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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Nature-based innovation systems
Jagt, Alexander P.N. van der; Raven, Rob ; Dorst, Hade ; Runhaar, Hens - \ 2019
Environmental Innovation and Societal Transitions (2019). - ISSN 2210-4224
Environmental governance - Geography of transitions - Nature-based solutions - Sustainability transitions - Technological innovation systems - Urban development

Transitions literature regards technologies as critical components in shifting systems towards sustainability, which has informed the development of the technology-oriented Technological Innovation System (TIS) framework. The emerging discourse on nature-based solutions (NBS) – multifunctional nature-integrated spatial planning and design innovations – raises the question to what extent TIS can account for the development and diffusion of NBS. Following a literature review, we present the Nature-Based Innovation System (NBIS) framework delineating critical factors for urban nature-based innovation. We find both commonalities and differences between TIS and NBIS, suggesting that the roles of place-based dynamics, agency and governance structure are more central to nature-based innovation, and market formation is more central to technological innovation. This has implications for the study of sustainability transitions, which has likely underplayed the potential of innovations at the nexus of socio-technical and socio-ecological systems. Future research is needed to refine the NBIS framework, for example by studying evolutionary developmental trajectories.

Broeders mijden de publiciteit
Jong, I.C. de - \ 2019
Urban greening through nature-based solutions – Key characteristics of an emerging concept
Dorst, Hade ; Jagt, Alexander van der; Raven, Rob ; Runhaar, Hens - \ 2019
Sustainable Cities and Society 49 (2019). - ISSN 2210-6707
Ecosystem-based adaptation - Environmental governance - Green infrastructure - Multifunctionality - Performance-based planning - Sustainable cities

As a result of urbanisation and climate change, many cities experience the necessity of efficient and sustainable land use. Nature-Based Solutions (NBS)are interventions that address social, economic and environmental sustainability issues simultaneously, thereby presenting a multifunctional, solution-oriented approach to increasing urban sustainability. As elements of the emerging NBS concept resemble related, existing approaches to urban greening, this review assesses the implications of this concept for discourse and practice in urban greening. The paper identifies key NBS principles and compares them with those of Ecosystem-Based Adaptation (EBA)and Green Infrastructure (GI). Key differences emerge: the NBS concept incorporates a broader array of interventions and a broader range of perspectives on what qualifies as ‘nature-based’, and it is most explicitly oriented towards providing solutions to complex challenges. NBS implementation could therefore benefit from a more performance-based planning approach; a flexible approach to urban planning which accommodates the integration of multiple land uses and considers urban complexity. We conclude that the NBS concept has potential to unite currently segregated bodies of knowledge generated as part of related approaches to urban greening, and can enable researchers and policymakers to more explicitly discuss the role of nature in addressing a broad range of sustainability challenges.

Warmer and browner waters decrease fish biomass production
Dorst, Renee M. Van; Gårdmark, Anna ; Svanbäck, Richard ; Beier, Ulrika ; Weyhenmeyer, Gesa A. ; Huss, Magnus - \ 2019
Global Change Biology 25 (2019)4. - ISSN 1354-1013 - p. 1395 - 1408.
biomass production - browning - Climate change - Eurasian perch - fish - individual body grwoth - lakes - length distribution - ontogeny - warming
Climate change studies have long focused on effects of increasing temperatures,
often without considering other simultaneously occurring environmental changes, such as browning of waters. Resolving how the combination of warming and browning of aquatic ecosystems affects fish biomass production is essential for future ecosystem functioning, fisheries, and food security. In this study, we analyzed individual‐ and population‐level fish data from 52 temperate and boreal lakes in Northern Europe, covering large gradients in water temperature and color (absorbance, 420 nm). We show that fish (Eurasian perch, Perca fluviatilis) biomass production decreased with both high water temperatures and brown water color, being lowest in warm and brown lakes. However, while both high temperature and brown water decreased fish biomass production, the mechanisms behind the decrease differed: temperature affected the fish biomass production mainly through a decrease in population standing stock biomass, and through shifts in size‐ and age‐distributions toward a higher proportion of young and small individuals in warm lakes; brown water color, on the other hand, mainly influenced fish biomass production through negative effects on individual body growth and length‐at‐ age. In addition to these
findings, we observed that the effects of temperature and brown water color on
individual‐level processes varied over ontogeny. Body growth only responded positively to higher temperatures among young perch, and brown water color had a stronger negative effect on body growth of old than on young individuals. Thus, to better understand and predict future fish biomass production, it is necessary to integrate both individual‐ and population‐level responses and to acknowledge within species variation. Our results suggest that global climate change, leading to browner and warmer waters, may negatively affect fish biomass production, and this effect may be stronger than caused by increased temperature or water color alone
African elephant in a cleft stick : choosing between starving or dying from thirst in arid savanna
Wato, Yussuf - \ 2016
Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Ignas Heitkonig; Frank van Langevelde. - Wageningen : Wageningen University - ISBN 9789463430005 - 126
loxodonta africana - starvation - thirst - savannas - arid zones - animal ecology - mortality - drought - loxodonta africana - uithongering - dorst - savannen - aride klimaatzones - dierecologie - mortaliteit - droogte

