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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    Tracing legume seed diffusion beyond demonstration trials: An exploration of sharing mechanisms
    Almekinders, Conny J.M. ; Ronner, Esther ; Heerwaarden, Joost van - \ 2020
    Outlook on Agriculture 49 (2020)1. - ISSN 0030-7270 - p. 29 - 38.
    gender - relationships - Seed diffusion - transactions

    Many interventions are assuming that introduced seeds diffuse. However, the details of this diffusion among farmers are poorly understood. This article presents data from eight sites in four on the diffusion of seed and associated information given to farmers involved in N2Africa’s demonstration trials. The study showed that 2–3 years after the trials had been organised, more than 90% of the farmers who had participating in the trial activities and were given a seed-input package with 1–5 kg of legume seed had shared this seed, on average with four other farmers. The farmers who received this seed from these directly involved farmers shared their seed less frequently. Eighty per cent of all the seed sharings were of 1–2 kg of seed given as a gift. Only 5% of the sharings involved a cash transaction. More than half of the seed sharings were with family members and around a third were between friends. Men shared at least as often as women and both men and women shared most with persons of their own sex. Information about rhizobium as an associated input for soya was shared by more than one-third of farmers, almost exclusively by farmers who had participated in the demonstration trials themselves. Extrapolation of data suggest that in addition to the 250,000 farmers who participated directly in the N2Africa demonstration trials, another 1,400,000 farmers may have received seed of a new legume crop or variety. The results show that knowing about the character of the seed sharing mechanisms may offer opportunities to influence the diffusion of seeds. Providing farmers with somewhat larger amounts of seeds, emphasise the importance of sharing seeds and information with relatives and friends could be an important factor in achieving a high multiplier effect.

    Updating the reference population to achieve constant genomic prediction reliability across generations
    Pszczola, M. ; Calus, M.P.L. - \ 2016
    Animal 10 (2016)6. - ISSN 1751-7311 - p. 1018 - 1024.
    dairy cattle - reference population - relationships - reliability

    The reliability of genomic breeding values (DGV) decays over generations. To keep the DGV reliability at a constant level, the reference population (RP) has to be continuously updated with animals from new generations. Updating RP may be challenging due to economic reasons, especially for novel traits involving expensive phenotyping. Therefore, the goal of this study was to investigate a minimal RP update size to keep the reliability at a constant level across generations. We used a simulated dataset resembling a dairy cattle population. The trait of interest was not included itself in the selection index, but it was affected by selection pressure by being correlated with an index trait that represented the overall breeding goal. The heritability of the index trait was assumed to be 0.25 and for the novel trait the heritability equalled 0.2. The genetic correlation between the two traits was 0.25. The initial RP (n=2000) was composed of cows only with a single observation per animal. Reliability of DGV using the initial RP was computed by evaluating contemporary animals. Thereafter, the RP was used to evaluate animals which were one generation younger from the reference individuals. The drop in the reliability when evaluating younger animals was then assessed and the RP was updated to re-gain the initial reliability. The update animals were contemporaries of evaluated animals (EVA). The RP was updated in batches of 100 animals/update. First, the animals most closely related to the EVA were chosen to update RP. The results showed that, approximately, 600 animals were needed every generation to maintain the DGV reliability at a constant level across generations. The sum of squared relationships between RP and EVA and the sum of off-diagonal coefficients of the inverse of the genomic relationship matrix for RP, separately explained 31% and 34%, respectively, of the variation in the reliability across generations. Combined, these parameters explained 53% of the variation in the reliability across generations. Thus, for an optimal RP update an algorithm considering both relationships between reference and evaluated animals, as well as relationships among reference animals, is required.

    Olaf van Kooten, hoogleraar Wageningen UR en lector InHolland: ‘hoezo slechte markt; we zijn zelf de markt’
    Kierkels, T. ; Kooten, O. van - \ 2014
    Onder Glas 11 (2014)8. - p. 32 - 33.
    glastuinbouw - glasgroenten - kwaliteitszorg - groenten - consumentenaangelegenheden - marketing van voedingsmiddelen - consumenten - relaties - klanttevredenheid - agrarische economie - greenhouse horticulture - greenhouse vegetables - quality management - vegetables - consumer affairs - food marketing - consumers - relationships - consumer satisfaction - agricultural economics
    Er is iets grondig mis in de afzetketen van met name groente en fruit; de samenwerking komt maar moeilijk van de grond. Als gevolg daarvan liggen er producten van een lage kwaliteit in de winkel en verdient niemand iets. Dat het anders kan bewijzen schaarse voorbeelden. Hoogleraar tuinbouwketens Olaf van Kooten van Wageningen UR vertelt het met duidelijke woorden.
    Governance of the member-cooperative relationship: a case from Brazil
    Cechin, A.D. - \ 2013
    Wageningen University. Promotor(en): Onno Omta, co-promotor(en): Jos Bijman. - S.l. : s.n. - ISBN 9789461736550 - 144
    landbouwcoöperaties - governance - kwaliteit - relaties - ketenmanagement - agro-industriële ketens - participatie - lidmaatschap - brazilië - agricultural cooperatives - governance - quality - relationships - supply chain management - agro-industrial chains - participation - membership - brazil

    Recent events in the agri-food sector increased the demand for quality attributes, from healthy and safe products to sustainable agricultural practices (Grunert, 2005). Particularly challenging is the connectedness of transactions between farmers, traders, processors, retailers and final customers in order to comply with quality requirements, which implies a need for value chain coordination. Combined with increased consumer demand for variety and convenience, these changes in sector have led to stronger sequential interdependencies, in which the output of one part is the input for another part. The increasing connectedness between transactions demands more vertical coordination. A major challenge for the agricultural cooperative is to combine horizontal coordination among the members with vertical coordination in the value chain (Bijman 2009; Hanf, 2009). Since they are member-oriented, agricultural cooperatives traditionally buy the farm products of its members regardless of its quality. Increasingly, however, cooperatives need to guarantee product quality towards their customers, and thus assure that members supply products of the right quality.

    The objective of this thesis is to disentangle the governance mechanisms that can be used by the cooperative to strengthen the member-cooperative relationship, and to assess the impact of the different governance mechanisms on the coordination of members’ adjustments to higher quality levels. The attempt to organize the participating farmers and firms along the food value chain generates transactional risks and coordination costs in the relationship between agricultural cooperative and farmer-member. This leads to the first research question of this thesis.

    R.Q. (1): What are the mechanisms for governing the member-cooperative relationship, and how do they affect transactional risks and coordination costs?

    This thesis (Chapter 2) poses that four governance mechanisms - market, hierarchy, community and democracy affect coordination costs and transactional risks through their effect on member commitment and cognitive heterogeneity. It is important that members of an agricultural cooperative are committed to customer orientation; otherwise the involved transactional risks would make vertical coordination more costly. It is necessary to disentangle two types of commitment: to collective action and to customer orientation. Member commitment to collective action prevents side selling, in particular, and free-riding behaviour in general. This leads to the second research question of this thesis.

    R.Q. (2): How do the four governance mechanisms - market, hierarchy, community and democracy - affect both types of commitment?

    One of the conclusions stemming from this thesis was that, on the one hand, a cooperative may assure members’ compliance in a less costly way if market incentives related to quality, productivity and effort are strengthened, as well as (hierarchy) input control and on-farm monitoring, since these mechanisms are positively related to commitment to customer orientation. On the other hand, democracy and community mechanisms do have an important role in enhancing commitment to collective action which is a sine qua non condition for the viability of the cooperative (Chapter 3).

    A large multi-product cooperative in which different activities of the cooperative cater to different groups of members, as the case that was chosen as the empirical basis of this thesis, may face problems related to membership heterogeneity (Hansmann, 1996; Fulton and Giannakas, 2001). The basic assumption in most of the literature on the impact of member heterogeneity on the process and outcomes of decision-making is that farmers pursue individual or subgroup interests when participating in the decision-making of the cooperative. If members primarily pursue individual economic interests, there might be a relationship between the economic reasons for becoming a member (and maintaining membership) and the motivation to participate in the governance of the cooperative. This leads to the third research question of this thesis.

    R.Q. (3): How do economic motivations for association affect members’ participation in the governance of a cooperative?

    The conclusion of this thesis, regarding this research question, was that besides the role of social mechanisms in enhancing commitment to collective action, there seems to be a role of social mechanisms in enhancing members’ control of their cooperative. Members who participate in boards or committees are not actuated to participate by the same economic motivations that drive their association to the cooperative. Cooperative ideology, in turn, appears to be an important motivation for them to actively participate (Chapter 4).

    The ability of cooperatives to adapt to a rapidly changing environment characterized by technological change and industrialization of agriculture has been questioned Fulton (1995). The organizational structure of the cooperative is said to have negative implications for its quality management (Mérel et al., 2009). On the one hand, cooperatives may be mimicking Investor-Owned Firms (IOFs) in applying more hierarchical mechanisms which enable them to define and effectively apply quality norms for their supply, control the quality of delivered products and monitor members’ production processes. On the other hand, cooperatives have unique organizational characteristics that could provide them with competitive advantage, such as the tight relationship between members and cooperative, which may enable less costly coordination of the transaction (Sykuta and Cook, 2001). This leads to the fourth and last research question of this thesis.

    R.Q. (4): What are the differences in quality performance between a cooperative and an IOF, and can these differences be explained by relationship characteristics?

    In the Brazilian broiler industry, suppliers delivering to a cooperative are performing better in terms of quality than suppliers delivering to an IOF. Cooperative and IOF have the same incentive and control mechanisms for production efficiency and high-quality chicken meat. The cooperative’s advantage over the IOF in terms of suppliers’ quality performance could be influenced by the characteristics of the supplier-buyer relationship. This thesis shows (Chapter 5) that there are some important differences regarding relationship characteristics that could account for this higher performance. Dependence on current buyer, which is higher for cooperative members, uncertainty regarding buyer’s behavior, which is lower for cooperative members, and market risk reduction by the buyer, which is higher for cooperative members, can help explain the higher rate of compliance to the “feet callus” quality standard. These three features of the supplier-cooperative relationship are likely to prevent suppliers from shirking behavior and to induce commitment. Moreover, cooperative suppliers receive more technical support from their buyer for adapting to new quality requirements than IOF suppliers do; this is likely to positively affect farmers’ competence in complying with quality standards.

    The main methodological approach of this thesis is quantitative. Qualitative data were collected through semi-structured interviews with professional managers of the industrial division, directors and farmers in order to guide the design of the questionnaire. The data that is analyzed in this thesis were collected by using a survey questionnaire applied among 148 farmers, all members of the same multi-product cooperative in Brazil, and 42 broiler suppliers of two major buyers in the same region.

    This thesis makes several theoretical contributions, which can be listed as follows:

    (1) Member commitment in agricultural cooperatives can be disentangled conceptually and empirically into two types. Commitment to collective action is related to Fulton’s (1995) definition: the willingness to patronize a cooperative even when the cooperative’s price or service is not as good as that provided by an IOF. It is an attitude that precedes loyal behaviour; it is the making of a sacrifice or an effort in the name of the relationship and the success of the organization. Commitment to customer orientation, in turn, is the willingness to give up a part of the autonomy at the farm level for the sake of the cooperative’s compliance with the requirements from downstream customers. It is a positive attitude of members towards the re-orientation of the cooperative and is related to Borgen’s (2001) view on commitment.

    (2) Membership heterogeneity might not be a source of inefficiency in decision-making if the organizational goal is precisely to satisfy diverse members’ interests, and if members who occupy representative and managing functions are genuinely seeking to further organizational goals rather than to follow private motives. Most conceptualizations of decision-making problems and influence costs derive from organizational economics, where agency theory has been quite influential. The findings of this thesis (Chapter 4) suggest that assumptions from agency theory, which are often adopted by cooperative studies, could better be treated as an empirical matter.

    (3) This thesis presents a different perspective on the comparative advantage of the cooperative in producing food products with higher quality attributes. The literature on the implications of the cooperative structure for quality management (Mérel et al., 2009) emphasizes that cooperatives often fail to adequately reward the highest quality producers, often causing the problem of “adverse selection”. However, despite starting with larger heterogeneity in terms of producers’ capacity to produce high-quality products, cooperatives may achieve high quality products through superior coordination and adaptation support. The findings of this thesis are in line with other empirical studies outside the domain of cooperatives that found that quality performance may be influenced by relationship characteristics, through their effect on transaction costs (Lu et al., 2009; Coronado et al., 2010).

