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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    Impact of nitrogen deposition on larval habitats: the case of the Wall Brown butterfly Lasiommata megera
    Klop, E. ; Omon, B. ; Wallis de Vries, M.F. - \ 2015
    Journal of Insect Conservation 19 (2015)2. - ISSN 1366-638X - p. 393 - 402.
    british butterflies - herbivorous insects - pararge-aegeria - limitation - climate - biodiversity - adaptation - phosphorus - landscape - trends
    Nitrogen deposition is considered as one of the main threats to biodiversity and ecosystem functioning. Three mechanisms have been proposed to explain the detrimental effect of excess nitrogen on butterflies: loss of host plants, deterioration of food plant quality and microclimatic cooling in spring. Here, we investigated whether these mechanisms might explain the dramatic recent decline of the Wall Brown butterfly Lasiommata megera. Monitoring data from the Netherlands indeed show a greater decline at higher critical load exceedance of nitrogen deposition. Loss of host plants is not a likely explanation of the decline for this grass-feeding species. In a greenhouse experiment, we only found beneficial effects of nitrogen fertilization on larval performance, which seems to rule out a nutritional cause; application of a drought treatment did not result in significant effects. Microclimatic conditions at overwintering larval sites of L. megera and the related but increasing Pararge aegeria provided a possible clue. In comparison with larval sites of P. aegeria, those of L. megera showed higher temperatures at the mesoscale and less plant cover and more dead plant material at the microscale. L. megera caterpillars were also found closer to the shelter of vertical structures. The greater dependence on warm microclimates suggests that microclimatic cooling through excess nitrogen contributes to the recent decline of L. megera.
    Restoration of acidified and eutrophied rich fens: Long-term effects of traditional management and experimental liming
    Diggelen, J. van; Bense, I.H.M. ; Brouwer, E. ; Limpens, J. ; Schie, J.M. van; Smolders, A.J.P. ; Lamers, L.P.M. - \ 2015
    Ecological Engineering 75 (2015). - ISSN 0925-8574 - p. 208 - 216.
    laagveengebieden - eutrofiëring - verzuring - ecologisch herstel - bekalking - fens - eutrophication - acidification - ecological restoration - liming - vegetation development - nutrient availability - nitrogen deposition - surface-water - groundwater - phosphorus - level - limitation - wetlands
    Rich fens are known for their high botanical diversity encompassing many endangered species. For decades, several management measures, including mowing and burning, have been applied to maintain a high biodiversity by means of slowing down the natural succession from calcareous rich fens to acidic poor fens or woodland. In this study, we assessed the long-term effects of these traditional management measures, and explored the effectiveness of liming as a measure to restore rich fen vegetation. Effects of summer mowing, and of burning after winter mowing, were assessed by comparing current (2013) and historical (1967) vegetation data. Effects of experimental liming, using different levels of lime addition (0, 1000, 2000, and 4000 kg Dolokal/ha), were monitored in the field during 7.5 years. Summer mowing led to more acidic and nutrient-poor conditions as indicated by a shift from rich to poor fen vegetation, including a well-developed bryophyte cover dominated by Sphagnum with some threatened species. Burning (after winter mowing) counteracted acidification but increased nutrient availability, as indicated by dominance of vascular species characteristic of productive tall-herb grasslands and a sparse bryophyte cover with common species. We conclude that the traditional measures were unable to maintain rich fen composition in the long term. Given the fact that the restoration of hydrological conditions, favouring rich fens, is not always feasible, liming could be an alternative to counteract acidification and improve rich fen conditions in the short term. This measure, however, appeared to be unsustainable as the re-establishment and dominance of Sphagnum spp. seriously complicated the development of rich fen vegetation in the longer term.
