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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Paracrine mechanisms in early differentiation of human pluripotent stem cells : Insights from a mathematical model
Gaspari, Erika ; Franke, Annika ; Robles-Diaz, Diana ; Zweigerdt, Robert ; Roeder, Ingo ; Zerjatke, Thomas ; Kempf, Henning - \ 2018
Stem Cell Research 32 (2018). - ISSN 1873-5061 - p. 1 - 7.
Differentiation - Human pluripotent stem cells - Mathematical modeling - Paracrine effects - Primitive streak

With their capability to self-renew and differentiate into derivatives of all three germ layers, human pluripotent stem cells (hPSCs) offer a unique model to study aspects of human development in vitro. Directed differentiation towards mesendodermal lineages is a complex process, involving transition through a primitive streak (PS)-like stage. We have recently shown PS-like patterning from hPSCs into definitive endoderm, cardiac as well as presomitic mesoderm by only modulating the bulk cell density and the concentration of the GSK3 inhibitor CHIR99021, a potent activator of the WNT pathway. The patterning process is modulated by a complex paracrine network, whose identity and mechanistic consequences are poorly understood. To study the underlying dynamics, we here applied mathematical modeling based on ordinary differential equations. We compared time-course data of early hPSC differentiation to increasingly complex model structures with incremental numbers of paracrine factors. Model simulations suggest at least three paracrine factors being required to recapitulate the experimentally observed differentiation kinetics. Feedback mechanisms from both undifferentiated and differentiated cells turned out to be crucial. Evidence from double knock-down experiments and secreted protein enrichment allowed us to hypothesize on the identity of two of the three predicted factors. From a practical perspective, the mathematical model predicts optimal settings for directing lineage-specific differentiation. This opens new avenues for rational stem cell bioprocessing in more advanced culture systems, e.g. in perfusion-fed bioreactors enabling cell therapies.

Projecting changes in the distribution and productivity of living marine resources: A critical review of the suite of modelling approaches used in the large European project VECTORS
Peck, Myron A. ; Arvanitidis, Christos ; Butenschön, Momme ; Canu, Donata Melaku ; Chatzinikolaou, Eva ; Cucco, Andrea ; Domenici, Paolo ; Fernandes, Jose A. ; Gasche, Loic ; Huebert, Klaus B. ; Hufnagl, Marc ; Jones, Miranda C. ; Kempf, Alexander ; Keyl, Friedemann ; Maar, Marie ; Mahévas, Stéphanie ; Marchal, Paul ; Nicolas, Delphine ; Pinnegar, John K. ; Rivot, Etienne ; Rochette, Sébastien ; Sell, Anne F. ; Sinerchia, Matteo ; Solidoro, Cosimo ; Somerfield, Paul J. ; Teal, Lorna R. ; Travers-trolet, Morgan ; De Wolfshaar, Karen E. Van - \ 2018
Estuarine Coastal and Shelf Science 201 (2018). - ISSN 0272-7714 - p. 40 - 55.
Ditribution - Modelling - Habitat - Resources - Man-induced effects
We review and compare four broad categories of spatially-explicit modelling approaches currently used to understand and project changes in the distribution and productivity of living marine resources including: 1) statistical species distribution models, 2) physiology-based, biophysical models of single life
stages or the whole life cycle of species, 3) food web models, and 4) end-to-end models. Single pressures are rare and, in the future, models must be able to examine multiple factors affecting living marine resources such as interactions between: i) climate-driven changes in temperature regimes and acidification,
ii) reductions in water quality due to eutrophication, iii) the introduction of alien invasive species, and/or iv) (over-)exploitation by fisheries. Statistical (correlative) approaches can be used to detect historical patterns which may not be relevant in the future. Advancing predictive capacity of changes in
distribution and productivity of living marine resources requires explicit modelling of biological and physical mechanisms. New formulations are needed which (depending on the question) will need to strive for more realism in ecophysiology and behaviour of individuals, life history strategies of species, as
well as trophodynamic interactions occurring at different spatial scales. Coupling existing models (e.g. physical, biological, economic) is one avenue that has proven successful. However, fundamental advancements are needed to address key issues such as the adaptive capacity of species/groups andecosystems. The continued development of end-to-end models (e.g., physics to fish to human sectors) will be critical if we hope to assess how multiple pressures may interact to cause changes in living marine resources including the ecological and economic costs and trade-offs of different spatial management strategies. Given the strengths and weaknesses of the various types of models reviewed here,
confidence in projections of changes in the distribution and productivity of living marine resources will be increased by assessing model structural uncertainty through biological ensemble modelling.
