Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Mapping cultural ecosystem services: A framework to assess the potential for outdoor recreation across the EU
    Paracchini, M.L. ; Zulian, G. ; Kopperoinen, L. ; Maes, J. ; Schagner, J.P. ; Termansen, M. ; Zandersen, M. ; Perez-Soba, M. ; Scholefield, P.A. ; Bidoglio, G. - \ 2014
    Ecological Indicators 45 (2014). - ISSN 1470-160X - p. 371 - 385.
    biodiversity - indicators - behavior - pattern
    Research on ecosystem services mapping and valuing has increased significantly in recent years. However, compared to provisioning and regulating services, cultural ecosystem services have not yet been fully integrated into operational frameworks. One reason for this is that transdisciplinarity is required to address the issue, since by definition cultural services (encompassing physical, intellectual, spiritual interactions with biota) need to be analysed from multiple perspectives (i.e. ecological, social, behavioural). A second reason is the lack of data for large-scale assessments, as detailed surveys are a main source of information. Among cultural ecosystem services, assessment of outdoor recreation can be based on a large pool of literature developed mostly in social and medical science, and landscape and ecology studies. This paper presents a methodology to include recreation in the conceptual framework for EU wide ecosystem assessments (Maes et al., 2013), which couples existing approaches for recreation management at country level with behavioural data derived from surveys and population distribution data. The proposed framework is based on three components: the ecosystem function (recreation potential), the adaptation of the Recreation Opportunity Spectrum framework to characterise the ecosystem service and the distribution of potential demand in the EU. Results show that 38% of the EU is characterised by a high outdoor recreation potential, which is easily accessible, and that such areas can host about 35.4% of potential demand for close-to-home trips (
    Factors influencing casein micelle size in milk of individual cows: Genetic variants and glycosylation of k-casein
    Bijl, E. ; Vries, R.F.M. de; Valenberg, H.J.F. van; Huppertz, T. ; Hooijdonk, A.C.M. van - \ 2014
    International Dairy Journal 34 (2014)1. - ISSN 0958-6946 - p. 135 - 141.
    protein-composition - bovine-milk - liquid-chromatography - electrophoresis - polymorphism - coagulation - genotypes - pattern - cattle
    The average casein micelle size varies widely between milk samples of individual cows. The factors that cause this variation in size are not known but could provide more insight into casein micelle structure and into the physiology of casein micelle formation. The objective of this research was therefore to determine factors that influence average casein micelle size in milk from individual cows. Average casein micelle size of milk samples was associated with the A and B genetic variants of k-casein, and differences in concentration of glycosylated k-casein as a fraction of total milk protein. Milk samples with a low average casein micelle size were associated with the B variant of k-casein and a higher relative concentration of glycosylated k-casein, compared with milk samples with a high average casein micelle size. Differences observed may be attributed to the effect of glycosylated k-casein groups on casein micelle formation in the mammary gland.
    Rooting plant development
    Scheres, B. - \ 2013
    Development 140 (2013)5. - ISSN 0950-1991 - p. 939 - 941.
    arabidopsis root - cell fate - meristem - differentiation - mechanism - shoot - framework - epidermis - division - pattern
    In 1993, we published a paper in Development detailing the anatomical structure of the Arabidopsis root. The paper described how root growth was maintained by the precisely tuned activity of a small set of 'initials', which acted as the source of dividing and differentiating cells, and how these stem cell-like cells surrounded a few infrequently dividing cells. This work underpinned subsequent research on root developmental biology and sparked a detailed molecular analysis of how stem cell groups are positioned and maintained in plants.
    Lactation Weight Loss in Primiparous Sows: Consequences for Embryo Survival and Progesterone and Relations with Metabolic Profiles
    Hoving, L.L. ; Soede, N.M. ; Feitsma, H. ; Kemp, B. - \ 2012
    Reproduction in Domestic Animals 47 (2012)6. - ISSN 0936-6768 - p. 1009 - 1016.