Elephant population studies have become important especially because of the long standing perception that high elephant densities have negative impact on vegetation and other wildlife species. Thus, in areas of high elephant density, managers attempt to re-distribute them or keep their numbers low through provision of water, translocation or culling. These approaches are thought to keep the population within the limits that can be sustained by the ecosystem, termed “the ecological carrying capacity”, a management option hinged on equilibrium theory. Equilibrium systems are considered stable, with resources and the animals that depend on them being at balance with each other. This stability is rarely the case in tropical savannas where the rule appears to be “a flux of nature” rather than “a balance of nature”.

Tropical savannas, where over half of the African elephant live, are prone to constant environmental fluctuations, especially prolonged droughts, and hence there is a growing understanding that populations of wildlife species and their communities are rarely at equilibrium. Therefore, it is critical to understand how the constant environmental flux in this system affects wildlife populations and the implication for their management. In this thesis, the central focus is to investigate the role of drought occurrences on elephant population dynamics in tropical savannas. To address this question, it is important to have a good understanding of the historical changes of elephant population in relation to drought events and the ecology of elephant in semi-arid savannas - their distribution and density, their movements and behaviour. For the historical data, I analysed the best existing long-term data in Africa of wild elephant population that has been consistently monitored for over 40 years where life histories of over 3000 wild individual elephant are known, at Amboseli National Park in Kenya. In addition, I also analysed geo-referenced elephant mortality data collected daily for 10 years from Tsavo Conservation Area. Further, I analysed 2 years data from 8 GPS collared African elephant to investigate their movement response to seasonal water and forage distribution in Tsavo Ecosystem.

First, I investigated the temporal effects of drought duration (number of consecutive dry months) and intensity (amount of rainfall) on elephant population structure in Amboseli National Park, Kenya. The result corroborates findings from past studies that calves (<2years) are more susceptible to drought caused mortality and the risk of dying decreased with age. A new finding in this study reveals that the effect of drought induced mortality for the adult elephant is sex and age dependent, with males older than 25 years being less likely to die as compared to females of the same age. This new result is because of the resolution of analysis in this study which focused on the length and severity of drought as opposed to past studies that restricted their analysis to seasonal and inter-annual differences in rainfall pattern. As they grow older and sexually mature, the foraging range of male elephant increase and they begin to take more risks and disperse to unfamiliar habitats to seek for quality forage and mates. Generally, foraging strategies between sexes in many species are more pronounced during periods of food scarcity, and the driving force in the differences appears to be driven by energy need requirements, reproductive status of an individual, body sizes and the social context, all of which differ between sexes.

In the next study, I investigated the spatial pattern of elephant mortality in relation to drought occurrences in Tsavo National Park using MaxEnt. The results shows that elephant carcasses were aggregated and elephant mortality was negatively correlated with four months cumulative precipitation prior to death, forage availability and distance to water, while local elephant density showed a positive correlation. This finding rules out dehydration as the cause of elephant mortality in Tsavo as the river where the carcasses were aggregated is perennial. Furthermore, forage availability was low close to water sources and did not show a significant difference close to or further away from the river despite high elephant density around the river. Hence, these elephant mortalities may have occurred as a result of starvation.

