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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    Analyzing Pellets and Feces of African Royal Terns (Thalasseus maximus albididorsalis) Results in Different Estimates of Diet Composition
    Veen, Jan ; Dallmeijer, Hanneke ; Damme, Cindy J.G. van; Leopold, Mardik F. ; Veen, Thor - \ 2018
    Waterbirds 41 (2018)3. - ISSN 1524-4695 - p. 295 - 304.
    African Royal Terns - Delta du Saloum - diet overlap - fish - otoliths - prey - Senegal - Thalasseus maximus albididorsalis.

    A frequently used method to estimate diet composition is based on the identification of fish otoliths present in pellets and feces. However, whether pellets and feces provide similar unbiased estimates of the diet remains poorly understood. The diet of African Royal Terns (Thalasseus maximus albididorsalis) breeding in the Parc National du Delta du Saloum, Senegal, was studied. Prey species composition based on otoliths in freshly regurgitated pellets and a mixture of pellets and feces (excrement) accumulated near nests during the incubation period were compared. Altogether, 59 fish species were identified. Pellets contained far less prey species than excrement. Maximum diet overlap between excrement and pellets varied between 0.34 and 0.43 (mean = 0.36). Differences between minimum and maximum overlap between both sample types were small in all years. Pellets contained almost exclusively large otoliths (widths 3.0-8.5 mm), whereas excrement contained two fractions: large sized ones, identical to those present in the pellets and smaller-sized ones (0.5-3.0 mm) originating from feces. It is hypothesized that large otoliths cannot pass the intestinal tracts of the birds and are therefore regurgitated. Differences in prey species composition in pellets and excrement could potentially be explained by a combination of seasonal changes in availability of prey species and size of otoliths. Neither pellets nor feces alone give an unbiased picture of the diet of African Royal Terns.

    Culturing soles on ragworms: growth and feeding behaviour
    Ende, S.S.W. - \ 2015
    Wageningen University. Promotor(en): Johan Verreth, co-promotor(en): Johan Schrama. - Wageningen : Wageningen University - ISBN 9789462575622 - 128
    solea - soleidae - kweekvis - voeropname - groei - prooi - wormen - foerageren - voedingsgedrag - prestatieniveau - vijverteelt - aquacultuur - solea - soleidae - farmed fish - feed intake - growth - prey - helminths - foraging - feeding behaviour - performance - pond culture - aquaculture

    Ende, S.S.W. (2015). Culturing soles on ragworms: Growth and feeding behaviour. PhD thesis, Wageningen University, The Netherlands.

    Despite the high market demand and intensive research efforts since the 1960s commercial culture of common sole (Solea solea L.) has been unsuccessful. Problems related to availability and price of suitable raw materials (invertebrates) and the low tolerance to crowding have hampered the development of intensive sole culture. Alternative extensive pond cultures systems are currently explored where common sole can graze on natural food. The general aim of this study was to get insight into which factors limit growth of common sole foraging on ragworms in ponds. The results did not show any nutritional effects that may hamper the growth of common sole. At non-limiting conditions, i.e. when fed chopped ragworms and when housed in sediment free tanks, common sole showed higher food intake, higher growth rates and higher nutrient utilization efficiencies than when fed mussels or a formulated diet. The results however suggest that growth in a pond with ragworms was limited by reduced foraging capabilities of common sole. To explore this hypothesis, the effect of prey size, predator size and prey density were tested. Overall, intake of buried ragworms was reduced by more than half in contrast to intake of unburied ragworms. Intake of buried ragworms was reduced regardless of ragworm size or common sole size. Increasing ragworm density only resulted in satiation intake values in smaller common sole. Our results additionally indicate that the presence of common sole hampers ragworm performance in a pond. Ragworms reduced their feeding activities when receiving water from tanks which contained common sole and ragworms, i.e. when common sole could graze on ragworms. Results from this PhD study suggest that the growth of common sole in ponds is not limited by nutritional but by their foraging abilities. However, the results of this study are too incomplete to fully predict growth performance of common sole in a pond. Factors such as temperature, oxygen supply or feeding activity need to be investigated to make comprehensive growth predictions.

