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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Using an expression cloning method, in which we screened for binding of 125I-labelled PYY (ref. 3), we isolated a rat hypothalamic cDNA encoding a new NPY/PYY/PP-receptor subtype, which we named Y5. This receptor is distinct from other Y-type receptors, known as Yl (refs 1,4-9), Y2 (refs ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Environmental management 22 (1998), S. 777-787 
    ISSN: 1432-1009
    Keywords: KEY WORDS: Simulation modeling; Timber harvest; Historical context; Spatial context; Landscape pattern; Forest interior; Forest edge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Landscape ecology 7 (1992), S. 101-110 
    ISSN: 1572-9761
    Keywords: percolation theory ; indices ; spatial pattern ; fractal ; proximity index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Recent studies have related percolation theory and critical phenomena to the spatial pattern of landscapes. We generated simulated landscapes of forest and non-forest landcover to investigate the relationship between the proportion of forest (Pi) and indices of patch spatial pattern. One set of landscapes was generated by randomly assigning each pixel independently of other pixels, and a second set was generated by randomly assigning rectilinear clumps of pixels. Indices of spatial pattern were calculated and plotted against Pi. The random-clump landscapes were also compared with real agricultural landscapes. The results support the use of percolation models as neutral models in landscape ecology, and the performance of the indices studied with these neutral models can be used to help interpret those indices calculated for real landscapes.
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  • 4
    ISSN: 1572-9761
    Keywords: agricultural landscapes ; bird abundance ; GIS ; landscape structure ; midwestern U.S. ; multivariate models ; Neotropical migrants ; reproductive success ; source-sink dynamics ; wood thrushes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Size of a forest patch is a useful predictor of density and reproductive success of Neotropical migratory birds in much of eastern North America. Within these forested landscapes, large forest tracts appear to be sources – fragments in which surpluses of offspring are produced and can potentially colonize new fragments including woodlot sinks where reproduction fails to balance adult mortality. Within agricultural landscapes of the midwestern U.S., where forests are severely fragmented, high levels of brood parasitism by brown-headed cowbirds (Molothrus ater) and intense predation on nests generally result in low reproductive success for Neotropical migrants regardless of forest size. In some midwestern U.S. landscapes, however, the variation in reproductive success among forest fragments suggests that `source' habitat could still exist for Neotropical migrants. We used vegetation, fragment and landscape metrics to develop multivariate models that attempt to explain the variation in abundance and reproductive success of Neotropical migrants nesting in an agricultural landscape in northern Indiana, USA. We produced models that reasonably described the pattern of species richness of Neotropical migrants and the abundance of wood thrushes (Hylocichla mustelina) and several other Neotropical migrant species within 14 forest fragments. In contrast, we were unable to produce useful models of the reproductive success of wood thrushes breeding in the same forest fragments. Our results suggest that (1) abundance patterns of Neotropical migrants are probably influenced by both landscape- and fragment-scale factors; (2) multivariate analyses of Neotropical migrant abundance are not useful in modeling the corresponding patterns of reproductive success; and (3) the location of any remaining `source' habitat for Neotropical migrants breeding within agricultural landscapes in North America will be difficult to predict with indirect measures such as vegetation composition or landscape context. As a result, the potential for developing conservation strategies for Neotropical migrants will be limited without labor-intensive, direct measurements of demographic parameters.
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  • 5
    ISSN: 1572-9761
    Keywords: Spatial pattern ; timber harvest ; clearcutting ; GIS model ; habitat fragmentation ; forest interior ; forest edge ; brown-headed cowbird ; brood parasitism ; neotropical migratory birds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Timber harvesting affects both composition and structure of the landscape and has important consequences for organisms using forest habitats. A timber harvest allocation model was constructed that allows the input of specific rules to allocate forest stands for clearcutting to generate landscape patterns reflecting the “look and feel” of managed landscapes. Various harvest strategies were simulated on four 237 km2 study areas in Indiana, USA. For each study area, the model was applied to simulate 80 years of management activity. The resulting landscape spatial patterns were quantified using a suite of landscape pattern metrics and plotted as a function of mean harvest size and total area of forest harvested per decade to produce response surfaces. When the mean clearcut size was 1 ha, the area of forest interior remaining on the landscape was dramatically reduced and the amount of forest edge on the landscape increased dramatically. The potential consequences of the patterns produced by the model were assessed for a generalized neotropical migrant forest bird using a GIS model that generates maps showing the spatial distribution of the relative vulnerability of forest birds to brood parasitism by brown-headed cowbirds. The model incorporates the location and relative quality of cowbird feeding sites, and the relation between parasitism rates and distance of forest from edge. The response surface relating mean harvest size and total area harvested to the mean value of vulnerability to cowbird brood parasitism had a shape similar to the response surfaces showing forest edge. The results of our study suggest that it is more difficult to maintain large contiguous blocks of undisturbed forest interior when harvests are small and dispersed, especially when producing high timber volumes is a management goal. The application of the cowbird model to landscapes managed under different strategies could help managers in deciding where harvest activity will produce the least negative impact on breeding forest birds.