    (4) Overall, the main scientific contribution of this thesis is the use of the ‘chemistry of organizations’ framework proposed by Grandori and Furnari (2008) in seeking a better understanding of the governance of cooperatives. By adopting that framework the thesis addressed in an integrated way the role of social capital (Ostrom, 1999) and community governance (Bowles and Gintis, 2002; Hayami, 2009) in facilitating collective action, and the role of relational contracts (Poppo and Zenger, 2002; Lazzarini, Miller and Zenger, 2004) in assuring commitment from parties in a transaction. Furthermore, with that framework, the thesis addressed the cognitive role of governance mechanisms, such as knowledge exchange (Conner and Prahalad, 1996; Grant, 1996) and competence enhancing (Nooteboom, 2004).

    The implications of this thesis for management and policy are listed in the three following groups:

    (1) Rewarding farmers appropriately and controlling and monitoring delivery and production processes are important for enhancing commitment both to collective action and to customer orientation. Giving “voice” and building a social community for members and their families are important to prevent members’ free-riding and selling “outside”. It is advised to combine at least the following governance mechanisms: hierarchy control, market incentives, community involvement and democratic voice. Finally, communication is an important tool for enhancing farmers’ commitment to customer orientation.

    (2) Cooperatives can participate in high-quality value chains and be as efficient and effective as other organizational arrangements in the agri-food sector. More importantly, cooperatives might even have an advantage in the production and marketing of goods with credence attributes, such as animal welfare, organic and fair trade. Therefore, policies aiming to promote sustainable food production may target cooperatives, as this organisational form is more effective in lowering the risks associated with farmer’ opportunistic behavior.

    (3) Member participation, commitment, satisfaction with leadership and with the cooperative’s strategy are examples of what could be additional performance criteria besides reported profits, which taken alone could be misleading. Because the cooperative’s objectives are beyond the economic viability of the collective enterprise, (Birchall and Ketilson, 2009), the intangible social assets should be assessed in order to evaluate the performance of the cooperative, and thereby to compare cooperatives with investor-owned firms and among cooperatives themselves.

    Inter-organizational information exchange, supply chain compliance and performance
    Peng, G. - \ 2011
    Wageningen University. Promotor(en): Onno Omta, co-promotor(en): Jacques Trienekens. - [S.l.] : S.n. - ISBN 9789085859529 - 220
    business management - supply chain management - communication - cooperation - businesses - relationships - governance - performance - improvement - information - bedrijfsmanagement - ketenmanagement - communicatie - samenwerking - bedrijven - relaties - governance - prestatieniveau - verbetering - informatie
    In modern business management today's companies no longer compete as solely autonomous entities, but rather as supply chains. Supply chain collaboration can bring with substantial benefits and advantages for companies. To strenghten supply chain collaboration, inter-organisational communication is an essential enabler.
    Gender, AIDS and food security : culture and vulnerability in rural Côte d'Ivoire
    Maiga, M.M. - \ 2010
    Wageningen University. Promotor(en): Leontine Visser; Anke Niehof. - [S.l. : S.n. - ISBN 9789085857891 - 199
    acquired immune deficiency syndrome - voedselzekerheid - cultuur - plattelandsvrouwen - sociologie - vrouwelijke arbeidskrachten - plattelandsbevolking - sociale economie - verwantschap - relaties - ivoorkust - afrika - geslacht (gender) - strategieën voor levensonderhoud - acquired immune deficiency syndrome - food security - culture - rural women - sociology - female labour - rural population - socioeconomics - kinship - relationships - cote d'ivoire - africa - gender - livelihood strategies
    Bos op arme gronden
    Kint, Vincent ; Geudens, Guy ; Ouden, J. den - \ 2010
    In: Bosecologie en Bosbeheer / den Ouden, J., Muys, B., Mohren, G.M.J., Verheyen, K., Leuven : ACCO - ISBN 9789033477829 - p. 511 - 526.
    zandgronden - bossen - relaties - eolische afzettingen - bodem-plant relaties - vlaanderen - sandy soils - forests - relationships - aeolian deposits - soil plant relationships - flanders
    Onder arme groeiplaatsen worden vooral de zandgronden verstaan. In Nederland liggen ze in het oosten en het zuiden van het land en ze lopen door naar de zandgronden in het noorden van Vlaanderen. De duinengordel langs de Noordzeekust behoort ook tot deze categorie. Zandgronden kunnen verder ingedeeld worden volgens hun geologische ontstaanswijze. Er kan onderscheid gemaakt worden tussen afzettingen door zee, rivieren of de wind, die bovendien uit het tertiair of het quartair tijdvak kunnen dateren. Zowel in Vlaanderen als Nederland ligt het grootste deel van het huidige bosareaal op de arme zandgronden: in Vlaanderen is het 60% van het totale areaal (90.000 ha) en in Nederland 86% (270.000 ha).
    Eerste resultaten onderzoek naar meest geschikte ras-onderstamcombinaties
    Maas, F.M. ; Beurskens, Stan - \ 2009
    De Wijngaard 17 (2009)2. - p. 29 - 30.
    druiven - rassen (planten) - relaties - onderstammen - stamverschillen - wijndruivenrassen - bodemtypen - landbouwkundig onderzoek - nederland - grapes - varieties - relationships - rootstocks - strain differences - wine cultivars - soil types - agricultural research - netherlands
    In 2008 is in samenspraak met het Wijngaardiersgilde en met subsidie van het ministerie van LNV een onderzoek gestart om verspreid over Nederland en voor verschillende bodemtypen te onderzoeken hoe de verschillende druiven ras-onderstamcombinaties zich ontwikkelen. 14 Rode en 14 witte druivenrassen staan op 9 verschillende bedrijven op 9 verschillende onderstammen. Dit eerste jaar zijn al grote verschillen per regio en per bedrijf gemeten, volgende 2 jaren zal het onderzoek zich toespitsen op de verschillen in groei, loofwandstructuur, gewasgezondheidsaspecten, oogsttijdstippen en de oogstgegevens.
    Internationaal belang van de nationale natuur : ecosystemen, vaatplanten, mossen, zoogdieren, reptielen, amfibieën en vissen
    Janssen, J.A.M. ; Stumpel, A.H.P. ; Bijlsma, R.J. ; Hennekens, S.M. ; Keizer-Sedlakova, I. ; Kuiters, A.T. ; Ottburg, F.G.W.A. ; Ozinga, W.A. ; Schaminée, J.H.J. ; Siebel, H.N. - \ 2007
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-rapport 43) - 54
    ecosystemen - natuurbescherming - bedreigde soorten - beschermde soorten - soorten - nederland - relaties - europa - natuurbeleid - ecosystems - nature conservation - endangered species - protected species - species - netherlands - relationships - europe - nature conservation policy
    In dit rapport wordt een analyse uitgevoerd van de ecosystemen en soorten (uit een beperkt aantal soortsgroepen) waarvoor ons land internationale verantwoordelijkheid draagt. Hierbij worden een vijftal criteria toegepast: aandeel areaal, aandeel populatie of oppervlakte, ligging ten opzichte van het areaal, voorkomen op internationale rode lijst en – voor ecosystemen en trekvissen – een specifieke reden. Uit de analyse komen 34 ecosystemen en 111 soorten naar voren waarvoor Nederland binnen Europa van groot belang is. Bekeken is voorts in welke landschappen de internationaal belangrijke ecosystemen en soorten voorkomen en in hoeverre ze aandacht krijgen in het nationale en internationale natuurbeleid. De belangrijkste landschappen met de internationaal belangrijke ecosystemen en soorten zijn de hogere zandgronden en het kustgebied, gevolg door het rivierengebied en het laagveen. In het internationale natuurbeleid (Habitatrichtlijn) krijgen vier van de resulterende ecosystemen onvoldoende aandacht, in het nationale beleid komen vooral de mossen er bekaaid af. Trefwoorden: Natuurbeleid, internationaal, ecosystemen, soorten, Europa
    The role of guanxi in buyer-seller relationships in China : a survey of vegetable supply chains in Jiangsu Province
    Lu Hualiang, - \ 2007
    Wageningen University. Promotor(en): Onno Omta, co-promotor(en): Jacques Trienekens. - [S.l.] : S.n. - ISBN 9789085046653 - 252
    food chains - vegetables - marketing - production - china - trade - markets - businesses - relationships - socioeconomics - supply chain management - agro-industrial chains - networks - social capital - voedselketens - groenten - marketing - productie - china - handel - markten - bedrijven - relaties - sociale economie - ketenmanagement - agro-industriële ketens - netwerken - sociaal kapitaal
    Keywords:Social capital,guanxinetworks, vegetable supply chains, buyer-seller relationships, channel performance,China

    Guanxiis ubiquitous inChinaand significantly influences people's behaviour in social life and in business. Guanxi refers to personal relationships or connections and is widely recognised as a Chinese form of social capital. This book focuses on the questions, if, and if so, how small-scale producers, together with processors and exporters, can be more successfully integrated into high-value supply chains (i.e., processors, supermarkets and international markets). In particular, our focus is on how Chinese vegetable farmers can use their guanxi networks to be integrated into these modern supply chains and can improve their market performance. We study the effectiveness of both formal (contracts) and relational ( guanxi ) governance mechanisms to improve the integration of buyer-seller relationships and ultimately, to enhance chain performance. We apply various theoretical approaches, supply chain management, social capital theory and transaction cost economics, to develop propositions regarding the interrelation of support from guanxi networks (what guanxi can do for you), buyer-seller relationships (interpersonal trust, transaction specific investments and contractual governance) and market performance (compliance with delivery/quality requirements, efficiency, quality/price satisfaction, and profitability). We combine case study with survey analysis and use structural equation modelling techniques to test the propositions.

    Background analysis of the Chinese vegetable sector indicates that small-scale farmers usually fail to integrate into high-value market outlets. This is because these farmers face several constraints, such as small production scale, less possibilities to implement quality standards, low negotiation power, and information asymmetry. However, empirical analysis based on three different buyer-seller relationships, including farmers, processors and exporters/supermarkets, shows that support from guanxi networks and integration of buyer-seller relationships significantly contribute to market performance (especially with downstream partners). The effects of guanxi networks differ between primary producers, processors and exporters/supermarkets, and across marketing channels. Vegetable farmers and their buyers show an idiosyncratic way to rely on their guanxi networks in doing business. Furthermore, vegetable farmers and their buyers follow different approaches to achieve market performance. Interpersonal trust and compliance with delivery requirements are important factors for all parties in supply chains to achieve superior performance. Particularly, in relationships with downstream partners, the sellers tend to rely on their guanxi networks when conducting transactions. In relationships with upstream partners, guanxi networks and contractual governance are less often used. This study shows that the combination of formal (contract) and informal ( guanxi ) governance mechanisms seems to be the best way to improve chain performance in vegetable supply chains inChina. Policy should be directed to improve farmers' capacity to participate in modern high-value markets as well as to enhance the prospects forChina's vegetables in the world.
    Female livelihoods and agrarian changes in Indonesia
    Oosterhout, D.W.J.H. van - \ 2006
    social anthropology - food - social structure - kinship - relationships - society - feeding habits - behaviour - south east asia
    Ketenomkering in kennisland
    Wals, A.E.J. ; Lans, T. ; Buurma, J.P. - \ 2005
    Gewasbescherming 36 (2005)suppl. - ISSN 0166-6495 - p. 7 - 9.
    kennis - verspreiding van onderzoek - netwerken (activiteit) - onderzoeksinstituten - technologieoverdracht - informatieverspreiding - onderzoeksimplementatie - onderzoek - onderwijs - particuliere sector - relaties - knowledge - diffusion of research - networking - research institutes - technology transfer - diffusion of information - implementation of research - research - education - private sector - relationships
    Themavoordracht waarin twee manieren van kennismobiliteit worden besproken: de doorstromingsrelatie, waarbij kennis wordt gezien als product en doorstroomt van onderzoeksinstituten naar onderwijs en de netwerkrelatie, waarbij kennis wordt gezien als proces tussen onderzoek, onderwijs en bedrijfsleven
    Livelihood and food security in rural Bangladesh- the role of social capital
    Ali, A. - \ 2005
    Wageningen University. Promotor(en): Anke Niehof. - Wageningen : - ISBN 9789085042969 - 264
    voedselzekerheid - levensomstandigheden - relaties - gemeenschappen - samenleving - menselijke relaties - man-vrouwrelaties - huishoudens - inkomen - platteland - levensstandaarden - vrouwen - Bangladesh - positie van de vrouw - sociale relaties - vrouw en samenleving - arbeid in de landbouw - strategieën voor levensonderhoud - food security - living conditions - relationships - communities - society - human relations - gender relations - households - income - rural areas - living standards - women - Bangladesh - woman's status - social relations - woman and society - farm labour - livelihood strategies
    This thesis describes the role of social capital of households and individuals in achieving livelihood and food security. In the research the temporal dimension and gender were cross-cutting perspectives. IFPRI panel data collected during 1996-1997 (pre-flood) and 1999-2000 (post-flood) were analyzed. To complement the IFPRI data an additional survey and the qualitative data was collected during 2001-2003. Panel data analysis shows that gender of the household head does not make a difference in achieving food security at the household level. However, gender of the household member is crucial for attaining individual level food security. Social capital plays an important role in averting vulnerability and sustaining livelihood, and is influenced by the landholding status of the house hold, which seems to function as collateral. The qualitative data revealed that women's social capital, when defined in a broader way, does play a crucial role in achieving household food security and averting vulnerability.
    The hillslope-storage Boussinesq model for variable bedrock slope
    Hilberts, A.G.J. ; Troch, P.A.A. ; Loon, E.E. van; Paniconi, C. - \ 2004
    regen - oppervlakkige afvoer - relaties - infiltratie - glooiend land - modellen - rain - runoff - relationships - infiltration - sloping land - models
    Managing business networks and buyer-supplier relationships. How information obtained from the business network affects trust, transaction specific investments, collaboration and performance in the Dutch Potted Plant and Flower Industry
    Claro, D.P. - \ 2004
    Wageningen University. Promotor(en): Onno Omta, co-promotor(en): Geoffrey Hagelaar; D. Zylbersztajn. - Veenendaal : Universal Press - ISBN 9789058089465 - 196
    bedrijven - relaties - potplanten - bloemen - informatie - nederland - productie - aanbod - landbouwindustrie - ketenmanagement - netwerken - bedrijfseconomie - businesses - relationships - pot plants - flowers - production - supply - agribusiness - information - netherlands - supply chain management - networks - business management
    Managing networks and buyer-supplier relationships " attempt to provide scientific sound discussion for problems faced in business linkages. Business networks, supply chains and buyer-supplier relationships all refer to business linkages, from a web of connected relationships to a dyadic relationship. At the beginning of our study, we were triggered by the impact of the business network on collaborative, long-term buyer-supplier relationships. In other words, does the information a company obtains from the network support the buyer-supplier relationship? In fact, yes. Our study provides a theoretical framework and empirical evidence that will assist practitioners in the management of their business network and buyer-supplier relationships. The empirical evidence was gathered on the basis of two constructive steps, namely case study and survey. Buyers and suppliers in the Dutch potted flower and plant industry offered valuable insights to estimate statistical models. The involvement of buyers and suppliers allowed discussions from both sides of the relationship - purchasing and marketing.