I went further to focus on two main limiting resources for elephants, namely forage and water, and their effect on elephant-habitat utilization in semi-arid savannas. I first investigated how water source distribution affect elephants’ seasonal movement patterns. Results indicate that male elephant moved maximally 20 km away from the nearest water source in the dry season while the female elephant foraged to a maximum of about 10 km and only moved further than this distances in the wet season. The strong directionality of elephant movement from a distance of 15km towards water sources (rho > 0.5) as they re-visited their watering source in the dry season suggest that elephant have information on location of the water sources.

Next, I investigated the factors that determine selection of a foraging site for elephant with a focus on forage nutrients or biomass. Because of their large body size, it is thought that elephant can survive on a less nutritious but high biomass of forage. The results from this study shows that elephant selected foraging site based on forage biomass in dry seasons, whereas they selected areas with higher nutrients in the wet season. Moreover, females selected sites with a higher forage biomass as compared to males. This result may be explained by the difference in social organisation and foraging strategies between the sexes. In the previous studies on human-elephant conflict, for instance, male elephant raided crops more than the mixed herd, perhaps to seek for high quality forage.

Together, the four studies in this thesis strongly suggest that elephant starve to death in prolonged drought contrary to the past studies that reported that adult elephant are less affected by drought. Even though prolonged droughts usually result in higher elephant mortalities, the resilience of semi-arid savannas may perhaps be as a result of these deaths that release the system from high browsing pressure and give it a window to regenerate. If that is the case, then drought induced elephant mortality may be a better way to regulate elephant numbers than culling. This finding strongly suggests that semi-arid savannas may in fact be a non-equilibrium system sustained by growth and crashes of herbivore populations. Maintaining the system as natural as possible may therefore keep elephant populations in savannas sustained for posterity. The modern day park managers have daunting challenges such as mass elephant deaths in drought, increased human-wildlife conflicts or changes in wildlife use of the landscape which may all be symptoms of wrong management interventions taken in the past or negative impacts of anthropogenic activities that have tipped the natural functioning of a non-equilibrium system. Therefore, park managers should undergo regular trainings on new conservation techniques and they should apply evidence-based science to make informed long term decision.

Response to habitat modification by foraging Dark-chanting Goshawks Melierax metabates in a West African savanna
Buij, Ralph ; Dorst, Nikie Van; Salomons, Henriëtte F. ; Croes, Barbara M. ; Dietz, Maurine W. ; Komdeur, Jan - \ 2015
Bird Conservation International 25 (2015)3. - ISSN 0959-2709 - p. 335 - 352.

Anthropogenic habitat alteration has probably contributed significantly to the decrease of raptor populations in West African savannas. To evaluate the impact of habitat degradation on foraging by sedentary Afrotropical raptors, we investigated the differences in microhabitat selection, foraging effort and energy returns between Dark-chanting Goshawks Melierax metabates inhabiting natural and transformed savannas in Cameroon. We expected that the agro-ecosystems in the transformed savannas have become unprofitable for Dark-chanting Goshawks due to scarcity of food resources. In both savanna types we radio-tracked six mated, adult males during the non-breeding season and determined foraging effort, by time spent at each perch and distance covered between perches, and energy intake through estimation of the energy value of prey items. Goshawks in natural habitats had smaller home-ranges and exploited their range more intensively than Goshawks in transformed habitats. In both natural and transformed habitats, Goshawks selected foraging patches with comparatively tall trees, underlining their importance to foraging Goshawks. The extent of shrub and herbaceous layer cover, agriculture cover, and tree density were other important predictors of foraging patch use, but their importance differed between habitats. The extent of shrub, herbaceous layer and agriculture cover were positively associated with foraging patch use in transformed habitats, suggesting that cultivated fields and ground vegetation support important prey resources for Goshawks in agro-ecosystems. The composition of broad prey categories to the diet, foraging effort and returns were comparable between habitats. However, we found indications that the proportion of heavy-bodied lizard species among reptile prey items was higher in natural than transformed habitats, whereas on average smaller lizards were more commonly caught in the latter. Mean herbaceous layer height and tree density within home ranges, both higher in natural habitat, were negatively related to prey capture rates. Tree clearance and livestock grazing thus favored greater prey capture rates in transformed habitat, offsetting a lower meal energy value compared to natural habitat. We conclude that foraging Dark-chanting Goshawks may cope with moderate land transformation, but practices focused on conservation of tall trees and ground vegetation cover would be beneficial by maintaining important prey resources and their exploitability under growing land pressure.

