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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    Economic essays on marine invasive species and international fisheries agreements
    Walker, A.N. - \ 2016
    Wageningen University. Promotor(en): Ekko van Ierland, co-promotor(en): Rolf Groeneveld; Hans-Peter Weikard. - Wageningen : Wageningen University - ISBN 9789462576308 - 165
    fisheries - fisheries ecology - agreements - biodiversity - invasive species - europe - marine fisheries - marine fishes - visserij - visserij-ecologie - overeenkomsten - biodiversiteit - invasieve soorten - europa - zeevisserij - zeevissen

    This thesis is divided into two parts, as explained in Chapter 1, which focus on different aspects of marine ecological change. Part A considers marine Invasive Alien Species (IAS), which are taxa introduced outside of their native range. The detrimental consequences of invasions for human welfare necessitate management of IAS. There are two types of IAS management. These are (i) management of the risks that an invasion will become established, termed “prevention”, and (ii) management of already established invasions, termed “control”. Chapter 2 considers prevention of invasive species with Ballast Water Management (BWM). Vessels transport invasive species in their ballast water. BWM involves treating ballast water to reduce the risk of successful invasion establishment. Chapter 2 studies the determinants of optimal ballast water treatment standards from a theoretical perspective. Chapter 3 considers control of already established invasions from a spatial and dynamic perspective. We model a non-native habitat divided into patches, where each patch may contain a population of the invasive species, and where spread of the invasion between patches is a stochastic process. In this context, we derive optimal management policies.

    The second part of this thesis: Part B, considers International Fisheries Agreements (IFAs). IFAs facilitate cooperation in the management of fish stocks. Cooperation is necessary to ensure sustainable management. Part B focuses on two issues which may affect the stability of cooperation within IFAs. These are; in Chapter 4, changes in stock location, which may occur due to climate change, and in Chapter 5, the risk of stock collapse, which may exist due to overfishing. Part B uses game theory to analyse the effects of these two issues on the stability of the Grand Coalition, which is the state of affairs where all parties cooperate to maximize their joint benefit from the fish stock.

    The methods and findings of the thesis are summarized as follows: in Chapter 2 (Part A), we construct a model to study optimal BWM standards. The model is built around the assumption that invasions arriving via ballast water are irreversible, i.e. once an invasion has arrived, it is not possible to reduce the size of the invasive population to zero. The hazard rate of invasion establishment can be reduced by setting a BWM standard. The hazard rate is also affected by the Minimum Viable Population (MVPs) of the species and the possibility of an Allee effect. An MVP exists if there is some population size below which there is an insufficient number of invasive individuals to sustain a population. An Allee effect exists if the probability that a population survives increases at an increasing rate in the size of the population. Our analysis focuses on the conditions under which a BWM standard which aims to reduce invasive populations in ballast water to below their MVPs (as is aimed for by the BWM convention) can be optimal. We find that the current aim of the BWM convention can only be optimal in the case that the hazard function (which determines the hazard rate) is not continuously differentiable around the MVP. We find that Allee effects are a requirement for a continuously differentiable hazard function. Therefore, we find that whether or not an Allee effect exists fundamentally affects whether it is optimal to aim to reduce an invasive population in ballast water to marginally below its MVP.

    In Chapter 3 (Part A), we combine aspects of previous modelling approaches to provide new generalized management insights for controlling established invasions. We employ a metapopulation network consisting of patches which are arranged one-dimensionally (i.e. in a line), which is relevant, among other cases, for invasive species spreading along coastlines. We allow for the population size of the invasion within patches to be reduced, which we term “removal”, and we allow for the probability of spread between patches to be reduced without affecting the population sizes directly, which we term “containment”. We employ numerical stochastic dynamic programming to explore how these two interventions (removal and containment) can be optimally applied to minimize the sum of damages from the invasion and the costs of removing and containing the invasion. We find that allowing for varying stock sizes within patches facilitates optimal timing of the application of containment. We also identify two novel optimal policies: the combination of containment and removal to stop spread between patches and the application of up to four distinct policies for a single patch depending on the size of the invasion in that patch.

    Chapter 4 (Part B) considers how Grand Coalitions can be stabilized in the face of changing stock location. To do so, we employ the Gordon-Schaefer fisheries model. We consider farsightedness as a mechanism by which stability of the Grand Coalition can be increased in the face of changing stock location. Farsightedness allows players to respond to deviations of other players by deviating themselves. This reduces the incentives to leave the Grand Coalition. This is in contrast to shortsightedness, whereby players cannot decide to leave the Grand Coalition in response to such a choice by another player. We begin by modifying the farsightedness concept such that it can be used in games with asymmetric players and transfer payments. We proceed to analyse the modified farsightedness concept in the case where players are symmetric (stock location does not change) in order to identify the properties of the concept in the base case. We find that farsightedness increases Grand Coalition stability with respect to shortsightedness. We proceed to analyse the extent to which farsightedness increases Grand Coalition stability, relative to shortsightedness, as fish stock location changes, using sensitivity analysis. We find that farsightedness increases the stability of the Grand Coalition, but also increases the sensitivity of stability to changes in fish stock location. Thus, for any fish stock location, a Grand Coalition is more likely to be stable if players are farsighted, but shifts between a stable and an unstable Grand Coalition will occur more frequently if players are farsighted.

