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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    Movement ecology of large herbivores in African savannas: current knowledge and gaps
    Owen-Smith, Norman ; Hopcraft, Grant ; Morrison, Thomas ; Chamaillé-Jammes, Simon ; Hetem, Robyn ; Bennitt, Emily ; Langevelde, Frank Van - \ 2020
    Mammal Review 50 (2020)3. - ISSN 0305-1838 - p. 252 - 266.
    Africa - daily activity - home range - migration - population dispersion - predation - ungulates

    Nearly 90% of the world's large herbivore diversity occurs in Africa, yet there is a striking dearth of information on the movement ecology of these organisms compared to herbivores living in higher latitude ecosystems. The environmental context for movements of large herbivores in African savanna ecosystems has several distinguishing features. African large herbivores move in landscapes with high spatiotemporal variability, low predictability, seasonal restrictions in surface water as well as food resources, and exposure to a diverse assemblage of competitors, predators, and pathogens. These features influence mobility, diel activity routines, home-range fidelity, and exposure to predation. We review the knowledge that has been gained about the movements of African herbivores from Global Positioning System (GPS) telemetry and identify important gaps in knowledge that exist. Topics addressed include seasonal movement patterns, daily activity schedules, space utilisation, water dependency, responses to risks of predation, pathogen transmission, social affiliations, and local population density determination. While the growing number of GPS telemetry studies has addressed a wide range of topics in Africa, they remain fragmentary in terms of places and species represented. Most research has been focussed on three species, and practices for data sharing and analysis should be improved. African landscapes are changing perhaps faster than any other region on Earth, with rapidly expanding human populations, massive infrastructure development projects, and changes in climatic regimes. There is a crucial need to establish relationships between herbivore movements and their changing environments, especially in Africa where most of the world's large herbivore diversity resides.

    Predation risk shapes the degree of placentation in natural populations of live-bearing fish
    Hagmayer, Andres ; Furness, Andrew I. ; Reznick, David N. ; Dekker, Myrthe L. ; Pollux, Bart J.A. - \ 2020
    Ecology Letters 23 (2020)5. - ISSN 1461-023X - p. 831 - 840.
    Life-history - live-bearing - matrotrophy - placenta - placentotrophy - Poeciliidae - predation - superfetation - Trexler–DeAngelis - viviparity

    The placenta is a complex life-history trait that is ubiquitous across the tree of life. Theory proposes that the placenta evolves in response to high performance-demanding conditions by shifting maternal investment from pre- to post-fertilisation, thereby reducing a female’s reproductive burden during pregnancy. We test this hypothesis by studying populations of the fish species Poeciliopsis retropinna in Costa Rica. We found substantial variation in the degree of placentation among natural populations associated with predation risk: females from high predation populations had significantly higher degrees of placentation compared to low predation females, while number, size and quality of offspring at birth remained unaffected. Moreover, a higher degree of placentation correlated with a lower reproductive burden and hence likely an improved swimming performance during pregnancy. Our study advances an adaptive explanation for why the placenta evolves by arguing that an increased degree of placentation offers a selective advantage in high predation environments.

    Protists: Puppet Masters of the Rhizosphere Microbiome
    Gao, Zhilei ; Karlsson, Ida ; Geisen, Stefan ; Kowalchuk, George ; Jousset, Alexandre - \ 2019
    Trends in Plant Science 24 (2019)2. - ISSN 1360-1385 - p. 165 - 176.
    amoeba - plant–microbe interactions - predation - Protists - rhizosphere microbiome

    The rhizosphere microbiome is a central determinant of plant performance. Microbiome assembly has traditionally been investigated from a bottom-up perspective, assessing how resources such as root exudates drive microbiome assembly. However, the importance of predation as a driver of microbiome structure has to date largely remained overlooked. Here we review the importance of protists, a paraphyletic group of unicellular eukaryotes, as a key regulator of microbiome assembly. Protists can promote plant-beneficial functions within the microbiome, accelerate nutrient cycling, and remove pathogens. We conclude that protists form an essential component of the rhizosphere microbiome and that accounting for predator–prey interactions would greatly improve our ability to predict and manage microbiome function at the service of plant growth and health.