    Frankincense tapping reduces the carbohydrate storage of Boswellia trees
    Mengistu, T. ; Sterck, F.J. ; Fetene, M. ; Bongers, F. - \ 2013
    Tree Physiology 33 (2013)6. - ISSN 0829-318X - p. 601 - 608.
    tropical forest - swiss treeline - rubber trees - pinus-cembra - wood - sink - photosynthesis - limitation - papyrifera - ecology
    Carbohydrates fixed by photosynthesis are stored in plant organs in the form of starch or sugars. Starch and sugars sum to the total non-structural carbohydrate pool (TNC) and may serve as intermediate pools between assimilation and utilization. We examined the impact of tapping on TNC concentrations in stem-wood, bark and root tissues of the frankincense tree (Boswellia papyrifera (Del.) Hochst) in two natural woodlands of Ethiopia. Two tapping treatments, one without tapping (control) and the other with tapping at 12 incisions, are applied on experimental trees. Trees are tapped in the leafless dry period, diminishing their carbon storage pools. If storage pools are not refilled by assimilation during the wet season, when crowns are in full leaf, tapping may deplete the carbon pool and weaken Boswellia trees. The highest soluble sugar concentrations were in the bark and the highest starch concentrations in the stem-wood. The stem-wood contains 12 times higher starch than soluble sugar concentrations. Hence, the highest TNC concentrations occurred in the stem-wood. Moreover, wood volume was larger than root or bark volumes and, as a result, more TNC was stored in the stem-wood. As predicted, tapping reduced the TNC concentrations and pool sizes in frankincense trees during the dry season. During the wet season, these carbon pools were gradually filled in tapped trees, but never to the size of non-tapped trees. We conclude that TNC is dynamic on a seasonal time scale and offers resilience against stress, highlighting its importance for tree carbon balance. But current resin tapping practices are intensive and may weaken Boswellia populations, jeopardizing future frankincense production.
    Soil and freshwater and marine sediment food webs: their structure and function
    Krumins, J.A. ; Oevelen, D. van; Bezemer, T.M. ; Deyn, G.B. de; Hol, W.H.G. ; Donk, E. van; Boer, W. de; Ruiter, P.C. de; Middelburg, J.J. ; Monroy, F. ; Soetaert, K. ; Thébault, E. ; Koppel, J. van de; Veen, J.A. van; Viketoft, M. ; Putten, W.H. van der - \ 2013
    Bioscience 63 (2013)1. - ISSN 0006-3568 - p. 35 - 42.
    global carbon-cycle - terrestrial ecosystems - real ecosystems - climate-change - biodiversity - stability - communities - limitation - patterns - sequestration
    The food webs of terrestrial soils and of freshwater and marine sediments depend on adjacent aboveground or pelagic ecosystems for organic matter input that provides nutrients and energy. There are important similarities in the flow of organic matter through these food webs and how this flow feeds back to primary production. In both soils and sediments, trophic interactions occur in a cycle in which consumers stimulate nutrient cycling such that mineralized resources are made available to the primary producers. However, aquatic sediments and terrestrial soils differ greatly in the connectivity between the production and the consumption of organic matter. Terrestrial soils and shallow aquatic sediments can receive organic matter within hours of photosynthesis when roots leak carbon, whereas deep oceanic sediments receive organic matter possibly months after carbon assimilation by phytoplankton. This comparison has implications for the capacity of soils and sediments to affect the global carbon balance.
    Potential of mechanical cleaning of membranes from a mebrane bioreactor
    Brink, P. van den; Vergeldt, F.J. ; As, H. van; Zwijnenburg, A. ; Temmink, H. - \ 2013
    Journal of Membrane Science 429 (2013). - ISSN 0376-7388 - p. 259 - 267.
