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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    Super-performance in a palm species
    Jansen, Merel - \ 2016
    Wageningen University. Promotor(en): Niels Anten; Pieter Zuidema, co-promotor(en): Frans Bongers; M. Martínez-Ramos. - Wageningen : Wageningen University - ISBN 9789462579996 - 193
    chamaedorea elegans - understorey - tropical forests - spatial variation - leaves - growth - population ecology - defoliation - genetic variation - chamaedorea elegans - onderlaag - tropische bossen - ruimtelijke variatie - bladeren - groei - populatie-ecologie - ontbladering - genetische variatie

    The world is changing rapidly due to anthropogenic disturbance. Effects include: global warming, massive pollution, a changed global nitrogen cycle, high rates of land-use change, and exotic species spread. This has a tremendous impact on both natural and agricultural systems. To understand these impacts, good understanding of ecological systems and underlying drivers is necessary. Ecological systems can be studied at different levels of aggregation. Different levels of aggregation influence each other and are also influenced by external drivers like the environment. The population level is of particular interest, because many important ecological processes occur at the population level, like evolution, extinction, and invasion. Ecologists are increasingly recognizing that population processes are strongly influenced by one level of aggregation lower, the individual level. Individual heterogeneity (i.e. differences between individuals in performance), determines many population processes including population growth rate. However, the exact relations between individual heterogeneity, the external drivers of it, and the population level are not always well understood. Furthermore, methods to analyze these relations are not always available.

    Individual heterogeneity occurs at different temporal scales, ranging from short- to long-term performance differences between individuals, where short- and long-term refer to the expected lifespan of the species in question. Short-term differences between individuals are relatively easily identifiable and are common in almost all species. But long-term differences are much harder to determine especially for long-lived organisms. Long-term differences between individuals in reproduction have been identified for several animal species, and in growth for several tree species, but less is known about the existence of such differences in other life forms (e.g. palms, lianas or clonal plants). Quantifying the extent to which individuals differ is essential for understanding the influence of individual heterogeneity on population processes. Super-performing individuals (i.e. individuals that persistently grow faster and reproduce more than others), probably contribute more to the growth of the population and therefore to future generations. Future populations will, therefore, have the genetic characteristics of the super-performers. Which characteristics this will be, depends on the genetic and environmental drivers of super-performance. Full understanding of the influence of individual heterogeneity on population processes, therefore, requires knowledge of the underlying causes of individual heterogeneity.

    For many species, it is known that spatial variation in environmental conditions can cause short-term performance differences between individuals, but it is often not clear if the same environmental factors that cause short-term performance differences are also the environmental factors that cause long-term performance differences. Furthermore, genetic variation is known to cause performance differences, but to what extent is not well studied in natural long-lived plant populations. Within-population genetic variation can be maintained in habitats that are characterized by strong temporal or spatial heterogeneity in environmental conditions if the performance of a genotype relative to others depends on the environment it experiences.

    Super-performing individuals possibly play an important role in the resistance and resilience of populations to disturbance (i.e. maintaining and recovering population growth rate under stress), because super-performers potentially contribute more to the recovery of the population. However, this depends on the relative tolerance to disturbance of super-performers compared to under-performers. A positive relation between performance and tolerance would make super-performers more important, while a negative relation would make them less important. Many types of disturbances entail leaf loss and tolerance to leaf loss is associated with performance being larger than what one would assume based on the amount of leaf area loss. Tolerance can be achieved by compensating for leaf loss in terms of growth rate, which entails either allocating more new assimilates to leaves, allocating new assimilates more efficiently to leaf area (i.e. by increasing specific leaf area), or growing faster with existing leaf area (i.e. by increasing net assimilation rate). Genetic variation in tolerance and compensatory responses would allow populations to adapt to changes in disturbance events that entail leaf loss.

    Individual heterogeneity could also have implications for management. Plant and animal populations are managed at many different levels ranging from harvest from natural populations to modern agricultural practices. When harvesting from natural populations, it might be beneficial to spare the individuals that are most important for future production. Individuals could be spared, either because they contribute most to population growth, because they are tolerant to harvesting (which is relevant when only part of a plant is harvested), or when they start producing less or lower quality product. The productivity of natural populations could also be increased by actively promoting those environmental conditions and genotypes that allow for high productivity, which is the basis of agriculture and common practice in forest management. To determine how this can best be done, knowledge of the causes of individual heterogeneity is necessary.

    The general aim of this thesis is to identify and quantify the mechanisms that determine individual heterogeneity and to determine how this heterogeneity, in turn, affects population level processes. This aim was divided into four main questions that I addressed: (1) To what extent do individuals differ in performance? (2) What causes individual heterogeneity in performance? (3) What are the demographic consequences of individual heterogeneity? (4) Can individual differences be used to improve the management of populations? To answer these questions, we used the tropical forest understorey palm Chamaedorea elegans as a study system, of which the leaves are an important non-timber forest product that is being used in the floral industry worldwide. We collected demographic data, measured spatial variation in environmental conditions, and applied a defoliation treatment to simulate leaf harvesting, in a natural population in Chiapas, Mexico. Furthermore, we grew seedlings from different mothers from our study population in the greenhouses of Wageningen University, where we also applied a defoliation treatment.