    This thesis is aimed at managers at different levels in firms, which includes every decision maker in purchasing, selling or strategic planning levels. Policy makers and researchers in the field of supply chain and network management may also find useful ideas and concepts in our theoretical framework. Researchers in the fields of relationship management may be particularly interested in theoperationalizationsof the conceptual elements of the framework and the interpretation of the estimated statistical models.

    The Emerging World of Chains and Networks, Bridging Theory and Practice
    Camps, Th. ; Diederen, P.J.M. ; Hofstede, G.J. ; Vos, B. - \ 2004
    Amsterdam : Reed Business Information - ISBN 9789059019287 - 348
    innovaties - bedrijfsvoering - relaties - informatie - ketenmanagement - netwerken - productieprocessen - management - relationships - innovations - information - supply chain management - networks - production processes
    Bodem, humus en vegetatie onder verschillende loofboomsoorten op de stuwwal bij Doorwerth
    Hommel, P.W.F.M. ; Waal, R.W. de - \ 2004
    Wageningen : Alterra (Alterra-rapport 920) - 66
    bossen - vegetatie - humus - tilia - ligstro - bosgronden - plantensuccessie - nederland - relaties - veluwe - bodem-plant relaties - natuurgebieden - forests - vegetation - humus - tilia - litter - forest soils - plant succession - netherlands - relationships - veluwe - soil plant relationships - natural areas
    Dit rapport gaat in op de relatie tussen loofboomsoort, humus en ondergroei op een zwak lemige stuwwalbodem bij Doorwerth (Gelderland). Er werden opstanden vergeleken van linde, esdoorn, haagbeuk, eik en beuk. Onder invloed van het `rijke¿, goed verterende bladstrooisel van linde, esdoorn en haagbeuk bleek een ontwikkeling in de richting van een `rijker¿ bostype op gang te zijn gekomen. Alleen onder linde was echter binnen 40 jaar een goed ontwikkelde, soortenrijke Carpinion-vegetatie met meerdere oud-bossoorten ontstaan. De vegetatieontwikkeling onder linde lijkt wel sterk afhankelijk te zijn van de hoeveelheid licht die tot de bosbodem weet door te dringen.
    Hillslope-storage Boussinesq model for subsurface flow and variable source areas along complex hillslopes: 2. Intercomparison with a three-dimensional Richards equation model
    Paniconi, C. ; Troch, P.A.A. ; Loon, E.E. van; Hilberts, A.G.J. - \ 2003
    Water Resources Research 39 (2003)11. - ISSN 0043-1397 - p. 1317 - 1317.
    regen - oppervlakkige afvoer - relaties - infiltratie - hydrologie van stroomgebieden - modellen - rain - runoff - relationships - infiltration - catchment hydrology - models - free-surface flow - capillarity correction - runoff generation - rainfall - soils - groundwater - scale
    The Boussinesq equation for subsurface flow in an idealized sloping aquifer of unit width has recently been extended to hillslopes of arbitrary geometry by incorporating the hillslope width function w(x) into the governing equation, where x is the flow distance along the length of the hillslope [ Troch et al., 2003 ]. Introduction of a source/sink term N allows simulation of storm-interstorm sequences in addition to drainage processes, while a function S c (x) representing the maximum subsurface water storage can be used to account for surface saturation response in variable source areas activated by the saturation excess mechanism of runoff generation. The model can thus simulate subsurface flow and storage dynamics for nonidealized (more realistic) hillslope configurations. In this paper we assess the behavior of this relatively simple, one-dimensional model in a series of intercomparison tests with a fully three-dimensional Richards equation model. Special attention is given to the discretization and setup of the boundary and initial conditions for seven representative hillslopes of uniform, convergent, and divergent plan shape. Drainage and recharge experiments are conducted on these hillslopes for both gentle (5%) and steep (30%) bedrock slope angles. The treatment and influence of the drainable porosity parameter are also considered, and for the uniform (idealized) hillslope case the impact of the unsaturated zone is examined by running simulations for different capillary fringe heights. In general terms, the intercomparison results show that the hillslope-storage Boussinesq model is able to capture the broad shapes of the storage and outflow profiles for all of the hillslope configurations. In specific terms, agreement with the Richards equation results varies according to the scenario being simulated. The best matches in outflow hydrographs were obtained for the drainage experiments, suggesting a greater influence of the unsaturated zone under recharge conditions due to transmission of water throughout the hillslope. In the spatiotemporal water table response a better match was observed for convergent than divergent hillslopes, and the bedrock slope angle was not found to greatly influence the quality of the agreement between the two models. On the basis of the intercomparison experiments we make some suggestions for further development and testing of the hillslope-storage model
    Hillslope-storage Boussinesq model for subsurface flow and variable source areas along complex hillslopes: 1. Formulation and characteristic response
    Troch, P.A.A. ; Paniconi, C. ; Loon, E.E. van - \ 2003
    Water Resources Research 39 (2003). - ISSN 0043-1397 - p. 1316 - 1316.
    regen - oppervlakkige afvoer - infiltratie - hellingen - relaties - modellen - hydrologie van stroomgebieden - rain - runoff - relationships - infiltration - slopes - models - catchment hydrology - watershed thermodynamics - unifying framework - soil-moisture - variability - catchment - hydrology - equation - terrain
    Hillslope response to rainfall remains one of the central problems of catchment hydrology. Flow processes in a one-dimensional sloping aquifer can be described by Boussinesq's hydraulic groundwater theory. Most hillslopes, however, have complex three-dimensional shapes that are characterized by their plan shape, profile curvature of surface and bedrock, and the soil depth. Field studies and numerical simulation have shown that these attributes are the most significant topographic controls on subsurface flow and saturation along hillslopes. In this paper the Boussinesq equation is reformulated in terms of soil water storage rather than water table height. The continuity and Darcy equations formulated in terms of storage along the hillslope lead to the hillslope-storage Boussinesq (HSB) equation for subsurface flow. Solutions of the HSB equation account explicitly for plan shape of the hillslope by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function. We investigate the behavior of the HSB model for different hillslope types (uniform, convergent, and divergent) and different slope angles under free drainage conditions after partial initial saturation (drainage scenario) and under constant rainfall recharge conditions (recharge scenario). The HSB equation is solved by means of numerical integration of the partial differential equation. We find that convergent hillslopes drain much more slowly compared to divergent hillslopes. The accumulation of moisture storage near the outlet of convergent hillslopes results in bell-shaped hydrographs. In contrast, the fast draining divergent hillslopes produce highly peaked hydrographs. In order to investigate the relative importance of the different terms in the HSB equation, several simplified nonlinear and linearized versions are derived, for instance, by recognizing that the width function of a hillslope generally shows smooth transition along the flow direction or by introducing a fitting parameter to account for average storage along the hillslope. The dynamic response of these reduced versions of the HSB equation under free drainage conditions depend strongly on hillslope shape and bedrock slope angle. For flat slopes (of the order of 5%), only the simplified nonlinear HSB equation is able to capture the dynamics of subsurface flow along complex hillslopes. In contrast, for steep slopes (of the order of 30%), we see that all the reduced versions show very similar results compared to the full version. It can be concluded that the complex derivative terms of width with respect to flow distance play a less dominant role with increasing slope angle. Comparison with the hillslope-storage kinematic wave model of Troch et al. [2002] shows that the diffusive drainage terms of the HSB model become less important for the fast draining divergent hillslopes. These results have important implications for the use of simplified versions of the HSB equation in landscapes and for the development of appropriate analytical solutions for subsurface flow along complex hillslopes
    De betekenis van landbouwhuisdieren in de hulpverlening : resultaten van interviews met professionals op zorg- en kinderboerderijen
    Hassink, J. - \ 2002
    Wageningen : Plant Research International - 50
    vee - mens - relaties - psychosociale aspecten - psychotherapie - jeugdzorg - beperkingen - risicoschatting - nederland - schoolboerderijen - zorgboerderijen - livestock - man - relationships - psychosocial aspects - psychotherapy - child welfare - risk assessment - netherlands - labour - school farms - social care farms
    Veranderingen in mens-dierrelaties en hun impact op de veehouderij van 2040
    Ketelaar-de Lauwere, C.C. ; Blokhuis, H.J. ; Dagevos, H. ; Ipema, A.H. ; Stegeman, J.A. - \ 2000
    Wageningen : IMAG (Rapport / IMAG 2000-6) - ISBN 9789067546096 - 52
    relaties - dieren - mens - dierhouderij - dierenwelzijn - biotechnologie - biologische landbouw - innovaties - relationships - animals - man - animal husbandry - animal welfare - biotechnology - organic farming - innovations
    Irrigating lives : development intervention and dynamics of social relationships in an irrigation project
    Magadlela, D. - \ 2000
    Agricultural University. Promotor(en): N.E. Long. - S.l. : S.n. - ISBN 9789058081575 - 294
    ontwikkelingsprojecten - irrigatie - ontwikkeling - interventie - plattelandsontwikkeling - sociale verandering - sociale interactie - relaties - dynamica - sociologie - zimbabwe - development projects - irrigation - development - intervention - rural development - social change - social interaction - relationships - dynamics - sociology - zimbabwe

    This study is about rural agricultural development and social processes of change in rural Zimbabwe. It is aimed at understanding how irrigation intervention in a remote rural context changed the cultural, social, political and farming lives of people. It is a study of people coping with changes in their livelihoods which had been introduced from outside by development intervention. The study was sustained by the realisation that irrigation is not just a matter of technical artefacts, but has much to do with people, especially the people it is meant to benefit. Development practitioners and researchers should be interested not only in irrigation performance, but also in how people manipulate the irrigation resources available to them. How does irrigation development change the lives of the irrigators over time? How is it transformed and adapted by them? How does it change their perceptions of each other in view of their local social identities and differences? What do irrigation farmers use to gain improved access to irrigation resources? How do they manipulate their social, political, technical and management environments to their benefit? What lessons can we derive from "targeted" beneficiaries' analyses of how their lives have been transformed by development intervention?

