Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

    Current refinement(s):

    Records 1 - 20 / 57

    • help
    • print

      Print search results

    • export

      Export search results

    Check title to add to marked list
    What happens in Europe stays in Europe : apparent evolution by an invader does not help at home
    Pal, Robert W. ; Maron, John L. ; Nagy, David U. ; Waller, Lauren P. ; Tosto, Ambra ; Liao, Huixuan ; Callaway, Ragan M. - \ 2020
    Ecology 101 (2020)8. - ISSN 0012-9658 - 10 p.
    biogeography - common garden experiment - competition - EICA hypothesis - invasion - reintroduction - Solidago gigantea - transcontinental research

    Some invasive plant species rapidly evolve greater size and/or competitive ability in their nonnative ranges. However, it is not well known whether these traits transfer back to the native range, or instead represent genotype-by-environment interactions where traits are context specific to communities in the new range where the evolution occurred. Insight into transferability vs. context specificity can be tested using experiments performed with individuals from populations from the native and nonnative ranges of exotic invasive species. Using a widespread invasive plant species in Europe, Solidago gigantea, we established reciprocal common garden experiments in the native range (Montana, North America; n = 4) and the nonnative range (Hungary, Europe; n = 4) to assess differences in size, vegetative shoot number, and herbivory between populations from the native and nonnative ranges. In a greenhouse experiment, we also tested whether the inherent competitive ability of genotypes from 15 native and 15 invasive populations differed when pitted against 11 common native North American competitors. In common gardens, plants from both ranges considered together produced five times more biomass, grew four times taller, and developed five times more rhizomes in the nonnative range garden compared to the native range garden. The interaction between plant origin and the common garden location was highly significant, with plants from Hungary performing better than plants from Montana when grown in Hungary, and plants from Montana performing better than plants from Hungary when grown in Montana. In the greenhouse, there were no differences in the competitive effects and responses of S. gigantea plants from the two ranges when grown with North American natives. Our results suggest that S. gigantea might have undergone rapid evolution for greater performance abroad, but if so, this response does not translate to greater performance at home.

    Assessing effect of rainfall on rate of alien shrub expansion in a southern African savanna
    Masocha, Mhosisi ; Dube, Timothy ; Skidmore, Andrew ; Holmgren Urba, Milena ; Prins, Herbert - \ 2017
    African Journal of Range and Forage Science 34 (2017)1. - ISSN 1022-0119 - p. 39 - 44.
    aerial photography - invasion - Kyle Game Reserve - Lantana camara - patch dynamics - rainfall variability

    Understanding the environmental factors governing the spread of alien shrubs is crucial for conserving biodiversity. In the semi-arid savannas of Africa, alien shrub invasion often occurs simultaneously with native shrub encroachment but climate-dependent differences in encroachments of native and alien shrubs have never been properly quantified. A combination of historical aerial photographs and field measurements was used to compare the spread of the invasive shrub Lantana camara L. with that of native encroaching shrubs over a 31-year period in a protected semi-arid savanna in Zimbabwe, southern Africa. We tested whether the response of this invasive alien shrub to rainfall differs from that of native shrub encroachers. Both the invasive shrub L. camara and native encroaching shrubs spread significantly faster during high rainfall years than in dry years. However, the response of L. camara to annual rainfall was stronger than the response of native encroaching shrubs. During years of above-average rainfall, the mean annual rate of spread of L. camara was at least twice that of native shrub encroachers, whereas in other years natives spread at the same rate as the alien shrub. This is a novel finding suggesting that in water-limited savannas, pulses in rainfall may accelerate the spread of some invasive alien species.

