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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Strengthening institutions or institutionalising weaknesses? : interactions between aid and institutions in Huíla Province, Angola
Serrano, M.M. - \ 2012
Wageningen University. Promotor(en): Thea Hilhorst. - [S.l.] : s.n. - ISBN 9789461731289 - 310
interventie - humanitaire hulp - ontwikkelingsprojecten - instellingen - plaatselijk bestuur - angola - afrika - interacties - intervention - humanitarian aid - development projects - institutions - local government - africa - interactions
This research analyses the interaction between aid interventions and local institutions through which people address needs during crisis. These include state and non- state institutions involved in social assistance and in the delivery of basic services such as healthcare. The study focuses on the case of Angola’s conflict, which lasted from independence in 1975 until 2002. It discusses aid policy and practice during the war and in the post-war context by examining various types of aid interventions and how they unfold on the ground. It shows that during the emergency, humanitarian practice largely ignored or bypassed local institutions. However, strengthening institutional capacity has become an explicit objective of post-conflict aid interventions. This thesis analyses the main types of institution-building interventions that have dominated Angola’s reconstruction period. It shows that these are strongly shaped by the legacy of relief practices on the legitimacy of local institutions, and on the functioning of the aid system. As a result, aid interventions rather than strengthening local institutions, often institutionalise their weaknesses.
Models to relate species to environment: a hierarchical statistical approac
Jamil, T. - \ 2012
Wageningen University. Promotor(en): Cajo ter Braak. - S.l. : s.n. - ISBN 9789461731395 - 146
statistiek - lineaire modellen - interacties - kenmerken - bayesiaanse theorie - plantenecologie - biostatistiek - statistics - linear models - interactions - traits - bayesian theory - plant ecology - biostatistics

In the last two decades, the interest of community ecologists in trait-based approaches has grown dramatically and these approaches have been increasingly applied to explain and predict response of species to environmental conditions. A variety of modelling techniques are available. The dominant technique is tocluster the species based on their functional traits and then summarize the response of the clusters to environmental change. In general, fitting explicit models to data is always more informative and powerful than more informal approaches. The central theme of the thesis is how to quantify the relation of traits with the environment using three data tables, data on species occurrence and abundance in sites, data on traits of species and data on the environmental characteristics of sites. In this thesis, we place the challenge of quantifying trait-environment relationships in the context of species distribution modelling, so in the context of species-environment relationships. We present a hierarchal statistical approach to species distribution modelling that efficiently utilize the trait information and that is able to automatically select the relevant traits and environmental characteristics. This model-based approach, coupled with recent statistical developments and increased computing power, opens up possibilities that were unimaginable before.

In the present study a hierarchical statistical approach is introduced for modeling and explaining species response along environmental gradients by species traits. The model is an extension of the generalized linear model with random terms that express the between-species variation in response to the environment. This so-called generalized linear mixed model (GLMM)is derived byintegrating a two-step procedure into one. As the basic GLMM we take the random intercept and random slope model. To introduce traits, the regression parameters (intercept and slope) are made linearly dependent on the species traits. As a consequence the trait-environment relationship is represented as an interaction term in the model. The method is illustrated using the famous Dune Meadow Data using Ellenberg indicator values as species traits.

Niche theory proclaims that species response to environmental gradients is nonlinear. Each species has preferred an environmental condition in which it can survive and reproduce optimally. Thus each species tends to be most abundant around a specific environmental optimum and the distribution of species along any environmental gradient is usually unimodal, with the maximum at some ecological optimum.For presence-absence data, the simplest unimodal (non-negative) species response curve is the Gaussian logistic response curve with three parameters that characterize the niche: optimum (niche centre), tolerance (niche width) and maximum (expected occurrence at the centre). Niches of species differ between species and species are assumed to be evolutionary adapted. It is difficult to fit the Gaussian logistic model with linear trait submodels for the parameters with the available (generalized) nonlinear mixed model software.

We develop the trait-modulated Gaussian logistic model in which the niche parameters are made linearly dependent on species traits. The model is fitted to data in the Bayesian frameworkusing OpenBUGS (Bayesian inference Using Gibbs Sampling).A Bayesian variable selection method is used to identify which species traits and environmental variables best explain the species data through this model. We extended the approach to find the best linear combination of environmental variables.

We explained why and when (generalized) linear mixed models can effectively analyse unimodal data and presented a graphical tool and statistical test to test for unimodality while fitting just a generalized linear mixed model without any squared or other polynomial term. A GLMM is, of course, a linear model. Despite this fact, it can be used to detect unimodality and to fit unimodal data, with the provision that the differences in niche widthsamongspecies are not too large. As graphical tool we suggested to plot the random site effects against the environmental variable. There is an indication for unimodality, when this graph shows a quadratic relationship. The efficacy of GLMM to analyse unimodal data is illustrated by comparing the GLMM approach with an explicit unimodal model approach on simulated data and real data that show unimodality.

When a system is described by a statistical model, model complexity leads to a very large computing time and poor estimation, especially if the number of predictors is large relative to the data size. As an alternative to and improvement over stepwise methods, shrinkage methods have been proposed. One of these is the Relevance vector machine (RVM). RVM assigns individual precisions to weights of predictors which are then estimated by maximizing the marginal likelihood (Type-II ML or empirical Bayes). We also investigated the selection properties of RVM both analytically and by experiments. We found that RVM is rather tolerant for predictors to stay in the model and concluded that RVM is not a real solution in high-dimensional data problems.

By further study the multi-trait and multi-environmental variablemodel selection method developed that used our previous study in a linear mixed model context. The method is called tiered forward selection. In the first tier, the random factors are selected, in the second, the fixed effects are selected and in the final tier non-significant terms are removed based on a modified Akaike information criterion. The linear mixed model with the tiered forward selection is compared with Type-II ML and existing methods for detecting trait-environment relationships that are not based on mixed models, namely the fourth corner method and the linear trait-environment method (LTE).