Moving beyond the MSY concept to reflect multidimensional fisheries management objectives
Rindorf, Anna ; Mumford, John ; Baranowski, Paul ; Clausen, Lotte Worsøe ; García, Dorleta ; Hintzen, Niels T. ; Kempf, Alexander ; Leach, Adrian ; Levontin, Polina ; Mace, Pamela ; Mackinson, Steven ; Maravelias, Christos ; Prellezo, Raúl ; Quetglas, Antoni ; Tserpes, George ; Voss, Rüdiger ; Reid, David G. - \ 2017
Marine Policy 85 (2017). - ISSN 0308-597X - p. 33 - 41.
Inclusive governance - Management objectives - MEY - MSOY - MSY - Sustainability pillars
Maximising the long term average catch of single stock fisheries as prescribed by the globally-legislated MSY objective is unlikely to ensure ecosystem, economic, social and governance sustainability unless an effort is made to explicitly include these considerations. We investigated how objectives to be maximised can be combined with sustainability constraints aiming specifically at one or more of these four sustainability pillars. The study was conducted as a three-year interactive process involving 290 participating science, industry, NGO and management representatives from six different European regions. Economic considerations and inclusive governance were generally preferred as the key objectives to be maximised in complex fisheries, recognising that ecosystem, social and governance constraints are also key aspects of sustainability in all regions. Relative preferences differed between regions and cases but were similar across a series of workshops, different levels of information provided and the form of elicitation methods used as long as major shifts in context or stakeholder composition did not occur. Maximising inclusiveness in governance, particularly the inclusiveness of affected stakeholders, was highly preferred by participants across the project. This suggests that advice incorporating flexibility in the interpretation of objectives to leave room for meaningful inclusiveness in decision-making processes is likely to be a prerequisite for stakeholder buy-in to management decisions.
Achieving maximum sustainable yield in mixed fisheries : A management approach for the North Sea demersal fisheries
Ulrich, Clara ; Vermard, Youen ; Dolder, Paul J. ; Brunel, Thomas ; Jardim, Ernesto ; Holmes, Steven J. ; Kempf, Alexander ; Mortensen, Lars O. ; Poos, Jan Jaap ; Rindorf, Anna - \ 2017
ICES Journal of Marine Science 74 (2017)2. - ISSN 1054-3139 - p. 566 - 575.
choke species - Common Fisheries Policy - fleet modelling - FMSY ranges - landing obligation - management plan - pretty good yield
Achieving single species maximum sustainable yield (MSY) in complex and dynamic fisheries targeting multiple species (mixed fisheries) is challenging because achieving the objective for one species may mean missing the objective for another. The North Sea mixed fisheries are a representative example of an issue that is generic across most demersal fisheries worldwide, with the diversity of species and fisheries inducing numerous biological and technical interactions. Building on a rich knowledge base for the understanding and quantification of these interactions, new approaches have emerged. Recent paths towards operationalizing MSY at the regional scale have suggested the expansion of the concept into a desirable area of "pretty good yield", implemented through a range around FMSY that would allow for more flexibility in management targets. This article investigates the potential of FMSY ranges to combine long-term single-stock targets with flexible, short-term, mixed-fisheries management requirements applied to the main North Sea demersal stocks. It is shown that sustained fishing at the upper bound of the range may lead to unacceptable risks when technical interactions occur. An objective method is suggested that provides an optimal set of fishing mortality within the range, minimizing the risk of total allowable catch mismatches among stocks captured within mixed fisheries, and addressing explicitly the trade-offs between the most and least productive stocks.