    growth-factor-i - dietary energy-source - feed-intake - reproductive-performance - hormone profiles - insulin - state - mobilization - restriction - pattern
    Our objective was to study reproductive consequences of lactation bodyweight loss occurring in primiparous sows with mild feed restriction and to relate these lactation weight losses and its consequences to metabolic profiles during lactation and subsequent early gestation. After weaning, 47 first-litter sows were retrospectively assigned to a high– (HWL, >13.8%, n = 24) or low (LWL, =13.8%, n = 23)–weight loss group. Thirty-six animals received an indwelling jugular vein catheter to determine lactational and gestational profiles of insulin-like growth factor-1 (IGF-1), non-esterified fatty acids (NEFA) and urea and gestational profiles of progesterone. At day 35 after insemination, sows were euthanized and their reproductive tract collected. Pregnancy rate was 75% (18/24) for HWL and 96% (22/23) for LWL sows. High–weight loss sows had a lower number of implantation sites (17.2 ± 0.8 vs 19.5 ± 0.7, respectively, p = 0.03) and a lower embryonic survival (65.6 ± 3.4 vs 77.4 ± 2.9%, p = 0.02), resulting in fewer vital embryos (14.9 ± 0.9 vs 16.8 ± 0.7, p = 0.07) than LWL sows. Progesterone peak values were reached later in HWL than in LWL sows (day 13.4 ± 0.5 vs 12.0 ± 0.5, respectively, p = 0.05). Gestational concentrations of IGF-1, NEFA and urea were almost identical for HWL and LWL sows, whilst numerical differences were seen during lactation. The current study shows negative consequences of lactational weight loss in mildly feed-restricted primiparous sows for embryonic survival and shows that these consequences seem only mildly related with metabolic alterations during lactation and not with metabolic alterations during subsequent gestation.
    Fish welfare assurance system: initial steps to set up an effective tool to safeguard and monitor farmed fish welfare at a company level
    Vis, J.W. van de; Poelman, M. ; Lambooij, E. ; Bégout, M.L. ; Pilarczyk, M. - \ 2012
    Fish Physiology and Biochemistry 38 (2012)1. - ISSN 0920-1742 - p. 243 - 257.
    dicentrarchus-labrax - feeding-activity - animal-welfare - bass - capacity - rhythms - pattern - haccp
    The objective was to take a first step in the development of a process-oriented quality assurance (QA) system for monitoring and safeguarding of fish welfare at a company level. A process-oriented approach is focused on preventing hazards and involves establishment of critical steps in a process that requires careful control. The seven principles of the Hazard Analysis Critical Control Points (HACCP) concept were used as a framework to establish the QA system. HACCP is an internationally agreed approach for management of food safety, which was adapted for the purpose of safeguarding and monitoring the welfare of farmed fish. As the main focus of this QA system is farmed fish welfare assurance at a company level, it was named Fish Welfare Assurance System (FWAS). In this paper we present the initial steps of setting up FWAS for on growing of sea bass (Dicentrarchus labrax), carp (Cyprinus carpio) and European eel (Anguilla anguilla). Four major hazards were selected, which were fish species dependent. Critical Control Points (CCPs) that need to be controlled to minimize or avoid the four hazards are presented. For FWAS, monitoring of CCPs at a farm level is essential. For monitoring purposes, Operational Welfare Indicators (OWIs) are needed to establish whether critical biotic, abiotic, managerial and environmental factors are controlled. For the OWIs we present critical limits/target values. A critical limit is the maximum or minimum value to which a factor must be controlled at a critical control point to prevent, eliminate or reduce a hazard to an acceptable level. For managerial factors target levels are more appropriate than critical limits. Regarding the international trade of farmed fish products, we propose that FWAS needs to be standardized in aquaculture chains. For this standardization a consensus on the concept of fish welfare, methods to assess welfare objectively and knowledge on the needs of farmed fish are required
    Serial translocation by means of circular intermediates underlies colour sidedness in cattle
    Durkin, K. ; Coppieters, W. ; Drogemuller, C. ; Ahariz, N. ; Cambisano, N. ; Druet, T. ; Fasquelle, C. ; Haile, A. ; Horin, P. ; Huang, L. ; Kamatani, Y. ; Karim, L. ; Lathrop, M. ; Moser, S. ; Oldenbroek, J.K. ; Rieder, S. ; Sartelet, A. ; Sölkner, J. ; Stalhammer, H. ; Zelenika, D. ; Zhang, Z. ; Leeb, T. ; Georges, M. ; Charlier, C. - \ 2012
    Nature 482 (2012). - ISSN 0028-0836 - p. 81 - 84.