    Invasive behavior of Campylobacter jejuni in immunosuppressed chicken
    Vaezirad, Mahdi M. ; Keestra-Gounder, A.M. ; Zoete, Marcel R. de; Koene, Miriam G. ; Wagenaar, Jaap A. ; Putten, Jos P.M. van - \ 2017
    Virulence 8 (2017)3. - ISSN 2150-5594 - p. 248 - 260.
    Campylobacter - chicken - colonization - glucocorticoids - innate immunity - invasion - Toll-like receptor
    Campylobacter jejuni is a predominant cause of gastroenteritis in humans but rather harmless in chickens. The basis of this difference is unknown. We investigated the effect of the chicken immune defense on the behavior of C. jejuni using glucocorticoid (GC)-treated and mock-treated 17-day old Ross 308 chicken bearing in mind that GCs have immunosuppressive effects and dampen the innate immune response. The effect of GC administration on the behavior of C. jejuni was compared with that on infection with Salmonella Enteritidis to address possible microbe-associated differences. Our results revealed that GC treatment fastened the intestinal colonization of C. jejuni (p <0.001) and enhanced its dissemination to the liver (p = 0.007). The effect of GC on intestinal colonization of S. Enteritidis was less pronounced (p = 0.033) but GC did speed up the spread of this pathogen to the liver (p <0.001). Cytokine transcript analysis showed an up to 30-fold reduction in baseline levels of IL-8 mRNA in the cecal (but not spleen) tissue at Day 1 after GC treatment (p <0.005). Challenge with C. jejuni strongly increased intestinal IL-8, IL-6, and iNOS transcript levels in the non-GC treated animals but not in the GC-treated birds (P <0.005). In vitro assays with chicken macrophages showed that GC dampened the TLR agonist- and C. jejuni induced-inflammatory gene transcription and production of nitric oxide (P <0.005). Together, the results support the hypothesis that C. jejuni has the intrinsic ability to invade chicken tissue and that an effective innate immune response may limit its invasive behavior.
    Eerste Advies Bruinvisonderzoek (Bac-2016-01)
    Meer, Jaap van der; Eijsackers, H.J.P. ; Haelters, Jan ; Bos, O.G. - \ 2016
    IMARES Wageningen UR (rapport / Bac Bac-2016-01) - 15
    dierenwelzijn - wilde dieren - zeezoogdieren - invasie - bijvangst - waterverontreiniging - diergezondheid - mariene ecologie - animal welfare - wild animals - marine mammals - invasion - bycatch - water pollution - animal health - marine ecology
    Bright fluorescent Streptococcus pneumoniae for live cell imaging of host-pathogen interactions
    Kjos, M. ; Aprianto, R. ; Fernandes, V.E. ; Andrew, P.W. ; Strijp, J.A.G. van; Nijland, R. ; Veening, J.W. - \ 2015
    Journal of Bacteriology 197 (2015)5. - ISSN 0021-9193 - p. 807 - 818.
    epithelial-cells - gene-expression - pneumococcal virulence - bacillus-subtilis - in-vivo - protein - capsule - colonization - disease - invasion
    Streptococcus pneumoniae is a common nasopharyngeal resident in healthy people, but at the same time one of the major causes of infectious diseases such as pneumonia, meningitis and sepsis. The shift from commensal to pathogen and its interaction with host cells is poorly understood. One of the major limitations for research on pneumococcal-host interactions is the lack of suitable tools for live cell imaging. To address this issue, we developed a generally applicable strategy to create genetically stable, highly fluorescent bacteria. Our strategy relies on fusing superfolder green fluorescent protein (GFP) or a far-red fluorescent protein (RFP) to the abundant histone-like protein HlpA. Due to efficient translation and limited cellular diffusion of these fusions, the cells are 25-fold brighter than the currently best available imaging S. pneumoniae strain. These novel bright pneumococcal strains are fully virulent and the GFP-reporter can be used for in situ imaging in mouse tissue. We used our reporter strains to study the effect of the polysaccharide capsule, a major pneumococcal virulence factor, on different stages of infection. By dual-color live cell imaging experiments, we show that unencapsulated pneumococci adhere significantly better to human lung epithelial cells compared to encapsulated strains, in line with previous data obtained by classical approaches. We also confirm with live cell imaging that the capsule protects pneumococci from neutrophil phagocytosis, demonstrating the versatility and usability of our reporters. The described imaging tools will pave the way for live cell imaging of pneumococcal infection and help understand the mechanisms of pneumococcal pathogenesis.
    A bead-based suspension array for the multiplexed detection of begomoviruses and their whitefly vectors
    Brunschot, S.L. van; Bergervoet, J.H.W. ; Pagendam, D.E. ; Weerdt, M. de; Geering, A.D.W. ; Drenth, A. ; Vlugt, R.A.A. van der - \ 2014