Hebben grauwe ganzen een negatief effect op weidevogels?
Kleijn, D. ; Hout, J.J. van der; Jansman, H.A.H. ; Kats, R.J.M. van; Knecht, E. ; Lammertsma, D.R. ; Muskens, G.J.D.M. ; Melman, T.C.P. - \ 2011
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2233) - 50
ganzen - weidevogels - biologische mededinging - interacties - populatiedichtheid - vegetatie - natuurbescherming - anser - nederland - geese - grassland birds - biological competition - interactions - population density - vegetation - nature conservation - netherlands
Dit tussenrapport beschrijft een deel van de werkzaamheden die in het kader van het onderzoeksproject ‘Populatiebeheer overzomerende (grauwe) ganzen’ (BO-02-013-005) in 2009 en 2010 hebben plaatsgevonden. Het aantal ganzen dat in Nederland broedt neemt de laatste decennia spectaculair toe. Onder natuurbeschermers is ongerustheid ontstaan dat ganzen een negatief effect hebben op weidevogels. Daarom worden sinds een aantal jaren in en om natuurreservaten aantal-regulerende maatregelen voor de Grauwe gans genomen. Dit rapport presenteert de resultaten van een studie die tot doel had vast te stellen of er een (negatieve) relatie bestaat tussen het voorkomen van overzomerende Grauwe ganzen en weidevogels. In negen gebieden waar ganzen en weidevogels in substantiële aantallen voorkwamen, is onderzocht of de dichtheid of populatietrends van ganzen en weidevogels met elkaar gerelateerd waren. Daarnaast is geanalyseerd hoe de ruimtelijke verdeling tussen ganzen en weidevogels zich gedurende het broedseizoen ontwikkelde: mijden ze elkaar of komen ze juist samen voor? Daarbij is onderscheid gemaakt tussen directe beïnvloeding (aanwezigheid van ganzen) en indirecte beïnvloeding (via de vegetatie).
Newcomers in plant communities : interactions with soil and climate change
Meisner, A. - \ 2011
Wageningen University. Promotor(en): Wim van der Putten, co-promotor(en): W. de Boer. - [S.l.] : S.n. - ISBN 9789085859826 - 136
plantengemeenschappen - invasieve soorten - stikstofkringloop - planten - klimaatverandering - bodem - geïntroduceerde soorten - stikstof - ecosystemen - interacties - plant communities - invasive species - nitrogen cycle - plants - climatic change - soil - introduced species - nitrogen - ecosystems - interactions
Shrubs in the cold : interactions between vegetation, permafrost and climate in Siberian tundra
Blok, D. - \ 2011
Wageningen University. Promotor(en): Frank Berendse, co-promotor(en): Monique Heijmans; Gabriela Schaepman. - [S.l.] : S.n. - ISBN 9789461730251 - 152
struiken - vegetatie - permafrost - kou - klimaat - interacties - toendra - arctische ecologie - plantenecologie - siberië - shrubs - vegetation - cold - climate - interactions - tundra - arctic ecology - plant ecology - siberia

The Arctic is experiencing strong increases in air temperature during the last decades. High-latitude tundra regions are very responsive to changes in temperature and may cause a shift in tundra vegetation composition towards greater dominance of deciduous shrubs. With increasing deciduous shrub cover, the surface albedo (proportion of sunlight that is reflected to the atmosphere) may be reduced and lead to air warming by trapping more solar radiation into the Arctic ecosystem. As a result of this warming, thawing of carbon-rich permafrost soils may increase and cause a large greenhouse gas flux to the atmosphere, thus contributing to global warming.

In my thesis I studied how climate influences shrub growth in the Siberian tundra and how climate-induced changes in shrub cover affect summer permafrost thaw and surface albedo. I investigated these interactions between climate, permafrost and Arctic shrub growth using a combination of shrub ring width analysis, field experiments and remote sensing techniques. I measured and compared growth ring widths with meteorological station data and observed that shrub growth is stimulated by higher summer air temperatures. By performing a shrub removal experiment, I demonstrated that a temperature-induced increase in shrub cover may reduce summer permafrost thaw. Shading by the shrub canopy reduced the transfer of energy to the soil. A denser shrub cover thus effectively reduces summer permafrost thaw, despite leading at the same time to a lower surface albedo. These results indicate it is important to incorporate feedbacks between shrub growth, climate and permafrost thaw in model predictions on the Arctic climate and stability of permafrost in a future warmer world.

Climate change induced range-expanding plants : aboveground and belowground interactions
Morriën, W.E. - \ 2011
Wageningen University. Promotor(en): Wim van der Putten. - [S.l.] : S.n. - ISBN 9789085859376 - 144
planten - geïntroduceerde soorten - klimaatverandering - bodemfauna - vrijlevende nematoden - bodembacteriën - rizosfeer - plaagresistentie - ziekteresistentie - herbivoren - interacties - plants - introduced species - climatic change - soil fauna - free living nematodes - soil bacteria - rhizosphere - pest resistance - disease resistance - herbivores - interactions

Burning of fossil fuels has raised the level of atmospheric carbon dioxide, which contributes to global climate warming. As a result the mean earth surface temperature has increased faster in the past decades than in the previous thousands of years before. This rapid climate warming together with habitat fragmentation and other land use changes puts a major pressure on many plants and animals. They should either adapt to the warmer climate conditions or disperse in order to keep up with their optimal climatic conditions. Range expansion brings new interactions within the ecosystem in the new range. This can lead to potential benefits, for example range shifting species that do not encounter natural enemies in the new range might become invasive. Although invasive species are a well-studied phenomenon, there is relatively little known about the general mechanisms of biological invasions under climate change. In this thesis I focus on plant species that expand range due to current climate warming. I examined how these range-expanding plants interact with aboveground herbivorous insects and - mostly - how they establish belowground interactions with components of the soil food web. I examined how these interactions in the new range may play a role in the successful establishment of climate change induced range-expanding plants in plant communities of the new range. The focus of my study was on riverine (riparian) areas along the great rivers in the Netherlands, which are well connected with southern Europe by the Rhine and Rhine-Danube canal.

