Overview of the international fishing activities on the Dogger Bank : update with Dutch, British, Danish, German, Belgian, Swedish and French data for 2010-2015
Hamon, Katell G. ; Hintzen, Niels T. ; Oostenbrugge, Hans J.A.E. - \ 2017
Wageningen : Wageningen Economic Research (Wageningen Economic Research memorandum 2017-050) - 35
fisheries - marine animals - fishery management - north sea - population dynamics - europe - cost benefit analysis - visserij - zeedieren - visserijbeheer - noordzee - populatiedynamica - europa - kosten-batenanalyse
This report is an update of the data and analysis on the value of the fishing activities of the Dutch, British, Danish, German, Belgian, Swedish and French fishing fleets on the proposed closed areas on the Dogger Bank. The effort, value and landings are presented for a five-year period (2010-2015) and show large variations over the last years, driven mainly by fishing opportunities for plaice for the Dutch and British fleets and sandeel for the Danish and German fleets.
Production efficiency of mussel bottom culture
Capelle, Jacob J. - \ 2017
Wageningen University. Promotor(en): Aad Smaal; P.M.J. Herman, co-promotor(en): Jeroen Wijsman. - Wageningen : Wageningen University - ISBN 9789463430869 - 240
mussels - mussel culture - bottom culture - efficiency - population dynamics - culture techniques - biomass production - improvement - shellfish culture - aquaculture - mossels - mosselteelt - bodemcultuur - efficiëntie - populatiedynamica - kweektechnieken - biomassa productie - verbetering - schaal- en schelpdierenteelt - aquacultuur
Mussel bottom culture is an extensive type of aquaculture; it depends on natural resources for feed, seed and space. It consists of the translocation of seed from natural beds to designed culture areas, where mussel farmers try to improve production efficiency. Production efficiency is measured by the relative biomass production (RBP) expressed as units of biomass harvested from one unit of biomass seeded, it increases with mussel growth and decreases with mussel mortality. Mussel bottom culture makes use of nature and also depends on nature. Cultured mussels are subject to similar environmental factors that influence growth and mortality on natural mussel beds, with additional effects of anthropogenic factors. In this thesis we focus on dynamics of mussel beds and the impact and effectivity of culture activities on mussel production yield. The major objectives are stated as: (1) to better understand the population dynamics of subtidal mussel populations, (2) to analyze what factors determine production efficiency in mussel bottom culture and how this can be improved. On natural mussel beds mussels organise in patterns that enhance food delivery and resilience of the bed. On culture plots mussels are seeded in concentric seeding patterns. Seeding techniques concentrate mussels locally within the culture plot area, resulting in high local mussel densities; this increases competition and limits the spatial re-organisation of mussels in the bed. Consequently, seeding on culture plots is followed by a large size and density dependent seeding loss that ranges from about 40% for seed from fishery to 69% for smaller SMC seed. This loss was the major factor in determining the maximum RBP. Losses in the grow-out stage were substantially lower, a subsequent density dependent loss was found for smaller mussels (<30 mm), and a non-density dependent loss for larger mussels (>30 mm). Shore crab predation is an important factor contributing to the higher losses at seeding. The effect of shore crab predation on mussel biomass production is higher than expected from previous studies. In an experiment on an intertidal culture plot in the Oosterschelde (NL), we observed that shore crab predation peaks directly after seeding and accounted for 33% of the total losses within five weeks after seeding. Spatial patterns in the survival rates of natural mussel beds in the Wadden Sea show better seed survival in areas with intermediate salinity (mean annual salinity 17.5-22.5 mg l-1). This suggests that mussel survival is negatively related to sea star distribution, which is largely controlled by salinity. Natural beds that escape predation are found at lower salinities and mussels on these beds showed low growth rates, also because of a lower food quality in these areas. Mussel culture strongly affects the population dynamics of the subtidal mussel population, through relaying of mussels from natural mussel beds to culture plots. Culture plots are located in more saline regions of the Wadden Sea (mean annual salinity 25.8 mg l-1), compared to natural mussel beds. This activity increased mussel growth and survival because food quality on culture plots is high and predation is prevented. As a result, average biomass production is higher on culture plots than on natural mussel beds and this difference increases over time. A more efficient seed use on the available area, that can be obtained by reducing seeding losses will increase RBP, maximum biomass production and increases maximum profit. Our results suggest that this can be achieved by seeding homogeneously in low densities.