Inclusion of ecological, economic, social, and institutional considerations when setting targets and limits for multispecies fisheries
Rindorf, Anna ; Dichmont, Catherine M. ; Thorson, James ; Charles, Anthony ; Clausen, Lotte Worsøe ; Degnbol, Poul ; Garcia, Dorleta ; Hintzen, Niels T. ; Kempf, Alexander ; Levin, Phillip ; Mace, Pamela ; Maravelias, Christos ; Minto, Coilín ; Mumford, John ; Pascoe, Sean ; Prellezo, Raul ; Punt, André E. ; Reid, David G. ; Rockmann, Christine ; Stephenson, Robert L. ; Thebaud, Olivier ; Tserpes, George ; Voss, Rüdiger - \ 2017
ICES Journal of Marine Science 74 (2017)2. - ISSN 1054-3139 - p. 453 - 463.
ecosystem-based fisheries management - multiple objectives - reference points - sustainability - variability
Targets and limits for long-term management are used in fisheries advice to operationalize the way management reflects societal priorities on ecological, economic, social and institutional aspects. This study reflects on the available published literature as well as new research presented at the international ICES/Myfish symposium on targets and limits for long term fisheries management. We examine the inclusion of ecological, economic, social and institutional objectives in fisheries management, with the aim of progressing towards including all four objectives when setting management targets or limits, or both, for multispecies fisheries. The topics covered include ecological, economic, social and governance objectives in fisheries management, consistent approaches to management, uncertainty and variability, and fisheries governance. We end by identifying ten ways to more effectively include multiple objectives in setting targets and limits in ecosystem based fisheries management.
The MSY concept in a multi-objective fisheries environment - Lessons from the North Sea
Kempf, Alexander ; Mumford, John ; Levontin, Polina ; Leach, Adrian ; Hoff, Ayoe ; Hamon, Katell G. ; Bartelings, Heleen ; Vinther, Morten ; Stäbler, Moritz ; Poos, Jan Jaap ; Smout, Sophie ; Frost, Hans ; Burg, Sander van den; Ulrich, Clara ; Rindorf, Anna - \ 2016
Marine Policy 69 (2016). - ISSN 0308-597X - p. 146 - 158.
Bio-economic - MEY - Mixed fisheries - MSY - Multi species - North Sea

One of the most important goals in current fisheries management is to maintain or restore stocks above levels that can produce the maximum sustainable yield (MSY). However, it may not be feasible to achieve MSY simultaneously for multiple species because of trade-offs that result from interactions between species, mixed fisheries and the multiple objectives of stakeholders. The premise in this study is that MSY is a concept that needs adaptation, not wholesale replacement. The approach chosen to identify trade-offs and stakeholder preferences involved a process of consulting and discussing options with stakeholders as well as scenario modelling with bio-economic and multi-species models. It is difficult to intuitively anticipate the consequences of complex trade-offs and it is also complicated to address them from a political point of view. However, scenario modelling showed that the current approach of treating each stock separately and ignoring trade-offs may result in unacceptable ecosystem, economic or social effects in North Sea fisheries. Setting FMSY as a management target without any flexibility for compromises may lead to disappointment for some of the stakeholders. To treat FMSY no longer as a point estimate but rather as a "Pretty Good Yield" within sustainable ranges was seen as a promising way forward to avoid unacceptable outcomes when trying to fish all stocks simultaneously at FMSY. This study gives insights on how inclusive governance can help to reach consensus in difficult political processes, and how science can be used to make informed decisions inside a multi-dimensional trade-off space.

