Strong Spatial Association Research Articles

Positive effects of native shrubs on Bromus tectorum demography

There is increasing recognition that overall interactions among plant species are often the net result of both positive and negative effects. However, the positive influence of other plants has rarely been examined using detailed demographic methods, which are useful for partitioning net effects at the population level into positive and/or negative effects on individual vital rates. This study examines the influence of microhabitats created by the native shrubs Artemisia tridentata and Purshia tridentata on the demography of the invasive annual grass Bromus tectorum in the Great Basin Desert, California, USA. Shrub understory environments differed significantly from intershrub space and were characterized by higher soil fertility and less extreme microclimates. There existed a strong spatial association between B. tectorum and the shrubs across four years, with more than double the density of B. tectorum in shrub microhabitats compared to intershrub space. Periodic matrix models were used to calculate population growth (lamda) and reproductive potential (RP, expected lifetime fecundity of seedlings) of B. tectorum in different microhabitats over two years. Modeled population growth was significantly increased in shrub microhabitats in the first of two years. This was primarily due to increased seedling establishment in Artemisia microhabitats, rather than effects during the growing season. In the following year, B. tectorum individuals in shrub microhabitats had a significantly greater reproductive potential than those in intershrub microhabitats, indicating shrub facilitation during the growing season. Loop analysis revealed an interacting effect of year and microhabitat on B. tectorum life history pathway elasticity values, demonstrating a fundamental influence of spatiotemporal factors on which life history pathways are important and/or possible. Life table response experiment (LTRE) analysis showed that increased survival and growth rates positively contributed to population growth in both years under Purshia, but only in the second year under Artemisia. This research provides evidence that the positive effects of native shrubs on B. tectorum can be strong enough to produce net positive effects at the population level, although positive effects were variable. In this study, a rigorous demographic approach was particularly useful in partitioning overall interactions into positive and negative components.

Landscape Epidemiology of Tularemia Outbreaks in Sweden

Summer outbreaks of tularemia that occurred from 1995 through 2005 in 2 locations in Sweden affected 441 persons. We performed an epidemiologic investigation of these outbreaks using a novel strategy, involving high-resolution genotyping of Francisella tularensis isolates obtained from 136 patients (using 18 genetic markers developed from 6 F. tularensis genome sequences) and interviews with the patients. Strong spatial associations were found between F. tularensis subpopulations and the places of disease transmission; infection by some subpopulations occurred within areas as small as 2 km(2), indicating unidentified environmental point sources of tularemia. In both locations, disease clusters were associated with recreational areas beside water, and genetic subpopulations were present throughout the tularemia season and persisted over years. High-resolution genotyping in combination with patients' statements about geographic places of disease transmission provided valuable indications of likely sources of infection and the causal genotypes during these tularemia outbreaks.

Land types and sustainable cocoa production: Lessons from GIS Application

Sustainable cocoa production demands a range of biophysical conditions of land. The paper reports on the levels of sustainability of cocoa production on different soil types under different tree cover intensities. Geographic Information System (GIS) analytical functionalities were extensively applied in the study. The spatial distribution of cocoa was modeled from geo-located samples, and related to tree cover generated from Landsat ETM+ image for 2000 and soils types. There was a strong spatial association between cocoa density-distribution surface, soil types and tree cover. It was observed that soils that are naturally suitable for cocoa were still supporting extensive cocoa farms, whereas unsuitable lands that were initially cultivated with cocoa had only remnant or no cocoa farms. The outcome of this study indicates that decisions for cocoa cultivation should be informed by accurate information on the suitability of lands for sustainable production.

Spatial associations between longest‐lasting winter snow cover and cold region landforms in the high drakensberg, southern africa

.Although snow is known to influence landform genesis and distribution, the spatial associations between snow and landforms within particular cold regions has received limited research attention. We present a case study from the high Drakensberg of southern Africa, comparing the contemporary spatial pattern of longest‐lasting cold‐season snow patches with the distribution patterns of active and relic cold region landforms. Two 30 m resolution sets of TM images dated 3 and 19 August 1990 and a DEM were used to demonstrate the geographic trends of snow patch depletion during late winter. Geomorphological phenomena with known coordinates were then incorporated into the GIS. The spatial distribution of several periglacial land‐forms (earth hummocks, stone‐/turf‐banked lobes, block deposits, large sorted patterned ground) coincides with topographic positions that limit snow accumulation. However, the strong spatial association between longest‐lasting snow patches and palaeo‐moraines implies substantial snow accumulation at some high altitude south‐facing sites during the last glacial cycle.