    Evaluation of mirid predatory bugs and release strategy for aphid control in sweet pepper
    Messelink, G.J. ; Bloemhard, C.M.J. ; Hoogerbrugge, H. ; Schelt, J. van; Ingegno, B.L. ; Tavella, L. - \ 2015
    Journal of Applied Entomology 139 (2015)5. - ISSN 0931-2048 - p. 333 - 341.
    frankliniella-occidentalis thysanoptera - macrolophus-pygmaeus - tuta-absoluta - heteroptera miridae - thrips thysanoptera - nesidiocoris-tenuis - host plants - dicyphus - hemiptera - prey
    Zoophytophagous predators of the family Miridae (Heteroptera), which feed both on plant and prey, often maintain a close relationship with certain host plants. In this study, we aimed to select a suitable mirid predatory bug for aphid control in sweet pepper. Four species were compared: Macrolophus pygmaeus (Rambur), Dicyphus errans (Wolff), Dicyphus tamaninii Wagner and Deraeocoris pallens (Reuter). They were assessed on their establishment on sweet pepper plants with and without supplemental food (eggs of the flour moth Ephestia kuehniella Zeller and decapsulated cysts of the brine shrimp Artemia franciscana Kellogg) and on their effects on aphids with releases before and after aphid infestations. None of the predator species was able to control an established population of aphids on sweet pepper plants; however, the predators M. pygmaeus and D. tamaninii could successfully reduce aphid populations when released prior to an artificially introduced aphid infestation. The best results were achieved with M. pygmaeus in combination with a weekly application of supplemental food. Hence, our results demonstrate that the order and level of plant colonization by mirid predators and aphids determines how successful biological control is. Further studies are needed to evaluate the performance of mirid predatory bugs in sweet pepper crops in commercial greenhouses with multiple pests and natural enemies, in particular to understand how increased variation in food sources affects their feeding behaviour and preferences.
    Supplemental food that supports both predator and pest: A risk for biological control?
    Leman, A. ; Messelink, G.J. - \ 2015
    Experimental and Applied Acarology 65 (2015)4. - ISSN 0168-8162 - p. 511 - 524.
    neoseiulus-cucumeris acari - mite amblyseius-swirskii - western flower thrips - orius-laevigatus - apparent competition - factitious foods - life-history - prey - phytoseiidae - pollen
    Supplemental food sources to support natural enemies in crops are increasingly being tested and used. This is particularly interesting for generalist predators that can reproduce on these food sources. However, a potential risk for pest control could occur when herbivores also benefit from supplemental food sources. In order to optimize biological control, it may be important to select food sources that support predator populations more than herbivore populations. In this study we evaluated the nutritional quality of four types of supplemental food for the generalist predatory mites Amblyseius swirskii Athias-Henriot and Amblydromalus (Typhlodromalus) limonicus (Garman and McGregor), both important thrips predators, and for the herbivore western flower thrips Frankliniella occidentalis Pergande, by assessing oviposition rates. These tests showed that application of corn pollen, cattail pollen or sterilized eggs of Ephestia kuehniella Zeller to chrysanthemum leaves resulted in three times higher oviposition rates of thrips compared to leaves without additional food. None of the tested food sources promoted predatory mites or western flower thrips exclusively. Decapsulated cysts of Artemia franciscana Kellogg were not suitable, whereas cattail pollen was very suitable for both predatory mites and western flower thrips. In addition, we found that the rate of thrips predation by A. swirskii can be reduced by 50 %, when pollen is present. Nevertheless, application of pollen or Ephestia eggs to a chrysanthemum crop still strongly enhanced the biological control of thrips with A. swirskii, both at low and high release densities of predatory mites through the strong numerical response of the predators. Despite these positive results, application in a crop should be approached with caution, as the results may strongly depend on the initial predator–prey ratio, the nutritional quality of the supplemental food source, the species of predatory mites, the distribution of the food in the crop and the type of crop.
    Development and thermal requirements of the Nearctic predator Geocoris punctipes (Hemiptera: Geocoridae) reared at constant and alternating temperatures and fed on Anagasta kuehniella (Lepidoptera: Pyralidae) eggs
    Calixto, A.M. ; Bueno, V.H.P. ; Montes, F.C. ; Lenteren, J.C. van - \ 2014
    European Journal of Entomology 111 (2014)4. - ISSN 1210-5759 - p. 521 - 528.