    drinking-water - biofilm reactor - critical flux - waste-water - exopolysaccharides - denitrification - precipitation - communities - limitation - bacteria
    Several membrane fouling mechanisms have been identified in membrane bioreactors. While cake layers can be removed by physical cleaning, irreversible fouling such as a gel layer is difficult to remove by physical cleaning during filtration. Harsh mechanical cleaning was applied in this study to evaluate how much fouling could be maximally removed and distribution of remaining fouling was investigated. The fouling resistance of several membranes operated at different relatively low fluxes was followed during long term continuous flux operation. Remaining fouling was observed with scanning electron microscopy (SEM) and magnetic resonance imaging (MRI). Dead-end filtration tests with mechanically cleaned membranes showed a decreased permeability. To determine whether bacteria were present in the remaining fouling, oxygen consumption was quantified. Even after harsh mechanical cleaning, membrane samples showed considerable oxygen consumption. SEM did not show fouling inside the membrane. Of several membranes operated for at least 1 year, the permeate side was covered with bacteria and extracellular polymeric substances (EPS). These results show that fouling cannot be removed completely by harsh mechanical cleaning and that both feed and permeate side of the membrane contains biofouling. This fouling on the permeate side should not be neglected when designing membrane cleaning.
    Mapping tropical forest trees using high-resolution aerial digital photographs
    Garzon-Lopez, C.X. ; Bohlman, S.A. ; Olff, H. ; Jansen, P.A. - \ 2013
    Biotropica 45 (2013)3. - ISSN 0006-3606 - p. 308 - 316.
    rain-forest - spatial-patterns - scale - dispersal - imagery - identification - biodiversity - limitation - management - dynamics
    The spatial arrangement of tree species is a key aspect of community ecology. Because tree species in tropical forests occur at low densities, it is logistically challenging to measure distributions across large areas. In this study, we evaluated the potential use of canopy tree crown maps, derived from high-resolution aerial digital photographs, as a relatively simple method for measuring large-scale tree distributions. At Barro Colorado Island, Panama, we used high-resolution aerial digital photographs (~0.129 m/pixel) to identify tree species and map crown distributions of four target tree species. We determined crown mapping accuracy by comparing aerial and ground-mapped distributions and tested whether the spatial characteristics of the crown maps reflect those of the ground-mapped trees. Nearly a quarter (22%) of the common canopy species had sufficiently distinctive crowns to be good candidates for reliable mapping. The errors of commission (crowns misidentified as a target species) were relatively low, but the errors of omission (missed canopy trees of the target species) were high. Only 40 percent of canopy individuals were mapped on the air photographs. Despite failing to accurately predict exact abundances of canopy trees, crown distributions accurately reproduced the clumping patterns and spatial autocorrelation features of three of four tree species and predicted areas of high and low abundance. We discuss a range of ecological and forest management applications for which this method can be useful.
    The good, the bad and the plenty: interactive effects of food quality and quantity on the growth of different Daphnia species
    Bukovinszky, T. ; Verschoor, A.M. ; Helmsing, N.R. ; Bezemer, T.M. ; Bakker, E.S. ; Vos, M. ; Domis, L.N.D. - \ 2012
    PLoS ONE 7 (2012)9. - ISSN 1932-6203 - 8 p.
    life-history - fresh-water - aquatic herbivores - body size - stoichiometry - zooplankton - limitation - performance - diets - cladocerans
    Effects of food quality and quantity on consumers are neither independent nor interchangeable. Although consumer growth and reproduction show strong variation in relation to both food quality and quantity, the effects of food quality or food quantity have usually been studied in isolation. In two experiments, we studied the growth and reproduction in three filter-feeding freshwater zooplankton species, i.e. Daphnia galeata x hyalina, D. pulicaria and D. magna, on their algal food (Scenedesmus obliquus), varying in carbon to phosphorus (C:P) ratios and quantities (concentrations). In the first experiment, we found a strong positive effect of the phosphorus content of food on growth of Daphnia, both in their early and late juvenile development. Variation in the relationship between the P-content of animals and their growth rate reflected interspecific differences in nutrient requirements. Although growth rates typically decreased as development neared maturation, this did not affect these species-specific couplings between growth rate and Daphnia P-content. In the second experiment, we examined the effects of food quality on Daphnia growth at different levels of food quantity. With the same decrease in P-content of food, species with higher estimated P-content at zero growth showed a larger increase in threshold food concentrations (i.e. food concentration sufficient to meet metabolic requirements but not growth). These results suggest that physiological processes such as maintenance and growth may in combination explain effects of food quality and quantity on consumers. Our study shows that differences in response to variation in food quality and quantity exist between species. As a consequence, species-specific effects of food quality on consumer growth will also determine how species deal with varying food levels, which has implications for resource-consumer interactions
    Phytoplankton species predictability increases towards warmer regions
    Kruk, C. ; Segura, A.M. ; Peeters, E.T.H.M. ; Huszar, V.L.M. ; Costa, L.S. ; Kosten, S. ; Lacerot, G. ; Scheffer, M. - \ 2012
    Limnology and Oceanography 57 (2012)4. - ISSN 0024-3590 - p. 1126 - 1135.