Patterns of frugivory, seed dispersal and predation of blue fan palms ( Brahea armata) in oases of northern Baja California

Variations in spatial and temporal availability of fruits and seeds in oases are important not only for animal seeking resources, but also for palm population dynamics. We explored spatial association patterns between avian frugivores and blue fan palms in two natural palm patches of Baja California. Spatial patterns were analyzed at the individual tree and at 2 ha patches. We evaluated seed predation by vertebrates and invertebrates, and vertebrate seed dispersal around palms. Birds responded to fruit aggregation at the individual tree and the patch scales, but responses varied between patches. Palm fruit variables—the quantity and the phenological phase—and avian visits showed strong spatial aggregation and association at both scales in one patch, but not in the other. The intensities of seed predation and seed dispersal were significantly higher directly below palms than at >3 m away from them. Patches differed in the intensity of seed predation around palms and in the diversity of mammalian dispersers, but not in the intensity of seed dispersal. Blue fan palms function as important resources' focuses for a great number of animals that use palm oases as corridors, bringing seeds as they move and connecting isolated populations of palms.

Origins of subcalcic garnets and their relation to diamond forming fluids—Case studies from Ekati (NWT-Canada) and Murowa (Zimbabwe)

Subcalcic, high-Cr (G10) garnets are found as inclusions within diamonds and in peridotitic xenoliths. The strong spatial associations between G10 garnets and diamond make them an important tool in the investigation of diamond genesis. We present an integrated study of the major and trace element composition and oxygen–Sr–Nd–Hf isotopic ratios of eight G10 garnets from the Ekati mine (NWT-Canada) and four from the Murowa mine (Zimbabwe) in an attempt to determine their petrogenetic evolution and to further examine a possible relationship between the metasomatic agents responsible for G10 garnet signatures and diamond forming fluids. All garnets display sinusoidal to mildly sinusoidal REE patterns and have negative Ti, Sr and positive U anomalies. They have variably radiogenic 87Sr/ 86Sr (0.703261–0.731191) and non-radiogenic ε Nd values (−8.1 to −27.1), except for one sample from Murowa that has a positive ε Nd of 2.5. One Ekati sample has an extremely low ε Hf value of −61.6. The Ekati garnets we have studied all appear to come from a single depth in the Slave lithospheric mantle. On the base of Cr–Ca relations they have crystallized at 4.9 GPa and display dunitic Ca intercept values. Their δ 18O values range between +5.23‰ and +5.42‰. The Ekati G10 garnets record a complex, multi-stage metasomatic history involving the interaction of several components during their genesis. One metasomatic agent was enriched in HFSE, LREE, Sr, and depleted in Nb. This agent had the least radiogenic Sr. Another metasomatic agent had highly radiogenic Sr, and was enriched in LREE, Sr, Nb, Th and U. The G10 garnets have very low ε Nd and ε Hf values combined with radiogenic Sr, thus, they require an early lithospheric mantle enrichment event at some stage during their genesis or during the evolution of any precursor material that they formed from. The only Hf isotope composition measurable from the Ekati suite is so unradiogenic ( ε Hf = −61) that it yields a Lu/Hf model age of 3521 Ma. This indicates that the lithospheric enrichment event seen by the Ekati garnets or their precursors may have occurred in the early stages of the craton stabilization, during the diamond forming event [Westerlund K., Shirey S., Richardson S., Carlson R., Gurney J. and Harris J. (2006) A subduction wedge origin for Paleoarchean peridotitic diamonds and harzburgites from the Panda kimberlite, Slave craton: evidence from Re–Os isotope systematics. Contrib. Mineral. Petrol. 152(3), 275–294]. Although our data cannot unequivocally discriminate between a variety of models for the genesis of subcalcic garnets it is clear that the host peridotite originated via melting at shallow depths followed by subduction and that the observed geochemical fingerprint of the garnets is strongly influenced by diamond forming fluids. Diamond forming fluids sampled from fibrous diamonds, have steep REE patterns, negative Ti and Sr anomalies and very low Sm/Nd ratios that are very similar to G10 garnet characteristics. These diamond forming fluids have been recently shown to have extreme Sr and Nd isotopic compositions [Klein-BenDavid O., Pearson D. G., Nowell G. M. and Cantigny P. (2008) Origins of diamond forming fluids—constraints from a coupled Sr–Nd isotope and trace element approach. Extended abstracts to the 9th International Kimberlite Conference, Frankfurt, Germany, 9IKC-A-00118.] that are closely concordant with G10 garnets. The fluids are also rich in LREE, P, K and water, sharing these features with mica-rich metasomes. These similarities suggest that ancient lithospheric metasomes could either provide a source region for, or be a product of diamond forming fluids. Diamond forming fluids appear to be intimately involved in the evolution of G10 garnets in the lithospheric mantle, either acting as a metasomatic agent, or being integral to triggering or enhancing garnet growth in a Cr-rich protolith. Such a link explains the strong association between G10 garnets and diamonds.