    The study focuses on social constructions of cultural identities, on social interaction and change among smallholder farmers in the context of irrigation development intervention in Eastern Zimbabwe. It shows how the introduction of an irrigation scheme not only created, but also nurtured and promoted processes of cultural identity and social differentiation among groups of rural producers who had previously had but few distinguishing social characteristics (such as ethnic affiliation). It is a study of how the irrigation context helps to highlight their social and cultural differences and leads to social conflicts and leadership struggles, and to how different individual actors devise strategies, such as enrolling outsiders into local struggles, to achieve their often conflicting group and individual objectives. The analysis portrays the irrigation scheme as a social and political 'domain' in which different groups of farmers and outsiders engage each other in negotiations over resources, and the meanings attached to these resources. In some instances, the irrigation domain is seen as an arena, a contested area where struggles take place over a diversity of livelihood resources such as water and land.

    The study used the actor-oriented perspective as the theoretical basis for the analysis of research findings. An actor-oriented approach helps one recognise the agency of social actors in interactive situations. It requires a full analysis of the ways in which different social actors manage and interpret new elements in their life-worlds. The capacity of social actors to influence and shape their social surroundings is one of the salient features of the approach used in this Nyamaropa study.

    The study is also about the omnipresence of encounters and clashes of different 'world-views' at the local level in the irrigation scheme. The clashes take place in the social, technical, administrative, managerial and political domains. It looks at how the different 'life-worlds' accommodate to each other in actors' daily interactions to give a semblance of harmony and attraction, co-existing with conflict and rejection. It is an analysis of the dynamism of social differences in irrigation intervention, and in any development intervention for that matter, that reveals the multiplexity of actors' interactions, and how their multiple relations and interlocking projects generate potentially explosive social exchanges. The study starts from the bottom, as it were, in its analysis of how different people in a specific rural development context create and live with complex social relations where daily interaction is characterised by strategic negotiation and mutual enrolment in other actors' projects. The analysis focuses more on local level dynamics, and does not deal, for example, with the politics of decision-making at higher levels of administration, such as the province or central government departments under which smallholder irrigation development falls. The study does, however, acknowledge the inevitable, sometimes useful role of macro-policy structures in influencing development outcomes at the local level.

    As a sociological study, this research work focused on how people interacted, worked together, settled differences and used community resources in their daily struggles for survival. Irrigation literature in Zimbabwe has only recently begun to pay specific attention to the fact that irrigation development is essentially a social process. Part of the objective here is to contribute to the debate about how rural actors manage their differentiated irrigating lives, discourses, struggles and negotiations, conflicts and accommodations in their constantly changing social environments. In order to examine this complex social process, it was proposed to undertake a detailed analysis of one irrigation scheme and its impact both on farmers practising irrigated agriculture and on surrounding dryland communities.

    The thesis is divided into four parts. Part One gives 'the story behind the study'. Then there is a background to the study in the form of Chapter 2. This chapter provides what I have called The Setting. This is Zimbabwe's agricultural history, the history of smallholder irrigation development in the country, a background to Nyamaropa irrigation intervention, and an introduction to the different social and political actors who appear throughout the book.

    Part Two is about the embeddedness of social, political and power relationships, social and economic differences, in land and water resources. Chapter 3 deals with struggles over land and water among irrigation farmers. There is a debate on water ownership from the different actors' standpoints in the Nyamaropa area. This chapter is central in the sense that it introduces the crucial issues of cultural and social identity in relations between formal irrigators and non-irrigators, between original inhabitants of the now irrigated area and immigrants to the same area. These are some of the issues that set the scene for case analyses of the dynamics of development intervention, constructions and reconstructions of cultural and social identities and differences.

    Chapter 4, also in Part Two, is about the issue of different claims to water use, between irrigation farmers in the Nyamaropa project, and villagers in the catchment area who use river water which is the source of water for the irrigation scheme downstream. Here the argument is that spatial distinctions, cultural identities, and a strong sense of communal existence, constitute a crucial entry point for the analysis of ways of assembling claims to resource use by different actors. Differences in community organisation feature as competing aspects of claims to resource utilisation.

    Part Three is about the irrigation domain as a shared life-world. Chapter 5 is on gender images and irrigation life. There are cases of widows who struggle to survive in a tough and competitive irrigation environment. A salient feature of this chapter is how women relate to the irrigation scheme through their families or individual plots. Walking through the irrigation scheme one is struck by a common feature of the area: over seventy percent of people one sees working or meets in the fields are women and children, with the majority of them being women. A surprising, yet refreshing, phenomenon in the Nyamaropa irrigation scheme is that almost thirty percent of registered plotholders are widows! Some of them registered as widows when their men worked in town, so that they would have access to irrigated plots. This was a stratagem to beat the rule prohibiting those with wage-earning spouses from having access to irrigated land. It worked, to their advantage.

    Chapter 6 focuses on irrigation extension specifically. This provides cases of farmers' encounters with Agritex (the national extension agency), and reveals the different views of similar situations between farmers and outsiders, and among farmers themselves in the presence of outsiders. This chapter focuses on one of the central issues in the study: that of how social differences among people impact on their responses to new knowledge and information. In this case, it is a matter of how farmers relate to Extension Workers as promoters of change, improvement and innovation.

    Part Four is on official (and unofficial) regulations and practices, looking especially at government practice through Agritex and the traditional institution through the Headman. Chapter 7 deals with a delicate and sensitive subject of age, inheritance, sub-leasing and renting, and the irrigation rules which were ignored. The average age of plotholders in Nyamaropa was approximately 55 years, though there were plotholders as old as 84 years. Most of them were first generation plotholders. These were farmers who cleared the plots themselves when the project started in the late fifties. Most of the elderly irrigators were too old to fully utilise their irrigation plots, but still retained their names in the register. They regarded irrigation land as their family asset, against the official rule that they were lessees on state land. To maintain productivity, they sub-leased their plots to dryland farmers who needed irrigated land for food. Some of them had established networks with local businessmen who rented part of their land in return for paying irrigation fees for the plotholders. There were some long-term relationships of mutual assistance between the different types of farmers. Rules and regulations are seen here as among the tools at farmers' disposal in their constant negotiations for 'better deals' among themselves and with their resident Extension Workers.

    Chapter 8 is the only chapter in Part Five. This section provides conclusions and theoretical analyses of research findings. It contextualises social difference and cultural identity in the life-situations of irrigators and drylanders in Nyamaropa. Discussed here are issues of how the different social groupings fit into the whole story of social dynamics of development intervention, and what some social theorists say on the issue of cultural identity and social difference (which is not much so far). This chapter brings together different theoretical issues raised in case material in the chapters before it. Chapter 8 also looks into problems facing 'irrigating lives' in smallholder irrigation schemes in the context of external intervention, and the issues and contradictions surrounding concepts such as cultural identity, and strategic difference in rural development.

    One hopes that such a study will initiate a process that will lead to bringing out and appraising differences among development programme beneficiaries to make interventions not merely effective (by externalised criteria), but also meaningful to the range of people whose lives are unavoidably affected by its introduction. The study will help in the general understanding of social dynamics of rural development, of land reform and of poverty-reduction strategies in Zimbabwe and the Southern African region.

    Trekkers naast de trap : een zoektocht naar de dynamiek in de relatie tussen boer en overheid
    Hees, E. - \ 2000
    Agricultural University. Promotor(en): J.D. van der Ploeg; J. de Vries. - S.l. : S.n. - ISBN 9789058083234 - 181
    boeren - regering - relaties - landbouwbeleid - belangengroepen - nederland - verhoudingen tussen bevolking en staat - farmers - government - relationships - interest groups - agricultural policy - netherlands - relations between people and state

    This book describes a sociological expedition to the core of the relationship between farmers and government in the Netherlands. It focuses on the concept of mediation of agricultural policies between government and the farming target group. A starting point in this expedition is the rejection of the idea of policy-formation as a rational-synoptical chronology, in which policy is the result of a well-defined rational choice by politicians and administrators from different scenario's. Instead, policy formation in this context is understood as an incremental process: policies as a result of interaction between context induced actors. However, instead of being coincidental the interactions show up patterns of regularity that formed the motivation for this study.

    Policy mediation is defined as:

    the interrelated moments of preparation, formation, implementation and evaluation of policies,which by means of interactive processes, in which various actors (public servants, politicians, citizens, farmers, etc.) participate with their groups and projects (strategically),are geared to one another in such a manner, thatexactly therefore a legitimacy is obtained which otherwise would definitely be absent.

    The target group of agricultural policies is a so-called difuse one. That is, in need of intermediary structures able to mediate policies. The Dutch Agricultural Board (Landbouwschap) played this intermediary structure role between 1954 en 1996, when it promptly disappeared.

    In the meantime, several farmers' cooperative initiatives in one way or another have assumed the role of intermediary organizations. Central government tended to standardize their attitude towards these structures, in order to manage the policy mediation fluently. The objective of this investigation, however, is to analize and maintain the diversity of intermediary organizations. The reason is the assumption that succesful policy mediation depends on the taking account of the specifity of each structure.

    The central questions therefore are:

    in which different arrangements has the mediation of agricultural policies taken place so far,by which means could be obtained more success in terms of dynamic and legitimated policy mediation.

    Chapter 2 provides a theoretical approach of the relation between farmer and government, defining it as a particularisation of the relation between actor and structure. Instead of adhering to dualistic theories, which focus upon the complete determination of the individual by its surrounding structure (determinism) or upon the complete absence of such a determination (voluntarism), this study prefers duality as a key concept. Duality focuses upon the co-existence of contraint and enableness of the individual versus itssurrounding structure. Individuals actively make and remake social structure.

    The relation between citizen and government is subject of a process of legitimation. Public administration and policies are legitimized by:

    the procedure, with given objectives (the instrumental side of legitimation);the objectives of policies (the social contract side); andthe interchange of both.

    The chapter ends up presenting a social scientific tool to capture this legitimation process: policy-mediation.

    In chapter 3 policy mediation is surveyed in the Dutch socio-cultural heritage. In the Netherlands a strong tradition of subsidiarity and functional decentralization was founded in past centuries. The social charter of neo-corporatism is known because of its emphasis on consensus, compromise and consultation.

    Growing claims, policy overload, role distortions between public and private parties and he public opinion have shocked the traditional charter and caused a legitimation problem. Different answers are possible, varying from enforcening the state to enforcening the consensus model. In this report, there is a strong case for investing more in interdependency and participative democracy. The Dutch case shows different examples: coproduction of local policies, convenants between public governement and private parties, the socalled Green Polder Model. Although there is room for doubt because of (a) gaps between frontiers ans crowds, (b) interaction used only for self-interest. That is the risks of pseudo-participation. Therefore, field investigations are urgently needed.

    In chapter 4 an overview is given of the legitimation of agricultural policies in the Netherlands since the 19th century. The co-production tradition of farmers' organizations and central government, founded on a consensus about (a) the type of agricultural development to be nagestreefd, and (b) the need of consultation and compromise, ended up in a policy-community or - more precisely - iron triangle between farmers-leaders, ministry of agriculture and national politicians. From the late 60's, tensions grew between these parties and the iron triangle eroded. A vacuum in policy mediation became clear. Farmers reacted by protest, adaptation, individual initiatives and creating new collectivities, that became seeds of new arrangements. The following chapters describe the investigation of these new arrangements.

    Chapter 5 is a methodological intermezzo. It motivates why the sociological expedition is founded in daily reality, by describing caracteristics of factual initiatives as many and as detailed as necessary to get a sharp distinction between policy arrangements.

    In chapter 6 and 7 an inventory is made of the variation of possible arrangements, making use of 14 real collectivities in the Dutch countryside between 1980 and 1997. By adopting a cluster analysis 6 different arrangements are identified: product cooperative, horzelorganisation, farmers' association, policy cooperative, investigation cooperative and sindical organisation.

    Describing various cases in the Netherlands, in chapter 8 each arrangement is examined on its potential in terms of producing more dynamics in policy mediation. Chapter 9 also examines this potential, but now by evaluating an official policy experiment with 8 socalled environmental cooperatives (milieucoöperaties) from 1995 to 1999.

    In chapter 10, the conclusions of the expedition are summarized. The experiences of farmers' collectivities up to 1997 make clear that the state and its institutions (first of all the ministry of agriculture) are rather confused when defining an attitude against the calls for self-regulation that come from below. The state seems to get paralyzed by pleas for self-regulation on one side and the necessity to maintain principles of Good Governance on the other, one of which is gelijkberechtiging. Tailor-made policy solutions may come in conflict with the tendency to govern unilaterally from a cockpit.

    By way of recommendations, several triggers are derived from the expedition process, triggers that may give impetus to a more dynamic and prosperous relation between government and farmers. First of all, the actual situation should be understood better and more systematically by all of the parties involved. Potentials for succesful policy-mediation often aren't recognized as such.