    In Chapter 2 we quantified the extent to which individuals differ in long-term growth rate, and analyzed the importance of fast growers for population growth. We reconstructed growth histories from internodes and showed that growth differences between individuals are very large and persistent in our study population. This led to large variation in life growth trajectories, with individuals of the same age varying strongly in size. This shows that not only in canopy trees but also in species in the light limited understorey growth differences can be very large. Past growth rate was found to be a very good predictor of current performance (i.e. growth and reproduction). Using an Integral Projection Model (i.e. a type of demographic model) that was based on size and past growth rate, we showed that fast-growing individuals are much more important for population growth than others: the 50% fastest growing individuals contributed almost two times as much to population growth as the 50% slowest growing individuals.

    In Chapter 3 we analyzed the extent to which observed long-term growth differences can be caused by environmental heterogeneity. Short-term variation in performance was mainly driven by light availability, while soil variables and leaf damage had smaller effects, and spatial heterogeneity in light availability and soil pH were autocorrelated over time. Using individual-based simulation models, we analyzed the extent to which spatial environmental heterogeneity could explain observed long-term variation in growth, and showed that this could largely be explained if the temporal persistence of light availability and soil pH was taken into account. We also estimated long-term inter-individual variation in reproduction to be very large. We further analyzed the importance of temporal persistence in environmental variation for long-term performance differences, by analyzing the whole range of values of environmental persistence, and the strength of the effect of the environmental heterogeneity on short-term performance. We showed that long-term performance differences become large when either the strength of the effect of the environmental factor on short-term performance is large, or when the spatial variation in the environmental factor is persistent over time. This shows that an environmental factor that in a short-term study might have been dismissed as unimportant for long-term performance variation, might, in reality, contribute strongly.

    In Chapter 4 we tested for genetic variation in growth potential, tolerance to leaf loss, compensatory growth responses, and if growth potential and tolerance were genetically correlated in our study population. We quantified compensatory responses with an iterative growth model that takes into account the timing of leaf loss. Genetic variation in growth potential was large, and plants compensated strongly for leaf loss, but genetic variation in tolerance and compensatory growth responses was very limited. Growth performances in defoliated and undefoliated conditions were positively genetically correlated (i.e. the same genotypes perform relatively well compared to others, both with and without the stress of leaf loss). The high genetic variation in growth potential and the positive correlation between treatments suggests that the existence of super-performing individuals in our study population likely has (at least in part) a genetic basis. These super-performing individuals, that grow fast even under the stress of leaf loss, possibly contribute disproportionately to population resistance and resilience to disturbance. The low genetic variation in tolerance and compensatory responses, however, suggests that populations might have limited ability to adapt to changes in disturbance regimes that entail increases in leaf loss. Furthermore, the high genetic variation in growth potential could potentially be used in management practices like enrichment planting.

    In Chapter 5 we explore the potential of using individual heterogeneity to design smarter harvest schemes, by sparing individuals that contribute most to future productivity. We tested if fast and slow growers, and small and large individuals, responded differently to leaf loss in terms of vital rates, but found only very limited evidence for this. Using Integral Projection Models that were based on stem length and past growth rate, we simulated leaf harvest over a period of 20 years, in several scenarios of sparing individuals, which we compared to “Business as usual” (i.e. no individuals being spared, BAU). Sparing individuals that are most important for population growth, was beneficial for population size (and could, therefore, reduce extinction risk), increased annual leaf harvest at the end of the simulation period, but cumulated leaf harvest over 20 years was much lower compared to BAU. Sparing individuals that produced leaves of non-commercial size (i.e. <25cm), therefore allowing them to recover, also resulted in a lower total leaf harvest over 20 years. However, a much higher harvest (a three-fold increase) was found when only leaves of commercial size were considered. These results show that it is possible to increase yield quality and sustainability (in terms of population size) of harvesting practices, by making use of individual heterogeneity. The analytical and modeling methods that we present are applicable to any natural system from which either whole individuals, or parts of individuals, are harvested, and provide an extra tool that could be considered by managers and harvest practitioners to optimize harvest practices.

    In conclusion, in this thesis, I showed that in a long-lived understorey palm growth differences are very large and persistent (Chapter 2) and that it is likely that long-term differences in reproduction are also very large (Chapter 3). I also showed that spatial heterogeneity in environmental conditions can to a large extent explain these differences and that when evaluating the environmental drivers of individual heterogeneity, it is important to take the persistence of spatial variation into account (Chapter 3). Individual heterogeneity also is partly genetically determined. I showed that genetic variation in growth potential to be large (Chapter 4), and that fast growers keep on growing fast under the stress of leaf loss (Chapters 4,5). Therefore it is likely that genetic variation contributes to long-term differences between individuals. Genetic variation for tolerance and compensatory responses was estimated to be low (Chapter 4), suggesting that the adaptive potential of our study population to changes in disturbance events that entail leaf loss might be low. I also showed that super-performing individuals are much more important for the growth of the population (Chapter 2) and that individuals that are important for future production could be used to improve the management of natural populations (Chapter 5).