    Journal of Virological Methods 198 (2014). - ISSN 0166-0934 - p. 86 - 94.
    leaf-curl-virus - time pcr assay - bemisia-tabaci - q biotypes - tomato - identification - geminiviruses - aleyrodidae - hemiptera - invasion
    Bead-based suspension array systems enable simultaneous fluorescence-based identification of multiple nucleic acid targets in a single reaction. This study describes the development of a novel approach to plant virus and vector diagnostics, a multiplexed 7-plex array that comprises a hierarchical set of assays for the simultaneous detection of begomoviruses and Bemisia tabaci, from both plant and whitefly samples. The multiplexed array incorporates genus, species and strain-specific assays, offering a unique approach for identifying both known and unknown viruses and B. tabaci species. When tested against a large panel of sequence-characterized begomovirus and whitefly samples, the array was shown to be 100% specific to the homologous target. Additionally, the multiplexed array was highly sensitive, efficiently and concurrently determining both virus and whitefly identity from single viruliferous whitefly samples. The detection limit for one assay within the multiplexed array that specifically detects Tomato yellow leaf curl virus-Israel (TYLCV-IL) was quantified as 200 fg of TYLCV-IL DNA, directly equivalent to that of TYLCVspecific qPCR. Highly reproducible results were obtained over multiple tests. The flexible multiplexed array described in this study has great potential for use in plant quarantine, biosecurity and disease management programs worldwide. (C) 2014 Elsevier B.V. All rights reserved.
    Soil biochar amendment in a nature restoration area: effects on plant productivity and community composition
    Voorde, T.F.J. van de; Bezemer, T.M. ; Groenigen, J.W. van; Jeffery, S.L. ; Mommer, L. - \ 2014
    Ecological Applications 24 (2014)5. - ISSN 1051-0761 - p. 1167 - 1177.
    nitrogen-fixation - activated carbon - charcoal - invasion - growth - performance - fertilizer - amazon - manure
    Biochar (pyrolyzed biomass) amendment to soils has been shown to have a multitude of positive effects, e.g., on crop yield, soil quality, nutrient cycling, and carbon sequestration. So far the majority of studies have focused on agricultural systems, typically with relatively low species diversity and annual cropping schemes. How biochar amendment affects plant communities in more complex and diverse ecosystems that can evolve over time is largely unknown. We investigated such effects in a field experiment at a Dutch nature restoration area. In April 2011, we set up an experiment using biochar produced from cuttings collected from a local natural grassland. The material was pyrolyzed at 400°C or at 600°C. After biochar or residue (non-pyrolyzed cuttings) application (10 Mg/ha), all plots, including control (0 Mg/ha) plots, were sown with an 18-species grassland mixture. In August 2011, we determined characteristics of the developed plant community, as well as soil nutrient status. Biochar amendment did not alter total plant productivity, but it had a strong and significant effect on plant community composition. Legumes were three times as abundant and individual legume plants increased four times in biomass in plots that received biochar as compared to the control treatment. Biomass of the most abundant forb (Plantago lanceolata) was not affected by biochar addition. Available phosphorous, potassium, and pH were significantly higher in soils that received biochar than in Control soils. The rate of biological nitrogen fixation and seed germination were not altered by biochar amendment, but the total amount of biological N fixed per Trifolium pratense (red clover) plant was more than four times greater in biochar-amended soil. This study demonstrates that biochar amendment has a strong and rapid effect on plant communities and soil nutrients. Over time these changes may cascade up to other trophic groups, including above- and belowground organisms. Our results emphasize the need for long-term studies that examine not only the short-term effects of biochar amendment, but also follow how these effects evolve over time and affect ecosystem functioning.
    A continuum approximation to an off-lattice individual-cell based model of cell migration and adhesion
    Middleton, A.M. ; Fleck, C. ; Grima, R. - \ 2014
    Journal of Theoretical Biology 359 (2014). - ISSN 0022-5193 - p. 220 - 232.
    extended potts-model - time blow-up - aggregation equation - collective motion - pattern-formation - tumor-growth - invasion - cancer - simulation - populations