Large herbivores as a driving force of woodland-grassland cycles : the mutual interactions between the population dynamics of large herbivores and vegetation development in a eutrophic wetland
Cornelissen, Perry - \ 2017
Wageningen University. Promotor(en): Frank Berendse; Karle Sykora, co-promotor(en): Jan Bokdam. - Wageningen : Wageningen University - ISBN 9789463430159 - 151
grasslands - woodlands - herbivores - population dynamics - vegetation - wetlands - graslanden - bosgebieden - herbivoren - populatiedynamica - vegetatie - wetlands
This thesis examines the mutual interactions between the population dynamics of large herbivores and wood-pasture cycles in eutrophic wetlands. Therefore, habitat use and population dynamics of large herbivores, the effects of large herbivores on vegetation development, and the mutual interactions between vegetation development and herbivore population dynamics were studied in the eutrophic wetland the Oostvaardersplassen. At the Oostvaardersplassen cattle, horses and red deer were introduced in a fenced area with no predators, and population numbers are bottom-up controlled by food supply. The study showed that high densities of cattle, horses and red deer were able to break down woody vegetation and create grasslands. As the populations of large herbivores increased, the amount of the preferred grass available per animal decreased. This forced the large herbivores to use other food plants in other vegetation types, such as scrub, and transforming these into grasslands. In this way, the large herbivores facilitated high numbers of geese. As geese can clip the grass very short (<2 cm), they forced the large herbivores even more to forage in alternative vegetation types. Cattle, the largest herbivore in the system, were the first to experience the negative consequences of this strong competition, and their numbers declined. This raises the question whether an assemblage of bottom-up regulated populations of cattle, horses and red deer, or other large herbivores, can sustainably coexist under these circumstances. The results of our modelling study and experiences in the field suggest that resource partitioning may be a more reliable mechanism for long term coexistence than temporal variability due to climatic extremes or disease outbreaks. The best way to provide opportunities for resource partitioning in the Oostvaardersplassen is to enlarge the area and connect it to other reserves in order to increase the heterogeneity of the grazed system. Although the results of our model suggest that weather variability and presence of geese gave minor opportunities for the coexistence of large herbivores, both factors were necessary for creating windows of opportunity for the establishment of thorny shrubs. Weather variability creates strong reductions of the large herbivore populations while geese influence the maximum and minimum numbers, which are lower when geese are present. The effects of geese on the minimum numbers are small, but apparently sufficient to make the wood-pasture cycle operate. This raises another question whether a large predator, such as the wolf, could have similar effects on these ecosystems as the geese in the model. The impact of geese combined with a possible positive effect of wolves on wood-pasture cycles could perhaps increase the frequency of the windows of opportunity and increase the survival of established thorny shrubs. Until now, we have seen that a few conditions for the wood-pasture cycle are met by the herbivores. However, a few important requirements are not satisfied: (a) a temporary reduction of large herbivore numbers allowing the establishment of light demanding thorny shrubs and the development of thorny scrubland within the created grasslands; (b) the establishment of palatable trees within these thorny scrubs; (c) the formation of closed canopies which shade out the shrubs and lead to unprotected groups of trees and groves. This means that we still cannot conclude if the large herbivores are a driving force for the whole cycle in a highly productive environment. As long as we have not experienced a complete wood-pasture cycle in the Oostvaardersplassen or any other area, it remains to be seen what will happen in the future. Whatever the outcome will be, the results of our study suggest that some adjustments would benefit the Oostvaardersplassen-system such as increasing heterogeneity through connecting the area with other large nature reserves. This will not only increase opportunities for resource and space partitioning and thus increase opportunities for the coexistence of the large herbivores, but also for wood-pasture cycles and increased biodiversity.
Plant-mediated insect interactions on a perennial plant : consequences for community dynamics
Stam, J.M. - \ 2016
Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Erik Poelman. - Wageningen : Wageningen University - ISBN 9789462578647 - 254
016-3976 - perennials - brassica oleracea - defence mechanisms - glucosinolates - insect pests - herbivory - plutella xylostella - mamestra brassicae - pieris rapae - herbivore induced plant volatiles - animal communities - population dynamics - overblijvende planten - brassica oleracea - verdedigingsmechanismen - glucosinolaten - insectenplagen - herbivorie - plutella xylostella - mamestra brassicae - pieris rapae - herbivoor-geinduceerde plantengeuren - diergemeenschappen - populatiedynamica
Plants interact with many organisms around them, and one of the most important groups that a plant has to deal with, are the herbivores. Insects represent the most diverse group of herbivores and have many different ways of using the plant as a food source. Plants can, however, defend themselves against those herbivores, either by constitutive defences, or by traits that are induced upon herbivory. These traits, such as the formation of more trichomes or the production of secondary metabolites, can deter an insect herbivore in its decision to eat from the plant, can be toxic, or otherwise hamper the insect to feed, grow or reproduce. The way a plant responds to herbivory is very specific, depending on the feeding mode or the species of the attacking insect. Furthermore, plant responses to dual herbivory differ from the sum of responses to each herbivore alone. Also the time and order at which multiple insects arrive on a plant, influence the plant’s response. Finally, plant species or populations can show different responses to herbivory. Altogether these factors result in a plant phenotype that the attacking herbivore has to deal with. In addition to the attacker, also subsequently arriving insects will be affected by a change in plant phenotype. Because plants and insects can respond to each other in a continuous chain of interactions, an herbivore early in the season can indirectly affect the later-season community composition through the induced plant response. However, we know only little about the consequences of a dual-herbivore induced plant phenotype for subsequent feeders, and ultimately, the effects on the assembly and dynamics of an insect community as a whole.