    This study provides improved insight into the extent of individual heterogeneity in a long-lived plant species and its environmental and genetic drivers, and clearly shows the importance of individual heterogeneity and its drivers for population processes and management practices. It also presents methods on how persistent performance differences between individuals can be incorporated into demographic tools, how these can be used to analyze individual contributions to population dynamics, to extrapolate short-term to long–term environmental effects, and to analyze smart harvesting scenarios that take differences between individuals into account. These results indicate that individual heterogeneity, underlying environmental and genetic drivers, and population processes are all related. Therefore, when evaluating the effect of environmental change on population processes, and in the design of management schemes, it is important to keep these relations in mind. The methodological tools that we presented provide a means of doing this.

    The wild life of tick-borne pathogens
    Hofmeester, Tim R. - \ 2016
    Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Sip van Wieren. - Wageningen : Wageningen University - ISBN 9789462579699 - 224
    ixodes ricinus - metastigmata - life cycle - tickborne diseases - disease vectors - mammals - birds - hosts - population ecology - tick infestations - host parasite relationships - ixodes ricinus - metastigmata - levenscyclus - ziekten overgebracht door teken - vectoren, ziekten - zoogdieren - vogels - gastheren (dieren, mensen, planten) - populatie-ecologie - tekenbesmettingen - gastheer parasiet relaties

    Diseases that are transmitted by arthropod vectors from animal hosts to humans – so called zoonotic vector-borne diseases – have increased in incidence in the last decades. In North America and Europe, tick-borne pathogens cause the majority of vector-borne diseases, including Lyme borreliosis and tick-borne encephalitis. The pathogens causing these diseases are transmitted by tick species within the Ixodes ricinus complex. These are generalist ticks that have a multi-year lifecycle with three active stages, larva, nymph and adult. Each stage passively waits for a vertebrate host by questing in the vegetation. Once a host is encountered these ticks feed on the host for several days sucking blood, after which they detach and moult to the next stage or lay eggs. Although these ticks spend the majority of their life in the vegetation, the availability of hosts is an important determinant of tick densities.

    In Europe, the Sheep tick (Ixodes ricinus) is the most important vector for tick-borne pathogens. These pathogens include Borrelia burgdorferi sensu lato (s.l.), the causative agent of Lyme borreliosis, Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis, Borrelia miyamotoi, the causative agent of acute febrile illness and Candidatus Neoehrlichia mikurensis, the causative agent of neoehrlichiosis. There are several genospecies within the B. burgdorferi s.l. complex, among which B. afzelii, B. bavariensis, B. garinii, B. lusitaniae, B. spielmanii, and B. valaisiana are found in questing ticks and patients in the Netherlands. All of these pathogens are maintained and amplified by vertebrate hosts. Host species differ in their ability to transmit the different pathogens (reservoir competence), as well as in their competence for ticks. Therefore, it has been hypothesized that changes in vertebrate assemblage composition can change tick-borne pathogen dynamics and thereby tick-borne disease risk, where a decrease in host species diversity might lead to an increased disease risk, the so-called dilution effect of host species richness hypothesis.

    In his thesis, Tim Hofmeester describes his research on the role of different vertebrate host species in maintaining I. ricinus populations and in infecting I. ricinus larvae with different tick-borne pathogens. By performing a systematic review, Hofmeester found that for both mammals and birds, there was a positive correlation between host body mass and tick burden for the different stages. Nymphal burden was positively correlated with infection prevalence with B. burgdorferi s.l. in hosts, which was again positively correlated with the average number of larvae that got infected with B. burgdorferi s.l. while feeding on a host. He also showed that the majority of I. ricinus individuals of the three stages (larva, nymph and adult) feed on only a few vertebrate host species (rodents, thrushes and deer, respectively). Using camera traps, Hofmeester showed that the presence of deer, such as Roe deer and Red deer, was a more important determinant of I. ricinus density than the number of deer available to ticks in twenty forested areas in the Netherlands. Ixodes ricinus densities were significantly reduced after two years of excluding deer by fencing four 0.75 ha forest plots in a forest near Apeldoorn, the Netherlands. Therefore, tick-borne disease risk can be reduced by placing fences around small forested areas with a high recreational pressure.

    Hofmeester showed that tick burdens on rodents were higher in areas with large numbers of deer, while they were lower in areas with large numbers of carnivores. These differences in tick burden on rodents between areas were strongly correlated to the number of questing nymphs in the vegetation that were infected with tick-borne pathogens that are transmitted by rodents. This implies that changes in vertebrate assemblage can lead to cascading effects on rodent-transmitted tick-borne disease risk, via larval burden on rodents. Furthermore, Hofmeester found that the percentage of ticks infected with a specific pathogen was correlated to the number of animals in an area that could transmit this pathogen, while this percentage decreased with the number of animals that could not transmit this pathogen. These parameters were, however, not correlated to species richness, something that was expected based on the dilution effect of species richness hypothesis. Therefore, there is no support for a dilution effect of species richness on tick-borne pathogens in the Netherlands.

    In his synthesis, Hofmeester presents a mathematical model in which the importance of spatial behaviour of hosts for tick-borne pathogens is shown and he proclaims the need for the integration of the field of behavioural ecology into disease ecology to better understand the effect of changes in vertebrate assemblages on pathogen prevalence and ultimately, disease risk. The data presented in this thesis show that it is not host diversity but the presence, abundance and behaviour of specific host species that drives tick-borne pathogen dynamics (identity effect). Vertebrate species change their behaviour in the presence or absence of predators and competitors. Hofmeester shows that this, theoretically, can have a major influence on the density of infected nymphs in the vegetation. Therefore, behavioural changes of reservoir-competent hosts should be taken into account when modelling the effect of changes in vertebrate assemblage composition on tick-borne disease risk.