    Cell–cell adhesion plays a key role in the collective migration of cells and in determining correlations in the relative cell positions and velocities. Recently, it was demonstrated that off-lattice individual cell based models (IBMs) can accurately capture the correlations observed experimentally in a migrating cell population. However, IBMs are often computationally expensive and difficult to analyse mathematically. Traditional continuum-based models, in contrast, are amenable to mathematical analysis and are computationally less demanding, but typically correspond to a mean-field approximation of cell migration and so ignore cell–cell correlations. In this work, we address this problem by using an off-lattice IBM to derive a continuum approximation which does take into account correlations. We furthermore show that a mean-field approximation of the off-lattice IBM leads to a single partial integro-differential equation of the same form as proposed by Sherratt and co-workers to model cell adhesion. The latter is found to be only effective at approximating the ensemble averaged cell number density when mechanical interactions between cells are weak. In contrast, the predictions of our novel continuum model for the time-evolution of the ensemble cell number density distribution and of the density–density correlation function are in close agreement with those obtained from the IBM for a wide range of mechanical interaction strengths. In particular, we observe ‘front-like’ propagation of cells in simulations using both our IBM and our continuum model, but not in the continuum model simulations obtained using the mean-field approximation.
    Diapause and post-diapause quiescence demonstrated in overwintering Harmonia axyeidis (Coleoptera: Coccinellidae) in northwestern Europe
    Raak-van den Berg, C.L. ; Jong, P.W. de; Hemerik, L. ; Lenteren, J.C. van - \ 2013
    European Journal of Entomology 110 (2013)4. - ISSN 1210-5759 - p. 585 - 591.
    lady beetle - photoperiodic response - winter survival - septempunctata - reproduction - temperature - netherlands - invasion - behavior - spread
    The Asian ladybird Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is regarded as an invasive species in many parts of the world. In a previous study we hypothesised that H. axyridis enters diapause at the end of October and then shifts to a quiescent state in December in northwestern Europe. In the present study we test this idea of a short, early period of diapause by sampling beetles from their hibernation sites immediately after their migratory flights in October, subsequently keeping them in outdoor cages, and then, after certain time-intervals, measuring the pre-oviposition time under optimal egg-laying laboratory conditions at 25 degrees C. We did this at both short (12L) and long (16L) photoperiods, since a photoperiodic response is an indicator of true diapause, rather than quiescence. A significant, albeit small, difference in pre-oviposition period between the two photoperiods, which disappears in December, corroborates our earlier hypothesis that the ladybirds are in a state of diapause until mid-December. Compared with that of native ladybirds the diapause of H. axyridis generally is relatively short and weak; moreover, it appears to have become shorter over the last decade. This flexibility in diapausing behaviour may be an important factor that contributes to the invasive success of H. axyridis.
    Smoking epidemic eradication in a eco-epidemiological dynamical model
    Voorn, G.A.K. van; Kooi, B.W. - \ 2013
    Ecological Complexity 14 (2013). - ISSN 1476-945X - p. 180 - 189.
    predator-prey oscillations - policy simulation-model - infectious-diseases - transmission - netherlands - bifurcation - prevalence - invasion
    Smoking is perceived as a major epidemic with regard to mortality. Modelling is a major tool used to obtain insight in the dynamics and possible solutions to decrease or even eradicate this epidemic. Most models on smoking consider the epidemiological context explicitly, in which smoking is regarded as an ‘infectious disease’, in which individuals ‘infect’ each other. However, the population dynamics are often ignored, while these occur at roughly the same timescale as smoking, and hence should explicitly be considered in the modelling of smoking. We present a simple but dynamical eco-epidemiological model. The model formulation consists of a resource-population dynamic part coupled to an epidemiological part resembling a SIR type model for the three compartments: non-smokers, smokers and ex-smokers. The coupling is via birth of non-smokers and death of the three classes with different death rates. The final four-dimensional system of ordinary differential equations are studied using brute force simulations for the short term dynamics and bifurcation analysis for the long-term dynamics. Due to a feed-back mechanism of the two coupling terms there is a codim-two tangent-transcritical bifurcation. This leads to bi-stability of one smoker endemic interior equilibrium and a smoker free boundary equilibrium. Changing parameters beyond the emerging tangent bifurcation leads on the short term to eradicating smoking. We consider the Netherlands in this paper for parametrization, but the modelling approach may be generally applicable.