In the first experiment we examined exotic plant exposure to aboveground and belowground enemies. We used plants that originated from Eurasia (intra-continental range expanders) and plants that originated from other continents (inter-continental range expanders). We compared these exotic plants with phylogenetically related natives. We grew the plants with and without non-coevolved polyphagous (generalist) herbivores, a locust Schistocerca gregaria and an aphid Myzus persicae. We also exposed all plants to a general soil community from the invaded range and compared their plant-soil feedback responses. Then I tested how individual plants responded to aboveground and belowground plant enemies and I compared this to their combined effects. I also tested whether the strength of aboveground control by generalist shoot-feeding insects was indicative of the strength of belowground control by plant-soil feedback.

In the next study I examined how the soil nematode community from the new range responds to exotic plant species compared to related native plants species. As a follow up, I determined the rhizosphere community composition of bacteria, fungi, arbuscular mycorrhizal fungi (AMF) and fusaria. All groups of microbes were analyzed qualitatively and the non-mycorrhizal fungal biomass and fusaria were also analyzed quantitatively. I tested the hypothesis that range-expanding plant species have a different rhizosphere microbial community composition than natives.

Finally, I compared the early establishment of range-expanding exotics and phylogenetically related plant species that are native in the invaded habitats. In a greenhouse I grew five range-expanding plant species and five related natives in sterilized and non-sterile inoculated soils from the new range, both alone and with a background community of plant species present in the invaded habitat. In the field, I grew the same plants species in artificially created sparse and dense plant communities. I tested whether range-expanding exotic plant species establish better under competition with native vegetation than phylogenetically related natives, because exotics may benefit from less negative interactions with the soil community compared to natives.

On the ecology and evolution of microorganisms associated with fungus-growing termites
Visser, A.A. - \ 2011
Wageningen University. Promotor(en): Rolf Hoekstra; Thomas Kuijper, co-promotor(en): Duur Aanen; Fons Debets. - S.l. : s.n. - ISBN 9789085859147 - 175
isoptera - schimmels - evolutie - symbiose - interacties - symbionten - ecologie - fungi - evolution - symbiosis - interactions - symbionts - ecology