    Data from: Carrying a logger reduces escape flight speed in a passerine bird, but relative logger mass may be a misleading measure of this flight performance detriment
    Mizumo Tomotani, Barbara ; Bil, Wender ; Jeugd, Henk P. van der; Pieters, R.P.M. ; Muijres, F.T. - \ 2018
    Wageningen University & Research
    bird flight - experiment - Eurasian blackcap - geolocator - predation - Sylvia atricapilla
    1. The recent boost in bird migration studies following the development of various tracking devices raised awareness of how detrimental attaching devices can be for animals. Such effects can occur during migration, but also immediately post-release if the device impairs escape flight performance and, consequently, the bird’s ability to evade predators. 2. In this study, we investigated the effect of carrying a device on the escape flight speed and aerodynamic force production in a migratory passerine. We recorded upward-directed escape flights of 15 male blackcaps. Each individual was tested without a tag, and when equipped with three different leg-loop dummy tags with masses representing around 3%, 5% and 7% of their body mass. The experiment was designed such that all individuals passed through all treatments in a randomized order. 3. We found that two factors affected flight speed in roughly equal amounts: first, tagged escape flights had lower flight speeds compared to the control flights, irrespective of tag mass. Second, we found an effect of the total mass, i.e. the sum of the masses of the individual bird and of the tag, with heavier birds being slower. In contrast, flight speed was not correlated with relative tag mass in percentage of body mass, the metric commonly used in ethical guidelines for tag attachment. Aerodynamic flight force production also depended on total mass, with heavier birds producing higher forces. But these flight forces did not differ between flights with or without a tag. 4. We conclude that, when tagging birds, it is misleading to choose heavy individuals for tagging in order to minimize the tag mass as a percentage of body mass. This is particularly relevant in species for which body mass is not necessarily related to size, like migratory birds that accumulate large fat reserves. The lower escape speed in “tagged” flights could not be explained by differences in net flight force production, because these did not differ between flights with and without a tag. This suggests that the tag also affected pre-flight take-off dynamics, possibly due to a leg harness-induced reduction in leg push-off performance.
    Mixed culture engineering for steering starter functionality
    Spuś, Maciej - \ 2016
    Wageningen University. Promotor(en): E.J. Smid; Tjakko Abee. - Wageningen : Wageningen University - ISBN 9789462578333 - 170
    bacteriophages - predation - microorganisms - starters - genetics - diversity - bacteriofagen - predatie - micro-organismen - zuursels - genetica - diversiteit

    Undefined mixed complex starter cultures are broadly used in Gouda-type cheese production due to their robustness to phage predation, resilience for changes in environmental conditions and aroma compounds production ability during ripening. These microbial communities of lactic acid bacteria prior their isolation and deposition in starter culture collections were continuously used at the farm-level production facilities. Thus, one can consider undefined mixed complex starters as domesticated microbial communities. The process of domestication was facilitated by humans who have been continuously repeating successful fermentations using part of previous batch as inoculum (i.e. back-slopping). Therefore, a term ‘community breeding’ can describe this human-driven domestication of microbial communities. Community breeding of a model complex starter Ur led to establishment of a simple two-species composition of Lactococcus lactis and Leuconostoc mesenteroides represented by, in total, 8 genetic lineages. At the same time, this simple microbial community displays a high degree of intraspecies diversity, presumably caused by evolutionary processes of horizontal gene transfer, genome decay and mutations. Such diversity at strain level is particularly interesting in the context of continuous bacteriophage predation pressure present in this microbial community. It is thought that constant-diversity (CD) dynamics, based on the ‘kill-the-winner’ principles, is operational in Ur starter at the strain level. According to CD model, the fittest strain(s), which feed on the most abundant substrate, will be selected against due to density-dependent phage predation. The control of the fittest strain abundance by bacteriophages opens space for differentiation of strains via eco-evolutionary feedbacks. In particular, strains of complex starter culture not only adapted to quickly acidify milk (via efficient consumption of lactose and protein to peptides degradation), but concurrently, to consume other substrates present in milk. In addition, throughout the process of community breeding microbe-microbe interactions between community members have evolved. These interactions have led to division of metabolic labor among strains present in the culture, and eventually to better starter microbial community functioning.

    The aim of this thesis was to investigate the factors impacting the formation of compositionally and functionally stable undefined mixed complex starter cultures to further use this knowledge in steering its functionality, and potentially in developing new strategies for robust starter culture design. To facilitate this study, well-characterized Ur culture strain isolates were used to systematically reconstitute the starter culture into multi-strain blends with increasing level of strain and genetic lineage diversity. The investigation of factors such as phage predation, level of strain and genetic lineage diversity as well as environmental conditions, was performed during experimental evolution studies in milk. The functionality of the (evolved) starter cultures was tested in an adapted lab-scale MicroCheese model system. The specific approach used in each of the research chapters is described below in more detail.

    Strains isolated from Ur starter culture were characterized in terms of their resistance against bacteriophages isolated from the same starter (Chapter 2). This test confirmed high diversity in phage resistance among strains belonging to different genetic lineages as well as among strains of the same lineage. Next, selected strains, which represented different levels of bacteriophage predation: resistant, moderately resistant, sensitive and no detectable sensitivity, were mixed in simple blends containing 4 strains representing 3 genetic lineages of Ur starter (3 such blends were designed). These blends were exposed to phage predation (one phage per blend) at the onset of prolonged sequential propagation experiment or propagated without phage addition (control). Throughout the serial propagation the genetic lineage composition was monitored. During the propagation of control blends we detected quick domination of a single lineage. This dominating lineage contained strains sensitive to phages. Genetic lineage level composition of the phage-challenged blends was much more dynamic suggesting the impact of phage predation. The relatively low strain diversity introduced in these blends was not high enough to sustain maximal diversity at the level of lineages.

    Chapter 3 describes a study using defined blends with higher complexity by extending the number of strains used. In total, 24 strains representing all 8 Ur starter lineages were exposed in sequential propagation experiment to a cocktail of 3 phages isolated from Ur starter. The propagation in milk of this multi-strain blend was executed for more than 500 generations and the abundance of genetic lineages was monitored throughout. Similarly as in the simple blends experiment, control blends were not exposed to bacteriophages. In control blends we observed a domination of one genetic lineage upon serial propagation, which resembles a periodic-selection-like (PS) behavior, where the fittest strains are dominating the microbial community and in result genetic-lineage diversity is being substantially reduced. In contrast, the composition of phage-challenged blends was again more dynamic than in control blends. In one of the phage-challenged blends behavior characteristic for a constant-diversity dynamics model was observed; throughout the serial transfer experiment, genetic lineage diversity was maintained by the presence of phage predation at relatively high level. In case of the second phage-challenged blend, due to a stochastic event, which likely caused a reduction in phage pressure, we observed a gradual recovery of the fittest strains, which again resembled a periodic-selection behavior. Therefore, phage predation, among other factors, can lead to shifts in microbial community population dynamics resulting in alternative stable states.

