212 research outputs found
Het Galgenwiel in de gemeente Loon op Zand
No full textThe author describes the vegetation, origin and history of the ‘Galgenwiel’, a lake near Loon op Zand (N.-Brabant)
UvA-DARE (Digital Academic Repository) Link to publication Citation for published version (APA)
No full textMicrobial dynamics and litter decomposition under a changed climate in a Dutch heathland van Meeteren, M.J.M.; Tietema, A.; van Loon, E.E.; Verstraten, J.M
Infochemical use in Brassica-insect interactions : a phenotypic manipulation approach to induced plant defences
No full textPlants have developed a range of strategies to defend themselves against herbivore attack. Defences can be constitutive, i.e. always present independent of attack, or induced, i.e. only elicited when the plant is under attack. In this thesis, I focused on induced chemical defence responses of plants and the response of associated insects to these phenotypic changes in plants. Herbivore attack is known to induce chemical defences in Brassicaceous plants. Using several elicitors and inhibitors of different steps of the signalling pathways underlying herbivore-induced plant responses, I studied how induced infochemicals affect interactions with associated insects. Jasmonic acid (JA) is a key plant hormone in the octadecanoid signalling pathway known to be involved in herbivore-induced plant defences. Application of JA can induce plant responses that are similar, although not identical, to herbivore feeding. Two specialist herbivores of Brassicaceous plants, the butterflies Pieris rapae and P. brassicae, preferred to oviposit on non-induced plants over JA-induced plants. Development of P. rapae caterpillars was shown to be reduced, suggesting that oviposition avoidance on JA-induced plants is adaptive. The levels of glucosinolates, secondary metabolites of Brassicaceous plants that are used by Pieris butterflies as oviposition stimulants, could not explain the observed oviposition preference of the butterflies. JA-induced changes in the plants also affected members of the third trophic level. Volatile emission of JA-induced plants attracted parasitoid wasps to the plants. Parasitoid attraction to JA-induced plants was shown to depend on dose and induction time. However, using JA to induce phenotypic changes had effects different from those induced by herbivores, both chemically and ecologically. Volatile emission of JA-induced and herbivore-induced plants differed; whereas JA-induced plants emitted larger amounts of volatiles, the parasitoids preferred herbivore-induced plants over JA-treated ones. Early events in plant defence responses, involved in attacker recognition, are damage-induced modulations of ion channel activities resulting in ion imbalances. The fungal elicitor alamethicin, an ion channel-forming peptide mixture, was used to mimic early steps in defence responses. Alamethicin treatment increased attractiveness of plants to parasitoid wasps. Although volatile emission of alamethicin-treated plants was much lower, they were equally attractive as JA-treated plants. This indicates that quality rather than quantity of induced plant volatile blends is important to parasitoids. Besides chemical elicitation of herbivore-induced responses, which is a widely applied approach, plant defence responses can also be chemically inhibited. This provides the opportunity to inhibit the rate of specific enzymatic steps in a signal-transduction pathway. Furthermore, visual cues associated with feeding damage can be present (and similar) in control- and inhibitor-treated plants. Phenidone is a compound that inhibits lipoxygenase, an enzyme catalyzing an early step in the octadecanoid pathway. Parasitoid attraction was reduced when the plants were treated with phenidone before infestation. Also herbivore oviposition preference was shown to be affected by inhibition of this signalling pathway. Herbivores can differ in their oviposition preferences. I studied two specialist herbivores with different oviposition preferences: Pieris brassicae avoids oviposition on herbivore-induced plants, whereas Plutella xylostella prefers to oviposit on Pieris-infested plants. I showed that these preferences have a chemical basis and are dependent on octadecanoid signalling, since treatment with the lipoxygenase inhibitor phenidone eliminated herbivore-induced oviposition avoidance or preference. Thus far, most of the studies on induced plant defences have been done with vegetative plants. However, since reproduction and defence are both processes that require energy and nutrients, this could result in a trade-off. Herbivore feeding on leaves, flowers or roots is known to affect pollinator visitation, but the mechanisms mediating this change have not been addressed. Effects of induction with JA on nectar secretion and pollinator visitation to flowers were investigated. JA-induced plants secreted less nectar, but the sugar concentrations did not change. Also visitation of honeybees and syrphid flies did not change upon JA induction. These results show the complexity of induced plant defence responses and the variety of behavioural responses of insects on different trophic levels. Combining the phenotypic manipulation approach to induced plant defences, as used in this thesis, with molecular genetic techniques and building on recent developments in plant biochemistry provides a promising way forward towards enhanced understanding of the intricate interactions between plants and insects. <br/
Final Report of the DAUFIN project