Organisms living in symbiosis fascinate us with their adaptations to live in extreme proximity to, or even inside, a partner that may be from a completely different Class, Phylum or Kingdom. Combinations of organisms that live in mutualistic symbiosis seem very exceptional, but when studying any organism more closely one may find involvement in mutualistic symbiosis to be the rule rather than an exception. For example, most of the animals have microorganisms in their guts that help digestion, and many plants have fungi around their roots that aid in uptake of nutrients from the soil. Having complementary traits and reciprocally benefitting each other, cooperating organisms may evolve into extremely successful species.
CHAPTER 1 introduces the topic of this thesis: fungus-growing termites. Fungus-growing termites play a dominant role as ecosystem engineers in sub-Saharan Africa and South Asia. They change soil properties by their building and foraging activities, and are major players in decomposition of wood and dead vegetation. Though they are often regarded as a pest, termites can be very useful for people. Besides eating the termites and mushrooms that emerge from the termite mound, people use termite soil-engineering to improve the fertility of agricultural fields.
The termite and fungus live in obligate mutualistic symbiosis. Termites (Blattodea: Termitidae, subfamily Macrotermitinae) provide the fungus Termitomyces (Basidiomycota: Agaricales: Lyophyllaceae) with fragmented dead plant material and create a controlled environment perfect for the fungus, whereas Termitomyces decomposes the low-quality matter into a nutritious food source and produces mushroom primordia both of which are eaten by the termites.
The symbiosis exists in a world where other organisms are awaiting their chance to exploit the richness of the termite nests. Hence, one could expect to find other organisms in the nest, next to termites and Termitomyces. There is at least one fungus associated with fungus-growing termites that emerges very prominently after termites are no longer active: species of Xylaria (Ascomycota: Xylariales: Xylariaceae, subgenus Pseudoxylaria) are frequently overgrowing the fungus gardens of dead termite nests. What is the status of Pseudoxylaria in the fungus-growing termite symbiosis, does it play a role? How are the fungus-growing termite gardens kept free of weeds, parasites and pathogens? These questions form the foundation of this thesis on the ecology and evolution of microorganisms associated with fungus-growing termites, with particular focus on the role and interactions with associated Pseudoxylaria.
CHAPTER 2 investigates the specificity of Pseudoxylaria for fungus-growing termites. I hypothesize that specificity or selectivity for fungus-growing termites would mean that Pseudoxylaria is not present coincidentally as opportunist, but truly associated with fungus-growing termite symbiosis. Hundred and eight South-African fungus-growing termite nests were sampled for Pseudoxylaria, and it was found in most of the nests. Partial rDNA sequences of the obtained isolates were compared with those of Xylaria from the environment and isolates from other parts of the world. I found 16 different molecular types (‘species’) of Pseudoxylaria. They formed a separate group, showing that Pseudoxylaria specifically occurs in fungus-growing termite nests indeed. No specificity for the termite genus or species was found, implying that Pseudoxylaria may have specialised on the fungus garden substrate, rather than on the termite host or the mutualistic fungus Termitomyces.
CHAPTER 3 focuses on the role of Pseudoxylaria in the fungus-growing termite nest. Pseudoxylaria is inconspicuous in healthy termite nests and usually only occurs when termites are no longer present in the nest, or when pieces of fungus garden are incubated without termites in the lab. Therefore, it seems to be suppressed and an unwelcome nest inhabitant. I postulate that Pseudoxylaria is a benign stowaway that practices a sit-and-wait strategy to survive in the termite nest. First, Pseudoxylaria and Termitomyces were grown independently on different carbon sources; to test if they have a complementary diet preference, degrading complementary substrate components as had been suggested previously. The carbon source use of both fungi overlapped, implying that Pseudoxylaria is not a beneficial or benign symbiont. Second, the role of Pseudoxylaria in termite nests was inferred from interactions between mycelia of Pseudoxylaria, Termitomyces, and their free-living relatives. Both fungi were grown on the same plate, and also combinations with each other’s free-living relatives were tested. This revealed that Pseudoxylaria is not parasitizing Termitomyces. Furthermore, Pseudoxylaria grew relatively less than its free-living relatives when combined with Termitomyces. This result suggests that the symbiotic lifestyle adopted by Pseudoxylaria went together with adaptations that changed the interaction between both fungi, consistent with Pseudoxylaria being a stowaway.
CHAPTER 4 tests the hypothesis that termite workers play a crucial role in maintaining the fungus garden hygiene. The occurrence of microorganisms other than Termitomyces was monitored for pieces of fungus garden that were incubated with, without, or temporarily without termite workers. The effect that workers had on the fungus-comb hygiene, as well as observations on worker cleaning behaviour and their response to mycelium tissue of Pseudoxylaria and Termitomyces, show that termites play an important role in maintaining the fungus-garden hygiene indeed.
CHAPTER 5 explores the potential of Actinobacteria for a mutualistic role as defensive symbiont against Pseudoxylaria in the fungus-growing termite nest. Actinobacteria play a mutualistic role as defensive symbionts in many biological systems. It was unclear by which mechanism the termites suppress Pseudoxylaria. Thirty fungus-growing termite colonies from two geographically distant sites were sampled for Actinobacteria. Resulting isolates were characterized based on morphology and 16S rRNA sequences. Next, the obtained Actinobacteria were tested for their antibiotic effect on both Pseudoxylaria and Termitomyces.
This chapter describes the first discovery of an assembly of Actinobacteria occurring in fungus-growing termite nests. Actinobacteria were found throughout all sampled nests and materials, and in the phylogenetic tree their 16S rRNA sequences were interspersed with those of Actinobacteria from origins other than fungus-growing termites. The bioassays showed that many Actinobacteria inhibited both the substrate competitor Pseudoxylaria and the termite cultivar Termitomyces. The lack of specificity of the Actinobacteria for fungus-growing termites, and lack of specific defence against Pseudoxylaria, make it unlikely that Actinobacteria play a role as defensive symbionts in fungus-growing termites.
Final CHAPTER 6 reflects on the previous chapters, focussing on underlying mechanisms. What caused fungus-growing termites to survive for thirty million years already, and what makes them so successful that they dominate semi-arid ecosystems in sub-Saharan Africa and South Asia? How are conflicts of interest between symbiotic partners resolved? How does cooperation between termites and Termitomyces remain stable over evolutionary time scales? The roles of termites, Termitomyces, Pseudoxylaria, and other organisms in the fungus-growing termite nest are discussed more elaborately. In addition, the question to what extent certain aspects determine whether an organism behaves parasitically or mutualistically, and the question whether symbiont role affects the level of specificity between symbiotic partners, are examined. An analogy is drawn with human agriculture and directions for future research are given.
The chapter ends with main conclusions of this thesis. Fungus-growing termites are so successful in maintaining a Termitomyces monoculture that the means by which they accomplish this may be further studied for human agricultural interests. Pseudoxylaria species occur specifically in fungus-growing termite nests, where they are suppressed by termites while awaiting an opportunity to overgrow the fungus garden.

Bovengrondse-ondergrondse biodiversiteit: het effect van bodemroofmijten op tabakstrips : verslag trips-roofmijt experiment in 2009
Belder, E. den; Elderson, J. - \ 2010
Wageningen : Plant Research International (Nota / Plant Research International 663) - 18
phaseolus vulgaris - insectenplagen - thrips tabaci - roofmijten - macrocheles - mulchen - bodembescherming - interacties - landbouwkundig onderzoek - methodologie - gewasbescherming - preien - boven- en ondergrondse interacties - insect pests - predatory mites - mulching - soil conservation - interactions - agricultural research - methodology - plant protection - leeks - aboveground belowground interactions
Het doel van dit onderdeel bovengrondse-ondergrondse biodiversiteitsproject is vast te stellen óf en in welke mate er interactie plaats vindt tussen ondergrondse roofmijtenpopulaties en mulchen met stro en de bovengrondse plaag tabakstrips.
The role of non-specific interactions in nuclear organization
Nooijer, S. de - \ 2010
Wageningen University. Promotor(en): Ton Bisseling; Bela Mulder, co-promotor(en): Joan Wellink. - [S.l. : S.n. - ISBN 9789085857921 - 117
arabidopsis - celkernen - chromosomen - genomen - chromatine - interacties - cytogenetica - moleculaire biologie - nuclei - chromosomes - genomes - chromatin - interactions - cytogenetics - molecular biology
The most important organelle in eukaryotic cells is the nucleus. Many processes occurring within the nucleus depend on spatial organization of the nucleus. The spatial organization of the eukaryotic nucleus derives from interactions between its constituents. Both specific interactions, for instance the interactions between a DNA binding protein and its target DNA sequence, and non-specific interactions occur. Non-specific interactions stem from physical encounters between molecules or particles, which can favour particular organizations, i.e. the ones that have the lowest entropy. The role of non-specific interactions in nuclear organization is so far not extensively studied. Here, we investigate the effects of non-specific interactions on nuclear organization, using molecular dynamics simulation techniques. Chromatin folding models can be implemented in these simulations as chains of monomers, which can form loops, branches or networks. Through a comparison of simulation results with experimental data, these models can be verified or falsified.