    biological-control agents - insidiosus say hemiptera - orius-insidiosus - tuta absoluta - life-history - prey - anthocoridae - heteroptera - lygaeidae - insect
    Knowledge of the optimal temperatures for development and survival of biological control agents is essential for efficient mass-rearing and introduction of natural enemies in augmentative biological control programs. We studied the effect of constant and alternating temperatures on development and survival of immature stages and the sex ratio at emergence of adults of the Nearctic generalist predator Geocoris punctipes (Say). We also determined its thermal requirements. They were reared in climatic chambers at alternating (21/11°C, 24/18°C, 27/21°C and 30/26°C ± 1°C) and constant temperatures (16.8°C, 21.5°C, 24.5°C and 28.3°C ± 1°C), RH 70 ± 10% and a 14 h photophase. Survival and development of G. punctipes were the same when reared at constant and alternating temperatures. Five instars were recorded in all temperature regimes. The duration of the egg stage and each instar, as well as that of total larval development were longer, and larval survival lower when reared at 16.8°C, 21/11°C, 21.5°C and 24/18°C than at 24.5°C, 27/21°C, 28.3°C and 30/26°C. The optimal temperature range for development and survival of G. punctipes is 24.5°C to 30°C, its lower development threshold temperature is 13.5°C and its thermal constant 295.9 DD. Sex ratios were not significantly different from 1 : 1 male : female ratio in all temperature regimes. There is an excellent match between the temperature regimes at which the prey Tuta absoluta (Meyrick) and predator G. punctipes are active, which indicates that this predator will function well in crops where this pest is present.
    Effect of sequential induction by Mamestra brassicae L. and Tetranychus urticae Koch on Lima bean plant indirect defense
    Menzel, T.R. ; Huang, T.Y. ; Weldegergis, B.T. ; Gols, R. ; Loon, J.J.A. van; Dicke, M. - \ 2014
    Journal of Chemical Ecology 40 (2014)9. - ISSN 0098-0331 - p. 977 - 985.
    induced volatile emission - host-plant - jasmonic acid - mediated interactions - arabidopsis-thaliana - methyl salicylate - induced responses - predatory mite - herbivores - prey
    Attack by multiple herbivores often leads to modification of induced plant defenses compared to single herbivory, yet little is known about the effects on induced indirect plant defense. Here, we investigated the effect of sequential induction of plant defense by Mamestra brassicae caterpillar oral secretion and an infestation by Tetranychus urticae spider mites on the expression of indirect plant defense in Lima bean plants. The effect on indirect defense was assessed using behavior assays with the specialist predatory mite Phytoseiulus persimilis in an olfactometer, headspace analysis of 11 major herbivore-induced plant volatiles (HIPVs) including (E)-ß-ocimene, and transcript levels of the corresponding gene Phaseolus lunatus (E)-ß-ocimene synthase (PlOS). Predatory mites were found to distinguish between plants induced by spider mites and caterpillar oral secretion but not between plants with single spider mite infestation and plants induced by caterpillar oral secretion prior to spider mite infestation. Indeed, the volatile blends emitted by plants induced by spider mites only and the sequential induction treatment of caterpillar oral secretion followed by spider mite infestation, were similar. Our results suggest that plant indirect defense is not affected by previous treatment with oral secretion of M. brassicae caterpillars.
    Fine-scale hydrodynamics influence the spatio-temporal distribution of harbour porpoises at a coastal hotspot
    Jones, A.R. ; Hosegood, P. ; Wynn, R.B. ; Boer, M.N. de; Butler-Cowdry, S. ; Embling, C.B. - \ 2014
    Progress in Oceanography 128 (2014). - ISSN 0079-6611 - p. 30 - 48.
    phocoena-phocoena - habitat preferences - relative abundance - continental-shelf - stratified flow - small bank - fundy - prey - bay - patterns
    The coastal Runnelstone Reef, off southwest Cornwall (UK), is characterised by complex topography and strong tidal flows and is a known high-density site for harbour porpoise (Phocoena phocoena); a European protected species. Using a multidisciplinary dataset including: porpoise sightings from a multi-year land-based survey, Acoustic Doppler Current Profiling (ADCP), vertical profiling of water properties and high-resolution bathymetry; we investigate how interactions between tidal flow and topography drive the fine-scale porpoise spatio-temporal distribution at the site. Porpoise sightings were distributed non-uniformly within the survey area with highest sighting density recorded in areas with steep slopes and moderate depths. Greater numbers of sightings were recorded during strong westward (ebbing) tidal flows compared to strong eastward (flooding) flows and slack water periods. ADCP and Conductivity Temperature Depth (CTD) data identified fine-scale hydrodynamic features, associated with cross-reef tidal flows in the sections of the survey area with the highest recorded densities of porpoises. We observed layered, vertically sheared flows that were susceptible to the generation of turbulence by shear instability. Additionally, the intense, oscillatory near surface currents led to hydraulically controlled flow that transitioned from subcritical to supercritical conditions; indicating that highly turbulent and energetic hydraulic jumps were generated along the eastern and western slopes of the reef. The depression and release of isopycnals in the lee of the reef during cross-reef flows revealed that the flow released lee waves during upslope currents at specific phases of the tidal cycle when the highest sighting rates were recorded. The results of this unique, fine-scale field study provide new insights into specific hydrodynamic features, produced through tidal forcing, that may be important for creating predictable foraging opportunities for porpoises at a local scale. Information on the functional mechanisms linking porpoise distribution to static and dynamic physical habitat variables is extremely valuable to the monitoring and management of the species within the context of European conservation policies and marine renewable energy infrastructure development.