    The behaviour of vertebrate species in Europe is changing, as multiple species have adapted to human-dominated and fragmented landscapes. The adaptation of small mammals, thrushes and deer to fragmented landscapes might be one of the driving factors behind the increase in tick-borne disease incidence in Europe. A further adaptation of important host species to urbanized landscapes might be expected as these are the safest areas for vertebrate species trying to avoid predation. This might result in an increase in population density of reservoir-competent host species in urban areas with a corresponding increase in tick-borne pathogen prevalence and therefore, tick-borne disease risk.

    Concluding, our world is changing and as a consequence vertebrate assemblages are also changing. This may lead to changes in I. ricinus density and infection prevalence with tick-borne pathogens. From the studies presented in his thesis Hofmeester concludes that the abundance and behaviour of several host species (e.g., Bank vole, Blackbird, Red deer, Red fox, Roe deer, and Wood mouse) determines tick-borne disease risk. Therefore, studying the drivers of animal abundance and behaviour related to ticks and pathogens will be the next step in better understanding and describing tick-borne disease risk. The ecology of tick-borne pathogens is very complex and targeting vertebrate hosts for intervention strategies will be both inefficient and costly due to the intricate interplay between multiple vertebrate host species. Therefore, Hofmeester concludes that prevention of tick bites is the best way to reduce tick-borne disease incidence.