    Testing the Australian Weed Risk Assessment with different estimates for invasiveness
    Speek, T.A.A. ; Davies, J.A.R. ; Lotz, L.A.P. ; Putten, W.H. van der - \ 2013
    Biological Invasions 15 (2013)6. - ISSN 1387-3547 - p. 1319 - 1330.
    assessment system - plant invasiveness - success - invasion - europe - flora - history - tool
    The Weed Risk Assessment (WRA) has become an effective tool in predicting invasiveness of exotic plant species. In studies testing the WRA, exotic plant species are usually divided into major weeds, minor weeds and non-weeds. However, these divisions are qualitative, as the categories are assigned by experts. Many studies searching for plant traits that are indicative of plant invasiveness use quantitative estimates to measure invasiveness. We compared how quantitative and qualitative estimates of invasiveness may relate to WRA scores. As quantitative estimates we used regional frequency (spread), change in regional frequency and local dominance of naturalized exotic plant species in The Netherlands. To obtain a qualitative estimate we determined if the exotic plant species occurred on a black list in neighbouring regions. We related WRA scores of the exotic plant species to these qualitative and quantitative estimates of invasiveness. Our results reveal that the WRA predicted the qualitative (black list) estimate more accurately than the quantitative (dominance and spread) ones. The black list estimate matches with the overall impact of exotic species, which is assumed to incorporate regional spread, local dominance and noxiousness. Therefore, the WRA predicts the noxiousness component, but to a lesser extent the spatial components of impact of exotic species. On the other hand, studies that use regional spread and other quantitative estimates of invasiveness tend not to include the noxiousness component of impact. We propose that our analyses may also help to further solve the recent debate on whether or not performing research on exotic species.
    Campylobacter jejuni Translocation across Intestinal Epithelial Cells Is Facilitated by Ganglioside-Like Lipooligosaccharide Structures
    Louwen, R. ; Nieuwenhuis, E.E.S. ; Marrewijk, L. van; Horst-Kreft, D. ; Ruiter, L. de; Heikema, A.P. ; Wamel, W.J. van; Wagenaar, J.A. ; Endtz, H.P. ; Samsom, J. ; Baarlen, P. van; Akhmanova, A. ; Belkum, A. van - \ 2012
    Infection and Immunity 80 (2012)9. - ISSN 0019-9567 - p. 3307 - 3318.
    lysosomal membrane-proteins - guillain-barre-syndrome - line caco-2 - tight junctions - adherence - invasion - infection - oligosaccharide - endocytosis - mechanisms
    Translocation across intestinal epithelial cells is an established pathogenic feature of the zoonotic bacterial species Campylobacter jejuni. The number of C. jejuni virulence factors known to be involved in translocation is limited. In the present study, we investigated whether sialylation of C. jejuni lipooligosaccharide (LOS) structures, generating human nerve ganglioside mimics, is important for intestinal epithelial translocation. We here show that C. jejuni isolates expressing ganglioside-like LOS bound in larger numbers to the Caco-2 intestinal epithelial cells than C. jejuni isolates lacking such structures. Next, we found that ganglioside-like LOS facilitated endocytosis of bacteria into Caco-2 cells, as visualized by quantitative microscopy using the early and late endosomal markers early endosome-associated protein 1 (EEA1), Rab5, and lysosome-associated membrane protein 1 (LAMP-1). This increased endocytosis was associated with larger numbers of surviving and translocating bacteria. Next, we found that two different intestinal epithelial cell lines (Caco-2 and T84) responded with an elevated secretion of the T-cell attractant CXCL10 to infection by ganglioside-like LOS-expressing C. jejuni isolates. We conclude that C. jejuni translocation across Caco-2 cells is facilitated by ganglioside-like LOS, which is of clinical relevance since C. jejuni ganglioside-like LOS-expressing isolates are linked with severe gastroenteritis and bloody stools in C. jejuni-infected patients.
    Ecological impacts of Prosopis invasion in Riverine forests of Kenya
    Muturi, G.M. - \ 2012
    Wageningen University. Promotor(en): Frits Mohren, co-promotor(en): Lourens Poorter; B.N. Kigomo. - S.l. : s.n. - ISBN 9789461734020 - 162
    prosopis - introduced species - invasion - impact - forests - forest ecology - genetic diversity - kenya - prosopis - geïntroduceerde soorten - invasie - impact - bossen - bosecologie - genetische diversiteit - kenya