We used MD simulations of models for Arabidopsis chromatin organisation to show that non-specific interactions can explain the in vivo localisation of nucleoli and chromocenters. Also, we quantitatively demonstrate that chromatin looping contributes to the formation of chromosome territories. Focussing on the forces driving nuclear organization in the rosette model, we derive effective interaction potentials for rosette-loop interactions. These potentials are weak, but nevertheless drive chromocenters and nucleoli to the nuclear periphery and away from each other.

We also study the folding of a single human chromosome within its territory. The results of our simulations are analysed using a virtual confocal microscope algorithm which has the same limitations as a real confocal microscope. Thus we show that chromatin looping increases the volume occupied by a 10Mbp chromosomal sub-domain, but decreases the overlap between two neighbouring sub-domains. Our results furthermore show that the measured amount of overlap is highly dependent on both spatial resolution and signal detection threshold of the confocal microscope, and that in typical fluorescence in situ hybridisation experiments these two factors contribute to a gross underestimation of the real overlap. Zooming out to whole nucleus organization, we show that an interplay between interactions between heterochromatin and nuclear lamina generates a wide variety of nuclear organizations, with those occurring in nature requiring a fine balance between both interactions.

The differences between chromosome folding in human and Arabidopsis can be explained through differences in genomic structure and chromosome loop formation, but the underlying mechanisms and forces that organize the nucleus are very similar. The insight how specific and non-specific forces cooperate to shape nuclear organization, is therefore the most important contribution of this thesis to scientific progress.