    copy number - gene - expression - pattern - genome
    Colour sidedness is a dominantly inherited phenotype of cattle characterized by the polarization of pigmented sectors on the flanks, snout and ear tips1. It is also referred to as ‘lineback’ or ‘witrik’ (which means white back), as colour-sided animals typically display a white band along their spine. Colour sidedness is documented at least since the Middle Ages and is presently segregating in several cattle breeds around the globe, including in Belgian blue and brown Swiss1, 2. Here we report that colour sidedness is determined by a first allele on chromosome 29 (Cs29), which results from the translocation of a 492-kilobase chromosome 6 segment encompassing KIT to chromosome 29, and a second allele on chromosome 6 (Cs6), derived from the first by repatriation of fused 575-kilobase chromosome 6 and 29 sequences to the KIT locus. We provide evidence that both translocation events involved circular intermediates. This is the first example, to our knowledge, of a phenotype determined by homologous yet non-syntenic alleles that result from a novel copy-number-variant-generating mechanism
    Historical review of land use changes in Portugal (before and after EU integration on 1986) and their implications for land degradation and conservation, with a focus on Centro and Alentejo regions
    Jones, N.M. ; Graaff, J. de; Rodrigo, I. ; Duarte, F. - \ 2011
    Applied Geography 31 (2011)3. - ISSN 0143-6228 - p. 1036 - 1048.
    soil-erosion - mediterranean landscape - sloping land - abandonment - pattern - future - cover - fire - food
    Changes in land use and production systems are to a large extent responsible for land degradation. In Portugal this process has been triggered mainly by socioeconomic drivers, such as agricultural technology, demography and policy changes. In this article land use changes in Portugal are discussed in terms of their main drivers and impacts, focussing on land degradation and conservation. The discussion includes a brief outline of historical land use changes in Portugal and a more detailed account of the changes in the period after 1986, when Portugal joined the European Union. An assessment of recent (1986–2006) land use changes and their impact was conducted for two selected research areas in the Centro and Alentejo regions. This assessment was based on information from the CORINE Land Cover programme (1985 and 2006) and the National Agricultural Census (1989 and 1999). In the Centro research area the land under forest declined from 52% to only 22% of the area, mainly as a result of forest fires. In the Alentejo research area the major change was the decline of miscellaneous shrub, declining from 23% to 11%, to open forest land, increasing as a result of afforestation measures from 1% to 22%. These land use changes resulted in a significant increase of soil loss estimates through RUSLE. In the Centro research area soil losses greater than 10 t ha-1 yr-1 were estimated to occur in 57% of the area in 1990, increasing as a result of land use change to 64% in 2006. In the Alentejo research area this change was from 65% in 1990 to 72% in 2006. The research raises questions regarding land use management, in relation to the Common Agriculture Policy support during the 1986–2006 period. Despite the increase in forest and permanent grassland areas, soil loss rates remain very high in the two research areas
    Land-use change simulation and assessment of driving factors in the loess hilly region - a case study as Pengyang County
    Zhanqiang Zhu, ; Liming Liu, ; Zhantao Chen, ; Junlian Zhang, ; Verburg, P.H. - \ 2010
    Environmental Monitoring and Assessment 164 (2010)1-4. - ISSN 0167-6369 - p. 133 - 142.
    pattern - model - accuracy - vietnam - china
    The main objective of this study is to evaluate the land-use change and its relationship with its driving factors in the loess hilly region. In this study, a case study was carried out in Pengyang County. We set two land-use demand scenarios (a baseline scenario (scenario 1) and a real land-use requirement scenario (scenario 2)) during year 2001-2005 via assuming the effect of driving factors on land-use change keeps stable from 1993 to 2005. Two simulated land-use patterns of 2005 are therefore achieved accordingly by use of the conversion of land use and its effects model at small regional extent. Kappa analyses are conducted to compare each simulated land-use pattern with the reality. Results show that (1) the associated kappa values were decreased from 0.83 in 1993-2000 to 0.27 (in scenario 1) and 0.23 (in scenario 2) in 2001-2005 and (2) forest and grassland were the land-use types with highest commission errors, which implies that conversion of both the land-use types mentioned above is the main determinant of change of kappa values. Our study indicates the land-use change was driven by the synthetic multiply factors including natural and social-economic factors (e.g., slope, aspect, elevation, distance to road, soil types, and population dense) in 1993-2000 until "Grain for Green Project" was implemented and has become the dominant factor in 2001-2005.