    Bruinvis verhongert soms in zee vol vis : tien jaar onderzoek naar menu zeezoogdier
    Leopold, Mardik - \ 2016
    phocoena - animal behaviour - animal ecology - population ecology - feeding behaviour - feeding ecology - marine biology
    Ecologische gevolgen van het stoppen met zwanendrift
    Schotman, A.G.M. ; Melman, T.C.P. - \ 2016
    Alterra, Wageningen-UR (Alterra-rapport 2682) - 29
    anatidae - zwanen - schade - wildbeheer - draagkracht - dierenwelzijn - populatie-ecologie - nederland - wilde dieren - diergezondheid - anatidae - swans - damage - wildlife management - carrying capacity - animal welfare - population ecology - netherlands - wild animals - animal health
    Het ministerie van EZ heeft Alterra gevraagd de gevolgen van het verbod op zwanendrift in beeld te brengen. Zwanendrift wordt hier gedefinieerd als het oogsten van jonge knobbelzwanen in het veld voor de handel in siervogels. Het beëindigen van zwanendrift heeft mogelijk gevolgen voor de populatieomvang, dierenwelzijn en wildschade. De populatie binnen het zwanendriftgebied wijkt in ontwikkeling niet af van de rest van Zuid-Holland & Utrecht en de rest van het land. Deze populatie lijkt met 3692 individuen en naar schatting 450–950 broedparen in overeenstemming met de geschatte draagkracht van het gebied: 267–900 paren. Er wordt bij beëindiging geen sterke toename van de populatie verwacht. Behalve aan afschot en legselbeheer is de huidige populatie sterk onderhevig aan natuurlijke regulatie door emigratie en immigratie. Lokale ingrepen hebben een beperkt effect. De knobbelzwaanschade in Zuid-Holland is nu € 2958 tot € 9365 per jaar. Het landelijke schadebedrag in 2015 was € 73.000. De schade in het zwanendriftgebied is niet uitzonderlijk groot. Aannemelijk is dat de wildbeheereenheden de schade onder controle kunnen houden. Ter voorkoming van de vestiging van groepen niet-territoriale vogels en uit het oogpunt van dierenwelzijn is het aan te bevelen daarbij territoriale broedparen met rust te laten, maar wel de eieren op één na onklaar te maken door prikken of dompelen in olie.
    Populatiebeheer van wilde hoefdieren: nog niet goed op orde
    Groot Bruinderink, G.W.T.A. ; Grift, E.A. van der - \ 2015
    Vakblad Natuur Bos Landschap (2015)december. - ISSN 1572-7610 - p. 26 - 29.
    wilde dieren - wildbescherming - wildbeheer - hoefdieren - regionaal beleid - populatiedichtheid - populatie-ecologie - bevolkingsspreiding - habitats - wild animals - wildlife conservation - wildlife management - ungulates - regional policy - population density - population ecology - population distribution - habitats
    In de afgelopen vijftig jaar groeide in grote delen van Europa, inclusief Nederland, zowel de aantallen als de verspreiding van ree, wild zwijn, damhert en edelhert. Verklaringen hiervoor zijn een betere bescherming en beheer, ontsnappingen, spontane (her)kolonisatie van leefgebieden in combinatie met (her) introducties, verbetering van connectiviteit, mildere winters en een verhoogd voedselaanbod. Tot voor kort werd de verspreiding van wild zwijn en edelhert in Nederland gehinderd door rijksbeleid: de soorten mogen alleen op de Veluwe, de Oostvaardersplassen en Nationaal park De Meinweg leven. Inmiddels zijn de provincies verantwoordelijk voor het faunabeleid en de kans is groot is dat wilde hoefdieren in de nabije toekomst verder zullen toenemen.
    Samenvatting onderzoek: Inventarisatie van dichtheden van kreeften op zowel bestorte als niet recentelijk bestorte vooroevers in de Oosterschelde
    Tangelder, M. ; Goudswaard, P.C. - \ 2015
    Yerseke : IMARES (Rapport / IMARES (samenvatting) C120/15 samenvatting) - 3
    monitoring - hoogwaterbeheersing - dijken - oevers - homarus gammarus - populatiedichtheid - oosterschelde - populatie-ecologie - monitoring - flood control - dykes - shores - homarus gammarus - population density - eastern scheldt - population ecology
    Om de veiligheid tegen overstromingen te kunnen blijven waarborgen versterkt Rijkswaterstaat de vooroevers van de dijken door vooroever bestortingen uit te voeren met staalslakken, breuksteen en zeegrind. De bestortingen hebben gevolgen voor het plaatselijke bodemleven. In de lopende monitoring wordt onderzoek gedaan naar mogelijke gevolgen van bestorten van vooroevers op hard en zacht substraat gemeenschappen. Echter, effecten op mobiele organismen zoals kreeften zijn onbekend. Rijkswaterstaat heeft IMARES gevraagd om een onderzoek uit te voeren waarmee meer inzicht verkregen kan worden in kreeft aantallen, schaallengte en verhouding tussen vangst en discard, op zowel verdedigde vooroevers (oevers met bestorting) en niet verstoorde vooroevers (oevers waar niet recentelijk een bestorting is uitgevoerd).
    Bruinvis volgt spiering naar westerschelde
    Ramaker, R. ; Leopold, M.F. - \ 2015
    Resource: weekblad voor Wageningen UR 10 (2015)8. - ISSN 1874-3625 - p. 9 - 9.
    phocoenidae - milieubeleid - westerschelde - habitats - habitatgeschiktheid - osmerus - rivieren - wilde dieren - populatie-ecologie - phocoenidae - environmental policy - western scheldt - habitats - habitat suitability - osmerus - rivers - wild animals - population ecology
    In de Westerschelde zwemmen voor het eerst in decennia weer bruinvissen. De dieren jagen op de eveneens teruggekeerde trekvis spiering. Het is een succesverhaal van het Nederlands milieubeleid, zegt Mardik Leopold, onderzoeker van Imares Wageningen UR, die vandaag promoveert op onderzoek naar het eetgedrag van bruinvissen.
    Veldleeuwerik heeft meer nodig dan faunaranden : themanummer Agrarisch natuurbeheer
    Kuiper, M.W. ; Ottens, H.J. - \ 2015
    Vakblad Natuur Bos Landschap 12 (2015)115. - ISSN 1572-7610 - p. 38 - 40.
    vogels - fauna - populatie-ecologie - foerageren - agrarisch natuurbeheer - habitats - broedplaatsen - akkerbouw - birds - fauna - population ecology - foraging - agri-environment schemes - habitats - breeding places - arable farming
    Lange tijd is er weinig aandacht geweest voor akkervogels. Zo is in de afgelopen 50 jaar de populatie veldleeuweriken met 96 procent afgenomen. Het is van belang om de juiste maatregelen uit te voeren om deze negatieve trend stoppen.
    Monitoring van de Nederlandse otterpopulatie
    Groot, G.A. de - \ 2015
    otters - populatie-ecologie - monitoring - genetische diversiteit - verwantschap - inteelt - natuurbeheer - wildbeheer - otters - population ecology - monitoring - genetic diversity - kinship - inbreeding - nature management - wildlife management
    Sinds in 2002 een nieuwe populatie otters (Lutra lutra) in ons land werd uitgezet, heeft Alterra de status van deze populatie nauwgezet gevolgd. Nadat de eerste dieren waren gevolgd met behulp van zenders, werd overgestapt op non-invasive genetische monitoring via spraints (otteruitwerpselen). Op deze manier kunnen de dieren langer worden gevolgd en kunnen meer dieren tegelijk worden gevolgd met beperkte kosten. Sinds juli 2002 werden meer dan vijfduizend spraints verzameld en geanalyseerd in het lab, ter bepaling van een genetisch profiel. Op basis daarvan kon een stamboom worden gemaakt, die uitwees dat slechts een klein deel van de aanwezige mannen verantwoordelijk was voor een groot deel van het nageslacht (sterke dominantie). De verwantschap tussen dieren, en daarmee het inteelt-niveau, loopt op. Dit is een belangrijk signaal dat voor de Nederlandse populatie ‘vers bloed’ nodig is, ofwel via aanvullende introducties, of door uitwisseling tussen populaties tot stand te brengen.
    Soortmanagementplannen en de Habitatrichtlijn : ruimtelijke onderbouwing duurzaamheid populaties Gewone dwergvleermuis
    Broekmeyer, M.E.A. ; Adrichem, M.H.C. van; Pouwels, R. ; Jochem, R. - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2608) - 45
    beschermde soorten - pipistrellus pipistrellus - populatie-ecologie - natuurbescherming - regionale planning - habitats - fauna - protected species - pipistrellus pipistrellus - population ecology - nature conservation - regional planning - habitats - fauna
    Een soortmanagementplan (SMP) is een instrument dat dient als ecologische onderbouwing bij een te verlenen gebiedsgerichte ontheffing onder de huidige Flora- en faunawet artikel 75c. In een SMP worden op een grootschalig gebiedsniveau maatregelen beschreven waarmee een soort beschermd wordt in dat betreffende plangebied, en worden bovendien de voorziene ruimtelijke ontwikkelingen binnen datzelfde gebiedsniveau beschreven. In dit rapport is onderzocht of er in twee van deze pilotgebieden voor de soort Gewone dwergvleermuis (Pipistrellus pipistrellus) sprake is van een duurzame populatie en of de maatregelen van een SMP voldoende zijn om te garanderen dat er geen afbreuk wordt gedaan aan het streven de populatie van de soort in zijn natuurlijke verspreidingsgebied in een gunstige staat van instandhouding te laten voortbestaan. Deze eis komt immers voort uit de Habitatrichtlijn, waaronder de Gewone dwergvleermuis beschermd is.
    Feasibility of Flat Oyster (Ostrea edulis L.) restoration in the Dutch part of the North Sea
    Smaal, A.C. ; Kamermans, P. ; Have, T.M. van der; Engelsma, M.Y. ; Sas, H. - \ 2015
    Yerseke : IMARES (Report / IMARES Wageningen UR C028/15) - 58
    oesters - populatie-ecologie - monitoring - ecologisch herstel - kustgebieden - noordzee - oysters - population ecology - monitoring - ecological restoration - coastal areas - north sea
    For the recovery of flat oyster beds, knowledge is required of the conditions under which the active restoration of this species in the North Sea can be successfully implemented. This is the subject of the current feasibility study. Living flat oysters have occasionally been found in wind farms. Flat oyster growth has also been demonstrated experimentally in areas where German wind farm are planned. Furthermore, the flat oyster population in the Delta area shows signs of recovery. This all shows that the proper environmental conditions for flat oyster restoration exist in the North Sea.
    Methods for integrated use of fisheries research survey information in understanding marine fish population ecology and better management advice : improving methods for evaluation of research survey information under consideration of survey fish detection and catch efficiency
    Nielsen, J.R. - \ 2015
    Wageningen University. Promotor(en): Adriaan Rijnsdorp. - Wageningen : Wageningen University - ISBN 9789462572553 - 187
    zeevisserij - onderzoek - karteringen - visserijbeheer - zeevissen - populatie-ecologie - evaluatie - methodologie - visvangsten - visbestand - visserijbiologie - marine fisheries - research - surveys - fishery management - marine fishes - population ecology - evaluation - methodology - fish catches - fishery resources - fishery biology


