agricultural systems. Natural patch mosaics may provide benchmarks for evaluating fragmentation effects and managing forests by mimicking natural landscape patterns. [source]

Birds on edge: avian assemblages along forest-agricultural boundaries of central Victoria, Australia

ANIMAL CONSERVATION, Issue 2 2001
Monica J. Campi
Habitat clearance generally produces fragmented landscapes. A major consequence is the creation of large amounts of new ,edge habitat', often of a kind not previously existing, such as abrupt forest- agricultural land interfaces. Much work from around the world suggests that proliferation of edge habitat seriously affects birds reliant on large forest blocks to persist, and the intrusion of edge specialists into areas they did not previously occupy. These processes often generate avifaunal gradients in which assemblages change from the interior to the edge. This effect is explored in the largest remnant block of box-ironbark forest of central Victoria, Australia (about 30,000 ha). Eight radially oriented survey lines were established around the periphery of the block. Along each survey line, five transects with long axes oriented parallel to the edge were positioned with midlines at 40 m, 160 m, 280 m and 400 m into the forest, and one transect 80 m into the agricultural land, yielding a total of 40 transects. Six identical transects were located deep within the forest (> 2 km). There was little evidence of a change in the avifauna from interior to edge, although mean richness was depressed in the edge habitats compared with forest interior transects. These results were essentially the same for ,all species' or ,forest dependent' species. Thus, there is little evidence for marked edge effects on the avifauna of these large forest blocks, although work in intermediate sized remnants (100-1000 ha) is needed to identify thresholds at which edge effects begin to be manifested. [source]

Impact of landscape spatial pattern on liana communities in tropical rainforests at Los Tuxtlas, Mexico

APPLIED VEGETATION SCIENCE, Issue 3 2009
Víctor Arroyo-Rodríguez
Abstract Questions: What are the species composition and species and stem densities of liana communities in tropical landscapes of different deforestation levels? Which spatial attributes (forest cover, patch area, shape and isolation) have the strongest influence on liana communities in these landscapes? Location: Forty-five rainforest patches in Los Tuxtlas Biosphere Reserve, Mexico. Methods: In three landscapes with different deforestation levels (HDL=4%; IDL=11%; and LDL=24% of remaining forest cover) liana communities (DBH ,2.5 cm) were characterized in 15 randomly selected patches per landscape (10 50 m × 2 m transects per patch=0.1 ha), and evaluated the effects of patch area, shape and isolation on liana species and stem density (number of species and stems per 0.1 ha). Results: A total of 64 taxa and 24 families were sampled. Species composition differed highly among landscapes, with HDL being the most dissimilar landscape. The response of lianas to landscape spatial pattern differed significantly among landscapes. Proximity to villages had a strong positive effect on species and stem densities in LDL and IDL. There was a sharp decrease in liana stem density in HDL, with four patches (27%) found to be unoccupied by lianas. Conclusions: Fragmentation may have a positive effect on lianas, partly because of edge effects. This positive effect seems to be limited by the proportion of remaining forest cover in the landscape, as the liana communities had collapsed in the most deforested landscape. [source]

Determination of grave locations in Dedemezari Necropolis (Western Turkey) using magnetic field derivatives

ARCHAEOLOGICAL PROSPECTION, Issue 4 2008
A. Büyüksaraç
Abstract The location of the study area for this research of a Middle Bronze Age Necropolis is situated in the west of Turkey near Afyonkarahisar. Magnetic surveying was carried out in two adjacent areas (Areas 4 and 5). Four trenches have been excavated so far and graves were located in positions interpreted from a magnetic survey carried out in 2005. Initial excavations have shown that cist, pithos and simple graves were placed randomly and it is suggested that Dedemezari Necropolis is similar to the well known necropoleis of Gordion and Sariket. This paper compares the results of some phase-based filters which show improved performance as edge detectors in different ways. The filters are demonstrated on synthetic magnetic data and magnetic field data from Dedemezari Necropolis. Magnetic field derivatives, both vertical and horizontal, are common and useful tools for interpretation of the magnetic anomalies. Interpretation of magnetic field derivatives, separately or together, provide images of shallow bodies from magnetic data. The horizontal derivatives of the total magnetic field were computed in the space domain by means of finite-difference relationships, and the vertical derivative was computed in the frequency domain by using fast Fourier transform filtering. Derivatives of the magnetic anomalies have been used for detection of causative bodies. The analytic signal (AS), the enhanced horizontal derivative (EHD), tilt derivative (TD), theta map, hyperbolic tilt angle (HTA) and total horizontal derivative (THDR) methods were applied not only to synthetic anomalies but also to the measured magnetic anomalies of Areas 4 and 5. However, AS and EHD produced the best results as the other methods created edge effects. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Response of fauna in seagrass to habitat edges, patch attributes and hydrodynamics

AUSTRAL ECOLOGY, Issue 5 2010
HANNAH M. MURPHY
Abstract This study has investigated the taxon-specific responses of fauna to patch edges, and how these relate to patch attributes (patch size, seagrass biomass and water depth), and hydrodynamics in the seagrass habitat. Faunal abundances were sampled at the edge, 2 m in from the edge, and in the middle of 10 seagrass patches of variable size in Port Phillip Bay, Australia. Five of nine taxa showed edge effects. There were higher abundances at the edge compared with the middle for porcellid harpacticoids, and an increase in abundance from the edge to the middle of the patches for tanaids and isopods. For caprellid and gammarid amphipods, the edge effect varied across patches. Changes in current within the patch and patch size were related to the variability in the edge effect pattern of caprellids. None of the measured environmental variables (seagrass biomass, current and water depth) or patch size had a role in the variable edge effect pattern of gammarid amphipods. At the patch level, the distribution of six of nine taxa in this study, namely isopods, polychaetes, ,other harpacticoids', porcellid harpacticoids, cumaceans and gammarid amphipods, was related to differences in average water depth, average seagrass biomass and patch size. Our study indicates that the faunal response to edges cannot be generalized across seagrass habitat, and the implications of habitat area loss will vary depending on the taxon under consideration. [source]