    Drylands occupy over 41% of the global land surface, with Africa and Asia accounting for 32% of the global total each. Because of poor resource management, resource overexploitation and periodic droughts, drylands have experienced severe land degradation. Land degradation is manifested in vegetation loss or deterioration, soil erosion and salinization of soil and water. In Kenya, drylands occupy over 87% of the land surface, and support about 30% of the national population, over 70% of national livestock and the bulk of wildlife that support the tourist sector. Following the prolonged sahelian droughts of the 1970’s Kenya’s drylands were seriously degraded through extensive loss of ground vegetation cover; thus threatening the survival of local populations, livestock production and sustenance of tourism sector. Subsequently, exotic trees and shrubs were introduced for land rehabilitation and fodder supply. Trees from from Prosopis genus emerged as the most adapted and were widely planted.
    Since introduction, Prosopis species have spread from target rehabilitation sites and invaded riverine and wetlands ecosystems but invasion mechanisms and impacts are not yet well understood. In this study we combined geographical information systems techniques; field, greenhouse and laboratory studies, to evaluate riverine habitat invasibility, invasion impacts, invasiveness of Prosopis species and the composition of invasive Prosopis species in Kenya. The following questions were addressed: 1) What abiotic factors make riverine forests vulnerable to Prosopis invasion?, 2) What are the ecological implications of Prosopis invasion in riverine forests?, 3) What mechanisms underlie inhibition of A. tortilis regeneration by Prosopis species invasion?, 4) What are the species composition in Prosopis invaded areas of Kenya, and 5) What are the implications of our results?
    The present study revealed indiscriminate Prosopis invasion in all land cover and land use types identified through satellite image analysis, field surveys and historical site information provided by local informants. As a result of this trend, we found a contrasting occurrence increase of Prosopis species and decrease of Acacia tortilis between 1998 and 2007. Accordingly, the study has demonstrated that Prosopis species invasion in the Turkwel Riverine forest is invoked more by species invasiveness rather than habitat susceptibility. Consequently, we investigated the invasiveness of Prosopis species by studying invasion impacts and the underpinning mechanisms
    Our study has shown reduction of herbaceous species ground vegetation cover and herbaceous species diversity, and termination of A. tortilis regeneration by Prosopis invasion. The negative regression coefficients found between herbaceous species ground cover or between herbaceous species diversity and Prosopis canopy dummy, clarifies the partial direct negative effect of Prosopis on herbaceous species. We corroborate this finding by greenhouse studies that show stronger inhibition A. tortilis and Prosopis seed germination by increasing the concentration of fresh Prosopis litter than by increasing the concentration A. tortilis litter in the soil. Indeed, our study demonstrates potential of seed germination termination at 50% fresh Prosopis litter concentration in the soil. After one month of watering of soil-litter mixture, we found no litter effect on seed germination. Since water leaching decreased the concentration of soluble phenols and leached litter had no effect on seed germination, our study has clarified that the inhibition of A. tortilis regeneration by Prosopis canopy was partially the result of allelopathic effect of Prosopis litter on A. tortilis seed germination.
    There has been great confusion on Prosopis species identity in Prosopis invaded areas of Kenya, because of similar morphology and introduction of several species within sites. Species misidentification may hamper invasion management. In this study we used Random Amplified DNA markers to differentiate species according to sites. Our study shows that only one species or a hybrid is adapted to any one site, despite the number of species that were introduced to any site. We have further clarified that P. juliflora and its hybrid are the most invasive germplasm in Kenya. However, P. juliflora and the hybrid trees tended to have similar tree characteristics in riverine forests and wetlands as we could predict tree volumes in wetlands from equations developed from a distant riverine site.
    Our study demonstrates potential for perpetual replacement of A. tortilis by Prosopis species in riverine ecosystems. A notable consequence is reduction of both herbaceous species productivity and diversity. Since both A. tortilis and herbaceous species are used for fodder; invasion may have severe consequences on the pastoral economy but this can be reversed by intensified utilization of Prosopis biomass for fuelwood and pods for fodder.