Combining efforts to make maximum sustainable yields and good environmental status match in a food-web model of the Southern North Sea
Staebler, Mortiz ; Kempf, Alexander ; Mackinson, S. ; Poos, J.J. ; Garcia, Clement ; Temming, A. - \ 2016
Ecological Modelling 331 (2016). - ISSN 0304-3800 - p. 17 - 30.
Multispecies - Mixed fisheries - MSY - GES - ecosystem model - Ecopath with Ecosim
The southern North Sea is the stage of conflicting objectives of beam trawlers targeting flatfish; of shrimp trawlers fishing for brown shrimp with bycatch of juvenile flatfish; and of demersal trawlers, the main fishery on cod, a key predator of shrimp and other groups. To expose trade-offs between the fleets’ objectives and to explore what a possible variant of a multispecies maximum sustainable yield (MSY) could look like, we parameterized an ecosystem model and subjected it to a range of different fishing effort levels of the three fleets. Long-term projections highlighted multiple fishing regimes that lead to catches of at least 30% of all focal stocks' single species MSYs at the same time. Trade-offs between the yields of shrimp fishers and demersal trawlers made higher simultaneous yields impossible. Besides optimizing multispecies catches, we identified effort regimes that satisfied a set of descriptors of good environmental status (GES). We found that GES can only be obtained through low efforts of beam and demersal trawlers, which cannot be aligned with our multispecies MSY variant without accepting trade-offs in fishing yields and/or conservation goals.
Bioactive tannins in forage legumes: Myths, Ignorance and Aspirations
Mueller-Harvey, I. ; Ramsey, Aina ; Fryganas, Christos ; Ropiak, Honorate ; Drake, Chris ; Ortiz, Marina Mora ; Smith, Lydia M.J. ; Skot, L. ; Malisch, Carsten ; Luescher, Andreas ; Kempf, Katharina ; Kolliker, R. ; Desrues, Olivier ; Williams, Andrew R. ; Thamsborg, S.M. ; Azuhnwi, Blasius N. ; Quijada, J.N. ; Hoste, H. ; Girard, M. ; Grosse Brinkhaus, A. ; Dohme-Meier, F. ; Bee, G. ; Nguyen, T.H. ; Pellikaan, W.F. ; Copani, Giuseppe ; Niderkorn, Vincent ; Engstrom, Marica ; Salminen, J.P. ; Wilkinson, Ian ; Totterdell, Paul ; Waghorn, G.C. - \ 2015
Tannin-containing legumes have attracted much interest due to their animal health and nutritional benefits. Although several tannins are anti-nutritional, a few can generate valuable benefits for controlling parasitic nematodes that are resistant to anthelmintic drugs, for improving protein utilization by ruminants and fatty acid profiles in meat and milk products and for reducing greenhouse gases. A 5% dietary maximum limit of tannins has been suggested, but information on structure-activity relationships are essential in order to fully exploit the potential of these natural plant compounds. Breeders also require guidelines and screening tools for optimal tannin compositions, and farmers require tannin-containing forages that provide consistent results.

Plants vary in tannin contents and composition depending on species, variety and growing conditions. Recent research in Europe (‘LegumePlus' and other projects) has focused on new tools for analyzing soluble and insoluble tannins in plants, silages and digesta. This involved isolating different types of tannin standards from a wide range of different plants and thiolysis to assess their purity and composition. We also developed new UPLC-MS/MS, NIR- and NMR-analysis methods and tested tannin-protein interactions. Agronomists and plant breeders assembled germplasm collections, identified sainfoin-specific markers, and strategies for weed control. Ruminant nutritionists studied in vitro and in vivo fermentations, N-balances and the quality of meat and milk products. Parasitologists explored the anti-parasitic properties using a wide range of different tannin types.

The presentation will summarize current knowledge and conclude with a wishlist for ‘ideal' tannin-containing forages. It will emphasize that robust and stable tannin concentrations and compositions are required in addition to high yield, good weed suppression and resistance to climatic stress.