    In Chapter 5 (Part B), we analyse how the stability of Grand Coalitions is affected by an endogenously determined risk of stock collapse. We do so using the Levhari and Mirman (LM) fisheries model, which is adapted such that there is a risk of stock collapse which increases as the fish stock size decreases. We numerically solve the model and calculate the stability of the Grand Coalition. We find that the effect of an endogenously determined risk of stock collapse depends heavily on the assumptions made regarding how payoffs are determined. A common assumption in the literature is that payoffs are determined at the steady state fish stock. Under this assumption, endogenous risk means that for specific discount and growth rates, a Grand Coalition is stable for any number of players. This is a very different result from the original LM model whereby Grand Coalitions can never be sustained. This is because players can essentially follow two strategies in response to the risk. Firstly, they can attempt to maintain the fish stock by fishing less. In doing so they are running the risk of collapse. Secondly, they can avoid the risk by pre-emptively depleting the fish stock, i.e. harvesting the stock to zero immediately to avoid the risk. Grand Coalitions of any number of players are stable for parameterizations for which a Grand Coalition attempts to maintain a non-zero fish stock and if a deviation from the Grand Coalition would result in pre-emptive depletion. We proceed by relaxing the assumption that payoffs are determined in the steady state by allowing for deviators to obtain payoffs in the transition between steady states. In this case, only Grand Coalitions of two players are stable, and then only for certain parameterizations. The reason is that players can now gain payoffs in the process of pre-emptively depleting the stock, i.e. payoffs are received from the process of fishing the stock down to zero. This increases the benefit of deviating from the Grand Coalition. In this case, Grand Coalitions are only stable for two players for specific parameterizations.

    Chapter 6 summarises the research questions formulated in Chapter 1 and evaluates the work of the thesis. Regarding Chapter 2, we justify our theoretical approach with the following two points. Firstly, BWM management is a global and complex problem, which means that the information required to formally calculate an optimal standard is prohibitively burdensome. Secondly, we argue that the complexity of BWM necessitates a sound theoretical understanding of the problem in order to evaluate the current BWM standard, and also to aid in future policy formulation. Similarly, in Chapter 3, we focus on deriving generalized management insights which are applicable to a variety of real-world cases, as opposed to deriving an optimal management strategy for a specific case. In addition to the data requirements necessary to derive such a management strategy, the complexity of such applied cases leads to potentially excessive computational burden. Chapter 3 analyses systems of two and three patches, which are likely to be too simple to analyse specific real world cases, but are sufficient to derive generalized management insights.

    The game theoretic methodologies in Part B are evaluated principally in terms of the assumptions about changes in stock location in Chapter 4 and the numerical method in Chapter 5. In Chapter 4, the fish stock is conceptualised as existing at a single point in space. The location of this point is determined in relation to fishing nations, which are also conceptualised as single points in space. Changes in stock location result from rises in ocean temperatures due to climate change. Such rises in temperature are likely to lead to other changes in the fish stock such as the size of the area where the fish stock can be found and increases in the maximum fish stock size which the ecosystem can support. These other aspects of changing stock location need to be considered in evaluating Chapter 4, as well as in formulating more applied models. In Chapter 5, a numerical method is adopted to analyse the effects of an endogenous risk of stock collapse. To do so, the utility function in the LM model is adapted such that it can be used in a numerical model. In order to isolate the effect of endogenous risk from changes in the utility function, a validation procedure is carried out by comparing analytically derived results in the deterministic case (without endogenous risk of stock collapse) to numerically derived results in the deterministic case. This reveals that changes to the utility function have a negligible effect and thus the results, in terms of the stability of Grand Coalitions can be attributed solely to endogenous risk of stock collapse.