    The experimental evolution approach, resembling traditional process of back-slopping, was used in a Long-term experimental evolution of Undefined Mixed Starter Culture (LUMSC) study described in Chapter 4. The aim of this study was to investigate the compositional and functional stability ascribed to the undefined mixed Ur starter during enclosed prolonged propagation without any possible external influx of bacterial or phage material. Surprisingly, during this 1000-generation long experiment the enforced conditions of specific incubation temperature and propagation regime resulted in enrichment of previously not detected strain of Lactococcus laudensis. This strain was found to consume a by-product of metabolism of another strain present in the community, in particular, D-mannitol produced by Le. mesenteroides. Thus, a new putative interaction in the microbial community of the complex starter culture was found. This new interaction and the possible ability of L. laudensis to efficiently use peptides released by caseinolytic L. lactis ssp. cremoris resulted in a relatively high abundance of L. laudensis in all evolved LUMSC cultures. The high abundance of L. laudensis had a certain effect on the functionality of the cultures. The aroma profiles of model lab-scale milli-cheeses manufactured with LUMSC cultures, showed significant differences in formation of esters and alcohols when compared to cheeses produced with the original Ur starter. Moreover, L. laudensis strain was not only under the radar of previously used culture-dependent and culture-independent methods, but as well, under the radar of phage predation continuously present throughout the LUMSC experiment. This observation sheds new light on the possibility of how a strain can emerge to relatively high abundance in an enclosed serially propagated microbial community operating in accordance with CD dynamics model.

    Finally, the aspect of adaptation to environmental conditions was addressed by the study of an adjunct strain of Lactobacillus helveticus DSM 20075 described in Chapter 5. The aim was to develop a strain with increased autolytic capacity in conditions resembling the cheese matrix to possibly improve cheese ripening. The approach used here was based on a previously reported study, where the incubation of Lactococcus lactis MG1363 at high temperature resulted in spontaneous mutations causing stable heat-resistant and, in some cases, salt-hypersensitive phenotypes. In present study, after incubation of the Lb. helveticus DSM 20075 adjunct at different high temperatures (45-50 °C), heat-sensitive variants were recovered from plates. These variants were further characterized in terms of their growth rates at elevated temperatures (42-45 °C) and their autolytic capacity in low pH buffer with addition of NaCl. One of the variants (V50) showed substantially increased intracellular lactate dehydrogenase enzyme activity in the buffer suggesting its increased autolytic capacity. Next, both wild type and variant V50 were tested as adjuncts in lab-scale model milli-cheeses to determine their possible impact on the cheese aroma profiles. Indeed, adjunct strains, both WT and the variant, impacted the aroma profiles by producing benzaldehyde. In case of the variant strain the relative abundance of this compound was 3-fold higher. The applied strategy of incubating Lb. helveticus DSM20075 at high temperature resulted in specific, but different than in case of L. lactis MG1363, mutations suggesting another, yet to be elucidated, mechanisms for increasing the autolytic capacity of industrially-relevant strains. The approach of high-temperature incubation can be applied in dairy industry for the selection of (adjunct) cultures targeted at accelerated cheese ripening and aroma formation.

    In conclusion, the work presented in this thesis highlights the importance of co-evolution of strains in compositional and functional stability of the complex undefined mixed starter culture. In particular, the factors such as heterogeneity of bacteriophage resistance among highly related strains, microbe-microbe interactions and division of metabolic labor are crucial for optimal functioning of a complex starter microbial community. Further investigation of the factors impacting the composition of starter cultures is crucial to steer the functionality in a desired direction. With straightforward methods, such as changing the incubation temperature or the propagation regime it is possible to induce shifts in strain composition and thereby obtain cultures with new characteristics. Moreover, experimental evolution studies with microbial communities used in food fermentation can lead to the discovery of new strains with potentially new characteristics. Additionally, the study of microbial communities of starter cultures not only delivers industrially applicable knowledge but also reveals the action of basic principles in microbial ecology and evolution.

    The role of the starfish (Asterias rubens L.) predation in blue mussel (Mytilus edulis L.) seedbed stability
    Agüera García, A. - \ 2015
    Wageningen University. Promotor(en): Aad Smaal, co-promotor(en): Jeroen Jansen; Tim Schellekens. - Wageningen : Wageningen University - ISBN 9789462572164 - 170
    mytilus edulis - mossels - voortplanting - predatie - zaaibedden - predator prooi verhoudingen - waddenzee - aquacultuur - mytilus edulis - mussels - reproduction - predation - seedbeds - predator prey relationships - wadden sea - aquaculture


    Mussel beds are an important ecological component in the Wadden Sea. Mussels’ offspring settle massively in new suitable areas, forming seedbeds that may disappear again within months. The probability of a seedbed to survive the first winter is defined as seedbed stability; a definition that plays a very important role in the management of newly settled seedbeds. Many factors are important in the survival or extinction of seedbeds. Predation is thought to be particularly important during the first year after settlement and therefore key to survival. Many predators feed on mussel beds, but for most of them the potential to exterminate a seedbed is restricted by different factors such as prey selection or competition. Common starfish (Asterias rubens) are capable of concentrating/aggregating in high densities on mussel seedbeds making them an especially important factor limiting/affecting survival of mussel seedbeds. This study assesses the capacities of starfish as a mussel seed predator. It also provides tools and information to assess the risks of a seedbed being attacked and exterminated by starfish.