Study on stomach content of fish to support the assessment of good environmental status of marine food webs and the prediction of MSY after stock restoration
Huwer, B. ; Neuenfeldt, S. ; Rindorf, A. ; Andreasen, H. ; Levinsky, S.E. ; Storr-Paulsen, M. ; Dalmann Ross, S. ; Haslund, O.H. ; Horbowy, J. ; Pachur, M. ; Pawlak, J. ; Ustups, D. ; Kruze, E. ; Sics, I. ; Uzars, D. ; Velasco, A. ; Kempf, A. ; Eberle, S. ; Floeter, J. ; Temming, A. ; Hal, R. van; Boois, I.J. de; Pennock-Vos, M.G. ; Hoek, R. ; Pinnegar, J. ; Hunter, E. ; Pliru, A. ; Casini, M. ; Belgrano, Andrea - \ 2014
European Commission (Final report for EU contract MARE/2012/02) - 58 p.
The current reform of the Common Fisheries Policy anticipates more extensive use of long-term management plans which are consistent with the ecosystem approach to fishery management. Both long term management plans and estimates of the fishing mortality providing MSY are particularly sensitive to changes in natural mortality, and a prerequisite for estimating natural mortality correctly is the accurate knowledge of species interactions for application in multispecies models. The use of historic data in the multispecies models has so far been limited by the need for data to represent a full spatial coverage. However, the recent model developments have made it possible to integrate regional samples of stomach content data into the multispecies and ecosystem models. It is hence no longer necessary to have complete spatial coverage in a given year, before new stomach data can be included into the models. This provided a unique opportunity to utilize the vast amount of historic data available at individual fisheries research institutes. DTU Aqua together with 8 partners from the Baltic and North Sea has conducted a stomach collection and analysis project in order to (i) include all appropriate historical stomach content information into the Baltic and North Sea stomach content databases, (ii) conduct stomach content analyses of new cod stomachs collected in the Baltic Sea, to support our knowledge of the spatial and temporal stability of cod preferences, and (iii) conduct stomach content analyses of whiting stomachs collected in the Baltic Sea and grey gurnard, mackerel and hake collected in the North Sea to support our knowledge of potentially important predators for which the diet is presently poorly known or is expected to have changed significantly since the last sampling efforts in this area. All existing and new samples and data are included in the final product of this tender, i.e. a common stomach database in ICES exchange format, which is going to be made available to the scientific community via ICES. This database can then be used to re-estimate multispecies reference points such as FMSY of the different fish species. Within the Baltic Sea, efforts were focused on stomach content analyses of Baltic cod as the most abundant piscivorous fish in this ecosystem. The latest data in the cod stomach content database are from 1993. Since then, the Baltic has changed markedly. Both abundance and spatial distribution of cod and its major fish prey, herring and sprat have changed. Furthermore, due to the occurrence of extended hypoxic areas on the sea-bed, the availability of benthic food may also have changed dramatically. In addition to cod, a limited number of whiting stomach samples from the westernmost areas of the Baltic were collected and analyzed, as this species is potentially another important piscivorous predator in these regions. Before the start of the project, stomach content data for 49476 Baltic cod from the period 1977-1993 were available. The initial estimate in the proposal for the present stomach tender was that this number could be increased by ca. 170% during the course of the project. However, considerably more data have been made available during the project, especially due to the initial underestimation of the available number of historic data. The new data that have been made available increased the number of data to 255% of the initially available data. Since the focus of this tender was on the Baltic Sea, only relatively limited resources were allocated for work in the North Sea. Thus, in the North Sea, a ‘most benefits for least cost’ strategy was employed. This involved (1) the collection and analysis of new stomachs from selected species which were judged to provide the most relevant new knowledge for multispecies modeling and (2) the transformation of existing historic data into ICES exchange format. Stomachs of 1907 grey gurnard, 517 hake and 702 mackerel have been analyzed, corresponding to 119, 65 and 44 % of target values, respectively. In contrast to the Baltic Sea part of the project, that already had a large number of samples available from the beginning, the North Sea partners had to wait with initiating the stomach analyses until sufficient numbers of samples had become available, and hence the number of analyzed stomachs was not as predictable as for the Baltic Sea. Furthermore, the conversion of historic data from the DAPSTOM database has provided a large number of additional data for these three target species as well as a multitude of other species (> 207.000 data records for 184 species). Both for the Baltic and the North Sea regions, the new data have already been used and generated great interest in the scientific community. In order to facilitate the application of these data, DTU Aqua will beyond this project make data extracts available on request and collaborate with ICES to make the database available on the ICES data portal as soon as possible.