    Overall, Part A of this thesis presents new insights into the determinants of optimal BWM standards. These insights demonstrate the conditions under which the current BWM standard, which aims to eliminate the risk of invasion establishment, may or may not be optimal. Part A therefore provides a novel theoretical framework which aids in the evaluation of current, and the determination of future standards. Part A also provides new insights into the control of established invasions, by extending existing spatially explicit optimal control models. Specifically, dividing space into patches and allowing for varying invasive population sizes within patches facilitates the optimal timing of management interventions and, in general, more detailed, and thus more efficient, management strategies. Part B provides a novel analysis of the effects of changing stock location on Grand Coalitions by explicitly introducing fish stock location in the analysis, and shows how farsightedness can stabilize Grand Coalitions in the face of such changes. Part B also shows how the effects of an endogenous risk of stock collapse on the stability of Grand Coalitions depends vitally on whether transition payoffs are included. These results can form the basis for more interdisciplinary analyses, analyses of different types of marine ecological change, and analyses of these changes in different settings, such as non-European countries.

    Invasieve soorten Waddenzee: : Introductiekansen van probleemsoorten via schelpdiertransport
    Tamis, J.E. ; Sneekes, A.C. ; Jak, R.G. - \ 2015
    Den Helder : IMARES (Rapport / IMARES C173/15) - 49
    invasieve soorten - schaaldieren - veevervoer - verspreiding - aquatische ecosystemen - milieueffect - waddenzee - nederland - invasive species - shellfish - transport of animals - dispersal - aquatic ecosystems - environmental impact - wadden sea - netherlands
    Invasieve soorten Waddenzee: : Ecosysteem resistentie en de Filipijnse tapijtschelp
    Sneekes, A.C. ; Mendez Merino, Natalia ; Weide, B.E. van der; Glorius, S.T. ; Tamis, J.E. - \ 2015
    Den Helder : IMARES (Rapport / IMARES C175/15) - 67
    invasieve soorten - schaaldieren - veevervoer - weerstand - aquatische ecosystemen - milieueffect - waddenzee - nederland - invasive species - shellfish - transport of animals - resistance - aquatic ecosystems - environmental impact - wadden sea - netherlands
    Patterns of exotic plant species in the Netherlands: a macroecological perspective
    Speek, T.A.A. - \ 2015
    Wageningen University. Promotor(en): Wim van der Putten, co-promotor(en): Bert Lotz. - Wageningen : Wageningen University - ISBN 9789462572898 - 158
    geïntroduceerde soorten - vegetatie - plantengeografie - invasieve soorten - plantengemeenschappen - dominantie - nederland - introduced species - vegetation - phytogeography - invasive species - plant communities - dominance - netherlands
    In dit proefschrift heb is onderzocht wat mogelijkheden zijn om het invasief potentieel van geïntroduceerde plantensoorten en de invasibiliteit van plantengemeenschappen in Nederland te voorspellen. Soorten zijn gebruikt die hier al geïntroduceerd zijn, omdat van deze hun invasief succes bekend is. Om hun invasiviteit te kwantificeren is informatie gebruikt over de regionale en lokale verspreiding. De unieke beschikbaarheid van deze datasets voor plantensoorten in Nederland bieden nieuwe kansen, die mogelijk helpen de voorspelbaarheid van invasiviteit te verhogen, uit te leggen hoe invasiviteit van een soort kan veranderen in de tijd en hoe de samenstelling van de plantengemeenschap kan bepalen welke geïntroduceerde soorten zich kunnen vestigen.
    Invasieve soorten, column juridica
    Kistenkas, F.H. - \ 2015
    Vakblad Natuur Bos Landschap 12 (2015)114. - ISSN 1572-7610 - p. 27 - 27.
    invasieve soorten - fauna - flora - habitats - eu regelingen - invasive species - fauna - flora - habitats - eu regulations
    Nu iedereen bezig is met PAS en onze eigen nationale wetsontwerpen voor nieuwe omgevings- en natuurbeschermingswetten, hoor je niemand over nieuwe Europese groene wetgeving die net in werking is gegaan. Terwijl onze omgevingswet blijft doormodderen in allerlei ontwerpfases en hooguit pas in 2018 in werking treedt, zijn er een paar EU-verordeningen inmiddels wel echt al in werking getreden. Toch hoor je er niks over.
    Proximate response of fish, conch, and sea turtles to the presence of the invasive seagrass Halophila stipulacea in Bonaire
    Becking, L.E. ; Bussel, T. ; Engel, M.S. ; Christianen, M. ; Debrot, A.O. - \ 2014
    Den Helder : IMARES (Report / IMARES Wageningen UR C118/14) - 35
    lespedeza stipulacea - invasieve soorten - marien milieu - zeeplanten - bonaire - lespedeza stipulacea - invasive species - marine environment - marine plants - bonaire
    In this report we examined the proximate response of fish assemblages, queen conch, and sea turtles on H. stipulacea meadows in Lac Bay, Bonaire, Caribbean Netherlands. Here we primarily focused on the differences between the invasive species H. stipulacea and the principal species of native sea grass in Lac Bay, namely turtle grass Thalassia testudinum.
    Invasion Biology and Ecosystem Theory: Insights from a Continent in Transformation
    Prins, H.H.T. ; Gordon, I.J. - \ 2014
    Cambridge : Cambridge University Press - ISBN 9781107035812 - 530
    invasies - invasieve soorten - ecologie - ecosystemen - planten - dieren - australazië - invasions - invasive species - ecology - ecosystems - plants - animals - australasia
    Many conservationists argue that invasive species form one of the most important threats to ecosystems the world over, often spreading quickly through their new environments and jeopardising the conservation of native species. As such, it is important that reliable predictions can be made regarding the effects of new species on particular habitats. This book provides a critical appraisal of ecosystem theory using case studies of biological invasions in Australasia. Each chapter is built around a set of 11 central hypotheses from community ecology, which were mainly developed in North American or European contexts. The authors examine the hypotheses in the light of evidence from their particular species, testing their power in explaining the success or failure of invasion and accepting or rejecting each hypothesis as appropriate. The conclusions have far-reaching consequences for the utility of community ecology, suggesting a rejection of its predictive powers and a positive reappraisal of natural history.
    Multitrophic interactions on a range-expanding plant species
    Fortuna, T.F.M. - \ 2013
    Wageningen University. Promotor(en): Louise Vet; J.A. Harvey. - Wageningen : Wageningen UR - ISBN 9789461737656 - 229
    planten - invasieve soorten - geïntroduceerde soorten - herbivoren - ongewervelde dieren - natuurlijke vijanden - predatoren - parasitoïden - multitrofe interacties - bunias orientalis - verdedigingsmechanismen - plants - invasive species - introduced species - herbivores - invertebrates - natural enemies - predators - parasitoids - multitrophic interactions - bunias orientalis - defence mechanisms