The aim of this thesis project was to study the consequences of feeding by multiple insects from the same plant, not only to a subsequent herbivore, but also to the dynamics of a whole insect community over the course of a growing season, and beyond. Furthermore, I studied how the order of herbivore arrival and timing of arrival affected both a next herbivore’s choice and performance in a greenhouse setting, as well as the development of the whole insect community in the field. In addition, I studied how plant populations vary in induced responses, have specific plant-mediated interactions among insect herbivores, and how long these induced responses influence the insect community and plant fitness. Finally, I identified non-additive effects of the history of insect attacks and plant ontogeny to the future insect community.
In the first chapter of this thesis, I introduce the study system. For this project I used several populations of the wild cabbage plant, Brassica oleracea. This is an herbaceous perennial plant that flowers from the second growing season onwards, and supports a large and diverse above-ground arthropod community of more than thirty different species. The plant belongs to the family of Brassicaceae, which is known for the biosynthesis of a group of secondary metabolites, the glucosinolates. These metabolites may deter insects, although some insect species use it as a feeding cue. Two specialist insect herbivores from different feeding guilds, the caterpillar of the diamondback moth Plutella xylostella and the cabbage aphid Brevicoryne brassicae, were used to study their effect as early-season inducer of plant responses either alone or in combination. The caterpillar of the generalist cabbage moth, Mamestra brassicae, was used in bioassays to assess the effects of the induced plant phenotype by single or dual herbivory. Furthermore, in three chapters (Chapters 4, 6 and 7) I have closely studied the composition of the naturally occurring insect community throughout the season for one or two years in a common-garden field setting. In the last of these three chapters, I used the caterpillars of the specialist cabbage white, Pieris rapae, to induce plants at different moments of their ontogeny, while excluding the insect community for varying periods of time by a net or exposing plants to their natural insect community.
In an elaborate literature review, I and my collaborators concluded in chapter 2 that plant responses to dual herbivory evoke different plant responses than the sum of each herbivore alone. This has consequences at all levels from arthropod community assembly to the choice and performance of individual insects. The mechanisms of plant responses to dual herbivory are found in gene expression, hormone production and other molecular processes within the plant. All these aspects of interactions between insects and plants occur and are connected at different time scales.
To follow up on the question how timing plays a role in dual herbivory, we varied the time between, as well as the order of arrival of aphids and/or caterpillars on a plant. We observed that both affected the preference and performance of a subsequently feeding caterpillar (Chapter 3). Mamestra brassicae performed better on plants with a longer time interval between the first and second feeder. Also in a field setting (Chapter 4), the order of herbivore arrival early in the season affected the insect community composition later in the season in two different years, likely through a chain of indirect insect interactions. In this field study, the plant population influenced the outcome of early-season herbivory to later community dynamics. In chapter 5 we found that three plant populations in response to simultaneous aphid and caterpillar attack differed in the expression of two genes that are important for the regulation of herbivore-induced responses. Also, the production of one of two important plant hormones, salicylic acid, responded differently to single or dual herbivory in a unique pattern for each of the plant populations. These different plant responses subsequently negatively affected a next caterpillar on the same plant; M. brassicae growth was impaired on plants which had been fed upon by both aphids and caterpillars, in comparison to control plants. These field and greenhouse studies thus show the implications of dual herbivory beyond effects in the plant; it affects subsequent herbivory, and through a chain of plant-mediated insect interactions, the dynamics of a whole insect community.
In the sixth chapter we show that variation in insect community dynamics can last beyond the moment that the insects were present, even across years. In this field study, the naturally occurring carnivore community influenced the carnivore community composition a year later. Importantly, the herbivore community affected plant fitness across years (but not within years). We propose that such legacy effects are mediated by plant traits, which vary upon insect induction in the first year, and affect the insect community in the next year.
Finally, the history of all insect attacks to a plant up until that moment shape the future insect community by influencing the colonisation of insect species on the plant. Moreover, also plant ontogeny plays a role in shaping the insect community; plant-mediated responses to herbivory at different plant ages resulted in different insect colonisation rates. The most important conclusion from this last data chapter (Chapter 7) is that the two processes, insect community history and plant ontogeny, are non-additive and affect the colonisation of insect species in the same (synergistic) or opposite (antagonistic) direction.
By framing my study results in a time line from minutes to months to years, I show in the general discussion (Chapter 8) that the consequences of dual herbivory for subsequently arriving insects are connected at different time scales. Plant responses to herbivory can occur within hours to days, which affect herbivore choices and performance in the following days and weeks. In their turn, variation of a few days in arrival time of insects may change how plants respond and prioritize their responses to insects throughout the rest of the season. The insects that subsequently arrive on a dual-herbivore induced plant may change the plant phenotype even further and through a chain of insect-plant interactions, the effects on the insects and the plant can last throughout the season, and even across seasons. Furthermore, various factors such as the species of the attacking insect and its feeding guild, the timing after previous attack and the plant age at which herbivory occurs, as well as the genotypic background of the plant, all affect the outcomes of dynamic insect-plant interactions.