    A SNP based linkage map of the turkey genome reveals multiple intrachromosomal rearrangements between the Turkey and Chicken genomes
    Aslam, M.L. ; Bastiaansen, J.W.M. ; Crooijmans, R.P.M.A. ; Vereijken, A. ; Groenen, M.A.M. ; Megens, H.J.W.C. - \ 2010
    BMC Genomics 11 (2010). - ISSN 1471-2164
    gene density - avian genome - evolution - microchromosomes - recombination - conservation - galliformes - pattern - markers - gallus
    Background The turkey (Meleagris gallopavo) is an important agricultural species that is the second largest contributor to the world's poultry meat production. The genomic resources of turkey provide turkey breeders with tools needed for the genetic improvement of commercial breeds of turkey for economically important traits. A linkage map of turkey is essential not only for the mapping of quantitative trait loci, but also as a framework to enable the assignment of sequence contigs to specific chromosomes. Comparative genomics with chicken provides insight into mechanisms of genome evolution and helps in identifying rare genomic events such as genomic rearrangements and duplications/deletions. Results Eighteen full sib families, comprising 1008 (35 F1 and 973 F2) birds, were genotyped for 775 single nucleotide polymorphisms (SNPs). Of the 775 SNPs, 570 were informative and used to construct a linkage map in turkey. The final map contains 531 markers in 28 linkage groups. The total genetic distance covered by these linkage groups is 2,324 centimorgans (cM) with the largest linkage group (81 loci) measuring 326 cM. Average marker interval for all markers across the 28 linkage groups is 4.6 cM. Comparative mapping of turkey and chicken revealed two inter-, and 57 intrachromosomal rearrangements between these two species. Conclusion Our turkey genetic map of 531 markers reveals a genome length of 2,324 cM. Our linkage map provides an improvement of previously published maps because of the more even distribution of the markers and because the map is completely based on SNP markers enabling easier and faster genotyping assays than the microsatellitemarkers used in previous linkage maps. Turkey and chicken are shown to have a highly conserved genomic structure with a relatively low number of inter-, and intrachromosomal rearrangements.
    Modeling urban growth using a variable grid cellular automaton
    Vliet, J. van; White, R. ; Dragicevic, S. - \ 2009
    Computers, Environment and Urban Systems 33 (2009)1. - ISSN 0198-9715 - p. 35 - 43.
    land-use maps - categorical maps - spatial models - pattern - netherlands - metrics
    Constrained cellular automata (CA) are frequently used for modeling land use change and urban growth. In these models land use dynamics are generated by a set of cell state transition rules that incorporate a neighborhood effect. Generally, neighborhoods are relatively small and therefore only a limited amount of spatial information is included. In this study a variable grid CA is implemented to allow incorporation of more spatial information in a computationally efficient way. This approach aggregates land uses at greater distances, in accordance with a hierarchical concept of space. More remote areas are aggregated into consecutively larger areas. Therefore the variable grid CA is capable of simulating regional as well as local dynamics at the same time. The variable grid CA is used here to model urban growth in the Greater Vancouver Regional District (GVRD) between 1996 and 2001. Calibration results are tested for goodness of fit at the cellular level by means of the kappa statistic and for land use patterns by means of cluster size analysis and radial analysis. Kappa results show that the model performs considerably better than a neutral allocation model. Cluster and radial analysis indicate that the model is capable of producing realistic urban growth patterns.
    Kinetic models of photosystem II should accommodate the effect of donor side quenching on variable chlorophyll a fluorescence in the microseconds time
    Vredenberg, W.J. - \ 2009
    Photosynthesis Research 102 (2009). - ISSN 0166-8595 - p. 99 - 101.
    single turnover flash - yield - chloroplasts - transients - pattern - cells
    Quantitative data on laser flash-induced variable fluorescence in the 100 ns to 1 ms time range (Belyaeva et al. in Photosynth Res 98:105–119, 2008) confirming those of others (Steffen et al. in Biochemistry 40:173–180, 2001, Biochemistry 44:3123–3132, 2005; Belyaeva et al. in Biophysics 51(6):976–990, 2006), need a substantial correction with respect to magnitude of the normalized variable fluorescence associated with single turnover-induced charge separation in RCs of PS II. Their data are conclusive with the involvement of donor side quenching, the release of which occurs with a rate constant in the range of tens of ms-1, and presumed to be associated with reduction of YZ+ by the OEC
    Narrow rows reduce biomass and seed production of weeds and increase maize yield
    Mashingaidze, A.B. ; Werf, W. van der; Lotz, L.A.P. ; Chipomho, J. ; Kropff, M.J. - \ 2009
    Annals of Applied Biology 155 (2009)2. - ISSN 0003-4746 - p. 207 - 218.