Integrating stochastic age-structured population dynamics into complex fisheries economic models for management evaluations: the North Sea saithe fishery as a case study
Simons, S.L. ; Bartelings, H. ; Hamon, K.G. ; Kempf, A.J. ; Doring, R. ; Temming, A. - \ 2014
ICES Journal of Marine Science 71 (2014)7. - ISSN 1054-3139 - p. 1638 - 1652.
There is growing interest in bioeconomic models as tools for understanding pathways of fishery behaviour in order to assess the impact of alternative policies on natural resources. A model system is presented that combines stochastic age-structured population dynamics with complex fisheries economics. Explicitly, the economic response of fleet segments to changes in stock development is analysed by applying observed values and stochastic recruitment. The optimization of net profits determines the fishing effort and the investment and disinvestment behaviour of fleet segments, which, in turn, affect the level of catch rates and discards. This tool was applied to the North Sea saithe fishery, where ICES re-evaluated the existing EU–Norway management plan, focusing on biological reference points only. Two scenarios were tested with alternative harvest control rules and then contrasted with one unregulated scenario with no quotas and driven by optimizing the net profit of the whole fleet. The model showed the success of both harvest control rules in rebuilding the stock and the associated costs to the fleets in terms of maximal 21% reduction in net profits, 21% reduction in crew wages and 11% reduction in fleet size in the midterm (2007–2015). In the long term (2022), successful stock recovery coincided with net profits almost equalling that of the unrestricted fishery. The model is highly sensitive to the parameter values but can be used strategically, providing a qualitative understanding of the anticipated relative changes.
Pyrrolizidine alkaloids in honey: comparison of analytical methods
Kempf, M. ; Wittig, M. ; Reinhard, A. ; Ohe, K. von der; Blacquière, T. ; Raezke, K.P. ; Michel, R. ; Schreier, P. ; Beuerle, T. - \ 2011
Food Additives & Contaminants. Pt. A, Chemistry, Analysis, Control, Exposure & Risk Assessment 28 (2011)3. - ISSN 1944-0049 - p. 332 - 347.
solid-phase extraction - medicinal-plants - senecio-vulgaris - root cultures - n-oxides - pollen - boraginaceae - patterns
Pyrrolizidine alkaloids (PAs) are a structurally diverse group of toxicologically relevant secondary plant metabolites. Currently, two analytical methods are used to determine PA content in honey. To achieve reasonably high sensitivity and selectivity, mass spectrometry detection is demanded. One method is an HPLC-ESI-MS-MS approach, the other a sum parameter method utilising HRGC-EI-MS operated in the selected ion monitoring mode (SIM). To date, no fully validated or standardised method exists to measure the PA content in honey. To establish an LC-MS method, several hundred standard pollen analysis results of raw honey were analysed. Possible PA plants were identified and typical commercially available marker PA-N-oxides (PANOs). Three distinct honey sets were analysed with both methods. Set A consisted of pure Echium honey (61–80% Echium pollen). Echium is an attractive bee plant. It is quite common in all temperate zones worldwide and is one of the major reasons for PA contamination in honey. Although only echimidine/echimidine-N-oxide were available as reference for the LC-MS target approach, the results for both analytical techniques matched very well (n¿=¿8; PA content ranging from 311 to 520¿µg¿kg-1). The second batch (B) consisted of a set of randomly picked raw honeys, mostly originating from Eupatorium spp. (0–15%), another common PA plant, usually characterised by the occurrence of lycopsamine-type PA. Again, the results showed good consistency in terms of PA-positive samples and quantification