The results presented in this thesis thus contribute to the knowledge and interpretation of plant interactions with multiple herbivores. As plants are seldom attacked by a single herbivore, this implies that we have to take into account that multiple herbivory is not the same as the additive effects of single herbivores, and that this has long-lasting consequences for the insect community and the plant. To further understand how plants and insects have adapted to such a dynamic environment, I suggest future research to focus even more on the kinetics of plant physiological responses to dual attack, and to aim at answering the question of how predictable insect communities on a plant really are.
Arriving at the right time : a temporal perspective on above-belowground herbivore interactions
Wang, Minggang - \ 2016
Wageningen University. Promotor(en): Wim van der Putten, co-promotor(en): T.M. Bezemer; A. Biere. - Wageningen : Wageningen University - ISBN 9789462578142 - 174
herbivores - aboveground belowground interactions - herbivory - defence mechanisms - roots - leaves - mycorrhizas - population dynamics - soil biology - herbivoren - boven- en ondergrondse interacties - herbivorie - verdedigingsmechanismen - wortels - bladeren - mycorrhizae - populatiedynamica - bodembiologie
Ontwikkeling van enkele mosselbanken in de Nederlandse Waddenzee, situatie 2014
Fey-Hofstede, F.E. ; Dankers, N.M.J.A. ; Meijboom, A. ; Sonneveld, C. ; Verdaat, J.P. ; Bakker, A.G. ; Dijkman, E.M. ; Cremer, J.S.M. - \ 2015
Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-technical report 57) - 72
mossels - populatiedynamica - biologische ontwikkeling - aquatische gemeenschappen - waddenzee - nederland - mussels - population dynamics - biological development - aquatic communities - wadden sea - netherlands
IMARES Wageningen UR is studying the long-term development of a number of individual mussel beds in the Dutch part of the Wadden Sea, and trying to identify the characteristics that determine the survival of such beds. The study is being carried out in the context of the WOT theme of ‘Nature Information Infrastructure’. The present report presents the 2014 situation. The annual reports of this multi-year project include interim results with yearly additions. The results of the annual mapping and population survey provide a picture of the development of the mussel beds over a large number of years. The results so far show that the mussel beds tend to gradually decrease in size, coverage and population density after the year in which they come into existence.
Helpdeskvraag: Variatie in de uittrek van schieraal
Keeken, O.A. van; Glorius, S.T. - \ 2015
IJmuiden : IMARES (Rapport / IMARES Wageningen UR C119/15) - 36
watertemperatuur - european eels - vismigratie - populatiedynamica - visserijbiologie - monitoring - water temperature - fish migration - population dynamics - fishery biology
In het Nederlands Aalbeheerplan is een visverbod op aal ingesteld in de maanden september, oktober en november. Dit omdat gedurende deze periode de meeste schieraal uittrekt in Nederland. Vanuit de visserijsector bestaat behoefte aan meer flexibiliteit in het aalbeheerplan om te kunnen inspelen op eventuele veranderende omstandigheden, zoals de veranderende watertemperatuur, welke mogelijk van invloed zouden kunnen zijn op de migratie van schieraal. Naar aanleiding van een Motie in de Tweede Kamer is aan IMARES gevraagd of de periode van uittrek van schieraal in Nederland varieert en of deze afhankelijk is van potentiële verandering in watertemperatuur. Met de beschikbare datasets wordt de invloed van watertemperatuur in het voorjaar en de zomer onderzocht op de timing van de schieraalmigratie.
Tracking butterflies for effective conservation
Swaay, C.A.M. van - \ 2014
Wageningen University. Promotor(en): Michiel Wallis de Vries; Marcel Dicke. - Wageningen : Wageningen University - ISBN 9789461739988 - 218
lepidoptera - zoögeografie - biogeografie - populatiedynamica - natuurbescherming - monitoring - nederland - europa - lepidoptera - zoogeography - biogeography - population dynamics - nature conservation - monitoring - netherlands - europe
Dit proefschrift bestaat uit drie delen: het volgen van veranderingen in de verspreiding van vlinders, het volgen van veranderingen in de populatiegrootte van vlinders en hoe deze kennis te gebruiken voor hun bescherming.