    The thesis developed and improved methods for the integrated analysis of different types of fishery independent research surveys (trawl surveys, acoustic surveys, hydrographical surveys, and gillnet surveys) to study the distribution, density, abundance, migration and biological population dynamic parameters of marine fish species. The topics in the thesis addressed different combinations of trawl, hydro-acoustic, gillnet, and hydrographical data and application of different survey data analysis methods under consideration of factors influencing the survey catch and detection efficiency. Each topic was investigated in one of more case studies.

    One thesis topic has been to provide more precise estimates of fish distribution and density patterns from survey data (Chapter 2). The 1st case study applied advanced statistical methods to Baltic trawl data and hydro-acoustic survey data in combination with survey sampled hydrographical data to estimate distri­bution and density patterns of juvenile 0-group Baltic cod. These patterns were largely unknown. In the 2nd case study new methodology was developed for analyzing trawl research survey data for Baltic cod and whiting including the corre­la­tion in distribution and density according to space, time, size, and species. The more precise density estimates improve the knowledge of the stock-recruitment relationship of Baltic cod and can improve the Baltic multi-species stock assessment. Furthermore, it will enable more precise marine management and spatial planning involving fish stocks and fisheries in the Baltic Sea. In context of Baltic cod stock assessment, the 3rd case study developed a new method for inter-calibration of trawl survey CPUE data by fish size group exemplified by Baltic cod (and flounder) where the concept of disturbance by one trawl haul in relation to the next have been developed and quantified when calibrating new research survey trawl gears with the former ones. These results have been based on introduction of a new international ICES BITS trawl research survey design.

    A second topic was to improve and develop hydroacoustic research survey methods for more precise detection and discrimination of fish species according to fish size and orientation in the water (Chapter 3). Here, the 4th case study focused on more precise acoustic target strength estimation of juvenile cod, while the 5th case study has focused on acoustic discrimination of juvenile gadoid fish in particular juvenile Baltic cod. This enables more efficient research survey estimation of juvenile cod (gadoid) density patterns to be used in stock recruitment estimates and stock assessment.

    The third topic was to estimate more precisely fish mortality, maturity, and growth parameters for small forage fish species using research survey information (Chapter 4). Associated to this, the 5th case study analysed these population dynamic parameters using trawl survey data taking into account spatial variation. This study provided more precise estimates and deeper understanding of Norway pout mortality, maturity, and growth dynamics. The more precise population dynamic parameters have been implemented in and improved the North Sea Norway pout stock assessment, management advice, management, and long term management plan evaluations.

    The fourth topic was to develop methodology to integrate hydroacoustic, gillnet, and hydro­gra­phi­cal research survey data to investigate pelagic fish migration patterns (Chapter 5). The methods were applied in the 6th case study to evaluate Western Baltic herring feeding and spawning migra­tion based on distribution and density estimates in a narrow over-wintering area of the stock. The more precise information on migration patterns gives better possibility for acoustic monitoring of the full stock abundance in different areas and seasons og the year to be used in stock assessment and marine spatial planning. Also, it increases knowledge on biological interactions and mixing with other stocks and species.  