    Terrestrial Ecosystem Responses to Species Gains and Losses
    Wardle, D.A. ; Bardgett, R.D. ; Callaway, R. ; Putten, W.H. van der - \ 2011
    Science 332 (2011)6035. - ISSN 0036-8075 - p. 1273 - 1277.
    climate-change - changing environment - nitrogen-fixation - plant-communities - diversity - biodiversity - invasion - impacts - restoration - herbivores
    Ecosystems worldwide are losing some species and gaining others, resulting in an interchange of species that is having profound impacts on how these ecosystems function. However, research on the effects of species gains and losses has developed largely independently of one another. Recent conceptual advances regarding effects of species gain have arisen from studies that have unraveled the mechanistic basis of how invading species with novel traits alter biotic interactions and ecosystem processes. In contrast, studies on traits associated with species loss are fewer, and much remains unknown about how traits that predispose species to extinction affect ecological processes. Species gains and losses are both consequences and drivers of global change; thus, explicit integration of research on how both processes simultaneously affect ecosystem functioning is key to determining the response of the Earth system to current and future human activities
    Earthworm-induced N mineralization in fertilized grassland increases both N2O emission and crop-N uptake
    Lubbers, I.M. ; Brussaard, L. ; Otten, W. ; Groenigen, J.W. van - \ 2011
    European Journal of Soil Science 62 (2011)1. - ISSN 1351-0754 - p. 152 - 161.
    nitrous-oxide emission - organic-matter - carbon-dioxide - soil-structure - agroecosystems - fluxes - populations - invasion - habitat - forests
    Earthworms can increase plant nitrogen (N) availability by stimulating mineralization of organic matter. However, recent studies show that they can also cause elevated emission of the greenhouse gas nitrous oxide (N2O). It is unclear to what extent these two effects occur in fertilized grasslands, where earthworm densities are typically greatest. The aims of this study were therefore to (i) quantify the effects of earthworm activity on N uptake and N2O emissions in fertilized grasslands and (ii) link these effects to earthworm functional groups. In a 73-day factorial mesocosm experiment, combinations of Lumbricus rubellus (Lr, epigeic), Aporrectodea longa (Al, anecic) and Aporrectodea caliginosa (Ac, endogeic) individuals were introduced into columns with grass growing on a fertilized (250 kg N ha-1) loamy soil. Introduction of Lr resulted in 50.8% (P <0.001) larger N2O emissions and 5.4% (P = 0.032) larger grass biomass. Grass-N uptake increased from 172 to 188 kg N ha-1 in the presence of Lr (P <0.001), from 176 to 183 kg N ha-1 in the presence of Ac (P = 0.001), and from 168 to 199 kg N ha-1 when all three earthworm species were present (P = 0.006). Lr increased soil NH4+-N concentrations (P = 0.010), further indicating enhanced mineralization of N caused by earthworm activity. We conclude that the previously observed beneficial effect of earthworm presence on plant-N availability has a negative side-effect: increased emissions of the mineralized N as N2O
    Stabilization and complex dynamics in a predator-prey model with predator suffering from an infectious disease
    Kooi, B.W. ; Voorn, G.A.K. van; Das, Krishna pada - \ 2011
    Ecological Complexity 8 (2011)1. - ISSN 1476-945X - p. 113 - 122.
    numerical bifurcation-analysis - 3-species food-chain - to-cycle connections - homoclinic bifurcations - conclusion drawn - chaos - population - parasites - communities - invasion
    We study the effects of a non-specified infectious disease of the predator on the dynamics a predator–prey system, by evaluating the dynamics of a three-dimensional model. The predator population in this (PSI) model is split into a susceptible and an unrecoverable infected population, while all newborn are susceptible. The incidence rate at which susceptible become infectious is described by a Holling type II functional response giving saturation when the number of susceptibles increases. From a modeling context this three-dimensional model is in the limit case similar to the well-known 3D Rosenzweig–MacArthur (RM) model, with the infected population replacing the top-predator. The RM model is known for the Shil’nikov bifurcation, which is associated to the chaotic behaviour. The effects of the disease are considered to be changes in the parameters that represent relative predation efficiency and mortality rates. A combination of analysis, numerical integration and numerical continuation techniques are used to perform a bifurcation analysis of the model. The positive stationary solution of the disease free, two-dimensional predator–prey system is either a stable equilibrium or a stable limit cycle where the transition occurs at the Hopf bifurcation. For a biologically applicable parameter set, it is found that when the infected individuals feed less fast or less effective than the susceptibles there is bi-stability where the two-dimensional disease free state co-exists with a stable equilibrium for the three-dimensional PSI system. The introduction of a disease can also cause chaos when the infected predator individuals are ecologically not functioning (not feeding and no offspring). However, under small parameter changes first the Shil’nikov bifurcation, and hence the chaotic behaviour, disappears followed by the Hopf bifurcation that marks the existence of limit cycles of the three-dimensional PSI system. As such, an infectious disease has a strongly stabilizing effect on the predator–prey system, similar to the existence of weak links in food webs.
    Achter ‘hooikoortsplant’schuilt gezondheidsgevaar; doortesten op specifiek IgE tegen ambrosia blijkt noodzakelijk
    Vliet, A.J.H. van - \ 2010
    News Reporter / Siemens Diagnostics 6 (2010). - p. 14 - 15.