Toetsing aannames populatiemodel Grauwe Gans : vergelijking aannames habitatgebruik en kuikenoverleving met feitelijke situatie
Schotman, A.G.M. ; Jansman, H.A.H. ; Hammers, M. ; Baveco, J.M. ; Melman, T.C.P. - \ 2014
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2515) - 51
anser - fauna - wildbeheer - broedfactoren - populatiedichtheid - populatiedynamica - habitats - foerageren - broedplaatsen - modellen - nederland - wildlife management - hatching factors - population density - population dynamics - foraging - breeding places - models - netherlands
Met een eerder ontwikkeld individu-gebaseerd, ruimtelijk expliciet populatie-dynamisch model zijn scenarioberekeningen uitgevoerd waarin verschillende vormen van aantalsregulatie met elkaar worden vergeleken: eieren onklaar maken, afschot ruiperiode, jaar-rond afschot. De met het model voorspelde effecten van reguleringsmaatregelen zijn vooralsnog vooral kwalitatief (relatieve effect van maatregelen) van aard. Om tot eigenstandige kwantitatieve voorspellingen van de absolute aantalsontwikkeling te komen moeten de onderliggende aannames van het model verder getoetst worden. In dit onderzoek werden aannames over het gebruik van bepaalde habitats voor broeden en foerageren nader onderzocht en voorstellen gedaan tot verbetering van deze aannames. Daarnaast werden aannames voor dichtheidsafhankelijke kuikenoverleving en broeddichtheid besproken.
Marine mammals in the Wider Caribbean - Current research and priorities for future studies
Lucke, K. ; Scheidat, M. ; Geelhoed, S.C.V. ; Debrot, A.O. - \ 2014
Den Helder : IMARES (Report / IMARES Wageningen UR C007/14) - 38
zeezoogdieren - distributie - populatiedynamica - beschermingsgebieden - kennisoverdracht - caribische zee - marine mammals - distribution - population dynamics - conservation areas - knowledge transfer - caribbean sea
Information on the distribution, abundance and ecology of marine mammal in the Wider Caribbean Region is scarce. This report aims at collating the on-going research in the Wider Caribbean Region, at identifying the most critical knowledge gaps that need to be addressed to inform and facilitate conservation actions and assess the most suitable research techniques to fill these knowledge gaps.
Population dynamics of Great Bittern (Botaurus stellaris) in the Netherlands: interaction effects of winter weather and habitat fragmentation
Cormont, A. ; Vos, C.C. ; Verboom-Vasiljev, J. ; Turnhout, C.A.M. van; Foppen, R.P.B. ; Goedhart, P.W. - \ 2014
Regional Environmental Change 14 (2014)3. - ISSN 1436-3798 - p. 943 - 952.
ardeidae - fauna - populatiedynamica - klimaatverandering - winter - weersgegevens - habitatfragmentatie - klimaatadaptatie - nederland - ardeidae - fauna - population dynamics - climatic change - winter - weather data - habitat fragmentation - climate adaptation - netherlands - climate-change - britain - variability - models - trends
The increased variability in weather as a manifestation of climate change is expected to have negative impacts on population survival in wildlife species, because it will likely lead to increased variation in vital demographic rates (mortality and reproduction) in these populations. For the effective protection of biodiversity, adaptation measures are needed to compensate for the expected increase in weather variability and the negative interaction with habitat fragmentation. As a case study, we studied the fluctuations in Great Bittern numbers (Botaurus stellaris) from 28 monitoring plots scattered over the Netherlands to explore the interaction between the effect of weather and possible remediating effects of the landscape structure. Great Bittern habitat surrounding these plots differs with respect to area, quality, and degree of isolation of this habitat. In western Europe, Great Bitterns are found to be susceptible to continuous loss of suitable habitat due to vegetation succession and fragmentation. Moreover, year-to-year fluctuations in local Great Bittern populations can be caused by severe winter weather or other weather extremes. Our results show that severe winter weather has indeed a significant negative impact on Great Bittern population growth rates. Furthermore, we found that an increased carrying capacity and spatial cohesion (i.e. inverse of habitat fragmentation) contribute to an increase in mean growth rates over the years. As growth rates are higher in large, well-connected habitats, we argue that recovery from negative effects of, e.g. severe winters on Great Bittern population numbers is enhanced in these less-fragmented habitats. We derived generic adaptation measures for enhancing the recovery rate of populations of species in general: one should invest in more large, well-connected nature areas, not only to diminish the negative effects of habitat fragmentation on wildlife populations, but additionally to reduce the impacts of climatic variability.
Is er ruimte voor wolven in Nederland?
Potiek, A. ; Wamelink, G.W.W. ; Jochem, R. ; Langevelde, F. van - \ 2013
Vakblad Natuur Bos Landschap 100 (2013). - ISSN 1572-7610 - p. 32 - 35.
wolven - fauna - habitatfragmentatie - populatiedynamica - schattingen - predatie - inventarisaties - wolves - habitat fragmentation - population dynamics - estimates - predation - inventories
De wolf nadert Nederland. Uit een modelstudie blijkt dat er genoeg geschikt leefgebied is voor mogelijk vijftig wolven. Door de aanwezigheid van ecoducten wordt de kans op een duurzame wolvenpopulatie aanzienlijk vergroot.