results (n¿=¿8; ranging from 0 to 625¿µg¿kg-1 retronecine equivalents). The last set (C) was obtained by consciously placing beehives in areas with a high abundance of Jacobaea vulgaris (ragwort) from the Veluwe region (the Netherlands). J. vulgaris increasingly invades countrysides in Central Europe, especially areas with reduced farming or sites with natural restorations. Honey from two seasons (2007 and 2008) was sampled. While only trace amounts of ragwort pollen were detected (0–6.3%), in some cases extremely high PA values were detected (n¿=¿31; ranging from 0 to 13019¿µg¿kg-1, average¿=¿1261 or 76¿µg¿kg-1 for GC-MS and LC-MS, respectively). Here the results showed significantly different quantification results. The GC-MS sum parameter showed in average higher values (on average differing by a factor 17). The main reason for the discrepancy is most likely the incomplete coverage of the J. vulgaris PA pattern. Major J. vulgaris PAs like jacobine-type PAs or erucifoline/acetylerucifoline were not available as reference compounds for the LC-MS target approach. Based on the direct comparison, both methods are considered from various perspectives and the respective individual strengths and weaknesses for each method are presented in detail
Reference effects in consumer food choice
Cramer, L. - \ 2009
University. Promotor(en): Gerrit Antonides. - [S.l. : S.n. - ISBN 9789085854562 - 112
voedselvoorkeuren - voedselconsumptie - besluitvorming - voedselproducten - voedingsgewoonten - consumenten - houding van consumenten - overtuiging - food preferences - food consumption - decision making - food products - feeding habits - consumers - consumer attitudes - persuasion
In general, people prefer their current situation, even if they would be better off in another situation. This concept is relevant to public policy aimed at changing food habits into healthier food intake in the population. The increasing prevalence of citizens in industrialized countries being overweight or obese in the last 25 years has direct consequences on development of cardiovascular diseases, diabetes and some cancers (WHO, 2000). This is often caused by an unbalanced energy management which can be attributed to changed patterns of food consumption and a more sedentary lifestyle. Because of their repetitive nature, unhealthy food choices can be characterized as habits. A conscious decision process is therefore less likely to occur and past behaviour is often a strong predictor of current choices (Albarracin & Wyer Jr., 2000; Betsch, Haberstroh, Molter, & Glöckner, 2004; Brug, De Vet, De Nooijer, & Verplanken, 2006). The popularity of unhealthy food products is commonly ascribed to the hedonic aspects of these goods. The intrinsic appeal of hedonic goods might cause difficulties in attempts to change preferences for unhealthy food. This thesis focuses on reference effects to relate unconscious processes to consumer decision making for food products.
In an intuitive type of reasoning, a person might be more vulnerable to the use of heuristics and biases in a choice situation (Kahneman, 2003). One of these biases is loss aversion which is explained by Prospect Theory (Kahneman & Tversky, 1979). According to Prospect Theory, the loss of utility associated with giving up a good is perceived as greater than the utility gain associated with receiving the good, causing a preference for one’s current endowments and resulting in consumers who rather stick to their status quo than switch to an alternative (Kahneman, Knetsch, & Thaler, 1990; Kahneman & Tversky, 1979; Knetsch, 1995). A broader perspective on loss aversion or the endowment effect may lead to consumer food habits being considered as a preference for the status quo type of food intake (Samuelson & Zeckhauser, 1988). This may lead to the prevalence of a lifestyle which is then difficult to change.