    ambrosia - onkruiden - invasie - geïntroduceerde soorten - allergieën - volksgezondheid - gevoeligheid - hooikoorts - groeiplaatsen - klimaatverandering - ambrosia - weeds - invasion - introduced species - allergies - public health - sensitivity - pollen allergy - sites - climatic change
    Is sensibilisatie voor ambrosiapollen een kruisreactie met de inheemse bijvoet, of zorgt de opkomst van de exoot wel degelijk voor een verlenging van het hooikoortsseizoen? Klinisch chemicus Cees Beijer van het Rijnland Ziekenhuis in Leiderdorp en het Diaconessenhuis in Leiden onderzocht de kruisreactiviteit van de allergenen. Conclusie: sensibilisatie voor specifieke allergenen van ambrosia kan ook in Nederland een probleem worden.
    Alien and invasive woody species in the dunes of the Wadden Sea Island of Vlieland: a remote sensing approach
    Hantson, W. ; Kooistra, L. ; Slim, P.A. - \ 2010
    Wageningen : Alterra (Alterra-report 2101) - 54
    struiken - invasie - cartografie - remote sensing - classificatie - prunus serotina - rosa rugosa - natuurbescherming - nederland - nederlandse waddeneilanden - shrubs - invasion - mapping - remote sensing - classification - prunus serotina - rosa rugosa - nature conservation - netherlands - dutch wadden islands
    In this study we mapped (alien) invasive shrubs for management and conservation purposes. On the study site, the Wadden Sea Island of Vlieland, they are a serious treat for the quality of the grey dune habitat. We developed a remote sensing approach that delivers detailed and standardized maps of (alien) shrub cover. Three classification methods are used: maximum likelihood (ML) classification of aerial photographs, maximum likelihood classification aerial photographs combined with vegetation heights derived from LIDAR data (ML+), and object-based shrub classification.
    On the risk of extinction of a wild plant species through spillover of a biological control agent: Analysis of an ecosystem compartment model.
    Chalak, M. ; Hemerik, L. ; Werf, W. van der; Ruijs, A. ; Ierland, E.C. van - \ 2010
    Ecological Modelling 221 (2010)16. - ISSN 0304-3800 - p. 1934 - 1943.
    agricultural landscapes - biocontrol - insect - weed - management - dispersal - habitats - invasion - prey
    Invasive plant species can be controlled by introducing natural enemies (insect herbivores) from their native range. However, such introduction entails the risk that the introduced herbivores attack indigenous plant species in the area of introduction. Here, we study the effect of spillover of a herbivore from a managed ecosystem compartment (agriculture) to a natural compartment (non-managed) and vice versa. In the natural compartment, an indigenous plant species is attacked by the introduced herbivores, whereas another indigenous plant species, which competes with the first, is not attacked. The combination of competition and herbivory may result in extinction of the attacked wild plant species. Using a modelling approach, we determine model parameters that characterize the risk of extinction for a wild plant species. Risk factors include: (1) a high attack rate of the herbivores on the wild non-target species, (2) niche overlap expressed as strong competition between the attacked non-target species and its competitor(s), and (3) factors favouring large spillover from the managed ecosystem compartment to the natural compartment; these include (3a) a high dispersal ability, and (3b) a moderate attack rate of the introduced herbivore on the target species, enabling large resident populations of the insect herbivore in the managed compartment. The analysis thus indicates that a high attack rate on the target species, which is a selection criterion for biocontrol agents with respect to their effectiveness, also mitigates risks resulting from spillover and non-target effects. While total eradication of an invasive plant species is not possible in the one-compartment-one-plant-one-herbivore system, natural enemy spillover from a natural to a managed compartment can make the invasive weed go extinct.
    Development and distribution of the non-indigenous Pacific oyster (Crassostrea gigas) in the Dutch Wadden Sea
    Fey-Hofstede, F.E. ; Dankers, N.M.J.A. ; Steenbergen, J. ; Goudswaard, P.C. - \ 2010
    Aquaculture International 18 (2010)1. - ISSN 0967-6120 - p. 45 - 59.
    Pacific oysters (Crassostrea gigas) were first observed in the Dutch Wadden Sea near Texel in 1983. The population increased slowly in the beginning but grew exponentially from the mid-1990s onwards, although now some stabilisation seems to be occurring. They occur on a variety of substrates such as mussel beds (Mytilus edulis), shell banks, dikes and poles. After initial settlement spat may fall on older individuals and congregate to dense clumps and subsequently form reefs. Individual Pacific oysters grow 3–4 cm long in their first year and 2–3 cm in their second year. Many mussel beds (Mytilus edulis) are slowly taken over by Pacific oysters, but there are also several reports of mussel spat settling on Pacific oyster reefs. This might in the end result in combined reefs. Successful Pacific oyster spat fall seems to be related to high summer temperatures, but also after mild summers much spat can be found on old (Pacific oyster) shells. Predation is of limited importance. Mortality factors are unknown, but every now and then unexplained mass mortality occurs. The gradual spread of the Pacific oyster in the Dutch Wadden Sea is documented in the first instance based on historical and anecdotal information. At the start of the more in-depth investigation in 2002, Pacific oysters of all size classes were already present near Texel. Near Ameland the development could be followed from the first observed settlement. On dense reefs each square metre may contain more than 500 adult Pacific oysters, weighing more than 100 kg per m² fresh weight
    Check title to add to marked list
    << previous | next >>

    Show 20 50 100 records per page

    Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.