Crop rotation design in view of soilborne pathogen dynamics : a methodological approach illustrated with Sclerotium rolfsii and Fusarium oxysporum f.sp. cepae
Leoni, C. - \ 2013
Wageningen University. Promotor(en): Ariena van Bruggen; Cajo ter Braak, co-promotor(en): Walter Rossing. - Wageningen : Wageningen University - ISBN 9789461738028 - 173
gewassen - rotaties - bodempathogenen - bodemschimmels - plantenziekteverwekkende schimmels - athelia rolfsii - fusarium oxysporum f.sp. cepae - populatiedynamica - modellen - crops - rotations - soilborne pathogens - soil fungi - plant pathogenic fungi - athelia rolfsii - fusarium oxysporum f.sp. cepae - population dynamics - models
Key words: Sclerotium rolfsii, Fusarium oxysporum f.sp. cepae, soilborne pathogens, crop rotation, population dynamic models, simulation.
During the last decades, agriculture went through an intensification process associated with an increased use of fossil fuel energy, which despite temporarily increasing yields often resulted in decreased overall sustainability. Crop rotation is considered a cornerstone of sustainable farming systems. The design of crop rotations is a complex process where several objectives should be combined.Models can support the design of crop sequences and help to reveal synergies and trade-offs among objectives.Despite their importance, pathogen dynamics are rarely taken into account in cropping system models, not in the least because quantitative information from classical crop rotation experiments to calibrate and evaluate the models is resource demanding, and therefore scarce.
The aim of this thesis was to develop a research approach where data (greenhouse pot experiments, microplot experiments, surveys on commercial farm fields) and model simulations were combined to identify crop sequences that minimize soilborne pathogen inoculum build up, and to subsequently include this information into models for designing sustainable crop rotations. The study was carried out based on two ecologically distinct and relevant pathogens in vegetable production systems: Sclerotium rolfsiiand Fusarium oxysporum f.sp.cepae(Foc).
Two aspects of the dynamics of S. rolfsiisclerotia were studied: survival after soil incorporation of green manures, and population changes under three cropping sequences. In pot experiments, sclerotia survival in soil after incorporation of a winter green manure and its decomposition during summer was generally lower than after summer green manure incorporation and decomposition during winter. The incorporation of various legume crops (black beans, cowpea, hairy vetch and lupines) allowed multiplication of sclerotia while various grasses (sudangrass, foxtail millet, oats and wheat) as well as sunhemp resulted in a reduction of sclerotia in the soil. The build-up of sclerotia populations in the microplots was dependent on the crop sequence. Multiplication in sweet pepper was greater after black oat than after onion or fallow.
The dynamics of Focwas studied at two different levels: multiplication in individual plants and population changes in different crop sequences.Foccolonized and multiplied in the root systems of 13 non-Allium plant species without inducing disease symptoms or growth retardation. These species thus constituted “reservoir-hosts” for Foc. The lowest Foclevels per g of dry weight of root were found in wheat, sunflower, cowpea and millet whereas the highest Foclevel was found in black bean.Fusariumpathogen dynamics was strongly affected by the cropping history in a particular field. Fusariumpopulations increased from transplant to harvest of onion when another onion crop had been planted in the same field during the previous winter, whereas Fusariumpopulations decreased when a winter green manure had been planted.
Pathogen dynamics in crop sequences was simulated by concatenating two simple models, the first one describing the build-up of the pathogen within a crop, and the second one describing the dynamic of the pathogen during the intercrop period. The simulations described differences among crop sequences and alternating cycles of increasing and decreasing soil pathogen populations, as well as differences at equilibrium populations related to host frequency and cropping history.
This thesis provides a methodological approach to the design of crop rotations and their effects on soil borne pathogen dynamics. The combination of data from controlled experiments, novel analytical tools (Bayesian analysis, modelling and simulation) and on-farm observations can lead to the identification of optimal crop rotations without extensive field experiments that require a lot of time, space and economic resources.
Conservation genetics of local and wild pig populations : insight in genetic diversity and demographic history
Herrero Medrano, J. - \ 2013
Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): Richard Crooijmans; Hendrik-Jan Megens. - S.l. : s.n. - ISBN 9789461737519 - 160
wilde varkens - sus scrofa - varkens - dna - genetische diversiteit - genetische bronnen van diersoorten - genomica - fylogenetica - zoögeografie - populatiedynamica - single nucleotide polymorphism - wildbescherming - wild pigs - sus scrofa - pigs - dna - genetic diversity - animal genetic resources - genomics - phylogenetics - zoogeography - population dynamics - single nucleotide polymorphism - wildlife conservation
Het doel van het onderzoek zoals beschreven in dit proefschrift was om de genetische diversiteit en demografische geschiedenis van lokale varkenspopulaties te verkennen middels het integreren van verschillende genetische merker systemen.