    Increased control of thrips and aphids in greenhouses with two species of generalist predatory bugs involved in intraguild predation
    Messelink, G.J. ; Janssen, A. - \ 2014
    Biological Control 79 (2014). - ISSN 1049-9644 - p. 1 - 7.
    macrolophus-pygmaeus hemiptera - biological-control - myzus-persicae - nesidiocoris-tenuis - tuta-absoluta - pepper plants - prey - heteroptera - miridae - communities
    The combined release of species of generalist predators can enhance multiple pest control when the predators feed on different prey, but, in theory, predators may be excluded through predation on each other. This study evaluated the co-occurrence of the generalist predators Macrolophus pygmaeus Rambur and Orius laevigatus (Fieber) and their control of two pests in a sweet pepper crop. Both predators consume pollen and nectar in sweet pepper flowers, prey on thrips and aphids, and O. laevigatus is an intraguild predator of M. pygmaeus. Observations in a commercial sweet pepper crop in a greenhouse with low densities of pests showed that the two predator species coexisted for 8 months. Moreover, their distributions in flowers suggested that they were neither attracted to each other, nor avoided or excluded each other. A greenhouse experiment showed that the predators together clearly controlled thrips and aphids better than each of them separately. Thrips control was significantly better in the presence of O. laevigatus and aphid control was significantly better in the presence of M. pygmaeus. Hence, combined inoculative releases of M. pygmaeus and O. laevigatus seem to be a good solution for controlling both thrips and aphids in greenhouse-grown sweet pepper. The predators are able to persist in one crop for a sufficiently long period and they complement each other in the control of both pests. This study also provides further evidence that intraguild predation does not necessarily have negative effects on biological control.
    Size-based species interactions shape herring and cod population dynamics in the face of exploitation
    Denderen, P.D. van; Kooten, T. van - \ 2013
    Ecosphere 4 (2013)10. - ISSN 2150-8925
    north-sea cod - clupea-harengus - intraguild predation - prey - model - recruitment - recovery - biomass - management - fisheries
    Size-specific competition and predation interactions often link the population dynamics of fish species in their response to exploitation. The effects of harvesting on interacting fish species is of increasing relevance as more and more fish populations worldwide are reduced by fishing. When stocks are harvested, effects of harvesting may percolate to populations of other species with which it interacts through competition, predation, etcetera. When multiple species are exploited, this can lead to interactions between fisheries, mediated by ecological interactions. Nevertheless, most fish stocks are managed using a single-species framework. We studied how single-species explanations of historical population dynamics work out when size-based interactions between harvested species are taken into account. We have taken as a case study the dynamics of cod (Gadus morhua) and herring (Clupea harengus) in the North Sea. These dynamics are generally considered to be shaped by fishing pressure on and food availability to single species. Our results indicate that the explanatory power of these factors is maintained with the inclusion of species interactions, but the processes leading to the observed patterns are altered as the fates of the species are interdependent. The sign and magnitude of the interaction between the species depends on the state of the populations, their exploitation history and environmental factors such as resource productivity. This context-dependent response to changing fishery intensity has important ramifications for management. We show that management plans for the exploitation of either one of these species, or for the recovery of North Sea cod, which do not account for these subtle interactions, may fail or backfire. Hence, such interactions link the fate of these species in complex ways, which must be taken into consideration for successful management of their exploitation, including harvesting at maximum sustainable yield, as we move towards an ecosystem-based management of marine fisheries.
    New records of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) predation by Brazilian Hemipteran predatory bugs.