    In Chapter 2 the role of temperature and shading on winter predation was studied. The results showed that temperature limits feeding rate and feeding activity of starfish during winter. However, starfish feeding rate exhibited very high sensitivity to temperature changes. Light intensity affected both feeding rate and feeding activity. We conclude that starfish may not be an important factor destabilizing seedbeds during the average winter, but its importance may grow along with the increasing mean winter temperature due to climate change.

    In Chapter 3 the impact of salinity changes on predation performance and survival was assessed. Salinity is the main driver of species distributions in the Wadden Sea. Results show that salinity affected predation performance by reducing feeding activity and causing changes in prey selection. Moreover, as acclimation occurred, A. rubens predation performance improved in all treatments with survivors. We conclude that osmotic stress due to a salinity decreases determines A. rubens distribution, abundance and potential impact on the prey population. However this effect is influenced by the magnitude of the change in salinity and its timescale.

    In Chapter 4 the effect of tidal currents on predation rate was assessed, however, the chapter also tackles the role of hydrodynamic stress amelioration by mussels on the A. rubens population. The results suggest that mussels interact with their own predator beyond the role of food source, by ameliorating environmental stress, creating an additional dependence link between the foundation species and the predator, which potentially has major implications for ecosystem structure and stability.

    In Chapter 5, we assessed the role of mussel association with conspecifics at high densities on prey selection by A. rubens. We concluded that size selection does not always lead to an improvement in net profit. Size selection is a trade-off between energy yield and predation energy costs, which is affected by prey behaviour.

    The results of the prior chapters were integrated in Chapter 6 with field observations and literature to develop a simulation model. This model was designed to simulate growth of mussels and starfish, predation by starfish and mussel mortality. It can also be used to predict the likely effect of future environmental change scenarios on the potential impact of A. rubens on this important resource.

    In the general discussion, Chapter 7, previous literature, field data and the results from this thesis are summarised and reviewed to explain the spatial distribution of A. rubens in the Wadden Sea and the role of environmental conditions on A. rubens predation rate. Model simulations are used to answer the question: What is the role of A. rubens predation in mussel seedbed stability?

    Intertidal biofilm distribution underpins differential tide-following behavior of two sandpiper species (Calidris mauri and Calidris alpina) during northward migration
    Jimenez, A. ; Elner, R.W. ; Favaro, C. ; Rickards, K. ; Ydenberg, R.C. - \ 2015
    Estuarine Coastal and Shelf Science 155 (2015). - ISSN 0272-7714 - p. 8 - 16.
    fraser-river estuary - western sandpipers - shorebird distribution - sediment - waders - microphytobenthos - invertebrates - predation - abundance - cycle
    The discovery that some shorebird species graze heavily on biofilm adds importance to elucidating coastal processes controlling biofilm, as well as impetus to better understand patterns of shorebird use of intertidal flats. Western sandpipers (Calidris mauri) and dunlin (Calidris alpina) stopover in the hundreds of thousands on the Fraser River estuary, British Columbia, Canada, during northward migration to breeding areas. Western sandpipers show greater modification of tongue and bill morphology for biofilm feeding than dunlin, and their diet includes more biofilm. Therefore, we hypothesized that these congeners differentially use the intertidal area. A tide following index (TFI) was used to describe their distributions in the upper intertidal during ebbing tides. Also, we assessed sediment grain size, biofilm (= microphytobenthic or MPB) biomass and invertebrate abundance. Foraging dunlin closely followed the ebbing tide line, exploiting the upper intertidal only as the tide retreated through this area. In contrast, western sandpipers were less prone to follow the tide, and spent more time in the upper intertidal. Microphytobenthic biomass and sediment water content were highest in the upper intertidal, indicating greater biofilm availability for shorebirds in the first 350 m from shore. Invertebrate density did not differ between sections of the upper intertidal. Overall, western sandpiper behaviour and distribution more closely matched MPB biofilm availability than invertebrate availability. Conservation of sandpipers should consider physical processes, such as tides and currents, which maintain the availability of biofilm, a critical food source during global migration.
    The effects of vessel approaches on the New Zealand fur seal (Arctocepahlus forsteri) in the Bay of Plenty, New Zealand
    Cowling, M. ; Kirkwood, R.J. ; Boren, L. ; Sutherland, D. ; Scarpaci, C. - \ 2015
    Marine Mammal Science 31 (2015)2. - ISSN 0824-0469 - p. 501 - 519.
    breeding-season - harbor seals - behavioral-responses - tourist disturbance - wildlife tourism - south-australia - vigilance - experiences - population - predation
    Animals that establish new sites near the edge of the species' range may be vulnerable to disturbance as they are low in numbers and are not tied to the sites. Pinniped distributions world-wide are changing as many species are recolonizing areas of their former ranges and establishing new colonies. Little research is available on the impact that vessel presence may pose on pinnipeds at such sites. This study documents responses of New Zealand fur seals to vessels in the Bay of Plenty, New Zealand, at a recently established breeding colony. Fur seal behavior at the breeding location was recorded in the presence of vessels. GLMM and GAM analyses revealed that fur seal responses varied with month, time of day, duration of vessel exposure, and the distance to the vessel. Age and sex of the seals, and the number of seals present also influenced fur seal response. Fur seals at this site became disturbed when vessels approached to the 10–20 m distance category, and a precautionary minimum approach distance of 50 m has been suggested. This research provides direction for monitoring and minimizing impacts of vessels on fur seals, especially where new sites are being colonized.
    Risico's van anticoagulantia rodenticides voor niet-doelsoorten en predatoren : een scan van beschikbare kennis in Europa en analyses in roofvogels uit Nederland
    Brink, N.W. van den - \ 2014
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2589) - 25
    knaagdieren - roofvogels - ecotoxicologie - predatie - voedselwebben - rodents - predatory birds - ecotoxicology - predation - food webs
    Knaagdierpopulaties kunnen zich lokaal ontwikkelen tot zeer hoge dichtheden en kunnen op deze manier een groot maatschappelijk probleem veroorzaken. Al eeuwen lang worden knaagdierplagen geassocieerd met de uitbraak van ziektes (waaronder de zwarte pest), maar ze kunnen ook economische schade toebrengen. Hierbij valt te denken aan het opeten en bederven van voedselvoorraden, transmissie van ziekteverwekkers tussen bijvoorbeeld boerderijen, terwijl tegenwoordig het knagen aan bedradingen e.d. ook een relevant probleem is. Het gedrag van deze dieren en het feit dat ze zeer snel in populatieomvang kunnen toenemen, maakt dat de bestrijding van knaagdieren continu aandacht behoeft. Er zijn verschillende methodes om knaagdieren te bestrijden.
    Harmonia axyridis: how to explain its invasion success in Europe
    Raak-van den Berg, C.L. - \ 2014
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): Peter de Jong; Lia Hemerik. - Wageningen : Wageningen University - ISBN 9789462571037 - 221
    harmonia axyridis - organismen ingezet bij biologische bestrijding - geïntroduceerde soorten - invasieve exoten - predatie - voedingsgedrag - nederland - harmonia axyridis - biological control agents - introduced species - invasive alien species - predation - feeding behaviour - netherlands