Opponents and supporters of water policy change in the Netherlands and Hungary
Werners, S.E. ; Warner, J.F. ; Roth, D. - \ 2010
Water Alternatives 3 (2010)1. - ISSN 1965-0175 - p. 26 - 47.
waterbeleid - verandering - individuen - interacties - communicatie - hongarije - nederland - invloeden - water policy - change - individuals - interactions - communication - hungary - netherlands - influences
This paper looks at the role of individuals and the strategies that they use to bring about or oppose major policy change. Current analysis of the role that individuals or small collectives play in periods of major policy change has focussed on strategies that reinforce change and on the supporters of change. This paper adds the perspective of opponents, and asks whether they use similar strategies as those identified for supporters. Five strategies are explored: developing new ideas, building coalitions to sell ideas, using windows of opportunity, playing multiple venues and orchestrating networks. Using empirical evidence from Dutch and Hungarian water policy change, we discuss whether individuals pursued these strategies to support or oppose major policy change. Our analysis showed the significance of recognition of a new policy concept at an abstract level by responsible government actors, as well as their engagement with a credible regional coalition that can contextualise and advocate the concept regionally. The strategies of supporters were also used by opponents of water policy change. Opposition was inherent to policy change, and whether or not government actors sought to engage with opponents influenced the realisation of water policy change.
Evaluatie Opvangbeleid 2005-2008 overwinterende ganzen en smienten. Deelrapport 10. Hebben overwinterende ganzen invloed op de weidevogelstand?
Kleijn, D. ; Winden, E. van; Goedhart, P.W. ; Teunissen, W. - \ 2009
Wageningen : Alterra (Alterra-rapport 1771) - 43
ganzen - biologische mededinging - interacties - populatiedynamica - ecologische verstoring - overwintering - nederland - weidevogels - geese - biological competition - interactions - population dynamics - ecological disturbance - netherlands - grassland birds
Dit rapport richt zich op de vraag of de sterk toegenomen dichtheden ganzen in bepaalde gebieden mede verantwoordelijk kunnen zijn voor de achteruitgang van de weidevogels ter plekke. Gebruik makend van data verzameld in de periode 1990-2005 in het kader van het weidevogelmeetnet en de watervogeltellingen in ganzentelgebieden werd onderzocht in hoeverre gebieden met hoge dichtheden ganzen overlappen met gebieden met hoge dichtheden weidevogels. De effecten van hoge dichtheden overwinterende ganzen op in Nederland broedende weidevogels lijken verwaarloosbaar of positief. Resultaten van onderzoek van SOVON en Alterra
Modelling habitat preference and estimating the spatial distribution of Australian Sea Lions (Neophoca cinerea); "A first exploration "
Aarts, G.M. ; Brasseur, S.M.J.M. - \ 2008
Texel : IMARES (Report / Wageningen IMARES C107/08) - 18
neophoca cinerea - ruimtelijke verdeling - populatie-ecologie - telemetrie - mitigatie - interacties - visserij - ruimtelijke ecologie - spatial distribution - population ecology - telemetry - mitigation - interactions - fisheries - spatial ecology
Managing the Australian sea lion (Neophoca cinerea) population and mitigating its interactions with commercial fisheries, requires an understanding of their spatial distribution and habitat preference at sea. Numerous wildlife telemetry devices have been attached to individual seals from different colonies, providing a detailed insight into there movement and activities. However, as data are only available from some individuals from 16 of 40 colonies in South Australia, these data represents only a small proportion of the population. Moreover, some colonies are poorly represented. To estimate the spatial distribution of the entire South Australian population, one can first investigate why individuals visit certain places and use this information to predict the spatial distribution for other regions lacking data. In this study we fit Generalized Additive Mixed Models (GAMMs) to wildlife telemetry data collected from adult female Australian sea lions to investigate the species’ habitat preference for the variables distance to the colony, depth and slope. The results show that in general they have a higher preference for shallow areas, places close to the colony and a steep slope, but they also display large individual variability. Preference for these variables does not seem to differ between individuals of different sizes. In some of the most western colonies, some individuals seem to spend more time further away from the colony, but apart from this, there is no apparent effect of the longitudinal capture position on preference. The predicted spatial distribution is largely driven by the distance from the departure colony and the actual distribution of individuals among the different colonies. Although depth and slope does seem to effect their distribution to some extent, the most important variables that explain fine-scale foraging activities at-sea are probably missing. Future studies using GPS transmitters attached to animals, that yield high resolution locations and more detailed environmental data, in combination with the analytical technique presented here, should provide more insight there foraging decisions. This should eventually also improve the spatial prediction of the population as a whole.
Plants on the move: plant-soil interactions in poleward shifting plant species
Grunsven, R.H.A. van - \ 2008
Wageningen University. Promotor(en): Frank Berendse; Wim van der Putten, co-promotor(en): Elmar Veenendaal. - [S.l.] : S.n. - ISBN 9789085852513 - 140
planten - plantenecologie - plantensuccessie - invasies - soorten - bodem - interacties - rizosfeer - bodemflora - bodemfauna - klimaatverandering - bodem-plant relaties - plants - plant ecology - plant succession - invasions - species - soil - interactions - rhizosphere - soil flora - soil fauna - climatic change - soil plant relationships
As a result of recent global climate change, areas that have previously been climatically unsuitable for species have now become suitable new habitats. Many plant-species are expanding their range polewards, colonizing these newly available areas. If these species are able to expand their range faster than their natural enemies they can become released from these limiting factors. A similar mechanism has been reported for invasive plant species, introduced into foreign continent, which are often found to be released from natural enemies.
An example of an invasive plant species that is introduced into a foreing contintinent is Carpobrotus edulis. This species was found to be negatively affected by the soil community collected in the native range, while the soil communities from the invaded range did not have an effect on plant performance compared to a sterilized control. I hypothesized that a similar reduction of the negative effects of the soil community can occur when plant species shift their range. This hypothesis was tested in a greenhouse experiment. I compared plant-soil feedbacks of three plant species that have recently expanded their range into The Netherlands, with three related native species. The non-native species experienced a significantly less negative effect of plant-soil feedback than the native plant species.
Concurrently with these range shifts local climate is changing and this might affect plant-soil feedback as well. In order to test this plant-soil feedbacks of six range expanding and six related native species were compared at two temperatures, 20°C and 25°C daytime temperature. While again native species showed a more negative plant-soil feedback than the non-native species, temperature did not affect the strength or direction of plant-soil feedback.
Besides pair wise comparisons between native and non-native species in the invaded range, comparisons between the native and non-native range of a range expanding plant can be used to test for effects of range shifts on plant-soil interactions. Rhizosphere soil was collected from populations of Tragopogon dubius in both the native and the recently colonized range. The soil communities from the native range had a more negative effect on plant performance than the soil communities from the invaded range as compared to sterilized controls. T. pratensis, which is native to the entire studied range, did not show this pattern.
As plant-soil interactions are the net effect of many positive and negative factors the less negative effect of plant-soil feedback can be either a result of more positive or less negative effects of the soil community. One of the mutualistic groups of organisms, the arbuscular mycorrhizal fungi (AMF) are known to be a major factor contributing to ecosystem functioning and to the maintenance of plant biodiversity and the most important soil-borne mutualists for many plants. I therefore focus on this group of soil organisms. I compared the association of T.dubius with AMF in the new part of its range with T. pratensis native to this area. Three measures for plant-fungal affinity were compared between these two plant species; the density of AMF propagules able to colonize the plant, the percentage of root length colonized by arbuscular mycorrhiza, and the composition of the resulting AMF community in the roots. This was done for four replicate soil inocula from different sites in The Netherlands. The two plant species did not differ in any of the tested factors. As there are no differences in the association with the most important mutualist the observed differences in plant-soil interaction are likely an effect of release from negative components in the soil community, e.g. soil pathogens, but further studies are needed to test this.
Alterations in biotic interactions, through climate change and range shifts, such as a release of soil-borne natural enemies, can have significant effects on the performance of plants. Predictions of future ranges and impact of range expanding plant species on invaded ecosystems can therefore not be accurately made without a thorough understanding of its biotic interactions and the way these interactions are changed by the range shifts.

A differential role for corticosteroid receptors in neuroendocrine-immune interactions in carp (Cyprinus carpio L.)
Stolte, H.H. - \ 2008
Wageningen University. Promotor(en): Huub Savelkoul; G. Flik, co-promotor(en): Lidy van Kemenade. - [S.l.] : S.n. - ISBN 9789085851998 - 231
karper - corticoïden - hormoonreceptoren - immunologie - immuniteit - immuniteitsreactie - interacties - stress - cytokinen - visteelt - neuroendocrinologie - carp - corticoids - hormone receptors - immunology - immunity - immune response - interactions - cytokines - fish culture - neuroendocrinology
In this thesis we investigated the involvement of the receptors for the stress hormone cortisol in stress and immune regulation. We set out to characterise the pro-inflammatory cytokine interferon gamma (IFN-γ). Furthermore, we used a genome wide screen (microarray) to search for additional genes that might be involved in regulation of the stress or the immune response.

In teleostean fishes cortisol can be bound by different receptors encoded by at least three different genes. An ancestral corticosteroid receptor (AncCR) is assumed to have been an effective receptor for cortisol in the ancestors of fishes. An early genomic duplication in the fish lineage, over 450 million years ago, led to separate glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) genes, both of which retained the ability to bind cortisol. A second major genomic duplication event took place only in teleostean fishes (not in other vertebrates), and gave rise to duplicate GR genes (GR1 and GR2). Even more variants developed as a result of alternative splicing of the GR1 gene which introduces a nine amino acid insert in the DNA-binding domain of GR1a, GR1b does not have this insert.