    latitudinal diversity gradient - fresh-water phytoplankton - multispecies competition - community - plankton - classification - biodiversity - disturbance - limitation - dispersal
    We explored systematic patterns in predictability of phytoplankton species from 83 lakes over a gradient ranging from subpolar to tropical regions in South America. We estimated the explained variance (proxy of predictability) of the presence and biomass (estimated as biovolume) of species using multiple regressions from commonly measured environmental variables such as nutrient levels, light, mixing depth, temperature, and zooplankton biomass. Both the presence and biomass of species occurring at least in 10 lakes were quite well predicted from the environmental variables, with average values of 35% and 58%, respectively. Predictability was not systematically related to phylogenetic affiliation or particular functional groups as defined by morphology. However, biomass predictability decreased with increasing occurrence, and improved with larger species size (maximum linear dimension). Species that were predictable in terms of biomass (R-2 >= 0.5, p
    Age structure in neutral theory resolves inconsistencies related to reproductive size threshold
    Rosindell, J. ; Jansen, P.A. ; Etienne, R.S. - \ 2012
    Journal of Plant Ecology 5 (2012)1. - ISSN 1752-9921 - p. 64 - 71.
    species-area relationships - biodiversity - speciation - model - biogeography - limitation - dispersal - diversity - abundance - forests
    Neutral theory consists of a suite of models that assume ecological equivalence among individual organisms. They have been most commonly applied to tropical forest tree communities either as null models or as approximations. Neutral models typically only include reproductive adults; therefore, fitting to empirical tree community data requires defining a reproductive-size threshold, which for trees is usually set arbitrarily to a diameter at breast height (DBH) of 100 mm. The inevitable exclusion of some reproductive adults and inclusion of some saplings cause a non-random sampling bias in neutral model fits. Here, we investigate this problem and resolve it by introducing simple age structure into a neutral model.
    Time-dependent, species-specific effects of N:P stoichiometry on grassland plant growth
    Fujita, Y. ; Ruiter, P.C. de; Wassen, M.J. ; Heil, G.W. - \ 2010
    Plant and Soil 334 (2010)1-2. - ISSN 0032-079X - p. 99 - 112.
    nutrient availability - wetland graminoids - 2nd-year growth - phosphorus - nitrogen - fens - acquisition - budgets - limitation - vegetation
    N and P have different eutrophication effects on grassland communities, yet the underlying mechanisms are poorly understood. To examine plant growth in response to the varying (relative) supply of N and P, we conducted a two-year greenhouse experiment. Five grasses and three herbs were grown with three N:P supply ratios at two overall nutrient supply levels. During the first year the plant growth was relatively low at both high and low N:P supply ratios, whereas during the second year the growth was especially low at a high N:P supply ratio. This second-year low growth was attributed to the high root death rate, which was influenced by a high N:P supply ratio rather than by the nutrient supply level. Species responded differently, especially in P uptake and loss at a high N:P supply ratio. Each species seemed to have a different strategy for P limitation, e.g. an efficient P uptake or a high P resorption rate. Species typical of P-limited grasslands had neither better P uptake nor better P retention at a high N:P supply ratio. This study quantitatively demonstrates an increased plant root death triggered by strong P limitation. This finding indicates a possible extra effect of N eutrophication on ecosystem functioning via changed N:P stoichiometry
    Past and future trends in nutrients export by rivers to the coastal waters of China
    Qu, H.J. ; Kroeze, C. - \ 2010
    Science of the Total Environment 408 (2010)9. - ISSN 0048-9697 - p. 2075 - 2086.