    Abstract of the thesis entitled “Harmonia axyridis: how to explain its invasion success in Europe”

    After introduction as biological control agent of aphids, the multicoloured Asian ladybird Harmonia axyridis has established and spread in Europe. Harmonia axyridis is now regarded as an invasive species because its establishment had negative effects on non-target species, fruit production, and human health. Life history characteristics were studied in order to find an explanation for its invasion success.

    With a meta-analysis I showed that life-history traits of H. axyridis differed between Asian and invasive populations of H. axyridis. However, the greatest differences in development rate were observed at temperatures above 24°C, while at temperatures characteristic for spring and summer in northwestern Europe (17 to 24°C) invasive populations of H. axyridis do not differ from native Asian populations; thus, the invasive success cannot be attributed to a change in life history characteristics of the invasive population. Compared to native species European ladybirds (Adalia bipunctata, Coccinella septempunctata, and Propylea quatuordecimpunctata), H. axyridis develops slower and starts reproduction later, suggesting no competitive advantage for the invader.

    Additionally, life history characteristics were studied under field conditions. I showed that in northwestern Europe H. axyridis has a period of real diapause starting at the end of October and shifts to a quiescent state in December. This diapause is relatively short and weak compared with published data of native ladybirds. Moreover, it appears to have become shorter over the last decade. Thus, H. axyridis can become active rapidly when temperature rises in spring, but, nevertheless, it is not reported to be active earlier in the year than native species.

    Overwintering survival of H. axyridis in the Netherlands is between 71 and 88%. At five sample sites I found that ladybirds that were hibernating at the southwestern sides of buildings, where most aggregations of ladybirds were found, had a higher winter survival than ladybirds hibernating at other orientations. At sheltered sites survival was higher compared to exposed sites. A high overwintering survival results in a large post-hibernation population and a rapid population build-up in spring. Compared with most common native species, winter survival of H. axyridis is similar or higher.

    In this research, i.e. under semi-field conditions, immature survival of H. axyridis and A. bipunctata reached high levels, but survival was generally considerably higher for H. axyridis than for the native A. bipunc­tata. Under semi-field conditions with high food availability, no effect of the presence of H. axyridis on the survival, development, weight, and size of the native species A. bipunctata was found. Under natural conditions, however, situations of prey scarcity do occur, as aphid colonies are relatively short-lived.

    Additionally, I demonstrated that in absence of food under semi-field conditions, intraguild predation between C. septempunctata, A. bipunctata, and H. axyridis does occur, although the contact frequency is low. When two fourth instar larvae were placed together on a single leaf, at least one contact was made in 23–43% of the observations, depending on the tested species combination. When contacts between ladybirds do occur, H. axyridis larvae are the winners in contacts with larvae of the native species.