Alken en Zeekoeten op het Friese Front
Bemmelen, R.S.A. van; Arts, F. ; Leopold, M.F. - \ 2013
Den Helder : IMARES (Rapport / IMARES Wageningen UR C160/13) - 42
zeevogels - habitatrichtlijn - natura 2000 - vogels - monitoring - populatiedynamica - noordzee - sea birds - habitats directive - birds - population dynamics - north sea
Het Friese Front, zoals omschreven en geografisch aangeduid in het rapport van Lindeboom et al. (2005) zal worden aangewezen als Vogelrichtlijngebied, c.q. Natura 2000 gebied. Eén belangrijke reden voor de aanwijzing is de aanwezigheid, in zomer, nazomer en herfst, van internationaal belangrijke aantallen Zeekoeten Uria aalge. Vanwege de bijzondere status van het gebied is het belangrijk om te weten welke aantallen Zeekoeten het gebied bezoeken en wat de trends in aantallen zijn. Nederland moet hierover in de toekomst aan de Europese Commissie rapporteren. In dit rapport wordt informatie van eerder uitgevoerde ESAS scheepstellingen (1987-2011) aangevuld met een recente integrale scheepstelling van het Friese Front (oktober-november 2012), gekoppeld aan de tweemaandelijks uitgevoerde MWTL vliegtuigtellingen.
The numbers game in wildlife conservation: changeability and framing of large mammal numbers in Zimbabwe
Gandiwa, E. - \ 2013
Wageningen University. Promotor(en): Herbert Prins; Cees Leeuwis, co-promotor(en): Ignas Heitkonig. - S.l. : s.n. - ISBN 9789461737465 - 204
wildbescherming - zoogdieren - jachtdieren - populatiedynamica - populatie-ecologie - populatiebiologie - jagen - wild - zimbabwe - wildlife conservation - mammals - game animals - population dynamics - population ecology - population biology - hunting - wildlife - zimbabwe
Wildlife conservation in terrestrial ecosystems requires an understanding of processes influencing population sizes. Top-down and bottom-up processes are important in large herbivore population dynamics, with strength of these processes varying spatially and temporally. However, up until recently the role of human-induced top-down and bottom-up controls have received little attention. This is despite the fact that almost all terrestrial ecosystems are influenced by human activities thereby likely altering the natural control of animal populations. Therefore, in this thesis, the role of natural and human-induced controls in influencing large herbivore populations and how human controls (i.e., policy instruments, incentives and provisions) influence human activities and wildlife conservation in a semi-arid African savanna ecosystem are investigated. This study primarily focuses on Gonarezhou National Park (hereafter, Gonarezhou), Zimbabwe and adjacent areas. Zimbabwe experienced an economic crisis and political instability between 2000 and 2008 following the land reforms that started in 2000 which were widely covered in the mass media.
The results indicated a weak synchrony in rainfall and drought occurrence (natural bottom-up process) in areas within the same “climatic” region, and variable responses of large herbivore species to the 1992 severe drought with most large herbivore species’ populations declining following the 1992 drought and increasing thereafter. Therefore, droughts are important in influencing large herbivore populations in semi-arid ecosystems. Furthermore, the results showed variation in the intensity of illegal hunting (top-down human control) which was associated with variation in law enforcement efforts in Gonarezhou. Law enforcement efforts in Gonarezhou were strengthened in 2004 following the employment of additional patrol rangers which resulted in increased park coverage and a decline in recorded illegal activities. Thus, the results show that political instability and economic collapse does not necessarily lead to increased illegal hunting in situations where policy instruments, such as laws, are enforced.
A higher perceived effectiveness of Communal Areas Management Programme for Indigenous Resources (CAMPFIRE - a community-based program that allows local people living in communal areas near protected areas in Zimbabwe to financially benefit from using the wildlife resources within their area) was partly associated with a decline in human-wildlife conflicts. In addition, local communities with higher perceived effectiveness of CAMPFIRE programs partly had more favourable attitudes towards problematic wild animals. Moreover, the results showed that in the 1990s, the majority of newspaper articles highlighted that wildlife conservation in Zimbabwe was largely successful. However, following the land reforms that occurred in 2000, the international media lost interest in wildlife conservation in Zimbabwe, as evidenced by a sharp decline in published articles. Also, the frames changed in the international media with the “political unrest and land reform” blame frame becoming more dominant, and nature conservation was portrayed more negatively. The change in media frames shows that there was a spill-over effect from the political domain into wildlife conservation following Zimbabwe’s land reforms in 2000.
Overall, this study provides new insights on the processes influencing large herbivore population dynamics in human-dominated semi-arid savanna ecosystems which consist of diverse wildlife management regimes and also illuminates the importance of media framing and (mis-)representation of wildlife conservation issues following political instability, crisis or societal unrest. With these findings, it is concluded that natural bottom-up processes (e.g., droughts) influence large herbivore population dynamics whereas policy instruments, incentives, provisions and societal frames mainly have a top-down effect on wild large herbivore populations in savanna ecosystems.