    corn zea-mays - crop density - competition - interception - cultivation - suppression - population - varieties - pattern
    Smallholder farmers in southern African countries rely primarily on cultural control and hoe weeding to combat weeds, but often times, they are unable to keep up with the weeding requirements of the crop because of its laboriousness, causing them to incur major yield losses. Optimisation of crop planting pattern could help to increase yield and suppress weeds and to reduce the critical period of weed control and the weeding requirements to attain maximum yield. Experiments were carried out in Zimbabwe during two growing seasons to assess the effect of maize density and spatial arrangement on crop yield, growth and seed production of weeds and to determine the critical period for weeding. Planting maize at 60 cm row distance achieved higher yields and better weed suppression than planting at 75 or 90 cm row distance. Increasing crop densities beyond the customary three to four plants m-2 gave modest reductions in weed biomass but also diminished crop yields, probably because of increased competition for water and nutrient resources. Maize planted in narrow rows (60 cm) intercepted more radiation and suffered less yield reduction from delaying hoe weeding than those planted in wider rows (75 or 90 cm), and the duration of the weed-free period required to attain maximum grain yield was 3 weeks shorter in the narrow spacing than that in the 75- and 90-cm row spacings. Weeding was more effective in curtailing weed seed production in the narrow row spatial arrangements than in the wide row planting. The results of these studies show that narrow row spacings may reduce weeding requirements and increase yields
    Farmer-specific relationships between land use change and landscape factors: Introducing agents in empirical land use modelling
    Bakker, M.M. ; Doorn, A.M. van - \ 2009
    Land Use Policy 26 (2009)3. - ISSN 0264-8377 - p. 809 - 817.
    multiagent systems - simulation - pattern - areas
    Traditional empirical land use change models generally assume one average land use decision-maker. Multi-Agent System (MAS) models, on the other hand, acknowledge existence of different types of agents, but their poor empirical embedding remains a serious handicap. This paper demonstrates how agent information can also be incorporated into empirical, biophysical land use models. Agent (farmer) information was captured in four farmer types by means of cluster analysis. The types were distinguished by age, education, property size, distance from residence, and the number of animals owned. This information was made spatially explicit as each field in the study area is related to a farmer, based on cadastral information. Statistical interaction terms between farmer type and landscape factors such as remoteness, soil quality, slope and aspect, were tested for significance in describing the observed occurrence of three land use changes: afforestation of arable land, abandonment of arable land, and restoration of the traditional Montado system. Results showed that each farmer type uses different criteria for selecting land for a certain land use change. For example, absentee farmers abandon the most remote areas while other farmer types do not use remoteness as a criterion for abandonment; active farmers select the most accessible fields for afforestation while other farmer types do not; absentee farmers select their best soils for restoration of the traditional Montado system, while active farmers tend to select poor soils. It is demonstrated that each farmer type shows a different relationship between landscape factors and land use changes. Hence, farmer-specific relationships between landscape and land use contribute significantly to the explanation of land use change.
    Kinetic Models of Photosystem II Should Incorporate a Role for Qb-Nonreducing Reaction Centers
    Vredenberg, W.J. - \ 2008
    Biophysical Journal 95 (2008)7. - ISSN 0006-3495 - p. 3113 - 3114.
    fluorescence yield - chloroplasts - pattern - flash
    Temporal mapping of deforestation and forest degradation in Nepal: Applications to forest conservation
    Panta, M. ; Kim, K. ; Joshi, C. - \ 2008
    Forest Ecology and Management 256 (2008)9. - ISSN 0378-1127 - p. 1587 - 1595.