    Bueno, V.H.P. ; Lenteren, J.C. van; Lins, J.C. ; Calixto, A.M. ; Montes, F.C. ; Silva, D.B. ; Santiago, L.D. ; Pérez, L.M. - \ 2013
    Journal of Applied Entomology 137 (2013)1-2. - ISSN 0931-2048 - p. 29 - 34.
    prey
    The tomato borer Tuta absoluta, native to western South America, is an extremely devastating pest in tomato crops in most of South America, Europe and Africa North of the Sahel, causes yield losses up to 100% and decreases fruit quality in open field and greenhouse crops if control methods are not applied. In Brazil two other important lepidopteran pests – Neoleucinodes elegantalis and Helicoverpa zea – occur in tomato, as well as thrips, whiteflies and aphids. For control of these pests, frequent applications of pesticides of up to 5 times per week are needed, and these resulted in the appearance of resistant populations to a number of active ingredients and decimation of natural enemies. Biological control may offer a better, safer and more sustainable opportunity for pest management. Mirid predatory bugs are currently used with success in southern Europe to control T. absoluta and other pests. In Brazil, four Hemipteran predatory bugs, not yet known to attack T. absoluta, were found to successfully prey on eggs and larvae of this pest. The first results on their predation capacity, development, survival and reproduction on T. absoluta on tomato plants are presented.
    Intraguild predation behaviour of ladybirds in semi-field experiments explains invasion success of Harmonia axyridis
    Raak-van den Berg, C.L. ; Lange, H.J. de; Lenteren, J.C. van - \ 2012
    PLoS ONE 7 (2012)7. - ISSN 1932-6203
    coccinella-septempunctata l - aphidophagous ladybirds - adalia-bipunctata - searching behavior - larval tracks - coleoptera - cannibalism - beetle - prey - ecology
    Harmonia axyridis has been introduced as a biological control agent in Europe and the USA. Since its introduction, it has established and spread, and it is now regarded as an invasive alien species. It has been suggested that intraguild predation is especially important for the invasion success of H. axyridis. The aim of this study was to compare the intraguild predation behaviour of three ladybird species (Coccinella septempunctata, Adalia bipunctata, and H. axyridis). Predation behaviour was investigated in semi-field experiments on small lime trees (Tilia platyphyllos). Two fourth-instar larvae placed on a tree rarely made contact during 3-hour observations. When placed together on a single leaf in 23%–43% of the observations at least one contact was made. Of those contacts 0%–27% resulted in an attack. Harmonia axyridis attacked mostly heterospecifics, while A. bipunctata and C. septempunctata attacked heterospecifics as often as conspecifics. In comparison with A. bipunctata and C. septempunctata, H. axyridis was the most successful intraguild predator as it won 86% and 44% of heterospecific battles against A. bipunctata and C. septempunctata respectively, whilst A. bipunctata won none of the heterospecific battles and C. septempunctata won only the heterospecific battles against A. bipunctata. Coccinella septempunctata dropped from a leaf earlier and more often than the other two species but was in some cases able to return to the tree, especially under cloudy conditions. The frequency with which a species dropped did not depend on the species the larva was paired with. The results of these semi-field experiments confirm that H. axyridis is a strong intraguild predator as a consequence of its aggressiveness and good defence against predation from heterospecific species. The fact that H. axyridis is such a strong intraguild predator helps to explain its successful establishment as invasive alien species in Europe and the USA.
    Worms under cover: relationships between performance in learning tasks and personality in great tits (Parus major)
    Amy, M. ; Oers, K. van; Naguib, M. - \ 2012
    Animal Cognition 15 (2012)5. - ISSN 1435-9448 - p. 763 - 770.
    risk-taking behavior - avian personalities - individual-differences - realized heritability - social information - evolution - cognition - traits - stress - prey
    In animals, individual differences in learning ability are common and are in part explained by genetic differences, developmental conditions and by general experience. Yet, not all variations in learning are well understood. Individual differences in learning may be associated with elementary individual characteristics that are consistent across situations and over time, commonly referred to as personality or temperament. Here, we tested whether or not male great tits (Parus major) from two selection lines for fast or slow exploratory behaviour, an operational measure for avian personality, vary in their learning performance in two related consecutive tasks. In the first task, birds had to associate a colour with a reward whereas in the second task, they had to associate a new colour with a reward ignoring the previously rewarded colour. Slow explorers had shorter latencies to approach the experimental device compared with fast explorers in both tasks, but birds from the two selection lines did not differ in accomplishing the first task, that is, to associate a colour with a reward. However, in the second task, fast explorers had longer latencies to solve the trials than slow explorers. Moreover, relative to the number of trials needed to reach the learning criteria in the first task, birds from the slow selection line took more trials to associate a new colour with a reward while ignoring the previously learned association compared with birds from the fast selection line. Overall, the experiments suggest that personality in great tits is not strongly related to learning per se in such an association task, but that birds from different selection lines might express different learning strategies as birds from the different selection lines were differently affected by their previous learning performance.