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  • 6
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A solar telescope has been built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field have been made daily since May 1975. The typical mean field magnitude has been about 0.15 G with typical measurement error less than 0.05 G. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (see near the Earth with a 4 day lag). The differences in the observed structures can be understood in terms of a ‘warped current sheet’ model.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Ecosystems 1 (1998), S. 143-156 
    ISSN: 1435-0629
    Keywords: Key words: spatial pattern; index; indices; spatial heterogeneity; patchiness; landscape ecology; scale; geostatistics; autocovariation; spatial models.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT Landscape ecology is based on the premise that there are strong links between ecological pattern and ecological function and process. Ecological systems are spatially heterogeneous, exhibiting considerable complexity and variability in time and space. This variability is typically represented by categorical maps or by a collection of samples taken at specific spatial locations (point data). Categorical maps quantize variability by identifying patches that are relatively homogeneous and that exhibit a relatively abrupt transition to adjacent areas. Alternatively, point-data analysis (geostatistics) assumes that the system property is spatially continuous, making fewer assumptions about the nature of spatial structure. Each data model provides capabilities that the other does not, and they should be considered complementary. Although the concept of patches is intuitive and consistent with much of ecological theory, point-data analysis can answer two of the most critical questions in spatial pattern analysis: what is the appropriate scale to conduct the analysis, and what is the nature of the spatial structure? I review the techniques to evaluate categorical maps and spatial point data, and make observations about the interpretation of spatial pattern indices and the appropriate application of the techniques. Pattern analysis techniques are most useful when applied and interpreted in the context of the organism(s) and ecological processes of interest, and at appropriate scales, although some may be useful as coarse-filter indicators of ecosystem function. I suggest several important needs for future research, including continued investigation of scaling issues, development of indices that measure specific components of spatial pattern, and efforts to make point-data analysis more compatible with ecological theory.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Ecosystems 1 (1998), S. 484-492 
    ISSN: 1435-0629
    Keywords: Key words: timber harvest; aggregation of harvests; dynamic zoning; spatial simulation model; forest interior; forest fragmentation; forest management policy; forest management planning.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT To integrate multiple uses (mature forest and commodity production) better on forested lands, timber management strategies that cluster harvests have been proposed. One such approach clusters harvest activity in space and time, and rotates timber production zones across the landscape with a long temporal period (dynamic zoning). Dynamic zoning has been shown to increase timber production and reduce forest fragmentation by segregating uses in time without reducing the spatial extent of timber production. It is reasonable to wonder what the effect of periodic interruptions in the implementation of such as strategy might be, as would be expected in a dynamic political environment. To answer these questions, I used a timber harvest simulation model (HARVEST) to simulate a dynamic zoning harvest strategy that was periodically interrupted by changes in the spatial dispersion of harvests, by changes in timber production levels, or both. The temporal scale (period) of these interruptions had impacts related to the rate at which the forest achieved canopy closure after harvest. Spatial dynamics in harvest policies had a greater effect on the amount of forest interior and edge than did dynamics in harvest intensity. The periodically clustered scenarios always produced greater amounts of forest interior and less forest edge than did their never clustered counterparts. The results suggest that clustering of harvests produces less forest fragmentation than dispersed cutting alternatives, even in the face of a dynamic policy future. Although periodic episodes of dispersed cutting increased fragmentation, average and maximum fragmentation measures were less than if clustered harvest strategies were never implemented. Clustering may also be useful to mitigate the fragmentation effects of socially mandated increases in timber harvest levels. Implementation of spatial clustering during periods of high timber harvest rates reduced the variation in forest interior and edge through time, providing a more stable supply of forest interior habitat across the landscape.
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  • 9
    ISSN: 1432-0878
    Keywords: Avian pancreatic polypeptide ; Neuropeptide Y ; Molluscan cardioexcitatory polypeptide ; Suprachiasmatic nucleus ; Lateral geniculate nucleus ; Circadian rhythms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Avian pancreatic polypeptide (APP)-like, molluscan cardioexcitatory peptide (FMRF)-like and neuropeptide Y (NPY)-like immunoreactivities were studied in a secondary visual pathway in rat brain. The cell bodies of this pathway are located in the lateral geniculate nucleus and its terminal plexus is found in the suprachiasmatic hypothalamic nucleus (SCN). The neurons and terminal plexus demonstrated by antiserum to each peptide are identical, and immunoreactivity is blocked by preabsorption of each antiserum with a low concentration of the antigen against which it was raised. Immunoreactivity is also blocked by preabsorption of each antiserum with either NPY or APP. In contrast, APP- and NPY-like immunoreactivities are blocked only partially when these antisera are preabsorbed with concentrations of FMRF as high as 100 μM. Since NPY is the only one of these peptides that has been isolated from mammalian brain, we conclude that NPY is the endogenous CNS peptide produced by neurons of the lateral geniculate-SCN projection.
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  • 10
    Publication Date: 2013-04-02
    Print ISSN: 1550-7998
    Electronic ISSN: 1550-2368
    Topics: Physics
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