To investigate how one ligand can regulate many and very diverse functions using multiple receptors, we describe the expression of GR1 (a and b), GR2 and MR and their sensitivity for cortisol in chapters 3 and 4. The three receptors are expressed in tissues that make up the neuroendocrine stress-axis (brain, hypothalamus and pituitary) and in cells that produce corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH). Decreased mRNA expression in brain after prolonged stress suggests an involvement in regulation of hypothalamo-pituitary-interrenal (HPI)-axis activity. In cells of the immune system MR expression is very low compared to GR expression and GR2 is preferentially expressed in lymphocytes. Transactivation assays shows that GR1 is a relatively ‘insensitive’ or ‘stress’ receptor, which can only become activated at stress levels of, whereas GR2 is a ‘sensitive’ receptor that will already be activated at basal levels of cortisol such as occur in non-stressed fish. MR sensitivity for cortisol is intermediate. We predict by tertiary protein modelling and confirmed by transfection assays, that the transactivation capacity of both splice variants (GR1a and GR1b) is similar. Based on the very low expression level in immune cells and the moderate transactivation capacity of MR we concluded that GRs rather then the MR primarily convey stress signals to the immune system. Next, we determined the expression profile of the duplicated GR genes in the immune system in chapters 4 and 5 to investigate the regulation of stress-induced immune modulation. Simultaneously we investigated the expression profile of (among others) heat shock protein 70 (Hsp70). This protein is required for binding of cortisol to the GR, but also has intrinsic immune modulatory functions, as it was shown to downregulate LPS-induced pro-inflammatory cytokine expression in vitro and in vivo. In head kidney phagocytes we found that only physiological stress levels of cortisol could reduce LPS-induced expression of pro-inflammatory cytokines, a response that appears mediated by the ‘stress’ receptor GR1. Moreover, we found that Hsp70 and GR1 (a and b) expression is increased after an immune stimulus in vitro and in vivo, whereas 24 hr restraint stress or 100nM cortisol-treatment hardly increases Hsp70 and GR1 expression levels. This suggests that an immune stimulus rather than increased cortisol levels increases the sensitivity for glucocorticoid regulation and thereby of the cytokine profiles in immune cells.

To find additional genes involved in bidirectional neuroendocrine-immune communication we applied a genome wide screen of 9000 randomly picked cDNA clones. This has the advantage of an unprejudiced overview of regulated genes, but the sensitivity of the technique is limited. In chapter 6 we describe a microarray experiment in which we compared mild acute stress, to prolonged severe immune stimulation. We show that an immune response after parasite infection appears tightly regulated and comparable between individuals, whereas a mild acute stressor allows for more variable gene expression profiles. We found LOC406744 of the DUF727 protein family and nephrosin as new interesting candidate genes that may be involved in neuroendocrine-immune communication.

The key pro-inflammatory cytokine IFN-γ, which is hypothesised to affect neurotransmitter and hormone release, had not been investigated in carp. In chapter 7 we show that carp have duplicate IFN-γ genes that are expressed in immune cells. IFN-γ-2 shows structural and functional characteristics simlar to those in other vertebrate IFN-γ genes and appears to be involved in T-lymphocyte function, whereas IFN-γ-1 is expressed in stimulated B-lymphocytes. Currently recombinant proteins are being produced which will enable us to further elucidate the role of both IFN-γ gene products in the immune system as well as in mediating the neuroendocrine stress response.

Interestingly, as explained in chapter 8, both the glucocorticoid receptor and the IFN-γ genes are duplicated. The duplication-degeneration-complementation (DCC) model has been proposed as an explanation for the high retention of duplicate genes in fishes. The hypothesis assumes that following gene duplication, the two gene copies degenerate over time by random mutation to perform complementary functions that jointly match that of the single ancestral gene, termed ‘subfunctionalisation’. Indeed it appears that the duplicate GR genes have divided the general and ‘stress-related’ functions, reflected by their different sensitivity for cortisol. The duplicate IFN-γ genes appear to have divided B- and T-lymphocyte functions as targets suggested by their gene expression profiles upon selective stimulation.