    tropical deforestation - developing-countries - bird communities - fragmentation - area - biodiversity - pattern - crisis - usa
    Deforestation and forest degradation are associated and progressive processes resulting in the conversion of forest area into a mosaic of mature forest fragments, pasture, and degraded habitat. Monitoring of forest landscape spatial structures has been recommended to detect degenerative trends in forest conditions. GIS and remote sensing play an important role in the generation of such data to identify degraded and deforested areas as well as potential areas for conservation. In this study we analyzed forest degradation and deforestation trends in Chitwan district in Nepal, which contains key habitat elements for wildlife in the region. An artificial neural network was used to predict forest canopy density in five classes using Landsat images of the year 2001. Forest canopy density was predicted with 82% overall accuracy. Except riverine forest, forest area of all other forest types was reduced. Terai Shorea robusta forest, which has high commercial value, showed a loss of 23% between 1976 and 1989 and an overall loss of 15% forest covers between the year 1976 and 2001. Deforestation and forest degradation disproportionately reduced the sizes of the different forest types, a finding that has important management implications. The maps presented in this article could be useful to prioritize limited resources for conservation.
    Detection of mastitis pathogens by analysis of volatile bacterial metabolites
    Hettinga, K.A. ; Valenberg, H.J.F. van; Lam, T.J.G.M. ; Hooijdonk, A.C.M. van - \ 2008
    Journal of Dairy Science 91 (2008). - ISSN 0022-0302 - p. 3834 - 3839.
    electronic nose - staphylococcus-aureus - bovine mastitis - milk - culture - system - network - pattern - phase
    The ability to detect mastitis pathogens based on their volatile metabolites was studied. Milk samples from cows with clinical mastitis, caused by Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli were collected. In addition, samples from cows without clinical mastitis and with low somatic cell count (SCC) were collected for comparison. All mastitis samples were examined by using classical microbiological methods, followed by headspace analysis for volatile metabolites. Milk from culture-negative samples contained a lower number and amount of volatile components compared with cows with clinical mastitis. Because of variability between samples within a group, comparisons between pathogens were not sufficient for classification of the samples by univariate statistics. Therefore, an artificial neural network was trained to classify the pathogen in the milk samples based on the bacterial metabolites. The trained network differentiated milk from uninfected and infected quarters very well. When comparing pathogens, Staph. aureus produced a very different pattern of volatile metabolites compared with the other samples. Samples with coagulase-negative staphylococci and E. coli had enough dissimilarity with the other pathogens, making it possible to separate these 2 pathogens from each other and from the other samples. The 2 streptococcus species did not show significant differences between each other but could be identified as a different group from the other pathogens. Five groups can thus be identified based on the volatile bacterial metabolites: Staph. aureus, coagulase-negative staphylococci, streptococci (Strep. uberis and Strep. dysgalactiae as one group), E. coli, and uninfected quarters
    The effect of chemical information on the spatial distribution of fruit flies: I model results
    Lof, M.E. ; Etienne, R.S. ; Powell, J. ; Gee, M. de; Hemerik, L. - \ 2008
    Bulletin of Mathematical Biology 70 (2008)7. - ISSN 0092-8240 - p. 1827 - 1849.
    drosophila-melanogaster - aggregation pheromone - species coexistence - free-flight - populations - competition - dispersal - simulans - behavior - pattern
    Animal aggregation is a general phenomenon in ecological systems. Aggregations are generally considered as an evolutionary advantageous state in which members derive the benefits of protection and mate choice, balanced by the costs of limiting resources and competition. In insects, chemical information conveyance plays an important role in finding conspecifics and forming aggregations. In this study, we describe a spatio-temporal simulation model designed to explore and quantify the effects of these infochemicals, i.e., food odors and an aggregation pheromone, on the spatial distribution of a fruit fly (Drosophila melanogaster) population, where the lower and upper limit of local population size are controlled by an Allee effect and competition. We found that during the spatial expansion and strong growth of the population, the use of infochemicals had a positive effect on population size. The positive effects of reduced mortality at low population numbers outweighed the negative effects of increased mortality due to competition. At low resource densities, attraction toward infochemicals also had a positive effect on population size during recolonization of an area after a local population crash, by decreasing the mortality due to the Allee effect. However, when the whole area was colonized and the population was large, the negative effects of competition on population size were larger than the positive effects of the reduction in mortality due to the Allee effect. The use of infochemicals thus has mainly positive effects on population size and population persistence when the population is small and during the colonization of an area.