Energiebesparing appel voor de dorst : interview met Pieter van Reeuwijk
Anonymous, ; Reeuwijk, P. van - \ 2011
Nieuwe Oogst : ledenblad van ZLTO en LLTB. Editie Zuid 7 (2011)21. - p. 16 - 16.
Acuut nierfalen door vergiftiging met gordijnzwam
Bouhbouh, S. ; Haverkamp, L. ; Kuyper, T.W. ; Wolff, F.A. ; Barendregt, J.N.M. - \ 2011
Nederlands Tijdschrift voor Geneeskunde 155 (2011). - ISSN 0028-2162 - p. A3019 - A3019.
Achtergrond Inname van bepaalde soorten gordijnzwammen kan leiden tot nierfalen. In Nederland is deze paddenstoelvergiftiging niet eerder beschreven. Casus Een 58-jarige vrouw presenteerde zich met hoofdpijn, braken en afnemende urineproductie, voorafgegaan door enkele dagen met pijnlijke, branderige dorst en malaise. Er was sprake van acuut en irreversibel nierfalen zonder bekende achterliggende aandoening. Volgens de anamnese had zij 2 dagen voor de eerste ziekteverschijnselen ragout gegeten met in het bos geplukte paddenstoelen. In een nierbiopt werd een interstitiële nefritis met necrose van proximale tubuli vastgesteld. In een restant van de ragout werden 2 fragmenten gevonden van een gordijnzwam, waarschijnlijk behorend tot het complex Cortinarius cinnamomeus (kaneelkleurige gordijnzwam). De eerste symptomen en het beloop passen bij vergiftiging door Cortinarius zoals beschreven in de literatuur. Ondanks hemodialyse en toediening van acetylcysteïne en glucocorticoïden herstelde haar nierfunctie niet. Conclusie Deze casus is de eerst beschreven paddenstoelvergiftiging met een gordijnzwam (Cortinarius sp.) in Nederland.
Een hypoallergeen appeltje voor de dorst
Maas, M.P. van der - \ 2008
Limburgs Dagblad (2008). - p. 1 - 1.
Een hypoallergeen appeltje voor de dorst
Maas, M.P. van der - \ 2008
Dagblad de Limburger (2008).
Welzijn van Paling (Anguilla anguilla) - gedrag en stress
Mheen, H.W. van der; Hillebrand, S.J.W. ; Vis, J.W. van de; Lambooij, E. - \ 2006
IJmuiden : IMARES (Rapport / IMARES 06.017) - 24
european eels - dierenwelzijn - diergedrag - visteelt - aquacultuur - animal welfare - animal behaviour - fish culture - aquaculture
Het is duidelijk dat er nog grote leemtes in onze kennis over welzijn van vissen bestaan, maar op basis van de huidige literatuur is het aannemelijk dat vissen gevoelens hebben. De Nederlandse overheid concludeert ook dat het aannemelijk is dat gewervelde vissen niet fundamenteel verschillen van andere gewervelde dieren, en dat het gewenst is om een welzijnsbeleid voor vissen te ontwikkelen. Binnen Europa zijn er tot op heden geen duidelijke richtlijnen voor het houden van vis. Eisen met betrekking tot het welzijn van vissen bestaan ook niet. Vijf vrijheden, van honger en dorst, van ongerief, van pijn, verwondingen en ziekte, van angst en stress en de vrijheid om normaal natuurlijk gedrag te kunnen