    Studies on the ecological impacts of exotic invasive plants have mainly focused on inter-continental invasions. However due to global environmental changes, a rapid increase in intra-continental range-expanding plants has been observed. In this context, multitrophic interactions between exotic plants, native herbivores and their natural enemies have been largely ignored. This thesis aimed at examining how an exotic range-expanding plant interacts with aboveground insect herbivores and their natural enemies and how it can contribute to the successful establishment of the exotic plant. In addition, it examines how resistance traits of different populations of the range-expander affect the behaviour and performance of herbivores and their natural enemies in the new habitat. Bunias orientalis (Capparales: Brassicaceae) is perennial plant from extreme south-eastern Europe and Asia that has recently expanded its range and become invasive in northern and central parts of Europe. In the Netherlands, it is considered naturalized but non-invasive.

    Firstly, using a community approach, I found that Bu. orientalis suffered less herbivore damage and harboured smaller invertebrate communities than sympatric native Brassicaceae in the Netherlands. The exotic plant has been found of low quality for the larval growth of the specialist herbivore (Pieris brassicae). Furthermore, two of its gregarious parasitoids were differentially affected by the quality of the exotic plant. The pupal parasitoid (Pteromalus puparum) survived better than the larval parasitoid (Cotesia glomerata), and the latter parasitized less hosts on the exotic than on native plants. Therefore, the herbivore can be selected to adapt to the new plant by conferring an enemy free space to the herbivore. In this case, a plant shift by the specialist herbivore might occur and thus preventing the further spread of the exotic plant. Conversely, in the field I found greater carnivore pressure on Bu. orientalis compared to other native Brassicaceae, particularly in the peak of arthropod abundance. Hence, top-down forces exerted by herbivore natural enemies may act in concert with bottom-up control of plant resistance traits to counteract herbivore plant shift and promote the successful range expansion of the exotic plant.

    Secondly, using a biogeographical approach, I found a considerable intraspecific variation in defence traits (trichomes, glucosinolates, metabolic fingerprints) of Bu. orientalis populations from the native and the exotic range. Plants collected in the native range were better defended than their exotic conspecifics. This variation matched with the performance of a generalist herbivore (Mamestra brassicae) and its parasitoid (Microplitis mediator), which developed poorly in plants from the native range. The results suggest that the defensive mechanisms of Bu. orientalis might have been counter-selected during the range expansion of the exotic plant. Further studies, however, need to examine if enemy release in the new range is followed by an increase in performance of the exotic plant. Finally, a comparative study of multitrophic interactions, both above- and belowground, in the plant native range and along the transect of its range expansion can help to clarify the mechanisms underlying the invasive success of Bu. orientalis.