    Next, cooperative initiatives shouldn't be put in one category too soon. Regionality, local culture and specifity are important factors for succes in policy-mediation along more selfregulation. The recognition and admission of the role local initiatives can play in succesful policy-arrangements should result in more incentives instead of penalties. State institutions should provoke and belonen a more entrepreneurial attitude of farmers. Another factor that may trigger a more dynamic relationship is the maintenance of the face-to-face caracter of policy-mediation. The personal committment of the parties involved, crucial within the agricultural population with so many individual interests and responsabilities, depends on the involvement of face-to-face contacts. This means more emphasis should be laid on local government instead of national.

    De academie van het ongewone leven : Columns over universiteit en gezin
    Hoog, K. de - \ 2000
    Wageningen : Stichting Cereales - ISBN 9789080572423 - 119
    gezinsleven - universiteiten - relaties - onderwijs - family life - universities - relationships - education
    Bosbouw en plattelandsontwikkeling in Europa
    Elands, B. ; Wiersum, F. - \ 1999
    Nederlands Bosbouwtijdschrift 71 (1999)5. - ISSN 0028-2057 - p. 204 - 207.
    bosbouw - bossen - bosbouwontwikkeling - ontwikkeling - bebossing - plattelandsontwikkeling - platteland - landbouw - relaties - bosbeleid - onderzoek - europese unie - europa - forestry - forests - forestry development - development - afforestation - rural development - rural areas - agriculture - relationships - forest policy - research - european union - europe
    Typologie van plattelandsontwikkeling en plattelandsvernieuwing, de verschillende visies op de gewenste richting van plattelandsvernieuwing (agri-ruraal; utilitair; hedonistisch), en de rol die bosbouw en vergroting van het bosareaal in Europees verband hierbij kan spelen
    Is er toekomst voor het agrarisch onderwijs?
    Bor, W. van den - \ 1998
    Agrarisch Onderwijs 40 (1998). - ISSN 0925-837X - p. 12 - 16.
    agrarisch onderwijs - onderwijs - samenleving - sociaal welzijn - sociale structuur - sociale verandering - scholen - relaties - lerarenopleiding - welzijn - bijscholing - agricultural education - education - society - social welfare - social structure - social change - schools - relationships - teacher training - well-being - continuing training
    Aandacht voor onderwijsvernieuwing waarbij vragen van arbeidsmarkt en maatschappij om antwoord vragen
    Suggestions for an oystercatcher population model
    Ens, B.J. ; Meer, J. van der - \ 1997
    Wageningen : IBN-DLO (IBN research report 97/1) - 83
    dieren - populatiedichtheid - populatie-ecologie - mortaliteit - populatiegroei - relaties - mens - wiskundige modellen - onderzoek - computersimulatie - simulatie - simulatiemodellen - waadvogels - animals - population density - population ecology - mortality - population growth - relationships - man - mathematical models - research - computer simulation - simulation - simulation models - waders
    Ketens en plattelandsontwikkeling; markt-, keten- en netwerkkennis toegepast op het landelijk gebied: een programmeringsstudie
    Hillebrand, J.H.A. ; Borgstein, M.H. ; Graaff, R.P.M. de; Scherpenzeel (Rijksuniv.), J.F. ; Sijtsma (RU.), F.J. ; Strijker (RU.), D. - \ 1997
    Den Haag : Nationale Raad voor Landbouwkundig Onderzoek - ISBN 9789050590426 - 96
    plattelandsplanning - plattelandsontwikkeling - sociale economie - marketing - bedrijfsvoering - markten - marktconcurrentie - aanbodsevenwicht - intermenselijke relaties - relaties - consumenten - onderzoek - vraag - consumentengedrag - landbouw - productiestructuur - agrarische structuur - overheidsbeleid - economie - wetgeving - Nederland - economische planning - rural planning - rural development - socioeconomics - marketing - management - markets - market competition - supply balance - interpersonal relations - relationships - consumers - research - demand - consumer behaviour - agriculture - production structure - agricultural structure - government policy - economics - legislation - Netherlands - economic planning
    Grondverwerving voor natuur: het rijk van provincies? De provinciale oriëntaties op grondverwerving voor bosuitbreiding in de Randstad, natuurontwikkeling en reservaatvorming
    Kuindersma, W. ; Zweegman, G.J. - \ 1997
    Wageningen : IBN-DLO - 89
    natuurbescherming - beleid - bedrijfsvoering - natuurreservaten - herstel - overdrachten van grond - land - acquisitie - regionaal bestuur - bosbouw - hulpbronnen - relaties - bossen - milieubescherming - conservering - nederland - natuur - natuurtechniek - provincies - districten - nature conservation - policy - management - nature reserves - rehabilitation - land transfers - land - acquisition - regional government - forestry - resources - relationships - forests - environmental protection - conservation - netherlands - nature - ecological engineering - provinces - districts
    Bosuitbreiding in Nederland ligt niet op schema
    Edelenbosch, N.H. - \ 1997
    Nederlands Bosbouwtijdschrift 69 (1997)5. - ISSN 0028-2057 - p. 231 - 236.
    bosbouw - weiden - bossen - landbouwgrond - relaties - ontbossing - bebossing - landbouwstatistieken - oppervlakte (areaal) - nederland - forestry - pastures - forests - agricultural land - relationships - deforestation - afforestation - agricultural statistics - acreage - netherlands
    Gemeenten kunnen meer bos aanleggen; evaluatie van bosuitbreiding door gemeenten
    Doppenberg, M.H. ; Landman, A.V. ; Edelenbosch, N.H. ; Hekhuis, H.J. - \ 1997
    Groen : vakblad voor groen in stad en landschap 53 (1997)11. - ISSN 0166-3534 - p. 40 - 45.
    bosbouw - landgebruik - pachtstelsel - bebossing - hulpbronnen - relaties - economie - gebruikswaarde - economische impact - forestry - land use - tenure systems - afforestation - resources - relationships - economics - use value - economic impact
    Mushrooms: more than just taste (in Dutch)
    Leguijt, C. ; Valk, H.C.P.M. van der; Sanders, M.G. ; Termeer, A.G.W. ; Vuurst de Vries, R.G. van der; Yüksel, D. ; Wichers, H.J. - \ 1997
    De Champignoncultuur 41 (1997)8. - ISSN 0009-1316 - p. 277 - 285.
    agaricus - chemische structuur - relaties - organoleptische kenmerken - markten - marketing - marktconcurrentie - aanbodsevenwicht - tuinbouwgewassen - biologische eigenschappen - agaricus - chemical structure - relationships - organoleptic traits - markets - marketing - market competition - supply balance - horticultural crops - biological properties
    Het versterken van de positie van Nederlandse champignonbedrijven is nodig om de afzetmogelijkheden te verruimen. Drie deelprojecten zijn genoemd die in het kader van de afzet worden uitgevoerd. Het eerste dat gaat over de karakterisering van smaak, geur en textuur van verse champignons is in dit artikel uiteengezet
    Economics of timber plantations on CO2-emissions in the Netherlands.
    Slangen, L.H.G. ; Kooten, G.C. van; Rie, J.P.P.F. van - \ 1997
    Tijdschrift voor sociaalwetenschappelijk onderzoek van de landbouw 12 (1997)4. - ISSN 0921-481X - p. 318 - 333.
    broeikaseffect - opwarming van de aarde - bosbouw - weiden - bossen - landbouwgrond - relaties - ontbossing - bebossing - overheidsbeleid - landbouwbeleid - agrarisch recht - nederland - greenhouse effect - global warming - forestry - pastures - forests - agricultural land - relationships - deforestation - afforestation - government policy - agricultural policy - agricultural law - netherlands
    Met een kosten-batenanalyse wordt nagegaan in welke mate bebossing van landbouwgronden in Nederland een kostenefficiente methode kan zijn om de CO2-concentratie te verlagen
    Essays in economics of renewable resources
    Bulte, E.H. - \ 1997
    Agricultural University. Promotor(en): H. Folmer; W.J.M. Heijman. - S.l. : Bulte - ISBN 9789054856993 - 283
    duurzaamheid (sustainability) - natuurlijke hulpbronnen - hulpbronnengebruik - bescherming - herstel - milieu - kwaliteit - controle - verontreinigingsbeheersing - milieubeheer - bosbouw - weiden - bossen - landbouwgrond - relaties - ontbossing - bebossing - vis vangen - visserij - economie - tropen - nationaal vermogen - sustainability - natural resources - resource utilization - protection - rehabilitation - environment - quality - control - pollution control - environmental management - forestry - pastures - forests - agricultural land - relationships - deforestation - afforestation - fishing - fisheries - economics - tropics - national wealth

    In dit proefschrift neem ik een aantal onderwerpen die betrekking hebben op de economische theorie van beheer van natuurlijke hulpbronnen onder de loep. Voorbeelden van natuurlijke hulpbronnen zijn visvoorraden, bossen en olie. Het onderzoeksveld is breed en biedt keuze uit een scala aan onderwerpen, ieder met zijn eigen problemen, eigenaardigheden en interessante aspecten. Aangezien de afzonderlijke hoofdstukken van dit proefschrift afgesloten worden met een concluderende en samenvattende sectie, zal ik deze samenvatting kort houden.

    De hoofdstukken 1 en 2 betreffen een inleidend literatuuronderzoek. In hoofdstuk 1 wordt het onderzoeksveld afgebakend en worden enkele basisbegrippen besproken. Twee centrale thema's zijn "duurzaamheid" en "efficientie". Duurzaamheid heeft betrekking op gelijke toegang tot natuurlijke hulpbronnen door verschillende generaties. Efficiëntie betekent het (intertemporeel) maximaliseren van een doelfunctie. Het maximaliseren van "de winst of "het nut voor de samenleving" zijn veel gebruikte voorbeelden van dergelijke functies. Na de Earth summit in Rio de Janeiro in 1992 zou "duurzaamheid" wellicht het belangrijkste thema van de twee dienen te zijn, maar er bestaat in de literatuur veel verschil van inzicht over de exacte interpretatie van dit begrip. De interpretatie is subjectief en onder andere afhankelijk van de inschatting van de toekomstige substitutie-mogelijkheden tussen de verschillende productiefactoren (bijvoorbeeld tussen natuurlijk en fysiek kapitaal), en van de mogelijkheden die in de toekomst door technologische vooruitgang geboden zullen worden.

    De interpretatie van efficiëntie is helder, en de mainstream van de neoklassieke economen is traditioneel gericht op dit thema. (Van meer recente aard zijn modellen waarin de beide thema's gecombineerd worden.) De meeste hoofdstukken in dit proefschrift gaan in de eerste plaats over het efficiënt gebruik van (vernieuwbare) natuurlijke hulpbronnen.

    Het exploiteren van een natuurlijke hulpbron heeft invloed op de mogelijkheden voor toekomstig gebruik van deze voorraad. In geval van mijnbouw, bijvoorbeeld, gaat de huidige extractie van ertsen ten koste van grondstofwinning in de toekomst. Dit impliceert dat bij het delven van een eenheid erts, in aanvulling op de pure extractiekosten, rekening moet worden gehouden met de zogenaamde opportunity costs . In dit verband wordt met opportunity costs bedoeld de mogelijke baten die de eenheid erts in de toe komst had kunnen opleveren. Deze "extra" kosten verlagen de optimale hoeveelheid die geëxploiteerd dient te worden. Een belangrijke regel voor efficiënt gebruik van een niet-vernieuwbare hulpbron, zoals olie of steenkool, is dat onder bepaalde voorwaarden de groeivoet van de zogenaamde rent van de hulpbron (gedefinieerd als het verschil tussen de prijs en de marginale exploitatiekosten) gelijk moet zijn aan de interestvoet. Als deze regel opgaat zijn eigenaren van een hulpbron indifferent tussen huidige en toekomstige extractie: het rendement van het aanhouden van een voorraad van een bepaal
    de hulpbron is even hoog als het rendement van exploiteren en het verdiende geld vervolgens elders investeren of op de bank zetten. Dit is de bekende Hotelling regel.

    Voor efficiënt gebruik van hulpbronnen die zichzelf binnen een redelijke termijn kunnen vernieuwen, zoals een voorraad vis of een bos, moet de Hotelling regel aangepast worden. In de economie van dit soort hulpbronnen worden economische principes gecombineerd met biologische groeimodellen. Met behulp van bosbouwmodellen kan dan bijvoorbeeld de optimale omlooptijd van een gelijkjarig bos berekend worden. Met behulp van visserijmodellen wordt de optimale visstand in een bepaald gebied berekend. Het afzien van oogsten, bijvoorbeeld door een hoeveelheid bomen nog een jaar te laten groeien of door de jaarlijkse vangst van een bepaalde vissoort te verlagen, kan geïnterpreteerd worden als "investeren" in de hulpbron. Omgekeerd geldt dat oogsten gelijk staat aan desinvesteren. In hoofdstuk 2 van dit proefschrift wordt door middel van een literatuurstudie ingegaan op deze materie en op verwante zaken als eigendomsrechten (immers, wie wil investeren in een hulpbron als niet duidelijk is of de toekomstige baten toevallen aan hemzelf?) en de rol van overheidsbeleid.