uiten worden over het algemeen gebruikt voor het vaststellen van het welzijn, of het ontbreken daarvan. Deze vrijheden zijn in eerste instantie opgesteld voor warmbloedige landbouwhuisdieren en vervolgens door de Fisheries Society of the British Ilses aangepast voor vissen. In de beleidsnota dierenwelzijn geeft de overheid aan dat de veehouderij en de houderij van gezelschapsdieren binnen 10 tot 20 jaar omgebogen moeten zijn in de richting van het perspectief van het soorteigen gedrag. Het houderijsysteem is daarbij aangepast aan het dier in plaats van dat het dier aan het houderijsysteem is aangepast. Omdat dit ook van toepassing is op de kweek van vis is het noodzakelijk het natuurlijk gedrag van vissen te kennen. In deze literatuurstudie bespreken wij de welzijnsaspecten en de situatie op een vijftiental aal kweek bedrijven binnen het kader van de genoemde vrijheden, waarbij de nadruk ligt op het gedrag van alen.
Verslag van de 159e zomerbijeenkomst te Den Hoorn
Cuppen, J.G.M. ; Vorst, O.F.J. ; Heijerman, Th. ; Maanen, B. ; Nunen, B.M.P.J. van; Dorst, M.B.P. ; Jansen, R.P. ; Huijbregts, J. ; Langeveld, S.C. ; Sande, C. van de; Tiemersma, S. - \ 2005
Entomologische Berichten 65 (2005). - ISSN 0013-8827 - p. 70 - 89.
inventarisaties - fauna - nederland - nederlandse waddeneilanden - noord-holland - inventories - fauna - netherlands - dutch wadden islands - noord-holland
Tijdens de 159e zomervergadering van de NEV, die plaatsvond op Texel van 4 tot 6 juni 2004, zijn 1117 taxa van veertien insectenordes waargenomen. Hoewel ook dit keer wat aantal soorten betreft, kevers de boventoon voerden zijn er geen nieuwe keversoorten voor de provincie Noord-Holland gevonden. Met soortenlijst en lijst van vindplaatsen
The effect of environmental temperature on metabolic rate of A.I. Boars.
Kemp, B. ; Verstegen, M.W.A. ; Hartog, L.A. den; Lammers, F.J. ; Dorst, M.P. van; Grooten, H.J.G. - \ 1988
In: Proc. 11th Int. Congr. Animal reproduction and A.I., Dublin, Ireland - p. 264 - 264.
Experiences with the freesia leaf necrosis agent and its presumed vector, Olpidium brassicae.
Dorst, H.J.M. van; Peters, D. - \ 1988
In: Viruses with fungal vectors / Cooper, J.I., Asher, M.J.C., - p. 315 - 322.
Enige fysiologische en psychofysische waarnemingen op het gebied van de smaakgevoeligheid van proefpersonen
Kouwenhoven, T. - \ 1974
Landbouwhogeschool Wageningen. Promotor(en): C. den Hartog. - Wageningen : Veenman - 86
smaak - honger - hongersnood - dorst - besluitvorming - intermenselijke relaties - gewoonten - voedsel - voedingsmiddelen - consumenteninformatie - consumenten - onderzoek - vraag - invloeden - taste - hunger - famine - thirst - decision making - interpersonal relations - habits - food - foods - consumer information - consumers - research - demand - influences