No full textDAUFIN = Data Assimulation within Unifying Framework for Improved river basiN modeling (EC 5th framework Project
Overland flow: interfacing models with measurements
No full textIndex words: overland flow, catchment scale, system identification, ensemble simulations.This study presents new techniques to identify scale-dependent overland flow models and use these for ensemble-based predictions. The techniques are developed on the basis of overland flow, rain, discharge, soil, vegetation and terrain observations that were collected over a three year period in two tropical catchments. The merits of the identification technique are its robustness with regard to unknown errors, the ability to adjust model resolution in response to data availability, and to interpret the entities of the identified model structures physically. Compared to a static regression model and a dynamic distributed model the predictive performance of the scale-dependent overland flow models is good, especially when using model ensembles. Further analysis of the scale-dependent models shows that rainfall largely determines overland flow when modelled at coarse resolutions, whereas soil moisture drives overland flow when defined at fine resolutions. Interestingly, the number of model parameters remains constant over the different resolutions. The use of the scale-dependent models for predictive purposes is demonstrated by applying Tikhonov regularization for recursive state as well as parameter estimation
Stacked space-time densities : a geovisualisation approach to explore dynamics of space use over time
Full text linkResearch presented in this paper is part of the collaboration under the COST (European Cooperation in Science and Technology) ICT Action IC0903, “Knowledge Discovery from Moving Objects (MOVE)” and facilitated by the Lorentz Center workshop on “Analysis and visualization of moving objects”(http://www.lorentzcenter.nl/lc/web/2011/453/info.php3?wsid=453)Recent developments and ubiquitous use of global positioning devices have revolutionised movement ecology. Scientists are able to collect increasingly larger movement datasets at increasingly smaller spatial and temporal resolutions. These data consist of trajectories in space and time, represented as time series of measured locations for each tagged animal. Such data are analysed and visualised using methods for estimation of home range or utilisation distribution, which are often based on 2D kernel density in geographic space. These methods have been developed for much sparser and smaller datasets obtained through very high frequency (VHF) radio telemetry. They focus on the spatial distribution of measurement locations and ignore time and sequentiality of measurements. We present an alternative geovisualisation method for spatio-temporal aggregation of trajectories of tagged animals: stacked space-time densities. The method was developed to visually portray temporal changes in animal use of space using a volumetric display in a space-time cube. We describe the algorithm for calculation of stacked densities using four different decay functions, normally used in space use studies: linear decay, bisquare decay, Gaussian decay and Brownian decay. We present a case study, where we visualise trajectories of lesser black backed gulls, collected over 30 days. We demonstrate how the method can be used to evaluate temporal site fidelity of each bird through identification of two different temporal movement patterns in the stacked density volume: spatio-temporal hot spots and spatial-only hot spots.Peer reviewe
Appropriate river basin modelling ta assess impact of climate change on river flooding
Full text linkHow good should a river basin model be to assess the impact of climate change on river flooding for a specific geographical area? The determination of such an appropriate model should reveal which physical processes should be incorporated and which data and mathematical process descriptions should beused at which spatial and temporal scales. It should be based on sensitivities and a right balance between uncertainties of inputs, parameters and processdescriptions resulting in an output uncertainty acceptable for the model user and feasible in view of data availability and computational possibilities. A procedure for determining an appropriate model is explained and applied to the above mentioned specific case. The results obtained with the appropriate model are compared with observations, results obtained with a simpler and a more complex model and uncertainties in the results.The model appropriateness procedur
Hydrologie symposium, georganiseerd door de KNAW, op 21 mei 2003 in het Trippenhuis te Amsterdam
No full textOm een samenhangende visie mbt hydrologie te ontwikkelen, heeft de KNAW de werkgroep voorstudie verkenning hydrologie ingesteld. Deze werkgroep organiseerde een symposium, om eerste resultaten van hun bevindingen te presenteren. Wellicht volgt er een strategische verkenning, zoals de KNAW dat ook gedaan heeft voor de aardwetenschappe
Hydrologie symposium, georganiseerd door de KNAW, op 21 mei 2003 in het Trippenhuis te Amsterdam
No full textOm een samenhangende visie mbt hydrologie te ontwikkelen, heeft de KNAW de werkgroep voorstudie verkenning hydrologie ingesteld. Deze werkgroep organiseerde een symposium, om eerste resultaten van hun bevindingen te presenteren. Wellicht volgt er een strategische verkenning, zoals de KNAW dat ook gedaan heeft voor de aardwetenschappe
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