    Hoofdstuk 3 en 4 zijn gewijd aan tropische ontbossing. Het directe verband tussen de commerciële kap van tropisch hardhout en ontbossing is uiterst zwak. Een veel belangrijkere factor is het "omzetten" van bossen in landbouwgrond (ongeveer 80% van alle ontbossing wordt veroorzaakt omdat ruimte voor landbouw, inclusief veehouderij, gemaakt moet worden). Zoals veel bosbouwers en milieubeschermers benadrukken bestaat er echter wel een sterk indirect verband tussen commerciële, selectieve houtkap en oprukkende landbouw. De bosbouwsector zorg namelijk voor het aanleggen van een infrastructuur in gebieden waar (selectief) gekapt is. Dit maakt het bedrijven van landbouw in deze gebieden aantrekkelijker.

    Een veel gehoorde beleidsaanbeveling is dat boeren uit de bossen geweerd moeten worden, bij voorkeur door een algemeen ontwikkelingsbeleid gericht op het tegengaan van te snelle bevolkingsgroei, het bevorderen van alfabetisering en het hervormen van de landbouwsector. Ongetwijfeld wordt hiervoor met de beste bedoelingen gepleit. Dit proefschrift toont echter aan dat dit beleid niet altijd bevorderlijk is voor natuurbehoud.

    In hoofdstuk 3 wordt de relatie tussen de (dreiging van) oprukkende boeren en het kaptempo van bosbouwers onderzocht. Omdat, zoals vermeld, conversie van bossen in landbouwgrond met name voorkomt in selectief gekapt bos, kunnen bosbouwers met kapconcessies voor meerdere jaren de schade door oprukkende landbouwers beïnvloeden door hun kapbeslissingen ("in welk tempo zet ik mijn ongestoorde, primaire bos om in makkelijk toegankelijk, secundair bos?") te veranderen. Het verminderen van schade zal overwogen worden indien het bosbouwers is toegestaan na verloop van tijd terug te keren naar het opengelegde gebied voor aanvullende kap. Met een model waar schade aan het bosbestand van een houtbedrijf positief gerelateerd is aan de omvang van het secundaire bos laten we zien dat de dreiging van oprukkende boeren twee effecten heeft. Aan de ene kant zullen bosbouwers de kap in toegankelijke bossen intensiveren om de brandende boeren vóór te zijn. Een andere reactie is het vertragen van de omzetting van ongestoorde (en ontoegankelijke) primaire bossen in secundaire bossen. We concluderen dat de dreiging van landbouwers leidt tot minder secundair en meer primair bos. Afhankelijk van de maatschappelijke waardering voor deze verschillende bossystemen kan dit uit oogpunt van natuurbehoud een verbetering of een verslechtering inhouden.

    Het huidige tempo van ontbossing is volgens velen te hoog. Een mogelijke verklaring is dat kapbedrijven een te hoge rentevoet hanteren bij het beslissen over de spreiding van kapactiviteiten over de tijd. Immers, veelal wordt verondersteld dat hogere discontovoeten (implicerend dat relatief meer belang wordt gehecht aan huidige consumptie dan aan toekomstige consumptie) ondubbelzinnig negatief uitpakken voor natuurbescherming. Een tweede doelstelling van hoofdstuk 3 is te onderzoeken of dit correct is in de context van een model waarin onderscheid gemaakt wordt tussen primaire en secundaire bossen en waarin een winstmaximaliserend bedrijf geconfronteerd wordt met een overheid die bepaalde eisen stelt. We laten zien dat hoge rentevoeten niet noodzakelijkerwijs versnelde kap uitlokken. Het selectief kappen van primair bos betekent namelijk automatisch dat secundair bos gecreëerd wordt. Bij optimaal bosbeheer wordt de winst door kap in beide typen bos in de afweging betrokken. We laten zien dat hoge discontovoeten de baten van het omzetten van primair bos in secundair bos verlagen. Daarmee wordt het tempo vertraagd waarin deze primaire bossen dienen te worden gekapt om de winst te maximaliseren.

    In hoofdstuk 4 onderzoeken we of het verschaffen van ontwikkelingsgeld aan ontwikkelingslanden een efficiënt instrument is om tropische ontbossing af te remmen. Op basis van een model waar de overheid van een Derde Wereldland de baten van bosbeheer maximaliseert, in dit geval opbrengsten uit verkoopbaar hout en niet-gebruikswaarden gekoppeld aan bosbescherming, is in het verleden geconcludeerd dat ontwikkelingshulp leidt tot extra bosbescherming. De redenering luidt als volgt: extra geld door middel van internationale transfers leidt tot meer consumptie in het Derde Wereldland, zodat de marginale baten van consumptie zullen dalen. Om het evenwicht te herstellen moeten de marginale baten van bosbescherming ook dalen, hetgeen alleen bereikt kan worden door het bosareaal uit te breiden. We hebben dit model uitgebreid en realistischer gemaakt door een risico-mijdende overheid en onzekerheid met betrekking tot toekomstige houtprijzen te veronderstellen. Uiteraard leidt deze uitbreiding normaliter tot afremmen van de kapinspanning. In aanvulling op dit effect hebben internationale donaties in het uitgebreide model een tweede effect: de overheid wordt door het extra geld minder risico-mijdend en laat zich in mindere mate door de onzekere prijzen afremmen om bos te kappen. De conclusie is dat de effectiviteit van internationale transfers als instrument om bij te dragen tot bosbescherming in het verleden is overschat.

    In hoofdstuk 5 en 6 behandelen we enkele economische achtergronden van het beschermen van bepaalde diersoorten. In hoofdstuk 5 staat het verbod op de handel in ivoor centraal. Met de bedoeling om olifanten te beschermen is hiertoe, na enkele decennia van grootschalige olifantenslacht, besloten aan het einde van de jaren '80. Tot op heden heeft dit beleid bijgedragen aan herstel van olifantenpopulaties. Met een eenvoudig economisch model hebben we onderzocht of een handelsverbod altijd dit effect zal blijven hebben. Dit is waarschijnlijk niet het geval. Voor een overheid levert het beheren van een populatie levende olifanten verschillende baten op: het trekt toeristen aan en, na eventuele opheffing van het verbod, zijn olifanten een bron van ivoor en andere nuttige producten. Aan de andere kant leveren olifanten schade op aan landbouwgewassen en mogelijkerwijs ook aan natuurparken. Zolang het handelsverbod gehandhaafd blijft zal een overheid proberen de baten van de bescherming van een extra olifant (in dit geval dus inkomsten uit toerisme) gelijk te stellen aan de kosten die deze olifant met zich meebrengt. Dit wordt bereikt door regelmatig olifantenpopulaties uit te dunnen, ook al mag het aldus verkregen ivoor niet verkocht worden. Dergelijke operaties zijn in enkele landen al aan de gang. Indien het handelsverbod wordt opgeheven zal de overheid olifanten ook beschouwen als een vernieuwbare bron van ivoor. Het bejagen van olifanten voor ivoor levert dan directe baten op en het laten leven van een olifant wordt een soort van investering. Met behulp van data voor Afrika in het algemeen en Kenia in het bijzonder laten we zien dat de optimale populatie olifanten zoals die met een handelsverbod door een overheid wordt nagestreefd niet noodzakelijkerwijs groter is dan de optimale populatie met handel in ivoor. Een belangrijke factor die de optimale hoeveelheid olifanten in de situatie met handel bepaald is de hoogte van de discontovoet die de overheid gebruikt. Een hoge discontovoet leidt tot lage olifantenpopulaties wanneer handel in ivoor is toegestaan, en omgekeerd. De discontovoet waarbij de hoeveelheid olifanten met handel in ivoor de optimale populatie met een handelsverbod overtreft is in de nabijheid van de "sociale discontovoet". Als de discontovoet zoals gehanteerd door Afrikaanse overheden lager wordt dan deze break even discount rate, dan zijn olifanten gebaat bij handel in ivoor. Aangezien de discontovoet waarschijnlijk niet constant is (veelal wordt verondersteld dat de discontovoet een afnemende functie van het inkomen is), concluderen we dat olifantenbeschermers in de toekomst wellicht zullen moeten pleiten voor opheffing van het handelsverbod. In het model hebben we geen rekening gehouden met stroperij. Dit beschouwen we een van de noodzakelijke uitbreidingen voor de toekomst.

    In hoofdstuk 6 bekijken we de economische achtergrond van het verbod op de commerciële walvisvaart. We berekenen de optimale hoeveelheid dwergvinvissen in het Noordoostelijk deel van de Atlantische oceaan met behulp van een model waarin we rekening houden met de niet-gebruikswaarden van levende walvissen (de populariteit van organisaties als Greenpeace geeft aan dat veel mensen "nut" ontlenen aan levende walvissen). In tegenstelling tot ander onderzoek concluderen we dat de huidige populatie dwergvinvissen te laag is. Bovendien blijkt dat het optimaal is om volledig van walvisvangst af te zien tot de populatie gegroeid is tot de optimale omvang. Het moratorium is dus economisch te verdedigen. In het hoofdstuk demonstreren we tot slot dat een simpel statisch model, dat door sommige onderzoekers wordt gebruikt om dit soort problematiek te benaderen, ongeschikt is. Het model leidt tot beleidsaanbevelingen die diametraal tegenover de beleidsimplicaties van een dynamische specificatie staan.

    De hoofdstukken 7, 8 en 9 betreffen visserijeconomie. Zoals besproken in hoofdstuk 2 heeft exploitatie van de zee gedurende een lange tijd plaatsgevonden onder condities van open access. Dit betekent dat het niet mogelijk was om geïnteresseerde vissers te weren van bepaalde visgronden. Omdat niemand geweerd kon worden, voelde niemand zich verantwoordelijk voor een duurzaam beheer. Iedereen zal proberen op zo kort mogelijk termijn zo veel mogelijk geld te verdienen door vis te vangen voordat een andere visser daar aan toe komt. Onder open access verdwijnt de rent volledig: er wordt zoveel gevist dat de prijs uiteindelijk gelijk is aan de marginale vangstkosten. Aan het eind van de jaren '70 is aan deze toestand een einde gekomen door het instellen van exclusieve zones waarbinnen overheden het recht krijgen om buitenstaanders te weren en eigen beleid te voeren. We hebben in hoofdstuk 7 onderzocht of de overgang van open access naar een situatie waar overheidsbeleid gevoerd kan worden heeft geleid tot een beter beheer van visbestanden. Op basis van de economische theorie kan voorspeld worden dat overheden (net als bedrijven met gegarandeerde eigendomsrechten) rekening houden met levende vissen als investering. Dit betekent dat de rent van de hulpbron positief moet worden. Empirisch onderzoek met behulp van Duitse data wijst uit dat de rent inderdaad positief geworden is na instellen van Europees visserijbeleid.

    De conclusie uit hoofdstuk 7 is zeker niet dat het huidige beleid optimaal is. Er werd slechts geconcludeerd dat vergeleken met vroeger de hulpbron nu efficiënter geëxploiteerd wordt. Ander onderzoek heeft aangetoond dat het huidige beleid verre van optimaal is. Een verklaring voor suboptimaal visserijbeheer (die verrassend vaak over het hoofd wordt gezien) is dat de standaard-veronderstelling dat overheden proberen "de welvaart voor de samenleving te maximaliseren", niet opgaat. De overheid wordt beïnvloedt door belangengroepen met bepaalde doelstellingen, die kunnen afwijken van wat sociaal wenselijk is. In hoofdstuk 8 laten we zien dat een belangengroepen- benadering, waarin we vissers, arbeiders en consumenten onderscheiden, leidt tot beheer dat afwijkt van hetgeen standaardmodellen voorschrijven. De observatie dat er onvoldoende vis rondzwemt in de Noordzee hoeft niet noodzakelijkerwijs te impliceren dat de overheid haar doelstellingen niet haalt door het verkeerd inzetten van bepaalde instrumenten. Het kan even goed wijzen op afwijkende doelstellingen als gevolg van lobbyende belangengroepen.

    In hoofdstuk 8 wordt expliciet rekening gehouden met de "macht" van de visserijsector. Het is niet realistisch om te veronderstellen dat een overheid simpelweg een bepaald beleid kan voeren dat rechtstreeks tegen de belangen van bepaalde groepen ingaat. In hoofdstuk 9 laten we zien hoe, in het geval van de visserij, een overheid beperkende maatregelen (zoals het verkleinen van quota) kan doorvoeren zonder de belangen van de vissers al te zeer te schaden. Het instellen van een termijnmarkt voor verhandelbare visquota neemt het prijsrisico dat vissers lopen voor deze quota weg. Dit betekent dat een risico-mijdende visser beter af is dan voorheen. Dit biedt het perspectief om op hetzelfde moment het quotum te verlagen, zodat per saldo de visser niet beter of slechter af is. Financiële instrumenten kunnen dus (in theorie) leiden tot bescherming van natuurlijke hulpbronnen.