Man is not merely a physiological organism, but is also a rational and social being. Therefore, problems of food choice and of other behaviour related to food have to be considered from a physiological, as well as from a social, cultural or economic point of view.

In the first chapter of this thesis a review is given of the principal cues of food behaviour and of the factors determining food choice.

Hunger appears to be the main physiological motive for food intake, while appetite is more related to its psychological regulation. The mechanisms reponsible for these cues are not totally understood. Evidence, however, is available that hormonal signals from the bloodstream and the fat tissues play an important role. Further is known that ventromedial and -lateral nuclei of the hypothalamus are involved in the regulation of food intake and that satiety feelings are evoked by the sense of taste in the mouth. Certain elasticity senses in the gastrointestinal tract are suggested to play a role as well.

As to the regulation of the quality and the quantity of the foods to ingest, some (older) authors suggested the existence in man of an inborn quality by which he is able to select adequately the right foods in the right amounts.

Food acceptance, however, is so strongly controlled by psychosocial, cultural and other factors that this selfselection quality is practically totally overshadowed by them. Consequently no practical meaning can be ascribed to it, at least in our society.

Since in food behaviour studies sensory experiments are commonly used tools, in chapter 2 a number of general and specific motives are given for further taste research. They are:
1. The important role of taste and odour in food selection and other behavioural phenomena.
2. Apart from its physiological function food has aesthetic functions, as well.
3. The consumer exhibits preferences and avoidances towards specific sensory food properties and is willing to pay considerable amounts of money for palatability and flavour.
4. The term 'quality' is gradually getting the meaning of 'sensory quality' in our countries.

The applicability of the sensory research on different fields forms another category of motives for taste research:

1. For the food technologist it is of great importance to have at his disposal possibilities for testing the sensory quality of his products and for evaluating the chances of acceptability a new product is likely to meet when it appears on the market.
2. For those concerned with planning and execution of nutritional and health projects, insight in and knowledge of the patterns of tastes and preferences of the target groups and categories are of great use.
3. Taste research has shown itself to be a tool for the tracing of ethnic relations between a variety of races and tribes.
4. It can be demonstrated that clear relations exist between taste sensitivity and some physiological and pathological variables. Although in these fields sensory experiments are rather common, frequently one is struck bij the lack of fundamental knowledge about taste sensitivity. Among others this is caused by the fact that between the different disciplines an exchange of thoughts is very difficult to obtain. The purpose of this thesis is therefore to integrate taste testing experiences from different application fields as much as possible and to make them accessible for others.

As usual in taste sensitivity research a restriction was made as regards the threshold value determination of the four primary taste qualities.

In chapter 3 a review is given of the main types of thresholds. The great variety of threshold data in the literature is discussed. The differences are due to variations in definitions, methodology, quality and purity of the taste substances used, solvent media, and so on. It is needless to say that differences in experimental subjects play an important role, too.

In this chapter attention is also drawn to the discussion about the possible existence of either one receptor system, in which all receptors respond to all taste stimuli or of a receptor system in which at least 4 types of receptors are present to respond selectively to any one of the primary tastes.

In a series of identification experiments (chap. 4) was shown that the mean threshold values resulting out of an arbitrarily increasing series of 15 concentrations of taste substances, were totally identical with those obtained from a series in which 12 concentrations were offered in a mathematically increasing order. Both series were caried out 4 times with sucrose, lactic acid and sodium chloride, with 10 and 15 tasters respectively in the 2 experimental groups. The mean threshold values for the 3 taste substances were 0,016 ± 0,012; 0,0072 ± 0,0038 and 0,016 ± 0,008 Mols/l, respectively. A positive, but weak correlation between the several sensitivities could be demonstrated so that lineair regression equations could be calculated.

Since the methods of determination of the threshold values as described appeared to be very laborious and time consuming, in the next experiment a design was developed in which at least 6 panel members could be examined for their taste sensitivity in the same time, This design actually consisted of a randomized presentation scheme in which were assembled all concentrations, repetitions, placebo's for the 4 taste substances under consideration. As taste substances were chosen 7 concentrations of sucrose, sodium chloride, citric acid an quinine sulphate. The experimental -design was planned in such a way that also the possible influence of the colour of a few kinds of artificial light could be studied (chap. 5). The total project consisted of presenting 7 concentrations of every taste substance in twelve fold, including 96 samples of demineralized water. Sixteen tasters completed the project (= 72 sessions). The mean threshold values of these tasters were in Mots per liter: 0,0091 ± 0,0047 (sucrose), 0,0078 ± 0,0054 (NaCl), 0,00023 ± 0,00022 (citric acid) and 0,000 00167 (quinine sulphate). All judges showed the following order of decreasing sensitivity: quinine sulphate>citric acid>NaCl>sucrose.