    Mitigatie van effecten van uitheemse grondels: kansen voor natuurvriendelijke oevers en uitgekiende kunstwerken
    Kessel, N. van; Kranenbarg, J. ; Dorenbosch, M. ; Bruin, A. de; Nagelkerke, L.A.J. ; Velde, G. van der; Leuven, R.S.E.W. - \ 2013
    Nijmegen : Instituut voor Water en Wetland Research, Radboud Universiteit (Verslagen Milieukunde 436) - 88
    invasieve soorten - gobio gobio - fauna - vissen - habitats - oevervegetatie - aquatische ecologie - invasive species - gobio gobio - fauna - fishes - habitats - riparian vegetation - aquatic ecology
    Het afgelopen decennium zijn de Nederlandse rivieren in hoog tempo gekoloniseerd door vier Ponto-Kaspische grondelsoorten, namelijk de marmergrondel (Proterorhinus semilunaris), zwartbekgrondel (Neogobius melanostomus), Kesslers grondel (Ponticola kessleri) en Pontische stroomgrondel (Neogobius fluviatilis). Deze uitheemse grondels zijn invasieve vissen met een bodemgebonden levenswijze en kunnen plaatselijk in hoge dichtheden voorkomen. Hoewel de verspreidingpatronen van invasieve grondels in Nederland tot op heden grofweg bekend zijn, bestaat geen duidelijk inzicht in de verspreidingprocessen en dichtheden van de grondels in verschillende watertypen, hun (ecologische) effecten en kansrijke mogelijkheden om ongewenste effecten te beperken.
    Amerikaanse vogelkers
    Nyssen, B. ; Ouden, J. den; Verheyen, K. - \ 2013
    Zeist : KNNV - ISBN 9789050114523 - 160
    prunus serotina - bosecologie - geïntroduceerde soorten - invasieve soorten - bosbedrijfsvoering - nederland - forest ecology - introduced species - invasive species - forest management - netherlands
    Hij is de schrik van veel bosbeheerders: de Amerikaanse vogelkers. Maar het verhaal achter de boom is verrassend. Want zijn positieve eigenschappen wegen wellicht op tegen de nadelen. Dit boek belicht alle kanten en laat zien hoe we deze boom een plek kunnen geven in het Europese bosecosysteem. In dit boek wordt een nieuw perspectief geschetst op de Amerikaanse vogelkers. Zij blijkt in haar oorsprongsgebied een waardevolle boomsoort, en in onze bossen heeft vogelkers uiteindelijk ook gunstige effecten op het bosecosysteem. Bovendien worden lang niet al onze bossen massaal gekoloniseerd. De auteurs pleiten voor een genuanceerdere kijk op de vogelkers, waarbij handvatten worden gegeven voor een gedifferentieerd beheer. Het boek behandelt de introductie en bestrijding en de huidige problematiek rondom deze exoot. Ook haar invloed op bossuccessie, biodiversiteit, houtteelt en beheerstrategieën komen aan de orde. Dit boek laat zien hoe we deze exoot een plek kunnen geven in het Europese bosecosysteem, en tegelijk de bestrijdingskosten kunnen verminderen. Actuele kennis zorgvuldig en toegankelijk bijeengebracht voor specialisten in boomteelt, bosbeheerders, beleidsmakers en ecologen.
    Reproduction in crabs: strategies, invasiveness and environmental influences thereon
    Brink, A.M. van den - \ 2013
    Wageningen University. Promotor(en): Han Lindeboom, co-promotor(en): Aad Smaal; C. McLay. - S.l. : s.n. - ISBN 9789461735232 - 164
    krabben (schaaldieren) - geslachtelijke voortplanting - geslachtsselectie - groei - voortplantingsvermogen - invasieve soorten - populatiedynamica - omgevingstemperatuur - milieufactoren - mariene ecologie - crabs - sexual reproduction - sexual selection - growth - reproductive performance - invasive species - population dynamics - environmental temperature - environmental factors - marine ecology

    This thesis provides insights into the interconnectedness of crab reproductive biology, the selective forces leading to their development, the possible links to invasiveness and the influences of environmental factors thereon. The empirical data collected and presented in this thesis can be used to compare different crab species and make predictions about the effect of climate change on their population dynamics and invasiveness.
    Two crab species in particular are examined in this thesis, Halicarcinus cookii and Hemigrapsus takanoi , which share similar size and habitat preferences, but have different reproductive strategies and statuses as endemic and invasive. The potential effects of increased water temperature due to climate change on the reproduction and eventual population changes in the species are investigated as well as the possible links reproduction and temperature have with the invasiveness of a species.
    Halicarcinus cookii is an endemic crab to the coasts of New Zealand and is not known anywhere else. The species shows determinate growth, hard shell mating, continuous brood production and ventral seminal receptacles. After the final moult the female produces numerous offspring limited only by sperm availability. With a hard shell the female also avoids mortality resulting from the regular vulnerable soft shell stage. Individuals mature over a range of sizes but do not continue growing after their pubertal moult. With such a terminal moult, brood size is limited by female size.