    Effect of light quality on movement of Pterostichus melanarius (Coleoptera: Carabidae)
    Allema, A.B. ; Rossing, W.A.H. ; Werf, W. van der; Heusinkveld, B.G. ; Bukovinszky, T. ; Steingröver, E.G. ; Lenteren, J.C. van - \ 2012
    Journal of Applied Entomology 136 (2012)10. - ISSN 0931-2048 - p. 793 - 800.
    red-light - patterns - beetles - discrimination - sensitivity - behavior - range - field - prey
    Behaviour of nocturnal insects is routinely observed under red light, but it is unclear how the behaviour under red light compares to behaviour in complete darkness, or under a source of white light. Here, we measure movement behaviour of the nocturnal carabid beetle Pterostichus melanarius Illiger (Coleoptera: Carabidae) using camera recording under a near-infrared (nir), red or white radiation source. Red light significantly reduced movement speed in females similar to the effect of white light and different from nir. Also movement activity and pause length were affected by radiation source, with a significant difference between nir and white light, and with intermediate values in red light. The results presented here indicate that P. melanarius has different movement behaviour under the three radiation sources and suggest that nir rather than red radiation is most appropriate for measuring behaviour in total darkness. However, in the field total darkness is rare both because of natural light sources such as the moon and stars but increasingly also because of ecological light pollution, and therefore red light may still be of use for observing ecologically and practically relevant natural night-time behaviour.
    Whether ideal free or not, predatory mites distribute so as to maximize reproduction
    Hammen, T. van der; Montserrat, M. ; Sabelis, M.W. ; Roos, A.M. ; Janssen, A. - \ 2012
    Oecologia 169 (2012)1. - ISSN 0029-8549 - p. 95 - 104.
    free distribution models - unequal competitors - egg predation - interference - density - prey - phytoseiidae - oviposition - tests
    Ideal free distribution (IFD) models predict that animals distribute themselves such that no individual can increase its fitness by moving to another patch. Many empirical tests assume that the interference among animals is independent of density and do not quantify the effects of density on fitness traits. Using two species of predatory mites, we measured oviposition as a function of conspecific density. Subsequently, we used these functions to calculate expected distributions on two connected patches. We performed an experimental test of the distributions of mites on two such connected patches, among which one had a food accessibility rate that was twice as high as on the other. For one of the two species, Iphiseius degenerans, the distribution matched the expected distribution. The distribution also coincided with the ratio of food accessibility. The other species, Neoseiulus cucumeris, distributed itself differently than expected. However, the oviposition rates of both species did not differ significantly from the expected oviposition rates based on experiments on single patches. This suggests that the oviposition rate of N. cucumeris was not negatively affected by the observed distribution, despite the fact that N. cucumeris did not match the predicted distributions. Thus, the distribution of one mite species, I. degenerans, was in agreement with IFD theory, whereas for the other mite species, N. cucumeris, unknown factors may have influenced the distribution of the mites. We conclude that density-dependent fitness traits provide essential information for explaining animal distributions
    Mononchoides composticola n. sp. (Nematoda:Diplogastridae) associated with composting processes: morphological, molecular and autecological characterisation
    Steel, H. ; Moens, T. ; Scholaert, A. ; Boshoff, M. ; Houthoofd, W. ; Bert, W. - \ 2011
    Nematology 13 (2011)3. - ISSN 1388-5545 - p. 347 - 363.
    laboratory culture - rhabditida - predation - prey - diplogasterinae - phylogeny - elegans - outline
    Mononchoides composticola n. sp. was isolated from compost and is described based on light and scanning electron microscopy, supplemented with SSU rDNA sequence data. It is characterised by the following features: a denticulate ridge in addition to the dorsal claw-like tooth, a small tooth-like swelling at the stegostom base, ca 26 longitudinal ridges on the female body, a uterine sac associated with two dumb-bell-shaped pouches, relatively small spicules (30-38 µm long), a simple gubernaculum shorter than half the spicule length, the genital subventral papillae (v6) consisting of three very small papillae, and a long filiform tail (female: 391-550 µm, 18-26 anal body diam.; male: 304-548 µm, 19-30 anal body diam.). Phylogenetic analyses placed the new species together with M. striatus, sister to Tylopharynx foetida. Since the use of nematodes as functional indicators often relies on the allocation of nematodes to feeding groups, experiments were performed to elucidate the feeding strategy of the new species. Both its ability to move actively to bacterial food sources and to prey on other compost nematodes were tested. Mononchoides composticola n. sp. actively moved towards the compost bacterium Achromobacter, a taxis that was temperature dependent, and also preyed on other nematodes. Predation was selective, with a higher predation rate on the relatively small and slow-moving Rhabditella sp. than on the considerably larger and more motile Rhabditis (Poikilolaimus) sp. Adults of M. composticola n. sp. have a dual feeding behaviour and can apparently alternate between bacterial and nematode prey
    Genetic variation in jasmonic acid- and spider mite-induced plant volatile emission of Cucumber accessions and attraction of the predator Phytoseiulus persimilis
    Kappers, I.F. ; Verstappen, F.W.A. ; Luckerhoff, L.L.P. ; Bouwmeester, H.J. ; Dicke, M. - \ 2010
    Journal of Chemical Ecology 36 (2010)5. - ISSN 0098-0331 - p. 500 - 512.