Vreemde vogels in de Nederlandse vogelbevolking: een verhaal van vestiging en uitbreiding
Lensink, R. ; Ottens, G. ; Have, T.M. van der - \ 2013
Limosa 86 (2013)2. - ISSN 0024-3620 - p. 49 - 67.
vogels - invasieve exoten - populatiedynamica - monitoring - birds - invasive alien species - population dynamics - monitoring
In de jaren negentig van de vorige eeuw is door de International Union for the Conservation of Nature (IUCN) het vergroten van kennis over het voorkomen van exoten hoog op de agenda gezet, omdat exoten een belangrijke bedreiging kunnen vormen voor de biodiversiteit. Van afgelegen eilanden zijn inmiddels talrijke voorbeelden bekend van introducties van uitheemse soorten die het uitsterven van inheemse vogelsoorten tot gevolg hadden. Sinds ¿¿¿¿ wordt door de Nederlandse overheid serieus aandacht besteed aan exoten, onder meer door het instellen van het Team Invasieve Exoten. Dit team brengt risico’s voor biodiversiteit en andere belangen in beeld. In Nederland zijn we sinds de jaren negentig goed geïnformeerd over het voorkomen van exoten in de vogelbevolking. Het is gebleken dat de populaties van diverse soorten snel kunnen groeien en zich uitbreiden. In dit artikel wordt de huidige kennis over aantallen en verspreiding van vogelexoten in Nederland op een rij gezet.
The European anchovy (Engraulis encrasicolus) increase in the North Sea
Raab, K.E. - \ 2013
Wageningen University. Promotor(en): Adriaan Rijnsdorp, co-promotor(en): Mark Dickey-Collas; Leo Nagelkerke. - S.l. : s.n. - ISBN 9789461736826 - 207
ansjovissen - engraulis - voedingsgedrag - populatiegroei - populatiedynamica - visserijbiologie - mariene ecologie - noordzee - anchovies - engraulis - feeding behaviour - population growth - population dynamics - fishery biology - marine ecology - north sea
Small pelagic fish such as anchovy are of high socio-economic importance worldwide. They are known for strong fluctuations in abundance, for which the mechanisms are not always understood. European anchovy (Engraulis encrasicolus) increased its population in the North Sea starting in the mid-1990s while previously it was found in more southern waters in Europe. Changed food availability (resulting from plankton changes) or changed habitat availability (due to warmer waters) seemed likely candidate explanations for this increase, based on understanding of the species’ general ecology.
In order to compare the two likely explanations, first, the food of anchovy in the North Sea had to be determined. Analysing the contents of anchovy stomachs and comparing the results with other similar fish (herring and sprat), it appeared that anchovy was a generalist feeder. Observed patterns of anchovy distribution in fisheries surveys were compared to relevant environmental factors related to food availability and temperature. This showed that temperatures experienced by anchovies in the first months after birth was a better explanation for how many anchovy were caught than any measure of food availability was. Modelling their body growth in those months showed that during the past decades, the conditions for juvenile growth improved, probably leading to better overwinter survival.
This doctoral thesis contributed to an increased understanding of the ecology of anchovy in the North Sea, and the insights gained can support studies of small pelagic fish in other systems of the world where fisheries scientists wish to integrate more ecological understanding into their management practice.
Genetica van wilde zwijnen in Limburg en Noord-Brabant : verspreiding, herkomst en verwantschap
Jansman, H.A.H. ; Hofmeester, T.R. ; Groot, G.A. de; Laros, I. ; Bovenschen, J. ; Speelman, M. ; Hout, J.J. van der; Casaer, J. ; Breyne, P. ; Koelewijn, H.P. - \ 2013
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2404) - 62
sus scrofa - wilde varkens - populatiedynamica - populatiegenetica - genetica - migratie - limburg - noord-brabant - fauna - wild pigs - population dynamics - population genetics - genetics - migration
In Limburg komen op verschillende plaatsen buiten het officiële leefgebied De Meinweg wilde zwijnen voor. De aantallen in deze zogenaamde nulstandsgebieden nemen toe, en ook in Noord-Brabant worden in toenemende mate wilde zwijnen gesignaleerd. In opdracht van de provincies Limburg en Noord-Brabant voerde Alterra een genetisch onderzoek uit naar de populatiestructuur en herkomst van de wilde zwijnen in Limburg en Noord-Brabant. Het onderzoek laat zien dat sprake is van een aantal afzonderlijke populaties met een unieke genetische samenstelling. Door gunstigere omstandigheden weten de populaties van wilde zwijnen in Noordwest Europa in aantal en verspreidingsgebied toe te nemen. Genetisch kon dan ook vastgesteld worden dan in de meeste gevallen de nieuwe populaties ontstaan zijn uit de naburige bestaande populaties. In enkele gevallen kan sprake zijn geweest van een (gedeeltelijke) onnatuurlijke oorsprong door ontsnappingen uit gevangenschap of illegale herintroducties. De genetische variatie in de populaties is redelijk, maar laag vergeleken met het buitenland. Onder de huidige omstandigheden lijkt de uitwisseling tussen deze jonge populaties echter voldoende om de variatie in de toekomst op z'n minst in stand te houden.
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.
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.