    Finally, I found that several natural enemies are starting to use H. axyridis as a host but are as yet not sufficiently abundant and/or effective to have a profound impact on populations of the invader. In the years 2003—2007 no natural enemies were found in ladybird samples. From 2008 onwards H. axyridis adults were infested by: Hesperomyces virescens fungi (summer and winter), Parasitylenchus bifurcatus nematodes (winter), Coccipolipus hippodamiae mites (winter), and Dinocampus coccinellae parasitoids (summer and winter).

    Summarising, the success­ful invasion of H. axyridis in the Netherlands cannot be explained by a change of the invasive H. axyridis populations in comparison with the native Asian population, but by a combi­nation of several characteristics: overwintering, immature survival, fecundity, longevity, number of generations per year, and intraguild predation. In comparison with native European ladybird species, H. axyridis survives better (in winter and the immature stages), it lays more eggs, has more generations per year, and lives longer: this results in a faster population growth than that of native ladybirds. Harmonia axyridis can potentially easily outnumber native species within a few years. Moreover, H. axyridis being a strong intra­guild predator, the slow immature development and late arrival at aphid colonies com­pared to native species is compensated by the ability of H. axyridis to feed on eggs, larvae, and pupae of other ladybirds, thereby completing its development.

    However, several facts, e.g. the quite stable diversity and abundance of ladybird species in Asia and the first evidence that natural enemies attack H. axyridis, suggest that the current situation in Europe may not be the terminal stage, but a transition to a new balance where native species are strongly reduced in abundance, but do not become extinct.