Response of cathodoluminescence to crystal-plastic deformation in zircon

Geochemical and geochronological studies of zircon are commonly supplemented by cathodoluminescence (CL) imaging because it provides a means of recognizing different generations of zircon growth at high-spatial resolution. Crystal-plastic deformation of zircon can have significant effects on zircon geochemistry. Detailed analyses from electron backscatter diffraction mapping combined with panchromatic CL imaging and hyperspectral CL mapping of several crystal-plastically deformed grains from different geological settings are used to establish the relationships between crystal-plastic deformation and CL in zircon. Results show a strong spatial association between deformation microstructures and CL response that lead to modification of CL that commonly cross-cuts primary zoning. Variable contributions from two fundamental deformation-related processes result in a variety of CL characteristics: A defect control on panchromatic CL intensity, particularly at low-angle (subgrain) boundaries; and changes in spectral CL response due to deformation-related modification of CL-active REE geochemistry. A framework is provided for the recognition of deformation-related microstructures using CL and the usefulness of CL imaging in the discrimination of these microstructures is critically evaluated.

Spatial data analysis and integration for regional-scale geothermal potential mapping, West Java, Indonesia

Conceptual modeling and predictive mapping of potential for geothermal resources at the regional-scale in West Java are supported by analysis of the spatial distribution of geothermal prospects and thermal springs, and their spatial associations with geologic features derived from publicly available regional-scale spatial data sets. Fry analysis shows that geothermal occurrences have regional-scale spatial distributions that are related to Quaternary volcanic centers and shallow earthquake epicenters. Spatial frequency distribution analysis shows that geothermal occurrences have strong positive spatial associations with Quaternary volcanic centers, Quaternary volcanic rocks, quasi-gravity lows, and NE-, NNW-, WNW-trending faults. These geological features, with their strong positive spatial associations with geothermal occurrences, constitute spatial recognition criteria of regional-scale geothermal potential in a study area. Application of data-driven evidential belief functions in GIS-based predictive mapping of regional-scale geothermal potential resulted in delineation of high potential zones occupying 25% of West Java, which is a substantial reduction of the search area for further exploration of geothermal resources. The predicted high potential zones delineate about 53–58% of the training geothermal areas and 94% of the validated geothermal occurrences. The results of this study demonstrate the value of regional-scale geothermal potential mapping in: (a) data-poor situations, such as West Java, and (b) regions with geotectonic environments similar to the study area.

Molecular mechanisms of chromosomal rearrangement during primate evolution

Breakpoint analysis of the large chromosomal rearrangements which have occurred during primate evolution promises to yield new insights into the underlying mechanisms of mutagenesis. Comparison of these evolutionary breakpoints with those that are disease-associated in humans, and which occur during either meiotic or mitotic cell division, should help to identify basic mechanistic similarities as well as differences. It has recently become clear that segmental duplications (SDs) have had a very significant impact on genome plasticity during primate evolution. In comparisons of the human and chimpanzee genomes, SDs have been found in flanking regions of 70-80% of inversions and approximately 40% of deletions/duplications. A strong spatial association between primate-specific breakpoints and SDs has also become evident from comparisons of human with other mammalian genomes. The lineage-specific hyperexpansion of certain SDs observed in the genomes of human, chimpanzee, gorilla and gibbon is indicative of the intrinsic instability of some SDs in primates. However, since many primate-specific breakpoints map to regions lacking SDs, but containing interspersed high-copy repetitive sequence elements such as SINEs, LINEs, LTRs, alpha-satellites and (AT)( n ) repeats, we may infer that a range of different molecular mechanisms have probably been involved in promoting chromosomal breakage during the evolution of primate genomes.