    phosphorus transport - continental shelves - nitrogen inputs - global system - consequences - estuaries - ocean - limitation - marine - carbon
    We analyzed the past and future trends in river export of dissolved and particulate nitrogen (N), phosphorus (P) and carbon (C) to the coastal waters of China, for sixteen rivers, as calculated by the Global NEWS models (Nutrient Export from WaterSheds). Between 1970 and 2000, the dissolved N and P export increased significantly, while export of other nutrients changed less. We analyzed the future trends (2000–2050) for the Millennium Ecosystem Assessment (MEA) scenarios. In general, the largest increases of dissolved nutrients export are projected for the Global Orchestration scenario, assuming a globalized world and a reactive approach toward environmental management. Future trends in river export of nutrients vary largely among basins, nutrient forms and scenarios. We calculate both increasing and decreasing trends between 2000 and 2050. We also identify the sources contributing to the nutrient export. For selected river basins we present results for alternative scenarios, which are based on the Global Orchestration scenario, but assume more environmental management. This illustrates how the NEWS models can be useful in regional analyses for decision making
    Chemodynamics and bioavailability in natural waters
    Buffle, J. ; Wilkinson, K.J. ; Leeuwen, H.P. van - \ 2009
    Environmental Science and Technology 43 (2009)19. - ISSN 0013-936X - p. 7170 - 7174.
    dynamic speciation - nutrient uptake - metal flux - diffusion - transport - limitation - complexes - bacteria - biofilm - systems
    Restoration of species-rich grasslands on ex-arable land: Seed addition outweighs soil fertility reduction
    Kardol, P. ; Wal, A. van der; Bezemer, T.M. ; Boer, W. de; Duyts, H. ; Holtkamp, R. ; Putten, W.H. van der - \ 2008
    Biological Conservation 141 (2008)9. - ISSN 0006-3207 - p. 2208 - 2217.
    food-web - nitrogen availability - prairie restoration - nature conservation - limiting processes - plant-communities - fungal biomass - heathland - succession - limitation
    A common practice in biodiversity conservation is restoration of former species-rich grassland on ex-arable land. Major constraints for grassland restoration are high soil fertility and limited dispersal ability of plant species to target sites. Usually, studies focus on soil fertility or on methods to introduce plant seeds. However, the question is whether soil fertility reduction is always necessary for getting plant species established on target sites. In a three-year field experiment with ex-arable soil with intensive farming history, we tested single and combined effects of soil fertility reduction and sowing mid-successional plant species on plant community development and soil biological properties. A controlled microcosm study was performed to test short-term effects of soil fertility reduction measures on biomass production of mid-successional species. Soil fertility was manipulated by adding carbon (wood or straw) to incorporate plant-available nutrients into organic matter, or by removing nutrients through top soil removal (TSR). The sown species established successfully and their establishment was independent of carbon amendments. TSR reduced plant biomass, and effectively suppressed arable weeds, however, created a desert-like environment, inhibiting the effectiveness of sowing mid-successional plant species. Adding straw or wood resulted in short-term reduction of plant biomass, suggesting a temporal decrease in plant-available nutrients by microbial immobilisation. Straw and wood addition had little effects on soil biological properties, whereas TSR profoundly reduced numbers of bacteria, fungal biomass and nematode abundance. In conclusion, in ex-arable soils, on a short-term sowing is more effective for grassland restoration than strategies aiming at soil fertility reduction.