    Predation threats to the Red-billed Tropicbird breeding colony of Saba: focus on cats
    Debrot, A.O. ; Ruijter, M. ; Endarwin, W. ; Hooft, P. van; Wulf, K. - \ 2014
    Den Helder : IMARES (Report / IMARES Wageningen UR C011/14) - 53
    natuurlijke vijanden - vogels - predatie - katten - inventarisaties - caribisch gebied - natural enemies - birds - predation - cats - inventories - caribbean
    Feral domestic cats (Felis catus) are recognized as one of the most devastating alien predator species in the world and are a major threat to nesting colonies of the Red-billed Tropicbird (Phaethon aethereus), on Saba island, Dutch Caribbean. Cats and rats are both known to impact nesting seabirds and hence are both potential threats to the tropicbird on Saba. However, whereas the tropicbird has coexisted with rats for centuries, cats have only recently become a problem (since about 2000). Several studies from the region suggest that the tropicbird may be less-vulnerable to rats but cats have been unequivocally implicated in the depredation of tropicbird nests on Saba (unpublished data, Michiel Boeken). In this study we collected baseline data on cat and rat distribution, and cat diet and health. We also conducted 83 questionnaire interviews with Saba residents to assess their views on cats, rats, tropicbirds and the acceptability of different management options.
    Growth of juvenile blue mussels (Mytilus edulis) on suspended collectors in the Dutch Wadden Sea
    Jacobs, P. ; Beauchemin, C. ; Riegman, R. - \ 2014
    Journal of Sea Research 85 (2014). - ISSN 1385-1101 - p. 365 - 371.
    spat collectors - macoma-balthica - temperature - larvae - recruitment - predation - responses - winters - seed
    In The Netherlands, fishing for juvenile blue mussels (Mytilus edulis) on wild beds is gradually replaced by harvesting of seeds from suspended collectors. Both the relaxation of fishing as well as the up-scaling of the number of seed collectors are expected to result in an increase in the number of mussels in the Wadden Sea. Consequently, an enhanced mussel population will cause an additional filtration impact on the system. The question is raised to what extent collectors can be used without negatively affecting the carrying capacity of an ecosystem. Therefore, a monitoring programme was initiated to study the growth of juvenile mussels on suspended collectors. This growth was related to food availability, measured as chlorophyll-a, and temperature both before and after settlement. Findings will serve as input for mathematical models predicting the carrying capacity for mussel seed collectors in this area. The results for 2010 and 2011 are presented. In 2011 settled mussels achieved a higher growth rate, while phytoplankton concentrations after settlement were lower. This contradicts the general agreement that higher phytoplankton concentrations result in higher growth rates. A positive relation between chlorophyll-a concentrations during the larval period and the growth rate of settled mussels was found. The number of settled larvae was higher in 2011. Results from existing studies on settlement and recruitment on tidal flats combined with estimated settlement date in the current study led to the hypothesis that the number of settled mussels on rope collectors is inversely related to the duration of the larval period (determined by water temperature). Our results indicated that in the Wadden Sea, the intra-annual differences in chlorophyll-a and temperature did not have an impact on the juvenile growth rate, while the interannual differences did. This is an indication that the larval stage is strongly discriminative in terms of juvenile growth rates. Modelling growth of juvenile mussels on collectors should thus include conditions before settlement.
    Spatial organisation and biomass development after relaying of mussel seed
    Capelle, J.J. ; Wijsman, J.W.M. ; Schellekens, T. ; Stralen, M.R. van; Herman, P.M.J. ; Smaal, A.C. - \ 2014
    Journal of Sea Research 85 (2014). - ISSN 1385-1101 - p. 395 - 403.
    mytilus-edulis l. - oystercatchers haematopus ostralegus - carcinus-maenas - fractal geometry - seasonal-changes - wadden sea - beds - size - predation - dynamics
    It is not known whether and by what factors spatial heterogeneity in mussels (Mytilus edulis L.) affects mussel production in human-created mussel beds. In a field experiment, the same number of mussels was relayed on four different areas within plots of the same size, resulting in four treatments with different mussel densities. Density, individual weight and spatial structure of mussels were followed per treatment. The uniformly placed mussels on different areas redistributed into new patches, but mussels did not spread out over a larger area. Initial mussel density affected redistribution and mussel survival. At high densities mussels redistributed into a uniform matrix or in a few larger patches, that showed larger losses than at low densities, where mussels redistributed into a high number of patches. Growth rate and condition index of the mussels did not differ between treatments and no relation was found between treatment and number of foraging shore crabs, which was the major predator of mussels in this experiment. We hypothesise that the relation between initial mussel density and mussel loss after relaying is associated with redistribution, with less competition for space when mussels are positioned at the edge of a mussel patch. The very high mussel losses that we observed in the experiment within four weeks after relaying were the major factor in biomass development. Mussel bed formation concerns mussel growers and managers involved in natural mussel bed restoration. Initial mussel survival determines the success of these activities. The present study shows the effects of mussel relaying on spatial redistribution for the first time under field conditions, and underlines the importance of edge effects in understanding mussel loss in redistribution. Mussel survival after relaying will be higher when the mussels are distributed homogeneously and in relatively low density.
    Breeding Biology and Diet of the African Swallow-Tailed Kite (Chelictinia riocourii) in Senegal and Cameroon
    Buij, R. ; Cavaillés, S. ; Mullié, W.C. - \ 2013
    Journal of Raptor Research 47 (2013)1. - ISSN 0892-1016 - p. 41 - 53.
    savanna - raptors - birds - hawk - populations - predation - survival - site
    We studied the breeding biology of the African Swallow-tailed Kite (Chelictinia riocourii) in two study areas located 3400 km apart in the central (Cameroon) and western (Senegal) portions of the species' breeding range. With 110 nests in 2.8 km2 of suitable breeding habitat, Kousmar islet (23 km2) in Senegal supports the largest documented colony of African Swallow-tailed Kites known to date. Breeding kites in Senegal nested in a single large colony near a massive winter roost. In Cameroon, breeding colonies averaged seven pairs/colony, with nest densities of 0.3 nests/km2 in protected woodland and 0.9 nests/km2 in cultivated habitat. Egg-laying coincided with the end of the dry season in Cameroon, but eggs were recorded from the middle of the dry season in Senegal. Eggs hatched between April and June in both study sites in 2010, but from March 2012 in Senegal. The incubation period was estimated at 27–31 d based on two nests, and the fledging period was 32–35 d (n ¿=¿ 3 fledglings). Mean clutch size was 2.5 eggs (n ¿=¿ 32) in Cameroon and 2.1 in Senegal (n ¿=¿ 29); one clutch of four eggs was recorded in Cameroon. Nest success estimated with the Mayfield method was low at 17% in Cameroon and exceptionally low at 4% in Senegal, possibly related to a combination of suboptimal food conditions, high predation pressure, intraspecific aggression, and lack of experience among breeding pairs. Prey items at nests were made up primarily of lizards (30–54% of items) and insects (27–49%), notably grasshoppers, whereas the diet at the winter roost in Senegal was predominantly Orthoptera (55%) and Solifugids (43%). Our study suggested that African Swallow-tailed Kites were able to adapt to moderate land transformation near floodplains.