An important conclusion of this thesis is that duplicated glucocorticoid receptors and heat shock proteins are an integral part of the immune system. Immune stimuli rather than increased cortisol levels control GR and Hsp70 expression in immune cells. The differentially regulated expression of GR genes is at the basis of a balanced pro- and anti-inflammatory
cytokine profile, immune cell viability and thus at the basis of the success of the fishes. This thesis illustrates the importance of extensive and effective bidirectional communication between the neuroendocrine and immune systems, which are at the basis of the successful evolution of the vertebrates.
Gewasbescherming van opkomst tot oogst in de gesloten productie
Janssen, A. ; Maanen, R. van; Messelink, G.J. ; Sabelis, M.W. - \ 2008
Gewasbescherming 39 (2008)Suppl.. - ISSN 0166-6495 - p. 17 - 17.
biologische bestrijding - kassen - voedselwebben - voedselketens - interacties - analytische methoden - risicoschatting - glastuinbouw - agro-ecosystemen - plant-herbivoor relaties - insect-plant relaties - biological control - greenhouses - food webs - food chains - interactions - analytical methods - risk assessment - greenhouse horticulture - agroecosystems - plant-herbivore interactions - insect plant relations
The essence of plants
Bouwmeester, H.J. - \ 2008
Wageningen : Wageningen UR - 24
planten - plantensamenstelling - plantenfysiologie - planteninteractie - interacties - plants - plant composition - plant physiology - plant interaction - interactions
Bladproblemen bij hoge daglichtsom en lage EC - Belichtings- en bemestingsonderzoek verschaft benodigde basiskennis (interview met Nieves García en Mary Warmenhoven)
Arkesteijn, M. ; Garcia Victoria, N. ; Warmenhoven, M.G. - \ 2008
Onder Glas 5 (2008)4. - p. 40 - 41.
kassen - teelt onder bescherming - cultuurmethoden - bromelia's als sierplanten - belichting - lichtsterkte - rassen (planten) - plantenvoeding - interacties - gewaskwaliteit - proeven op proefstations - glastuinbouw - bemesting - groenten - potplanten - greenhouses - protected cultivation - cultural methods - ornamental bromeliads - illumination - light intensity - varieties - plant nutrition - interactions - crop quality - station tests - greenhouse horticulture - fertilizer application - vegetables - pot plants
Bij WUR-Glastuinbouw in Bleiswijk vindt een onderzoek plaats naar de effecten van belichtingsintensiteit en -duur en de interacties met voeding bij drie verschillende bromeliarassen. Eind april 2008 is de teeltproef afgerond. De plantgrootte en plantkwaliteit laten een duidelijke interactie zien tussen voeding, lichtintensiteit en belichtingsduur. De ontwikkeling tijdens de bloei lijkt op dezelfde wijze te reageren als de vegetatieve groei
Onkruiden en insecten
Booij, C.J.H. ; Weide, R.Y. van der - \ 2008
onkruidbestrijding - onkruiden - insecten - interacties - waardplanten - onkruidkunde - weed control - weeds - insects - interactions - host plants - weed science
Onkruiden spelen een belangrijke rol in de ecologie van zowel plaaginsecten als hun natuurlijke vijanden. Daardoor kan onkruidbeheersing zowel positieve als negatieven effecten hebben op insectenplagen. Daarom is een verkenning gedaan naar alle mogelijke interacties tussen onkruiden en insecten
Researching with farmers : a study of KARI participatory research practices in context
Kamau, G. - \ 2007
Wageningen University. Promotor(en): Paul Richards, co-promotor(en): R. Karega; Paul Hebinck; Conny Almekinders. - [S.l.] : S.n. - ISBN 9789085047605 - 248
ontwikkelingsstudies - boeren - landbouwkundig onderzoek - onderzoeksinstituten - onderzoeksprojecten - participatie - interacties - sociale interactie - onderzoekers - onderzoeksbeleid - afrika ten zuiden van de sahara - kenya - participatieve methoden - landbouwvoorlichting - development studies - farmers - agricultural research - research institutes - research projects - participation - interactions - social interaction - research workers - research policy - africa south of sahara - participation methods - agricultural extension
Participatory research was introduced into the Kenyan Agricultural research institute to facilitate a farmer driven research process. The present research analysed the historical and current contexts and practices which could have led to partial achievement of the intended objective. Studies conducted on selected farmer research groups, farmer self organized groups, farmer partnerships and school groups’ provided insights for an enhanced research practice. Analysis of the institute’s history revealed continuities and discontinuities in spatial outlay and mandates, institutional culture and operational policies. The ambivalence in commercial and subsistence focus, diverse collaborators’ and donors’ agenda besides researchers’ disciplinary bias and professional ambitions were shown to influence research implementation Overlooking of farmers’ perspectives was shown to render existent structures like joint planning and evaluation committees mostly symbolic. Farmer flexibility in response to emergent realities was illustrated by the dynamic farmers’ technical and social innovations while harnessing of synergy through mutual interaction was illustrated by partnerships and the school groups’. In conclusion, it is argued that existent structures to enhance mutual interaction ought to be re-juvenated through enabling strategies at various levels. This would enhance utilization of innovations by farmers and incorporation of farmer perspectives by the researchers. Areas proposed for further research include how to create functional partnerships, communities of practice and mechanisms to change researchers’ views of farmers perspectives aimed at a research process with capacity to respond to dynamic contextual changes.
Ondergrondse communicatie: de driehoeksrelatie gastheerplant, parasitaire plant en mycorrhiza-schimmel
Kohlen, W. ; Bouwmeester, H.J. - \ 2007
Gewasbescherming 38 (2007)4. - ISSN 0166-6495 - p. 145 - 149.
detectie - zintuiglijke waarneming - waardplanten - parasitaire planten - striga - mycorrhizaschimmels - scrophulariales - interacties - plantenvoeding - wortels - bodemflora - symbiose - detection - organolepsis - host plants - parasitic plants - mycorrhizal fungi - interactions - plant nutrition - roots - soil flora - symbiosis
De ontdekking van strigolactonen laat zien dat planten op grote schaal ondergronds communiceren. Planten produceren die strigolactonen niet om te communiceren met de parasitaire planten, maar met de mycorrhiza schimmels en mogelijk ook andere voor de plant nuttige organismen. De parasitaire planten hebben een mechanisme ontwikkeld om deze communicatie af te luisteren en te gebruiken in hun eigen voordeel. Om het grote belang van deze stoffen verder te onderzoeken heeft Harro Bouwmeester begin 2006 van NWO een Vici-fellowship ontvangen ter waarde van 1.2 miljoen euro. Met een onderzoeksgroep, waartoe ook auteur Wouter Kohlen behoort, probeert hij de genen in kaart te brengen die zijn betrokken bij de productie van strigolactonen en inzicht te krijgen in hoe ze gereguleerd worden. Ook wil het team weten hoe de strigolactonen worden waargenomen door de parasitaire planten en hoe deze stoffen de interactie tussen de gastheer en beide bezoekers - parasitaire planten en mycorrhiza schimmels - reguleren. De bedoeling is dat het onderzoek niet alleen het begrip zal verbeteren van hoe gastheren communiceren met mycorrhiza schimmels en parasitaire planten, maar ook zal bijdragen aan het verminderen van een reusachtig probleem in Afrika, waar in vele landen Striga de oorzaak is van catastrofale oogstverliezen
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