Analysis of the responses to the given placebo's made it possible to discriminate between relatively 'good' and relatively 'bad' tasters, according toe their capacity to describe and recognize the samples as water. Both categories showed a different pattern of incorrect responses:
1. All tasters are inclined to describe the demineralized water erroneously as 'bitter'.
2. The good tasters, moreover, seem to describe it frequently as 'sweet'.
3. A decrease in capacity to describe and to recognize the water correctly, is accompanied by a decrease in inclination to call it 'sweet', and an increase in mistakingly calling it 'bitter', 'sour' or 'salty'.
4. Consequently the ratios (incorrectly) sweet: bitter, sweet: sour, and/or sweet: salty, decrease. Probably this is also valid for the ratio salty: sour.

In chapter 4 the effects of training and experience are also studied. An active training period in which the taster gets instructions and advice is usually rather short (4 or 5 sessions) but its effects are very clear. Frequently it is followed by a period during which no further instructions are given, but in which a taster builds up his own experience. Although the effects are usually rather small, they last much longer. Training periods are necessary whenever one starts a new method of research, but experiences appeared to persist for more than half a year.

In the experiment described, the process of building up experience was manifest during the first 50 sessions. The number of correct responses (y) appeared to increase with the number of sessions (x) according to the regression equation y = 57,27 + 0,176x. The correlation coefficient r = 0,489 is significantly different from 0, with p < 0,01. Differences were observed between the tasters as well as in the taster themselves (inter- and intra taster differences). From taster to taster the number of correct responses varied from 53,2 % to 75,2 %.

For an estimation of the intra-individual differences a mathematical treatment of the results obtained was needed. With help of the method of maximum likelyhood it could be shown that the relation between the concentration and the fraction correct responses can be described by the equation for the cumulative normal frequency distribution.

With help of this relation and the observed number of correct responses estimations could be made of the individual parameters p o , μan σfor the different taste substances (table 28).

Finally an analysis is made of the frequencies with which taste qualities the panel members are inclined to confuse the presented samples. In general, tasters appear to confuse relatively seldom the given taste substances with salt or sour, but relatively often with demineralized water or bitter. Probably the degree of familiarity with primary tastes plays a role. From the incorrect responses an order of decreasing familiarity could be deducted: salt>sour>sweet>bitter>demineralized water. Deviations of this order are connected with the research design used, the circumstances during the experiments, and the 'quality' of the tasters. In tasting subthreshold concentrations of quinine sulphate or of sodium chloride, good tasters do describe them much more frequently as sweet than as sour, while the less good judges confuse them as often with sour as wich sweet.

The effects of colours on taste perception are discussed in chapter 5. These effects are partly associative, partly physiological in character. While the associative character of colours in relation to foods is well known, the physiological aspects in this context need further experimentation. A critical discussion of the scarce data in the literature shows that knowledge about this is mainly empirical. From the experiments of chapter 4 it appears that the physiological action of the different colours in relation to the individual results of the panel members is so weak, that as to the inspected results on an individual basis the influence is negligible, but for the panel members as a group, one ought to take it into account.

Analysis of the group data shows that colour effects are significantly present. Application of identical intensities of sodium light (yellow) and mercury light (blueish) resulted for the panel as a group in a significantly higher amount of correct responses compared with artificial daylight of the same intensity. This was valid at least for the taste substances sucrose, citric acid and sodium chloride. For the bitter substance quinine sulphate this phenomenon was not observed.