    In the final synthesis Chapter 6, the thesis reviews relevant analysis methods of research survey data and underlying data distributions, survey design and stratification, trawl survey inter-calibration and standardization, as well as estimation procedures and data processing methods in context of the obtained results and methods developed in the thesis. This is done with focus on survey precision and uncertainty (bias, sources of errors) for trawl and acoustic surveys and factors affecting it.





    Zeldzame vogels in Nederland in 2012
    Bemmelen, R.S.A. van; Groenendijk, D. ; Ovaa, A.H. - \ 2014
    Limosa 87 (2014)4. - ISSN 0024-3620 - p. 216 - 221.
    vogels - fauna - zeldzame rassen - populatie-ecologie - monitoring - birds - fauna - rare breeds - population ecology - monitoring
    This contribution is a summary of the annual report of the Dutch rarities committee (CDNA) for 2012. In 2012, two new taxa were added to the Dutch list: Sooty Tern Onychoprion fuscatus and North Caspian Stonechat Saxicola maurus hemprichii. Other remarkable records were the second Steppe Grey Shrike Lanius lahtora pallidirostris, the second and third Eastern Black Redstart Phoenicurus ochruros phoenicuroides, the third Bufflehead Bucephala albeola and the fifth Bonaparte's Gull Chroicocephalus Philadelphia. High numbers were recorded for River Warbler Locustella fluviatilis (7 records), Radde's Warbler Phylloscopus schwarzt (8 records), Buff-breasted Sandpiper Calidris subruficollis (11 records) and Olive-backed Pipit Anthus hodgsoni (18 records). All records of the latter species are from October and were part of the largest influx of this species in North-Western Europe ever recorded. Following recent advances in identifying flight calls from this species, the number of accepted records has grown since the publication of the annual report and may still grow. Out of a total of 511 species now on the Dutch list, 207 species (41%) are regarded as vagrants, with less than two records per year during the last 30 years. All records and their documentation can now be accessed through a new website:
    The status of the American mink (Neovison vison) in the Netherlands
    Dekker, J.J.A. ; Hofmeester, T.R. - \ 2014
    Lutra 57 (2014)1. - ISSN 0024-7634 - p. 5 - 15.
    fauna - martes - nerts - wilde dieren - populatie-ecologie - nederland - fauna - martes - mink - wild animals - population ecology - netherlands
    The American mink (Neovison vison) is a north American mustelid that has been farmed for its fur in Europe since the 1920s. It has been feral in the Netherlands since 1958. This paper discusses its distribution, diet, the indications for reproduction, and whether feral animals are born in the wild or are escapees. The American mink mostly occurs in areas where many mink are kept in farms. The largest distance between an observation and the nearest farm was 45 km. Sixteen animals caught by muskrat control officers were dissected. The stomach content of the 16 animals revealed a diet of amphibians, birds and small mammals. The dissections gave no clues about reproduction: one of three males was sexually active, but none of the 13 females showed placental scars, a thickened uterus or signs of lactation. Only one observation of reproduction in the wild was received. Isotope analyses of teeth and nails indicate that the animals generally only stay feral for a short period of time before being caught. The ratios of carbon and nitrogen isotopes of the wild caught animals were very close to the isotope ratios of ten reference animals from a fur farm, except for one adult female, whose teeth isotope values were different from the farm animals and as such she seems to have remained in the wild for longer and was possibly born in the wild. In general however most animals are caught shortly after escaping and only remain in the wild for a short period of time. It seems that feral mink stem from constant escapes and that muskrat control removes these feral animals. Thus, the existence or development of a feral population in the Netherlands is unlikely, especially since it is planned to phase out mink farming by 2024.
    Sterke toename verkeerssterfte bij otters
    Kuiters, A.T. ; Lammertsma, D.R. ; Jansman, H.A.H. ; Niewold, F.J.J. - \ 2014
    Zoogdier 25 (2014)4. - ISSN 0925-1006 - p. 10 - 12.
    otters - lutra lutra - populatie-ecologie - verkeersongevallen - inventarisaties - natuurgebieden - noordwest-overijssel - friesland - otters - lutra lutra - population ecology - traffic accidents - inventories - natural areas - noordwest-overijssel - friesland
    De afgelopen jaren heeft de Nederlandse otterpopulatie zich sterk uitgebreid. Maar zowel in de uitzetgebieden als in de nieuwe kolonies ontbreekt het vaak aan ottervoorzieningen, waardoor er jaarlijks veel verkeersslachtoffers vallen. Alterra heeft binnen het huidige verspreidingsgebied de knelpuntlocaties geïnventariseerd en een lijst samengesteld met urgente knelpunten die met voorrang zouden moeten worden aangepakt.
    Population densities of eastern black rhinoceros : unravelling the controls
    Ouma, B.O. - \ 2014
    Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Ignas Heitkonig; Sip van Wieren. - Wageningen : Wageningen University - ISBN 9789461739599 - 158
    rhinoceros - populatiedichtheid - populatie-ecologie - savannen - afgrazen - voedingsstoffenbeschikbaarheid - regen - temperatuur - kenya - rhinoceros - population density - population ecology - savannas - browsing - nutrient availability - rain - temperature - kenya

    Key words: black rhinoceros, browser, corticosterone, diet, density dependence, minerals, moisture, physiological stress, savanna, soil nutrients, woody cover.