    methyl jasmonate - isoprenoid biosynthesis - terpenoid metabolism - medicago-truncatula - tetranychus-urticae - indirect defenses - maize - arabidopsis - varieties - prey
    Cucumber plants (Cucumis sativus L.) respond to spider-mite (Tetranychus urticae) damage with the release of specific volatiles that are exploited by predatory mites, the natural enemies of the spider mites, to locate their prey. The production of volatiles also can be induced by exposing plants to the plant hormone jasmonic acid. We analyzed volatile emissions from 15 cucumber accessions upon herbivory by spider mites and upon exposure to jasmonic acid using gas chromatography-mass spectrometry. Upon induction, cucumber plants emitted over 24 different compounds, and the blend of induced volatiles consisted predominantly of terpenoids. The total amount of volatiles was higher in plants treated with jasmonic acid than in those infested with spider mites, with (E)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-alpha-farnesene, and (E)-beta-ocimene as the most abundant compounds in all accessions in both treatments. Significant variation among the accessions was found for the 24 major volatile compounds. The accessions differed strongly in total amount of volatiles emitted, and displayed very different odor profiles. Principal component analysis performed on the relative quantities of particular compounds within the blend revealed clusters of highly correlated volatiles, which is suggestive of common metabolic pathways. A number of cucumber accessions also were tested for their attractiveness to Phytoseiulus persimilis, a specialist predator of spider mites. Differences in the attraction of predatory mites by the various accessions correlated to differences in the individual chemical profiles of these accessions. The presence of genetic variation in induced plant volatile emission in cucumber shows that it is possible to breed for cucumber varieties that are more attractive to predatory mites and other biological control agents.
    Are white-beaked dolphins Lagenorhynchus albirostris food specialst? Their diet in the southern North Sea
    Jansen, O.E. ; Leopold, M.F. ; Meesters, H.W.G. ; Smeenk, C. - \ 2010
    Journal of the Marine Biological Association of The United Kingdom 90 (2010)8. - ISSN 0025-3154 - p. 1501 - 1508.
    eumetopias-jubatus - halichoerus-grypus - marine mammals - hard parts - digestion - otoliths - prey - waters - cod - cetaceans
    The white-beaked dolphin Lagenorhynchus albirostris is the most numerous cetacean after the harbour porpoise Phocoena phocoena in the North Sea, including Dutch coastal waters. In this study, the diet of 45 white-beaked dolphins stranded on the Dutch coast between 1968 and 2005 was determined by analysis of stomach contents. Although 25 fish species were identified, the diet was dominated by Gadidae (98.0% by weight, 40.0% in numbers), found in all stomachs. All other prey species combined contributed little to the diet by weight (2.0%W). The two most important prey species were whiting Merlangius merlangus (91.1% frequency of occurrence (FO), 30.5%N, 37.6%W) and cod Gadus morhua (73.3%FO, 7.4%N, 55.9%W). In numbers, gobies were most common (54.6%N), but contributed little to the diet by weight (0.6%W). Three stomachs contained different prey compared to the others: one animal had taken 2250 gobies, accounting for 96.4% of all gobies found; one animal had fed on 29 small sepiolids; and one animal had solely taken haddock Melanogrammus aeglefinus. Squid and haddock were not found in any other stomach. The overall diet showed a lasting predominance of whiting and cod, without clear changes over time (35 years) or differences between sexes or size-classes of dolphins. This study adds to earlier published and unpublished data for Dutch coastal waters and agrees well with studies of white-beaked dolphins from other parts of the species’ range, in the North Sea and in Canadian waters, with Gadidae dominating the diet on both sides of the Atlantic.