    Het proefschrift bevat tot slot twee hoofdstukken over bosbouw waarin onzekerheid een belangrijke rol speelt. In hoofdstuk 10 laten we zien hoe een bepaald soort onzekerheid met betrekking tot de (veelal strijdige) voorkeuren van beleidmakers (bijvoorbeeld: "werkgelegenheid is heel belangrijk, maar de hoeveelheid natuur mag niet veel kleiner worden") geïncorporeerd kan worden in een landgebruiksmodel. Daarnaast behandelen we onzekerheid die samenhangt met gebrekkige kennis omtrent technische coëfficiënten in bosbouwmodellen. We gebruiken fuzzy set theorie, gebaseerd op membership functions, om onzekerheid te modelleren. Een cruciaal aspect van fuzzy logic is dat elementen gedeeltelijk tot een bepaalde set kunnen behoren. We vinden dat de resulterende landallocatie te verkiezen valt boven de uitkomsten van een rechttoe-recht-aan model.

    In hoofdstuk 11 behandelen we een heel ander soort onzekerheid. Zoals boven vermeld fluctueren houtprijzen in de praktijk. In tegenstelling tot .fuzzy set theorie (waarbij niet het plaatsvinden van een gebeurtenis onzeker is, maar de gebeurtenis zelf) is de kansverdeling van de stochastische prijs bekend. In de literatuur is een zoekmodel met reserveringsprijzen ontwikkeld om de baten van een strategisch, flexibel kapbeleid (kappen wanneer de prijs hoger is dan de reserveringsprijs, afzien van kappen indien de prijs lager is) te kunnen vergelijken met de opbrengsten van het meer rigide Faustmann model (zie ook hoofdstuk 2). Uit studies blijkt dat de winsten van Boseigenaren met ongeveer 30% stijgen wanneer een reserveringsprijs-benadering gekozen wordt. In hoofdstuk 11 hebben we dit model uitgebreid door in aanvulling op strategische eindkap ook strategisch uitdunnen in ogenschouw te nemen. We vinden dat de reserveringsprijs voor uitdunnen altijd lager is dan de reserveringsprijs voor kappen en dat een strategisch kapbeleid ten aanzien van uitdunnen de winst van een boseigenaar substantieel verhoogd. De extra baten van flexibel uitdunnen zijn, in overeenstemming met de verwachtingen, minder groot dan de extra baten van het volgen van een strategisch eindkapbeleid.

    The structure of particle gels as studied with confocal microscopy and computer simulations
    Bos, M.T.A. - \ 1997
    Agricultural University. Promotor(en): B.H. Bijsterbosch; P. Walstra; J.H.J. van Opheusden. - S.l. : Bos - 108
    chemische structuur - optische eigenschappen - relaties - chemical structure - optical properties - relationships

    This thesis contains the results of a PhD-study on the structure of particle gels. Part of it is directed at a quantification of this structure from measured data, part of it at modelling the aggregation processes that lead to particle gels. Chapter 1 of this thesis is a general introduction describing the aim of this study.

    Chapter 2 introduces aggregation and gelation of particles. As to the modelling of aggregation we conclude that there are two types of approach: one based on thermodynamics and one based on fractal aggregation (Diffusion Limited Cluster Aggregation or DLCA). The former is appropriate for reversible aggregation, the latter for irreversible aggregation. For all types of colloidal aggregation which are in between these two extremes, an understanding based on both approaches is needed. We use fractal aggregation models as a starting point, but recognise the importance of cluster reorganisation, which will cause gels with structures different than predicted in DLCA. As to quantification of fractal structure, a lower cutoff length scale r 0 is suggested as a valuable addition to the fractal dimensionality d f .

    Chapter 3 describes Confocal Scanning Laser Microscopy (CSLM) as a tool to study the structure of various particle gels. An in-depth optical treatment of imaging in CSLM is presented, along with a new way of image enhancement using calculated three dimensional point spread functions. It is concluded that image enhancement is essential in order to get useful results from an analysis of CSLM micrographs.

    Chapter 4 shows the results on the fractal structure of particle gels derived from CSLM micrographs of colloidal model systems. It explains thoroughly the details of the image analysis procedure and identifies possible problems, most notably background intensities. From the results it appears that all fractal dimensionalities are about equal, with values larger than the DLCA limit. The values of r 0 show that there are significant differences between gel structures despite the similarities in d f . These differences are difficult to connect with properties of the colloidal model systems. A hypothesis about a ' pre- aggregation stage' is formulated which might serve as a starting point for further research.

    In Chapters 5 and 6 Brownian Dynamics simulations are used as a tool for forming a better connection between aggregation and gel structure. For aggregating Lennard-Jones systems (Chapter 5) we find percolating networks at high volume fractions; these appear to be formed by reorganisation of large aggregates, during which branched strands are formed with voids in between. The gel structure is influenced by both cluster growth and cluster reorganisation; fractal analysis gives non-universal, i.e. time dependent results. For the Lennard-Jones potential, the aggregation is dominated by cluster reorganisation. Aggregating particles with a shorter potential range (Chapter 6) also show time dependent fractal results, but by decreasing the potential range the balance between cluster growth and cluster reorganisation becomes more subtle. Reorganisation of clusters occurs at a lower rate when the potential range is decreased. A large potential well depth εboth promotes reorganisation and inhibits it because of irreversible clustering. A thermodynamical analysis shows that this effect will become more pronounced for shorter ranged potentials.

    Chapter 7 generalises the conclusions of all previous chapters and gives suggestions for further research. All results in this thesis have used available computing resources up to the maximum. Given the ever growing computing power, significantly more sophisticated techniques for simulation or image analysis will become available within years.
    The work described in this thesis has led to the following publications:

    J.H.J. van Opheusden, M.T.A. Bos, 'Induced flocculation of casein micelles - a Brownian Dynamics
    simulation on the Parsytec Gcel MPP', Future. Gener. Comp. Sy. 11123-133, 1995

    BE. Bijsterbosch, M.T.A. Bos, E. Dickinson, J.H.J. van Opheusden, P. Walstra, "Brownian dynamics simulation of particle gel formation: From argon to yoghurt", Faraday Discuss. 10151-64, 1995

    M.T.A. Bos, J.H.J van Opheusden, "Brownian dynamics simulation of gelation and aging in interacting colloidal systems", Phys Rev E 53 5044-5050, 1996

    Plant domestication and evolution : a monovular twin or not?
    Raamsdonk, L.W.D. van - \ 1996
    Wageningen : CPRO-DLO - 101
    oorsprong - distributie - vestiging - wilde planten - genetica - genetische variatie - evolutie - soortvorming - immunogenetica - fylogenie - fylogenetica - relaties - gewassen - acclimatisatie - domesticatie - plantkunde - nieuwe cultuurgewassen - economische botanie - origin - distribution - establishment - wild plants - genetics - genetic variation - evolution - speciation - immunogenetics - phylogeny - phylogenetics - relationships - crops - acclimatization - domestication - botany - new crops - economic botany
    Runoff and sediment transport in the arid regions of Argentina and India - a case study in comparative hydrology
    Sharma, K.D. ; Menenti, M. ; Huygen, J. ; Fernandez, P.C. ; Vich, A. - \ 1996
    Annals of Arid Zone 35 (1996)1. - ISSN 0570-1791 - p. 17 - 28.
    argentinië - woestijnen - economische impact - economie - india - regen - relaties - oppervlakkige afvoer - gebruikswaarde - aride klimaatzones - argentina - deserts - economic impact - economics - india - rain - relationships - runoff - use value - arid zones
    The arid zones of Argentina and India have been compared. In both regions run-off is often generated by the Hortonian infiltration surplus overland flow, and run-off response to precipitation input tends to be rapid. The sediment transport is governedby the transport capacity of run-off rather than by the availability of erodible material. The magnitude of hydrological processes is different in response to the different rainfall regimes.
    Establishing temporally and spatially variable soil hydraulic data for use in a runoff simulation in a loess region of the Netherlands
    Stolte, J. ; Ritsema, C.J. ; Veerman, G.J. ; Hamminga, W. - \ 1996
    Hydrological Processes 10 (1996)8. - ISSN 0885-6087 - p. 1027 - 1034.
    hydraulisch geleidingsvermogen - infiltratie - modellen - regen - relaties - onderzoek - oppervlakkige afvoer - kwel - geostatistiek - limburg - hydraulic conductivity - infiltration - models - rain - relationships - research - runoff - seepage - geostatistics - limburg
    Soil hydraulic functions for run-off simulation were collected in catchment areas in a loess region. Each soil horizon was sampled and water retention and hydraulic conductivity characteristics were determined. Run-off generation during standard rain events was quantified by simulation. Based on the simulation outcome, soil horizons were merged. The soil physical composition was mapped with these soil physical building blocks. The maps can be used as input for soil and water erosion models on catchment scale. Comparison of potential run-off figures with measured data showed that the soil physical schematization was appropriate.
    LISEM: a single-event physically based hydrological and soil erosion model for drainage basins; I: theory, input and output
    Roo, A.P.J. de; Wesseling, C.G. ; Ritsema, C.J. - \ 1996
    Hydrological Processes 10 (1996)8. - ISSN 0885-6087 - p. 1107 - 1117.
    erosie - geografische informatiesystemen - modellen - regen - relaties - onderzoek - oppervlakkige afvoer - bodem - erosion - geographical information systems - models - rain - relationships - research - runoff - soil
    The Limburg Soil Erosion Model (LISEM) is a physically based model incorporated in a raster geographical information system. This incorporation facilitates easy application in larger catchments, improves the user-friendliness by avoiding conversion routines and allows the use of remotely sensed data. Processes incorporated in this model are rainfall, interception, surface storage in microdepressions, infiltration and vertical movement of water in the soil, overland flow, channel flow, detachment by rainfall and through-fall, detachment by overland flow and transport capacity of the flow. Special attention has been paid to the influence of tractor wheeling, small roads and surface sealing.
    Inzet van een tendersysteem bij de SBL-regeling
    Ham, A. van den; Kolkman, G. - \ 1996
    Wageningen : IBN-DLO - 45
    bosbouw - weiden - bossen - landbouwgrond - relaties - ontbossing - bebossing - subsidies - premies - regering - bedrijfsvoering - bestedingen - dienstensector - overheidsbestedingen - nederland - voorzieningen - forestry - pastures - forests - agricultural land - relationships - deforestation - afforestation - subsidies - grants - government - management - expenditure - services - public expenditure - netherlands - facilities
    Boerenbosbouw is zo gek nog niet; Noordelijke agrariërs stappen over op bosbouw.
    Konijnendijk, C.C. ; Laar, J.N. van - \ 1996
    Nederlands Bosbouwtijdschrift 68 (1996)1. - ISSN 0028-2057 - p. 7 - 11.
    bosbouw - weiden - bossen - landbouwgrond - relaties - bebossing - veenkolonien - forestry - pastures - forests - agricultural land - relationships - afforestation - veenkolonien
    Particuliere bosbouw in Nederland: een nieuwe toekomst?
    Wiersum, K.F. - \ 1996
    Nederlands Bosbouwtijdschrift 68 (1996)1. - ISSN 0028-2057 - p. 12 - 17.
    bosbouw - bosbezit - particuliere bosbouw - bossen - particulier eigendom - weiden - landbouwgrond - relaties - ontbossing - bebossing - inkomen - rendement - bestedingen - winsten - kosten - bosbedrijfsvoering - investering - financiën - nederland - forestry - forest ownership - private forestry - forests - private ownership - pastures - agricultural land - relationships - deforestation - afforestation - income - returns - expenditure - profits - costs - forest management - investment - finance - netherlands
    Wat ga jij nu doen? Leren voor oordeelsvorming en besluitvaardigheid.
    Haarlem, R. van - \ 1996
    Agrarisch Onderwijs 38 (1996)18. - ISSN 0925-837X - p. 8 - 10.
    besluitvorming - scholen - samenwerking - relaties - organisaties - genetische modificatie - recombinant dna - ethiek - onderwijs - mentale vaardigheid - duurzaamheid (sustainability) - projecten - agrarisch onderwijs - hoger onderwijs - beroepsopleiding - colleges - universiteiten - onderwijsmethoden - moraal - utilisme - probleemgestuurd onderwijs - decision making - schools - cooperation - relationships - organizations - genetic engineering - recombinant dna - ethics - education - mental ability - sustainability - projects - agricultural education - higher education - vocational training - colleges - universities - teaching methods - moral - utilitarianism - problem-based learning
    Heidegger en de wereld van het dier.
    Blans, G.H.T. ; Lijmbach, S.E.E.M. - \ 1996
    Assen : Van Gorcum - 78
    diergedrag - dieren - antropologie - mens - filosofie - psychologie - relaties - metafysica - geest - filosofische stelsels - animal behaviour - animals - anthropology - man - philosophy - psychology - relationships - metaphysics - mind - philosophical systems
    The effects of changing land use on the behavior of copper in the soil
    Koopmans, G.F. - \ 1995
    Haren (Gr.) : AB-DLO (Rapport / DLO - Instituut voor Agrobiologisch en Bodemvruchtbaarheidsonderzoek 30) - 24
    koper - bodem - bosbouw - weiden - bossen - landbouwgrond - relaties - ontbossing - bebossing - copper - soil - forestry - pastures - forests - agricultural land - relationships - deforestation - afforestation
    Neerslagspreiding en aanvoerreductie in het regionale afvalwatertransportstelsel van het Hoogheemraadschap West-Brabant
    Dircke, P.T.M. ; Witter, J.V. ; Stricker, J.N.M. - \ 1995
    Wageningen : Landbouwuniversiteit Wageningen (Rapport / Landbouwuniversiteit, Vakgroep Waterhuishouding 49) - 134
    afvalwater - hydrologie - modellen - regen - afvalwaterbehandeling - oppervlakkige afvoer - nederland - noord-brabant - waste water - analogues - hydrology - models - waste water treatment - relationships - water treatment - noord-brabant
    Nederlandse ervaringen met de biomassaproduktie van populier en wilg in zeer korte omlopen
    Burg, J. van den; Dik, E.J. - \ 1995
    Nederlands Bosbouwtijdschrift 67 (1995)1. - ISSN 0028-2057 - p. 23 - 27.
    bosbouw - bosplantages - intensieve houtteelt - biomassa - snelgroeiende stammen - weiden - bossen - landbouwgrond - relaties - ontbossing - bebossing - nederland - forestry - forest plantations - intensive silviculture - biomass - rapidly growing strains - pastures - forests - agricultural land - relationships - deforestation - afforestation - netherlands
    Woody plants in agro-ecosystems of semi-arid regions
    Breman, H. ; Kessler, J.J. - \ 1995
    Springer Verlag (Advanced Series in Agricultural Sciences ) - ISBN 9783642792090
    bosbouw - agroforestry - ecologie - gewassen - landbouw - fenologie - acclimatisatie - gemengde teelt - tussenteelt - meervoudige teelt - tussenplanting - bedrijfssystemen - relaties - steppen - pampa's - semi-aride klimaatzones - agro-ecosystemen - forestry - agroforestry - ecology - crops - agriculture - phenology - acclimatization - mixed cropping - intercropping - multiple cropping - interplanting - farming systems - relationships - steppes - pampas - semiarid zones - agroecosystems
    A quantitative analysis of the role of woody plants in semi-arid regions, focusing on the Sahel and Sudan zones in West-Africa, is given for the assessment of their benefits in agro-sylvopastoral land-use systems with productive and sustainability objectives.
    La regeneration de l'espace sylvo-pastoral au Sahel : une etude de l'effet de mesures de conservation des eaux et des sols au Burkina Faso
    Hien, F.G. - \ 1995
    Agricultural University. Promotor(en): L. Stroosnijder. - S.l. : Hien - 223
    bosbouw - weiden - bossen - landbouwgrond - relaties - ontbossing - bebossing - silvopastorale systemen - bosweiden - erosiebestrijding - waterbescherming - bodembescherming - duurzaamheid (sustainability) - natuurlijke hulpbronnen - hulpbronnengebruik - bescherming - herstel - burkina faso - forestry - pastures - forests - agricultural land - relationships - deforestation - afforestation - silvopastoral systems - woodland grasslands - erosion control - water conservation - soil conservation - sustainability - natural resources - resource utilization - protection - rehabilitation - burkina faso
    Sahelian rangelands are subject to degradation caused by physical and human factors. This report presents the results of recent research in Burkina Faso on methods for regenerating such rangelands. It begins with an overview of existing regeneration methods. Quantitative ecological field work conducted at two representative sites to understand the regeneration processes, to determine the sustainability of these processes and to understand reasons for success or failure of regeneration technology is described. Water and nutrient (N,P and K) balances as well as vegetation dynamics were studied for different soil and water conservation technologies. A major conclusion is that degraded and crusted soils can only be regenerated by modifying the water balance. Under improved infiltration, subsequent biological processes appear to be able to transform degraded soils into productive soils. However, an improved availability of water often triggers an immediate shortage of nitrogen. Deep infiltration of water stimulates the growth of trees and shrubs which have a stabilizing effect on the overall regeneration process of Sahelian rangelands.
    Interspecific competition, predation, and the coexistence of three closely related neotropical armoured catfishes (Siluriformes - Callichthyidae)
    Mol, J.H.A. - \ 1995
    Agricultural University. Promotor(en): J.W.M. Osse. - S.l. : Mol - ISBN 9789054854388 - 174
    dieren - relaties - Siluridae - ecologie - diergedrag - gewoonten - Neotropisch gebied - animals - relationships - Siluridae - ecology - animal behaviour - habits - Neotropical Region