    Understanding the forces that cause variability in population sizes is a central theme in ecology. The limiting factor in populations of large mammals which are not controlled top‐down by predation is food, i.e., such populations are controlled by bottom‐up processes. However, there is little evidence of density dependence in large‐ to mega-herbivores. Yet, conservationists have managed Critically Endangered mega‐herbivores like rhinoceros as if their population growth were density dependent, i.e., following a logistic growth curve, focusing on large growth at population densities presumed to be at half‐carrying capacity (K/2). This would enable them to translocate animals at presumed half‐carrying capacity to retain local population densities and to create new populations in areas of suitable habitat, where animals are considered safe against poaching. This study focused on one such mega‐herbivore, the eastern black rhinoceros (Diceros bicornis michaeli) to re‐consider the density dependence population regulation in a mega‐herbivore and uses the findings to contribute to possible solutions towards conservation challenges facing this species. The expectations were that increases in population density would result in a decrease in reproductive performance, and that physiological stress levels in animals in populations of high density would be higher than in animals in populations of low densities. Nine populations of black rhinoceros across Kenya were studied, with variation in their respective densities, Plant Available Moisture (‘PAM’ i.e., ‘soil moisture’) and Plant Available Nutrients (‘PAN’ i.e., ‘soil fertility’). Data from available records (1993‐2010) were used to assess reproductive performance. Dietary quality and levels of corticosterone were estimated through faecal analysis from animals sampled in the field and from data on feeding trials of black rhinoceroses in zoos (dietary analysis only). Woody cover estimates were used to assess available browse for black rhinoceros. Two measures of density were used, i.e., absolute density (animals/km2) and relative density, i.e., absolute density as a ratio to the estimated maximum stocking density or ‘carrying capacity’. The effects of PAM and PAN, and subsets of PAM (rainfall and temperature) were incorporated and controlled in testing expectations. No evidence for density dependence was found. Reproductive performances tended to be better where PAM was high, PAN was low and woody cover was sparse. PAM was found to be directly correlated with quality of dietary browse. Black rhinoceros populations appeared controlled more by bottom‐up processes through key resources, even though their densities were perhaps too low to fully support this alternative view. It was apparent that the density dependence concept still requires more investigation. Deliberate efforts should be made to secure high PAM – low PAN – sparse woody cover areas for conservation of black rhinoceros. Conservation managers are advised to consider set percentage translocations, as opposed to the current translocation of black rhinoceros on the basis of an imaginary ‘carrying capacity’ and density dependence.

    Herring larvae surveys 2012 - 2013: Survey reports and results
    Damme, C.J.G. van; Bakker, C. - \ 2014
    IJmuiden : IMARES (Report / IMARES Wageningen UR 14.001) - 36
    haringen - larven - aquatische ecosystemen - monitoring - populatie-ecologie - noordzee - herrings - larvae - aquatic ecosystems - monitoring - population ecology - north sea
    The international herring larvae surveys (IHLS) are carried out to sample larvae of the North Sea autumn and winter spawning herring populations. The abundance of larvae is used as an index for the estimation of North Sea herring spawning stock biomass. These surveys are performed within the statutory research tasks within the framework of EZ-programs (WOT).
    Pilot polderbemonstering 2013: beheersgebied Hoogheemraadschap Hollands Noorderkwartier
    Keeken, O.A. van; Beentjes, R. ; Wolfshaar, K.E. van de; Graaf, M. de; Boois, I.J. de - \ 2014
    IJmuiden : IMARES (Rapport / IMARES Wageningen UR C039/14) - 31
    european eels - populatie-ecologie - fauna - migratie - polders - inventarisaties - noord-holland - european eels - population ecology - fauna - migration - polders - inventories - noord-holland
    Sinds de jaren ’50 van de vorige eeuw loopt de aalstand achteruit. Om te zorgen dat deze niet verder achteruit gaat, is in Europa en dus ook in Nederland een aalbeheerplan ingesteld. Onderdeel van dit plan is een inschatting maken van het aantal schieraal dat jaarlijks uit Nederland richting de Sargasso Zee migreert. Hiervoor is het nodig een inschatting te maken van de aanwezigheid van aal in polders. Daarom is in 2013 een pilotbemonstering gedaan in het beheersgebied van Hoogheemraadschap Hollands Noorderkwartier.
    Development of automated tools for detailed monitoring of mussel and oyster beds using satellite data: spatial, temporal and vertical development
    Davaasuren, N. ; Stapel, J. ; Dankers, N.M.J.A. ; Jansen, J.M. - \ 2013
    Den Helder : IMARES (Report / IMARES Wageningen UR C146/13) - 42
    waddenzee - remote sensing - populatie-ecologie - mossels - schaal- en schelpdierenvisserij - wadden sea - remote sensing - population ecology - mussels - shellfish fisheries
    The main focus of this report is to develop the application of a novel technique in mapping of mussel and oyster beds using remote sensing, which can be combined with regular field monitoring to obtain an optimal monitoring strategy.
    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.

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