    Hemigrapsus takanoi is native to the north west Pacific, but has been introduced and is very successful in Europe. The species shows indeterminate growth, hard-shell mating, a defined breeding season and ventral seminal receptacles. With indeterminate growth they continue moulting and growing throughout their adult life. After their pubertal moult, these species can mate throughout the year and produce 2-3 broods between each moult. They are not limited in growth or regeneration of limbs and can safely hide from predators during the vulnerable soft-shell inter-moult period rather than mating which exposes them to predators.

    Despite their different reproductive strategies, broods of both species showed a similar reaction to increased water temperature in that the duration of development of the brood decreased as temperature increased. Extrapolating the results to a climate change scenario, it is suggested that with a temperature rise of 2°C H. cookii could produce one extra brood of over 1000 offspring per female life time, potentially leading to a 10-15% increase in fecundity and possible population growth. As H. takanoi does not show continuous brood production, predicting the effect of temperature rise is more difficult, but evidence suggests that fecundity is also likely to increase in this species with an increase in water temperature.

    Temperature increase may also lead to a change in invasiveness of a species. If areas currently below the optimum temperature for a species become warmer, it is possible that a species may spread to the new locations. Hemigrapsus takanoi may spread further north in Europe than it’s current distribution (assuming it is limited by temperature). Furthermore, if temperatures increase the rate of reproduction in a non-indigenous species, they may become more invasive in their present location.

    The colonisation of a new habitat will involve new interactions, such as predation and competition, with species not previously encountered. The interactions of the two invasive crab species H. takanoi and Hemigrapsus sanguineus with the native Carcinus maenas in the delta waters of SW Netherlands was also investigated in this thesis. Whereas C. maenas was the most common shore crab in these waters, its numbers have declined on the soft sediment substrates during the last 20 years. As the two invasive crab species were first recorded in the Dutch delta in 1999, they could not have initiated the decline of the native C. maenas. However, within a few years H. takanoi completely dominated the intertidal hard substrate environments; the same environments on which juvenile C. maenas depend. On soft sediment substrate the native and invasive crab species are presently more or less equally abundant. Nowadays H. takanoi appears to be a fierce interference competitor or predator for small C. maenas specimens by expelling them from their shelters. However, due to the habitat generalist nature of C. maenas, it is unlikely that the Hemigrapsus species will cause it’s local extinction. More likely is that they will learn to live together.

    The objective to provide new information about a rarely studied species (Halicarcinus cookii) was fulfilled in this thesis and the information can be used as bases for comparison for future research.

    The hypothesis that temperature has no effect on the reproductive rate of crabs was rejected as both study species showed similar increases in brood development rate with increased temperatures. This suggests that global temperature rises may increase the reproductive rate of wider crab populations.

    The hypothesis that the arrival, presence and effect of Hemigrapsus takanoi in the Dutch delta waters has had no effect on the native green crab Carcinus maenas was complicated by the fluctuations and the decrease in C. maenas numbers prior to the arrival of H. takanoi. It was concluded that while H. takanoi did not cause the initial decrease in the C. maenas population, it did take advantage of it and now dominates niches previously occupied by juvenile C. maenas where size dependent competition and/or predation on juvenile C. maenas occurs.