It could be demonstrated that the colour effects manifest themselves especially in the steep parts of the log dose response curves. As a consequence of the chosen experimental design this meant for the salt and sour taste substances an influence in the lower range of concentrations used and for the sweet substance an influence in the higher range. The steepness of the curve (a) plays an important role in this. As a consequence of the applied colours the curves showed a shift towards the lower concentrations; in other words: the panel members seemed to be a bit more sensitive. Finally attention is drawn to the fact that the observed phenomena do not form an isolated case, but that in the physiological and psychological literature analogous heteromodal interactions are discussed. According to this literature weak interacting stimuli can result into an enhancement of the cortical alertness in general, and as a consequence into a lowering of the threshold values. Strong interacting stimuli should have the opposite effects. It is concluded that the observed fall in threshold values and its accompanying features can result from the interacting effect of the applied light and that in comparison with the intensity of the taste stimuli, the light stimuli probably are perceived as very weak. The results seem to support YOUNG and HELMHOLTZ'S conception about the existence of several systems of coulour vision.

Twee nieuwe ziekteverschijnselen bij knolfresia's
Dorst, H.J.M. van - \ 1972
Naaldwijk : Proefstation voor de Groenten- en Fruitteelt onder Glas - 12
De bodemgesteldheid van de boswachterij Dorst
Vrielink, J.G. ; Buitenhuis, A. - \ 1969
Wageningen : STIBOKA (Rapport / Stichting voor Bodemkartering no. 782) - 23
bodemkarteringen - kaarten - bosbouw - bossen - bosbestanden - rekeningen - nederland - noord-brabant - soil surveys - maps - forestry - forests - forest resources - accounts - netherlands
Arabis mozaiek virus bij komkommer in Nederland
Dorst, H.J.M. van; Hoof, H.A. van - \ 1965
Naaldwijk : [s.n.] (Publikatie / Proefstation voor de groenten- en fruitteelt onder glas no. 119) - 4
cucumis sativus - komkommers - nederland - cucumbers - netherlands
The effect of skips on the grain yield of the adjacent hills in trials with maize hybrids under different conditions
Hindi, L.H.A. - \ 1962
Wageningen University. Promotor(en): J.C. Dorst. - Wageningen : Veenman - 34
cultuurmethoden - zea mays - maïs - genetica - cultural methods - zea mays - maize - genetics
Experiments were carried out with maize during 1959-61 to find the effect of skips (gaps) on adjoining hills and some factors influencing this effect. The effect of skips was influenced by the size and shape of skips, the type of stand, nitrogen fertilizer, the maize hybrids and the weather.

There was an increase in the yield of hills adjoining a skip in the same row and in adjacent rows. The effect of a skip on the direct neighbour in the row was very high.

The present study clearly demonstrated that both size and shape of the skip had to be considered.

Hybrids differed widely in response to skips, stand and nitrogen levels.

The use of adjustment formulae based on the oversimplified concept of a constant adjustment percentage of compensation for the loss of yield due to skips generally led to erroneous conclusions.

The 'normal plant method' of adjustment gave the best estimate of plot yield.

Bastaard-necrose bij tarwe
Hermsen, J.G.T. - \ 1962
Wageningen University. Promotor(en): J.C. Dorst. - Wageningen : Pudoc - ISBN 9789022000731 - 130
genetica - triticum aestivum - tarwe - hexaploïdie - afwijkingen, planten - voortplanting - cum laude - genetics - triticum aestivum - wheat - hexaploidy - plant disorders - reproduction
Hybrid necrosis in wheat was shown to be based on two complementary genes Ne 1 and Ne 2 . Variation in degree of necrosis proved to depend on multiple alleles. The existence of weak, moderate and strong alleles of Ne 1 and Ne 2 could be demonstrated. The degree of necrosis was shown to depend also on environment. Normally lethal plants could even produce seed under artificial environmental conditions.
The author studied the sources of the necrosis genes and their distribution. The genotypes of wheat available were determined by test crosses while their origin was found where possible. The frequent use of certain carrier varieties as parents had contributed to the spread of necrotic genes.

All wheat varieties, selections and species studied (about 500) were classified into 3 genotype classes (Ne 1 -carriers, Ne 2 -carriers, non-carriers) with indication of the strength of the necrosis gene. In designing a wheat-crossing programme a breeder could thus ascertain whether the first filial generation would become necrotic and usually also the allelic combination of the first filial generation.

The occurrence of carrier and non-carrier lines in several varieties was shown to provide sometimes the possibility of avoiding necrosis.
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