Remote Sensing-Measured Impacts of the Conservation Reserve Program (CRP) on Landscape Structure in Southwestern Kansas

Changes in landscape structure caused by the introduction of the U.S. Conservation Reserve Program (CRP) were examined. Using imagery-derived land cover maps for the pre- and post-CRP enrollment periods, we identified regions of cropland that had been converted to CRP in a six-county area in southwestern Kansas. The major impact of CRP in the study area has been the reversal of an overall trend of grassland fragmentation. The introduction of CRP has substantially modified the spatial structure of the southwest Kansas landscape, generally with important positive implications for wildlife habitat, by changing the count, size, shape, interior areas, and connectivity of grassland patches. The authors also concluded that CRP enrollments had a strong spatial association with the distribution of points of water diversion for irrigation.

Earthworm responses to long term agricultural management practices: Spatial relationships with soil properties

We used a long-term arable cultivation experiment to investigate spatial relationships between earthworm populations and soil physico-chemical properties using Spatial Analysis by Distance Indices methods (SADIE). Red-blue analyses showed that soil C and N were both spatially heterogeneous (patchy) as were total and juvenile earthworm counts. In contrast, theta probe and shear vane measurements, adult earthworm counts and earthworm biomass did not exhibit patchiness. All potential relationships between data classes were analysed using SADIE spatial association tests. Soil chemical properties were generally dissociated from earthworms whereas physical properties were positively associated. These results were largely attributable to juvenile counts, suggesting that this age group may be a more sensitive indicator of spatial relationships between earthworms and soil properties than are adults. We also found that earthworm counts had stronger spatial associations with soil chemical properties than did biomass; the obverse was seen with the measures of soil physical properties. This may provide evidence that earthworm dynamic responses vary between different aspects of the soil environment.

Characterizing spatial–temporal tree mortality patterns associated with a new forest disease

A new forest disease called Sudden Oak Death, caused by the pathogen Phytophthora ramorum, occurs in coastal hardwood forests in California and Oregon. In this paper, we analyzed the spatial–temporal patterns of overstory oak tree mortality in China Camp State Park, CA over 4 years using the point patterns mapped from high spatial resolution remotely sensed imagery. Both univariate and multivariate spatial point pattern analyses were performed with special considerations paid to the spatial trends illustrated in the mapped point patterns. In univariate spatial point pattern analyses, we investigated inhomogeneous K-functions and Neyman–Scott point processes to characterize and model the spatial dependence among dead oak trees in each year. The results showed that the point patterns of dead oak trees are significantly clustered at different scales and spatial extents through time; and that both the extent and the scale of the clustering patterns decrease with time. In multivariate spatial point pattern analyses, we developed two simulation methods to test the spatial–temporal dependence among dead oak trees over time and the spatial dependence between dead oak trees and California bay trees, an important host for the pathogen. The results showed that new dead oak trees tend to be located within up to 300 m of past dead oak trees; and that a strong spatial association between oak tree mortality and California bay trees exists 150 m away.

Textural, mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke, Zimbabwe and the precious metals zone of the Sonju Lake Intrusion, Minnesota, USA

Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion. The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides, antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides, and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of PGE in mineralized layered intrusions of this type.

Fine scale spatial distributions of two entomopathogenic nematodes in a grassland soil