    De Wolf: getolereerd of geschoten?
    Wamelink, G.W.W. ; Lelieveld, G. ; Ottburg, F.G.W.A. ; Bodegom, P.M. van - \ 2013
    Vakblad Natuur Bos Landschap 2013 (2013)10. - ISSN 1572-7610 - p. 19 - 21.
    wolven - habitats - predatie - migratie - inventarisaties - centraal-europa - wolves - habitats - predation - migration - inventories - central europe
    De wolf is in aantocht, zowel vanuit het oosten als vanuit het zuiden. Waarom rukt hij op en is hij ineens zo succesvol? Wat eet hij? Welke invloed heeft hij op andere dieren? Vragen die een licht werpen op hoe we ons moeten voorbereiden. Omdat we dat niet kunnen op basis van eigen ervaring kijken we in dit artikel naar het buitenland en proberen een aantal van de meest prangende vragen over de wolf te beantwoorden op basis van literatuur
    De komst van de wolf naar Nederland
    Lammertsma, D.R. ; Groot Bruinderink, G.W.T.A. ; Jansman, H.A.H. ; Jacobs, M. - \ 2013
    Vakblad Natuur Bos Landschap 100 (2013). - ISSN 1572-7610 - p. 16 - 18.
    wolven - fauna - predatie - schade - financieren - wildbeheer - natuurbeleid - wolves - fauna - predation - damage - financing - wildlife management - nature conservation policy
    In de afgelopen tientallen jaren is de wolf begonnen aan een opmars door Europa, waarbij de Nederlandse grens steeds dichter wordt genaderd. De kans bestaat dan ook dat de wolf de komende jaren zal opduiken in Nederland. Deze ontwikkeling roept bij verschillende organisaties en bevolkingsgroepen uiteenlopende reacties op over de effecten op de natuur, de recreatie, de veeteelt, het faunabeheer en de veiligheid van de mens. Een belangrijke vraag is daarom hoe we met de eventuele komst van de wolf moeten omgaan. Alterra schreef in opdracht van het ministerie van Economische Zaken, de provincies en het Faunafonds een ‘factfinding study’.
    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 - fauna - 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.
    When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs
    Denderen, P.D. van; Kooten, T. van; Rijnsdorp, A.D. - \ 2013
    Proceedings of the Royal Society. B: Biological Sciences 280 (2013)1769. - ISSN 0962-8452
    southern north-sea - benthic community - interspecific competition - marine systems - disturbance - sediment - model - management - predation - impacts
    Bottom trawls are a globally used fishing gear that physically disturb the seabed and kill non-target organisms, including those that are food for the targeted fish species. There are indications that ensuing changes to the benthic invertebrate community may increase the availability of food and promote growth and even fisheries yield of target fish species. If and how this occurs is the subject of ongoing debate, with evidence both in favour and against. We model the effects of trawling on a simple ecosystem of benthivorous fish and two food populations (benthos), susceptible and resistant to trawling. We show that the ecosystem response to trawling depends on whether the abundance of benthos is top-down or bottom-up controlled. Fishing may result in higher fish abundance, higher (maximum sustainable) yield and increased persistence of fish when the benthos which is the best-quality fish food is also more resistant to trawling. These positive effects occur in bottom-up controlled systems and systems with limited impact of fish feeding on benthos, resembling bottom-up control. Fishing leads to lower yields and fish persistence in all configurations where susceptible benthos are more profitable prey. Our results highlight the importance of mechanistic ecosystem knowledge as a requirement for successful management.
    Effects of resources and mortality on the growth and reproduction of Nile perch in Lake Victoria
    Downing, A.S. ; Nes, E.H. van; Wolfshaar, K.E. van de; Scheffer, M. ; Mooij, W.M. - \ 2013
    Freshwater Biology 58 (2013)4. - ISSN 0046-5070 - p. 828 - 840.
    lates-niloticus l - size-structured populations - life-history traits - haplochromine cichlids - east-africa - mwanza gulf - nyanza-gulf - competition - predation - dynamics
    1. A collapse of Nile perch stocks of Lake Victoria could affect up to 30 million people. Furthermore, changes in Nile perch population size-structure and stocks make the threat of collapse imminent. However, whether eutrophication or fishing will be the bane of Nile perch is still debated. 2. Here, we attempt to unravel how changes in food resources, a side effect of eutrophication, and fishing mortality determine fish population growth and size structures. We parameterised a physiologically structured model to Nile perch, analysed the influence of ontogenetic diet shifts and relative resource abundances on existence boundaries of Nile perch and described the populations on either side of these boundaries. 3. Our results showed that ignoring ontogenetic diet shifts can lead to over-estimating the maximum sustainable mortality of a fish population. Size distributions can be indicators of processes driving population dynamics. However, the vulnerability of stocks to fishing mortality is dependent on its environment and is not always reflected in size distributions. 4. We suggest that the ecosystem, instead of populations, should be used to monitor long-term effects of human impact.
    Tracking rodent-dispersed large seeds with Passive Integrated Transponder (PIT) tags
    Suselbeek, L. ; Jansen, P.A. ; Prins, H.H.T. ; Steele, M.A. - \ 2013
    Methods in Ecology and Evolution 4 (2013)6. - ISSN 2041-210X - p. 513 - 519.
    quercus-robur seedlings - yellow pine chipmunks - cotyledon removal - cache pilferage - identification - growth - predation - regeneration - technology - management
    1.Seed dispersal, a critical phase in the life history of many plants, is poorly understood due to the difficulty of tracking and monitoring dispersing seeds until they reach their ultimate fate. Scatter-hoarding rodents play a substantial part in the seed dispersal process of many plant species, however, existing tracking methods do not allow seed monitoring without risk of influencing the hoarding process and seed fate. 2.Here, we describe and test the use of Passive Integrated Transponders (PIT) tags inserted into seeds for the tracking and monitoring of large seeds dispersed by rodents. Unlike other tagging methods, PIT tagging combines the advantages of leaving no external cues and being readable without disturbance of caches. Rodents cannot remove these tags. 3.We evaluated the performance of PIT tagging through a series of trials with Quercus acorns dispersed by rodents, both in North America and in Europe, with equipment from different manufacturers. We quantified effects of tagging on seed removal and caching, cache pilferage and seed germination, by comparison between PIT-tagged and untagged acorns. We evaluated the detectability of buried tags to researchers. 4.Minimal effects of PIT tagging on seed removal, caching, pilferage and germination were found. Buried PIT tags were retrieved with high reliability by naïve researchers, even at burial depths up to 30 cm. Identification codes could be read even when multiple tags were buried at a single location, as in larder hoarding. 5.The method was successfully applied in two field studies of dispersal of Quercus palustris and Q. rubra acorns by Eastern grey squirrels Sciurus carolinensis in North America, and Q. robur acorns by Wood mice Apodemus sylvaticus in the Netherlands. The proportion of seeds recovered was comparable to that in studies using traditional thread tags. 6.We conclude that PIT tagging is a particularly suitable method for tracking and monitoring of seeds dispersed by scatter-hoarding rodents. PIT tagging solves most of the main problems generally encountered when following the fate of rodent-dispersed seeds over time.
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