    Uitheemse ectomycorrhizapaddenstoelen
    Vellinga, E.C. ; Kuyper, T.W. - \ 2012
    Coolia 55 (2012). - ISSN 0929-7839 - p. 55 - 64.
    invasieve soorten - ectomycorrhiza - schimmels - ecosystemen - geïntroduceerde soorten - invasive species - ectomycorrhizas - fungi - ecosystems - introduced species
    Exotische paddenstoelen zijn paddenstoelen waarvan het oorspronkelijke verspreidingsgebied ver buiten Nederland ligt en die pas sinds het begin van de twintigste eeuw in ons land ingeburgerd zijn. Hoewel het begrip ‘exoot’ vooral beschrijvend is, kleeft er een negatieve bijklank aan, evenals aan het begrip ‘invasieve soort’. Een exoot wordt invasief genoemd na sterke uitbreiding. Vaak wordt verondersteld dat die snelle uitbreiding voor problemen zorgt, bijvoorbeeld doordat inheemse soorten worden weggeconcurreerd of doordat ecosysteemprocessen verstoord raken. Het feit dat uitheemse soorten zich na introductie succesvol kunnen handhaven wijst erop dat sporenverbreiding een beperkende factor kan zijn, en dat het bekende gezegde van Baas Becking “alles is overal, maar het milieu selecteert” niet zonder meer opgaat voor paddenstoelen
    Invasieve exoten in Vlaanderen en Nederland : resultaten uit het Invexo-project en aanbevelingen voor verbetering van de exotenaanpak
    Burg, W.J. van der; Lotz, L.A.P. - \ 2012
    Wageningen : Plant Research International - 128
    flora - fauna - schadelijke waterplanten - invasieve soorten - inventarisaties - natuurbeleid - samenwerking - zuid-nederland - vlaanderen - aquatic weeds - invasive species - inventories - nature conservation policy - cooperation - south netherlands - flanders
    De casus-overkoepelende werkgroep „Voorstel Beleid en Samenwerking‟ inventariseerde de mogelijkheden om beleid in de verschillende regio‟s op elkaar af te stemmen en samenwerking te stimuleren. De resultaten van deze werkgroep staan in dit rapport. Invasieve exoten kennen geen grenzen. Daarom is het nodig dat gemeenten, provincies, regio‟s en landen samenwerken om probleemsoorten te bestrijden en te voorkomen. De Europese Unie stimuleert die grensoverschrijdende aanpak van invasieve exoten. 24 partners uit Vlaanderen en Zuid-Nederland deden mee aan het Invexo-project (Europees Interreg-project IV A, 2009-2012). In dit project werden vier probleemsoorten of soortengroepen in Vlaanderen en/of Zuid-Nederland aangepakt: grote waternavel (en ook waterteunisbloem en parelvederkruid), Amerikaanse vogelkers, stierkikker en zomerganzen.
    Risico's van introductie van niet-gereguleerde plagen in Nederland
    Helsen, H.H.M. ; Moraal, L.G. - \ 2012
    Randwijk : Praktijkonderzoek Plant en Omgeving, Bloembollen, Boomkwekerij & Fruit (PPO-rapport 2012-20) - 45
    plantenplagen - insectenplagen - bomen - openbare ruimte - fruitteelt - europa - invasieve soorten - plant pests - insect pests - trees - public space - fruit growing - europe - invasive species
    Op dit moment ontbreekt een goed overzicht van plaagorganismen die in Europa, maar niet in Nederland voorkomen. In deze studie wordt dat overzicht gemaakt voor plaagorganismen die kunnen optreden in de fruitteelt en op bomen in de groene ruimte. In dit onderzoek wordt een antwoord gegeven op de vraag: Welke plaagorganismen komen voor in Zuid- en/of Midden-Europa die nu nog niet in Nederland voorkomen, maar wel een risico (kunnen gaan) vormen voor teelten en/of de groene ruimte in Nederland. Deze studie beperkt zich tot insecten en mijten die kunnen optreden op bomen in de groene ruimte en in de fruitteelt.
    Economic impact assessment of invasive plant pests in the European Union
    Soliman, T.A.A. - \ 2012
    Wageningen University. Promotor(en): Alfons Oude Lansink, co-promotor(en): Wopke van der Werf; Monique Mourits. - S.l. : s.n. - ISBN 9789461733474 - 158
    plantenplagen - plantenziekten - plantenparasitaire nematoden - invasieve soorten - economische impact - beoordeling - europese unie - plant pests - plant diseases - plant parasitic nematodes - invasive species - economic impact - assessment - european union
    According to the International Plant Protection Convention (IPPC) and the Agreement on the Application of Sanitary and Phytosanitary measures (SPS Agreement) of the World Trade Organization (WTO), phytosanitary measures should be economically justifiable. The economic impact assessments within a pest risk analysis are currently based on a framework with qualitative questions and not on an explicit quantification of costs. Available quantitative methodologies to assess plant health risks, and in particular economic impacts, are currently hardly applied in the assessment of plant health risks for the EU, restricting the economic justification of plant health policies.
    Risk assessment of Sika deer Cervus nippon in the Netherlands
    Lammertsma, D.R. ; Groot Bruinderink, G.W.T.A. ; Griffioen, A.J. - \ 2012
    Wageningen : Alterra, Wageningen-UR (Alterra-report 2295)
    cervus nippon - invasieve soorten - risicoschatting - ecologische risicoschatting - risicobeheersing - bosschade - oogstschade - concurrentie tussen dieren - geïntroduceerde soorten - nederland - cervus nippon - invasive species - risk assessment - ecological risk assessment - risk management - forest damage - crop damage - animal competition - introduced species - netherlands