This thesis describes several experiments to understand the impact of reference effects in consumer decision making with respect to hedonic versus utilitarian food products. Two basic consumption effects: (1) consummatory affective (hedonic) gratification from sensory attributes, and (2) instrumental, utilitarian functions or consequences of consumption (Batra & htola, 1991; Dhar & Wertenbroch, 2000; Hirschman & Holbrook, 1982) suggest that some types of food choices might also be more susceptible to loss aversion or status quo effects than other types. In experimental classroom settings, participants (16-18 years old) received either a hedonic or a utilitarian type of food product and made a decision between keeping their endowment or exchanging it for the other type of food. The outcomes of the experiments showed that the endowment effect was significantly stronger for hedonic than for utilitarian food products. Also, the strong influence of the hedonic value difference in the choice of hedonic food products was shown which was consistent with our assumption predicting different endowment effects for the two goods.
Basically, there are two different ways in which consumers can make decisions: by reasoning and by using emotions or cues. A few additional experiments focused on the effects of cognitive constraints on food choices. Cognitive constraints tend to reduce consumers’ attention to the food choice process such as in the process of a food habit. The outcomes of two experiments showed that the endowment effect was significantly stronger under cognitive constraint than without constraint, which was consistent with our assumption. In addition, the influence of cognitive constraints on consumer choices was significantly stronger for hedonic than for utilitarian food items. Being forced to rely on a more intuitive type of decision making, in case of distractions, increased the endowment effect of specifically hedonic food products.
Although there is some agreement on the influence of gender in different consumer decision domains like verbal or analytic skills, consumption or investments, there is still much unknown about the meaning of gender differences in consumer food choices. Males more often than females use the intuitive mode of processing, whereas females on the other hand, are more likely to use a detailed analytic processing mode (Kempf, Palan, & Laczniak, 1997; Meyers-Levy, 1989; Meyers-Levy & Maheswaran, 1991). Comparisons across the cognitive load conditions showed that girls’ endowment effects, independent of product type and in case of a hedonic good in endowment, were significantly stronger when they experienced cognitive constraints, compared to the unconstrained case. A stronger preference for hedonic goods in the choice condition, in addition to the finding that cognitive constraints did not influence the endowment effects for boys suggests that a heuristic processing style seemed indeed most appropriate for boys’ food choices.
Because losses are considered as more painful than the same gain provides pleasure, choice preferences may change subject to whether they are experienced in the loss or gain domain of the value function (Knetsch, 2001). Providing information about positive or negative aspects of choice alternatives may result in a change of the reference point of evaluation resulting in preference reversals and leading to, for example, less strong ‘want’ preferences. In addition, focusing on the alternative instead of the status quo in choice situations may increase the attractiveness of the alternative and consequently lead to preference reversals for both goods (Tversky & Kahneman, 1991). The results of the experiments showed that message framing influenced the status quo bias for a hedonic food product leading to a healthier food choice. When participants were asked to retrieve information about the goods from their own memory, the effect on product choice was relatively strong. Especially preferences to keep a Mars bar in endowment decreased when the focus of attention was on including an apple in one’s consumption pattern.
A final study was designed to test the endowment effect on food product bundles to relate endowment effects of single food products to food portfolios and food consumption patterns. The results showed that endowment effects significantly decreased when an extra choice option was introduced to keep one of the two goods and exchange the other item confirming our assumptions. In addition, giving up on only one good required less willpower compared to giving up on two goods. A probit regression analysis showed that when participants indicated that their choice was driven by their emotions and heart, indicating impulsiveness, they were more inclined to keep both goods in endowment, whereas desire for variety did not significantly influence their choice.
Although many aspects related to reference effects and consumer food choice are worthwhile to investigate further, the outcomes of this thesis might already be useful in attempts to influence consumers’ unhealthy food choices. Endowment effects may be important in establishing a status quo bias for an unhealthy food consumption pattern. A more intuitive type of reasoning leads to stronger endowment effects for especially hedonic goods. Distractions in everyday life may lead to more intuitive decision processes. Outcomes of several experiments suggested that it might be useful to take unconscious processes such as reference effects into account when changing consumer preferences. In addition it might be interesting to focus on the magnitude of the change. Changing consumer food choices is difficult, but findings presented in this thesis indicated that reference effects might be useful to include in this process.
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