    Complete compensation in Daphnia fecundity and stage-specific biomass in response to size-independent mortality
    Nilsson, K.A. ; Persson, L. ; Kooten, T. van - \ 2010
    Journal of Animal Ecology 79 (2010). - ISSN 0021-8790 - p. 871 - 878.
    amplitude cycles - body-size - populations - prey - growth - reproduction - variability - plants - model
    1. Recent theory suggests that compensation or even overcompensation in stage-specific biomass can arise in response to increased mortality. Which stage that will show compensation depends on whether maturation or reproduction is the more limiting process in the population. Size-structured theory also provides a strong link between the type of regulation and the expected population dynamics as both depend on size / stage-specific competitive ability. 2. We imposed a size-independent mortality on a consumer-resource system with Daphnia pulex feeding on Scenedesmus obtusiusculus to asses the compensatory responses in Daphnia populations. We also extended an existing stage-structured biomass model by including several juvenile stages to test whether this extension affected the qualitative results of the existing model. 3. We found complete compensation in juvenile biomass and total population fecundity in response to harvesting. The compensation in fecundity was caused by both a higher proportion of fecund females and a larger clutch size under increased mortality. We did not detect any difference in resource levels between treatments. 4. The model results showed that both stages of juveniles have to be superior to adults in terms of resource competition for the compensatory response to take place in juvenile biomass. 5. The results are all in correspondence with that the regulating process within the population was reproduction. From this, we also conclude that juveniles were superior competitors to adults, which has implications for population dynamics and the kind of cohort cycles seen in Daphnia populations. 6. The compensatory responses demonstrated in this experiment have major implications for community dynamics and are potentially present in any organisms with food-dependent growth or development.
    On the risk of extinction of a wild plant species through spillover of a biological control agent: Analysis of an ecosystem compartment model.
    Chalak, M. ; Hemerik, L. ; Werf, W. van der; Ruijs, A. ; Ierland, E.C. van - \ 2010
    Ecological Modelling 221 (2010)16. - ISSN 0304-3800 - p. 1934 - 1943.
    agricultural landscapes - biocontrol - insect - weed - management - dispersal - habitats - invasion - prey
    Invasive plant species can be controlled by introducing natural enemies (insect herbivores) from their native range. However, such introduction entails the risk that the introduced herbivores attack indigenous plant species in the area of introduction. Here, we study the effect of spillover of a herbivore from a managed ecosystem compartment (agriculture) to a natural compartment (non-managed) and vice versa. In the natural compartment, an indigenous plant species is attacked by the introduced herbivores, whereas another indigenous plant species, which competes with the first, is not attacked. The combination of competition and herbivory may result in extinction of the attacked wild plant species. Using a modelling approach, we determine model parameters that characterize the risk of extinction for a wild plant species. Risk factors include: (1) a high attack rate of the herbivores on the wild non-target species, (2) niche overlap expressed as strong competition between the attacked non-target species and its competitor(s), and (3) factors favouring large spillover from the managed ecosystem compartment to the natural compartment; these include (3a) a high dispersal ability, and (3b) a moderate attack rate of the introduced herbivore on the target species, enabling large resident populations of the insect herbivore in the managed compartment. The analysis thus indicates that a high attack rate on the target species, which is a selection criterion for biocontrol agents with respect to their effectiveness, also mitigates risks resulting from spillover and non-target effects. While total eradication of an invasive plant species is not possible in the one-compartment-one-plant-one-herbivore system, natural enemy spillover from a natural to a managed compartment can make the invasive weed go extinct.
    Length-weight relationships of 216 North Sea benthic invertebrates and fish
    Robinson, L. ; Greenstreet, S.P.R. ; Reiss, H. ; Callaway, R. ; Craeymeersch, J.A.M. ; Boois, I.J. de - \ 2010
    Journal of the Marine Biological Association of The United Kingdom 90 (2010)1. - ISSN 0025-3154 - p. 95 - 104.
    size-based model - community structure - food webs - hermit-crabs - body-size - abundance - diversity - prey - indicators - biomass
    Size-based analyses of marine animals are increasingly used to improve understanding of community structure and function. However, the resources required to record individual body weights for benthic animals, where the number of individuals can reach several thousand in a square metre, are often prohibitive. Here we present morphometric (length weight) relationships for 216 benthic species from the North Sea to permit weight estimation from length measurements. These relationships were calculated using data collected over two years from 283 stations. For ten abundant and widely dispersed species we tested for significant spatial and temporal differences in morphometric relationships. Some were found, but the magnitude of differences was small in relation to the size-ranges of animals that are usually present and we recommend that the regression relationships given here, based on pooled data, are appropriate for most types of population and community analyses. Our hope is that the availability of these morphometric relationships will encourage the more frequent application of size-based analyses to ben hue survey data, and so enhance understanding of the ecology of the benthic/demersal component of marine ecosystems and food webs.
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