Entomopathogenic nematodes (EPNs) are widespread lethal parasites of many insect species and are known to play an important part in the regulation of soil food webs. We studied the fine scale (5 × 5 cm) distribution and spatial pattern of EPNs in three replicate 0.25 m 2 plots of grassland. All soil was removed from plots (100 samples per plot at 0–5 cm and 100 samples at 5–10 cm depth) and the entire nematode community was extracted using a sieving/centrifugal flotation technique. Entomopathogenic nematode larvae were examined microscopically and identified to species. We found Steinernema feltiae in all three sampled plots and S. affine in two plots. Distribution and spatial pattern were analysed using Lloyd's index of patchiness and spatial analysis by distance indices (SADIE). Both methods showed that the two nematode species had aggregated distributions, and in the two plots where both species coexisted, SADIE showed a strong spatial association between the two species. In addition, we assigned all EPN larvae to one of four groups (I–IV) of increasing physiological age, based on the retention of the sheath and visible lipid content. Lloyds index identified group I as being the most aggregated, whereas SADIE identified group II as the most aggregated, probably because group I nematodes were aggregated at a scale finer than our sampling regime. Groups III and IV nematodes were found to have random distributions by SADIE, and Lloyd's index of patchiness had low values for these groups. Our findings are consistent with the hypothesis that when EPNs emerge from host insects they exist in large numbers of highly aggregated individuals, but as time after emergence increases, a combination of dispersal and death results in lower numbers of more randomly distributed individuals.

Urban Clustering, Development Similarity, and Local Growth: A Case Study of Canada

ABSTRACT The effect of urban clustering on the long-term patterns of urban growth is arguably two-fold: in sparsely populated areas, the presence of neighbouring towns increases the chances of facilitating local development due to inter-urban exchanges, while in more densely populated core areas, increasing clustering of the urban field reduces development rates due to inter-town competition for potential investors and migrants. In the present study, the effect of urban clustering on the patterns of urban growth is investigated for both centrally located and peripheral areas of Canada. Neighbouring towns in urban clusters of the country appear to exhibit similar levels of socio-economic development. However, when measured by different development indicators, inter-town development association differs in both nature and degree. In core areas, for instance, only population and housing variables appear to exhibit a strong spatial association, while that of employment-related variables—average income, and unemployment rate—is weaker. As suggested, this tendency reflects fundamental differences between the two groups of variables. While population and housing variables are associated with the clustering of residents in socially homogenous areas, inter-town development similarity in respect to employment-related variables is weaker, due to long-distance commuting.

Geology, mineralogy and geochemistry of the gold-bearing stibnite and cinnabar deposits in the Emirli and Halıköy areas (Ödemiş, İzmir, West Turkey)

Deposits of stibnite and cinnabar show a strong spatial association with metamorphic rocks and occur mainly within orogenic belts. Our study addresses the Emirli stibnite and Halıköy cinnabar deposits within the Menderes Massif in western Turkey. Stibnite mineralisation occurs as stratabound lenses in graphite- and mica-schist, and as structurally controlled veins. Both types have a common mineral paragenesis containing pyrite, arsenopyrite, stibnite, gold, base metal sulphides, marcasite, realgar, orpiment and cinnabar. Realgar, orpiment and cinnabar are not present in the stratabound lenses. Quartz is the principle gangue mineral in all the deposits. The initial fluids were dilute, carbonic and rather hot (with Th > 300 °C). Deposition of pyrite and arsenopyrite is probably due to cooling of the fluids and to sulphidation and/or decreasing fO 2, caused by interaction with syn-sedimentary sulphides in the country rocks. Arsenopyrite geothermometry indicates an average depositional temperature of 330 °C in the initial quartz vein. Vein formation increased the fluid pressure and caused effervescence, which resulted in a sudden pressure drop from 1.4 kbar during the initial quartz formation to ∼440 bars, and stibnite precipitated at 232 to 307 °C. Boiling and concomitant sulphur loss during stibnite precipitation may have also initiated gold deposition. Further cooling below 190 °C under a pressure of ≤ 600 bars caused cinnabar deposition, mainly in the Halıköy deposit. Salinity of the fluids during stibnite and cinnabar precipitation is 0.8 to 7.1 wt.% NaCl eq. and suggests a meteoric fluid. The structural framework induced by the initiation of extensional tectonics served as conduits for the penetration of surficial fluids to the environs of a possible magmatic heat source evidenced by thermal waters in the region. Stibnite from the stratabound (graphite-schist hosted) lenses and the crosscutting veins in the Emirli deposit have sulphur isotope compositions in a range of − 5.8‰ to − 8.9‰. δ 34S values of pyrite from the graphite-schist zones and mica-schists are in the ranges of − 8.9‰ to − 7.7‰ and − 10.2‰ to − 11.7‰, respectively. It is therefore concluded that the sulphur in stibnite originated from sulphide minerals in the country rocks, which in turn may have a source related to bacterial reduction of sulphate within the pre-metamorphic sediments. Cinnabar has heavier δ 34S contents (− 6.5‰ to − 6.8‰), suggesting a minor magmatic sulphur contribution towards the final stages of mineralisation.