    Sika Deer (Cervus nippon) is considered an invasive alien species in Europe. They were introduced in the 19th and 20th century in Europe and have established self-sustaining populations in various countries. Main concerns for Sika, without preventive measures taken and without population control, are about damage to forestry (silviculture, timber production), agriculture, Natura 2000 areas, competition with native ungulates and hybridization and introgression with native Red Deer. Risk assessment for Sika Deer in this study was done using two methods assuming no human intervention (no preventive measures, no population control).
    Introduced agricultural pests, plant and animals diseases and vectors in the Dutch Caribbean, with an alert species list
    Buurt, G. van; Debrot, A.O. - \ 2012
    Den Helder : IMARES (Report / IMARES Wageningen UR C193/11) - 35
    invasieve soorten - aedes aegypti - plagen - plantenplagen - plantenziekten - caribisch gebied - leeward islands - invasive species - aedes aegypti - pests - plant pests - plant diseases - caribbean - leeward islands
    Most information on invasive alien pests is available for the leeward Dutch islands while the least is known for the windward Dutch islands. The principal means of entry is the importation of unsterilized soil and plant material through container shipment, import of ornamental plants and air traffic. The economic costs, both in terms of damages and control measures, as well as missed opportunities that these species cause, has not been estimated but certainly runs in the millions of dollars annually. By far the most economically costly invasive species is the yellow fever mosquito Aedes aegypti, a pest and disease vector closely associated with man. In a few cases, biological control and eradication has been successful. Introduction of invasive pest species continues at a high rate in the Dutch Caribbean and preventive measures are urgently needed to limit future costs and risks in terms of economy and health.
    Onderzoek naar de effectiviteit van de combinatie van twee beheermaatregelen voor rode Amerikaanse rivierkreeften : de Amerikaanse rivierkreeft in het Veenweidegebied: managementsamenvatting
    Boerkamp, A. ; Roessink, I. ; Giels, J. van; Ottburg, F.G.W.A. - \ 2012
    Wageningen : Alterra (Alterra-rapport 2244) - 92
    rivierkreeft - invasieve soorten - biologische bestrijding - predatie - vissen - experimenteel veldonderzoek - crayfish - invasive species - biological control - predation - fishes - field experimentation
    Dit onderzoek is uitgevoerd in opdracht van het ‘Hoogheemraadschap De Stichtse Rijnlanden’ (HDSR), i.s.m. Waternet, gemeente Woerden, STOWA en Team Invasieve Exoten. In deze studie wordt onderzocht wat de impact van de, uit de literatuur, twee meest veelbelovende beheers/bestrijdingsmaatregelen van invasieve kreeften is op een populatie rode Amerikaanse rivierkreeften (Procambarus clarkii). De twee maatregelen bestaan uit het wegvangen van adulte dieren en het inzetten van predatore vis om de aantallen van de jonge dieren te controleren. In dit experiment is gekozen voor paling als roofvis omdat dit de meest voor de hand liggende keuze was gezien het beheersgebied van HDSR en Waternet. Echter deze combinatie geeft in dit experiment niet de duidelijke resultaten die vooraf verwacht werden. Dit geeft in ieder geval aan dat de impact van predatore paling op kreeftenpopulaties niet sterk genoeg was om binnen 81 dagen duidelijke effecten te sorteren of dat deze impact van andere factoren (die niet of niet afdoende in de test vertegenwoordigd waren) afhankelijk is.
    Naturalised and invasive alien plant species in the Caribbean Netherlands: status, distribution, threats, priorities and recommendations : report of a joint Imares/Carmabi/PRI project financed by the Dutch Ministry of Economic Affairs, Agriculture & Innovation
    Burg, W.J. van der; Freitas, J. de; Debrot, A.O. ; Lotz, L.A.P. - \ 2012
    Wageningen : Plant Research International, Business Unit Agrosystems Research (Report / IMARES Wageningen UR C185/11) - 82
    invasive species - biodiversity - nature conservation - caribbean - invasieve soorten - biodiversiteit - natuurbescherming - caribisch gebied
    Exotic and invasive terrestrial and freshwater animal species in the Dutch Caribbean
    Buurt, G. van; Debrot, A.O. - \ 2011
    Texel : IMARES (Report / IMARES Wageningen UR C001/12) - 37
    invasieve exoten - zoetwaterdieren - invasieve soorten - plagen - ecologie - dierecologie - caribisch gebied - invasive alien species - freshwater animals - invasive species - pests - ecology - animal ecology - caribbean
    An overview of 72 invasive animals of the terrestrial and freshwater environments of the Dutch Caribbean, eleven of which are no longer present. All invasive animals that are principally agricultural pests and or animal and plant diseases (46 species) are excluded as these are discussed separately elsewhere. The 61 species documented and discussed here as presently living in the wild or semi-wild state on one or more of the Dutch Caribbean islands, amount to 12 exotic mammals, 16 birds, 13 reptiles, 5 amphibians, 2 freshwater fishes, 3 insects, 2 mollusks and 8 exotic earthworms. For most species, the ecology, distribution, status and current impact remains poorly known as few invasive species have been object of directed studies.
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