    Comparing the input, output, and validation maps for several models of land change
    Pontius Jr., R.G. ; Boersma, W. ; Castella, J.C. ; Kok, K. ; Veldkamp, A. ; Verburg, P.H. - \ 2008
    Annals of Regional Science 42 (2008)1. - ISSN 0570-1864 - p. 11 - 37.
    multiple resolutions - categorical maps - spatial scales - costa-rica - netherlands - pattern - extrapolations - madagascar - simulation - expansion
    This paper applies methods of multiple resolution map comparison to quantify characteristics for 13 applications of 9 different popular peer-reviewed land change models. Each modeling application simulates change of land categories in raster maps from an initial time to a subsequent time. For each modeling application, the statistical methods compare: (1) a reference map of the initial time, (2) a reference map of the subsequent time, and (3) a prediction map of the subsequent time. The three possible two-map comparisons for each application characterize: (1) the dynamics of the landscape, (2) the behavior of the model, and (3) the accuracy of the prediction. The three-map comparison for each application specifies the amount of the prediction¿s accuracy that is attributable to land persistence versus land change. Results show that the amount of error is larger than the amount of correctly predicted change for 12 of the 13 applications at the resolution of the raw data. The applications are summarized and compared using two statistics: the null resolution and the figure of merit. According to the figure of merit, the more accurate applications are the ones where the amount of observed net change in the reference maps is larger. This paper facilitates communication among land change modelers, because it illustrates the range of results for a variety of models using scientifically rigorous, generally applicable, and intellectually accessible statistical techniques.
    Are weed patches stable in location? Application of an explicitly two-dimensional methodology
    Heijting, S. ; Werf, W. van der; Stein, A. ; Kropff, M.J. - \ 2007
    Weed Research 47 (2007)5. - ISSN 0043-1737 - p. 381 - 395.
    glycine-max fields - spatial-distribution - seedling populations - winter-wheat - stability - pattern - scale - distributions - parameters - dependence
    Field observations were made in three years continuous maize cultivation in the Netherlands to study the spatial pattern and stability of spatial pattern over time in agricultural weeds. Two-dimensional correlograms were made, using data from single years, to characterise spatial correlation and pattern, while data from two different years were used to calculate correlation over space and time, to characterise the stability of pattern. Weeds that were able to attain high recruitment also exhibited the strongest spatial correlations. These weeds were Echinochloa crus-galli, Chenopodium album, Chenopodium polyspermum and Solanum nigrum. Weeds that were less successful in attaining high densities in the maize rotation, also showed less spatial correlation. Wind dispersing Compositae, e.g. Taraxacum officinale, had spatially uncorrelated patterns. All weeds that showed spatial correlation also showed stability in space, except E. crus-galli. The latter species showed marked population increase and the locations and extent of its patches changed over the years. Statistical interpretation of the data is discussed, as are potential consequences for site-specific management and optimal sampling of weeds.
    1-Allyloxy-2-hydroxy-propyl-starch : synthesis and characterization
    Huijbrechts, A.M.L. ; Huang, J. ; Schols, H.A. ; Lagen, B. van; Visser, G.M. ; Boeriu, C.G. ; Sudhölter, E.J.R. - \ 2007
    Journal of Polymer Science. Part A, Polymer Chemistry 45 (2007)13. - ISSN 0887-624X - p. 2734 - 2744.
    sweet-potato starches - acetyl substitution - amylopectin populations - amylose - cellulose - granules - acetate - pattern - waxy
    New reactive unsaturated starch derivatives, 1-allyloxy-2-hydroxy-propyl-starches (AHP-starches), were synthesized by the reaction of waxy maize starch (WMS) and amylose-enriched maize starch (AEMS) with allyl glycidyl ether in a heterogeneous alkaline suspension containing NaOH and Na2SO4. The degree of substitution (DS) was determined by H-1 NMR spectroscopy, and a DS of 0.20 +/- 0.01 was found for both AHP-WMS and AHP-AEMS, respectively. The AHP derivatives of WMS and AEMS were further characterized with H-1 and C-13 NMR. It was shown that the AHP substitution was located on the C-6 hydroxyl group of the glucose residues in the starch. The substitution pattern of the AHP groups along the polymer chain was randomly clustered, as determined by enzymatic digestion using pullulanase, a-amylase, and amyloglucosidase, followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of the digestion products. With X-ray diffraction and scanning electron microscopy, no changes in the granular morphology and crystallinity between the unmodified starches and AHP-starches were detected. (c) 2007 Wiley Periodicals, Inc.
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