Efficient discovery of multilevel spatial association rules using partitions

Spatial data mining has been identified as an important task for understanding and use of spatial data- and knowledge-bases. In this paper, we present a new approach to discover strong multilevel spatial association rules in spatial databases based on partitioning the set of rows with respect to the spatial relations denoted as relation table R. Meanwhile, the introduction of the equivalence partition tree makes the discovery of multilevel spatial association rules easy and efficient. Experiments show that the new algorithm is efficient.

Human T-lymphotropic Virus, Type 1, Tax Protein Triggers Microtubule Reorientation in the Virological Synapse

We showed recently that the human T-lymphotropic virus, type 1 (HTLV-1), spreads directly from cell to cell via a virological synapse. The HTLV-1 virological synapse resembles the immunological synapse; each is a specialized contact between a lymphocyte and another cell that contains organized protein microdomains, and each involves repolarization of the T-cell microtubule cytoskeleton. However, formation of the virological synapse is not triggered by T-cell receptor-mediated antigen recognition. On the basis of our previous data, we postulated that formation of the viral synapse was triggered by a conjunction of two signals, one from HTLV-1 infection of the T-cell and one from cell-cell contact. We have recently identified ICAM-1 engagement as a cell-contact signal that causes the microtubule polarization associated with the virological synapse. Here we used confocal microscopy of T-lymphocytes naturally infected with HTLV-1 or transfected with individual HTLV-1 genes to investigate the role of the viral transcriptional transactivator protein Tax. Polarization of the microtubules was induced by cell-cell contact or by cross-linking T-cell surface molecules with monoclonal antibodies adsorbed to latex beads. We show that Tax, which is mainly found in the nucleus, is also present at two specific extranuclear sites as follows: around the microtubule organizing center in association with the cis-Golgi and in the cell-cell contact region. We show that expression of Tax provides an intracellular signal that synergizes with ICAM-1 engagement to cause the T-cell microtubule polarization observed at the virological synapse.

Predatory activity and spatial pattern: the response of generalist carabids to their aphid prey

Summary The spatial distribution of cereal aphids infesting a field of winter wheat during the population establishment, development and decline phases were studied using a field‐scale grid of sampling locations. The distribution of two generalist predators, Pterostichus melanarius and P. madidus, were sampled contemporaneously. Using spatial analysis by distance indices (SADIE), spatial pattern in the aphid population, predator activity–density, predator hunger and aphid predation was detected and mapped. We tested the hypothesis that carabids and aphids were spatially associated with one another through predation. Aphid predation by individual beetles was detected using enzyme‐linked immunosorbent assays (ELISA) and hunger was assessed by measurement of foregut weights. Initially, there was a strong spatial dissociation between aphids and P. melanarius activity–density. While the aphid population was increasing there was a strong spatial association between aphids and both P. melanarius and P. madidus activity–density. During aphid population decline there was no measurable association between aphids and predatory activity–density. Predation of aphids was strongly locally associated with predator activity–density on all sample dates for both predator species, regardless of the association with aphid spatial pattern. Areas within the field most isolated from P. melanarius predation had the highest rates of aphid population increase. Although the proportion of P. melanarius individuals consuming aphids was much lower compared to P. madidus, it was concluded that it was a more effective biological control agent due to its comparative abundance.

Development similarity based on proximity: A case study of urban clusters in Canada

Abstract. Neighbouring towns in urban clusters of Canada exhibit similar levels of socio‐economic development. However, when measured by different development indicators, inter‐town development association differs in both nature and degree. In core areas, for instance, only population and housing variables exhibit a strong spatial association, while that of employment‐related variables – average income, and unemployment rate – is weaker. This tendency reflects the fundamental difference between the two groups of variables. While population and housing variables are associated with the clustering of residents in socially homogenous areas, inter‐town development similarity in respect to employment‐related variables is weaker, apparently due to long‐distance commuting. The article discusses the importance of urban clustering as a factor in regional development policies and programmes, and provides support for including cluster‐related elements in a strategy to enhance urban growth in underdeveloped regions.