    Tropical ecosystems are renowned for their high biodiversity with many closely related species living together. Alpha diversity of tropical freshwater fishes is also extremely high, as exemplified by the cichlid fauna of the Great African lakes and the neotropical characins. Since Hutchinson in 1959 posed his often quoted question: "Why are there so many animals?", factors affecting species diversity have been important subject of study and discussion in ecology. Given the limits of the physical environment, two different biological processes are probably responsible for most of the organization of equilibrial communities: competition and predation. Critics of the view that competition and predation play a major role in structuring communities argued that several factors keep populations below a level where competition or predation could be strong. Reviews of the literature on field experiments designed to demonstrate the influence of competition and predation revealed that only 9% of the studies were conducted in the tropics.

    The tropical rainforest is one of the most stable environments in the world. Temperature and humidity are almost constant, but important fluctuations in the water level of streams and swamps occur. Extreme conditions limiting population densities and leading to the extinction of populations are often hard to imagine. The high number of species will lead to complex biological interactions. More studies on competition and predation in the stable environment of the tropical rainforest are necessary to evaluate the importance of both processes in structuring communities.

    A case study is presented concerning three medium-sized armoured catfishes of the family Callichthyidae: Callichthys callichthys, Hoplosternum littorale and Hoplosternum thoracatum. In order to evaluate the influence of competition and predation on the catfish communities, four factors were investigated in detail: 1) geographical distribution, 2) diet overlap, 3) reproductive seasonality and nest-site differentiation, and 4) predation.

    In Suriname (South America), both C. callichthys and H. thoracatum occur all over the country. Both catfishes are abundant in both coastal plain swamps with standing water and rainforest creeks in the interior with running water. Hoplosternum littorale, on the other hand, is restricted in its distribution to coastal plain swamps. Salinity tolerance experiments demonstrated that one-week old larvae of H. littorale could not survive in electrolyte-poor water (e.g. rain water). The 'clear water' of rainforest creeks in the interior may be compared to slightly contaminated distilled water with very low electric conductivity. Larvae of both C. callichthys and H. thoracatum survived and developed further in rain water. The pattern of distribution in Suriname can be considered as a model of the distribution of the three catfishes in South America. In South America, H. littorale is not only conspicuously absent from clear water streams draining the weathered Precambrium Guyana and Brazilian Shields, but also from 'black water' streams with humic acids and also a low conductivity (e.g. the Rio Negro). Within the Amazon drainage system H. littorale seems restricted to 'white water' streams loaded with Andean sediments and with a higher conductivity than both clear water and black water. In Suriname, actual syntopy of the three species occurs in coastal plain swamps. In rainforest creeks of the interior C. callichthys and H. thoracatum occur syntopically. Consequently interspecific competition among the three callichthyids is possible.

    Analysis of the stomach contents of larvae, juveniles and adults of the three armoured catfishes revealed no significant interspecific differences in the diet of larvae, juveniles and adults. However, ontogenetic differences in diet composition among larvae, juveniles and adults where significant for all three catfishes. Larvae of C . callichthys, H. littorale and H. thoracatum fed almost exclusively on Rotifera, Cladocera and Copepoda. The stomach contents of juveniles were more diverse and included micro-crustacea, insect larvae, aquatic insects and some detritus. Adults ingested large quantities of detritus which probably reflected the inability of large fish to seperate effectively benthic invertebrates from substrate. Chironomid larvae where found in large numbers in the stomach of adult specimens. The short alimentary tract of the three catfishes and the structure of its wall make it improbable that these fishes are able to assimilate detrital nonprotein amino acids. The posterior part of the intestine is thin-walIed and has a respiratory function. The anterior digestive portion is relatively short. Morphologically the three callichthyids are adapted to a benthic way of life and a diet of soft-bodied aquatic invertebrates. The similarity in the diet and their bottomdwelling habit provide the basis for grouping the three armoured catfishes into one ecological guild. Competitive interactions are expected to be potentially strong among members of a guild.

    Male C. callichthys, H. littorale and H. thoracatum construct and guard a floating bubble nest in flooded swamps. Although the habit of constructing a floating bubble nest probably evolved as an adaptation to the oxygen-depleted environment of tropical standing waters, some of the characteristics of the nests of C.callichthys and H. thoracatum may have evolved as a response to the unpredictability of the fluctuations in water level and water velocity in rainforest creeks. The conspicuous nests allow the study of the temporal pattern of breeding, the spatial distribution of the nests and the differentiation of the nest-site microhabitat among the three species. Daily surveys in coastal plain swamps revealed a similar, bimodal breeding season in the three catfishes. Nests were observed in both the short and long rainy season. The bimodal breeding pattern in Suriname is probably related to the unreliability of the rainfall in the short rainy season of December-January. In French Guiana the rains of December-January usually do not fail and an unimodal breeding season of H. littorale is found. Significant differences in nest macrohabitat selection were found among the three callichthyids. Nests of H. littorale were built in herbaceous swamps, while C . callichthys and H. thoracatum nested in swamp forest under trees. The two forest nesting species differed in the microhabitat at the nest site. Nests of C . callichthys were constructed in extremely shallow water and in holes of tree roots and earth. Nest densities in the selected habitat were low in C.callichthys and H. littorale, but relatively high in H . thoracatum. Nest-site differentiation in the rainy season (the main feeding period) may prevent competitive exclusion among the three catfishes.

    The potential predation pressure on eggs, larvae and juveniles of H. thoracatum was estimated by combining laboratory predation rates of 24 predator species (both invertebrates and vertebrates) with the density of the predators in the swamp as determined by chemofishing with rotenone. The contribution of a particular predator species to the total predation pressure on H.thoracatum was determined to a large extent by the density of the predator in the swamp. Seemingly innocuous predators with low or moderate predation rates in the laboratory may be extremely important in the swamp due to their abundance. Smallsized fishes and aquatic invertebrates are probably major predators of early developmental stages of H. thoracatum. The potential predation pressure on eggs is high, but the aggressive nest guarding behaviour of the male catfish and concealment of the nests probably protects the eggs effectively from most aquatic predators. Larvae are not guarded by the male and the potential impact of the 24 predators on the larvae of H. thoracatum is large. Although the experiments were performed with H. thoracatum there is no good reason to expect important differences in predation rates on larvae of the three armoured catfishes. Even if only 2.5 % of the potential predation will be realized due to other prey available, the high mortality of early developmental stages of H. thoracatum (and C. callichthys and H. littorale ) in the swamp could be easily explained as the effect of predation. Potential predation pressure and the number of predators that were able to prey on H. thoracatum sharply declined with increasing age (size) of the juvenile catfish. The heavy armour of bony plates and stout pectoral spines protect older juveniles and adults from most potential predators. The high potential predation pressure in the swamps and the low density of juvenile catfish at the end of the rainy season suggest that predation is important in structuring these catfish communities.

    Although larvae of the three armoured catfishes C. callichthys , H. littorale and H. thoracatum show differences in tolerance to electrolyte-poor water, the three species occur together in coastal swamps. Interspecific diet overlap is very high, and the three catfishes show no differentiation in their breeding season and diel pattern of activity. Ontogenetic changes in the defense mechanisms of armoured catfishes result in a situation in which both predation and competition exert control at different times in the life cycle. Predators probably kill most of the larvae and juveniles, leaving only a few individuals to escape and reach adulthood. If the number of escapes would exceed the number of adult deaths, the populations eventually become sufficiently dense to compete. However, in this situation nesthabitat segregation may prevent competitive exclusion of one of the three species .

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