    Elevated CO2 does not favor a fungal decomposition pathway
    Groenigen, K.J. van; Six, J. ; Harris, D. ; Kessel, C. van - \ 2007
    Soil Biology and Biochemistry 39 (2007)8. - ISSN 0038-0717 - p. 2168 - 2172.
    atmospheric co2 - grassland soils - amino-sugars - nitrogen - carbon - responses - agroecosystems - limitation - bacterial
    We examined the effect of prolonged elevated CO2 on the concentration of fungal- and bacterial-derived compounds by quantifying the soil contents of the amino sugars glucosamine, galactosamine and muramic acid. Soil samples were collected from three different terrestrial ecosystems (grassland, an aspen forest and a soybean/corn agroecosystem) that were exposed to elevated CO2 under FACE conditions for 3¿10 years. Amino sugars were extracted from bulk soil and analyzed by gas chromatography. Elevated CO2 did not affect the size or composition of the amino sugar pool in any of the systems. However, high rates of fertilizer N applications decreased the amount of fungal-derived residues in the grassland system. We suggest that these results are caused by a decrease in saprophytic fungi following high N additions. Furthermore, our findings imply that the contribution of saprophytic fungi and bacteria to SOM in the studied ecosystems is largely unaffected by elevated CO2.
    Contrasting nitrogen and phosphorus resorption efficiencies in trees and lianas from a tropical montane rain forest in Xishuangbanna, south-west China.
    Cai, Z.Q. ; Bongers, F.J.J.M. - \ 2007
    Journal of Tropical Ecology 23 (2007)1. - ISSN 0266-4674 - p. 115 - 118.
    nutrient resorption - senescing leaves - retranslocation - proficiency - limitation - patterns - biomass - plants - panama
    Tropical montane rain forest is widely considered to be a highly threatened hotspot of global diversity (Brummitt & Nic Lughadha 2003), and one of the least understood humid tropical forest ecosystems in terms of nutrient cycling (Bruijnzeel & Proctor 1995). There is, therefore, an urgent need to improve our understanding of nutrient cycling processes in this ecosystem, including the absorption of nutrients (mainly N and P) from senescing leaves, which may be a key component of adaptive mechanisms that conserve limiting nutrients (Killingbeck 1996). Nutrients which are not resorbed, however, will be circulated through litterfall in the longer term (Aerts 1996). The degree of nutrient resorption affects litter quality, which consequently affects decomposition rates and soil nutrient availability (Aerts & Chapin 2000). The importance of resorption in nutrient conservation has led to general hypotheses that species adapted to nutrient-poor environments have high resorption efficiencies (Richardson et al. 2005), and that low leaf nutrient concentrations are associated with high resorption efficiencies within species (Aerts 1996, Kobe et al. 2005). Nutrient resorption has also been shown not to differ greatly between growth forms (e.g. shrubs, grasses, forbs and trees) (Aerts 1996). However, its relative importance among plant functional groups is still highly controversial (Richardson et al. 2005).
    The relation between unpalatable species, nutrients and plant species richness in Swiss montane pastures.
    Kleijn, D. ; Muller-Scharer, H. - \ 2006
    Biodiversity and Conservation 15 (2006)12. - ISSN 0960-3115 - p. 3971 - 3982.
    agricultural land - alpine pastures - diversity - grassland - communities - limitation - europe - availability - recruitment - abandonment
    In agriculturally marginal areas, the control of unpalatable weeds on species rich pastures may become problematic due to agricultural and socio-economic developments. It is unclear how increased dominance of unpalatable species would affect the botanical diversity of these grasslands. We investigated whether there was any relationship between plant species diversity and the abundance of unpalatable species and whether soil conditions affected this relationship. In three species-rich montane pastures in western Switzerland, we related plant species richness to soil attributes, the relative cover of all unpalatable species and the relative cover of the locally dominant, toxic Veratrum album in 25 plots of 4 m2. We furthermore determined species richness in small transects through patches of V. album. Species richness was significantly lower in and near (¿0.3 m) patches of V. album. At the field scale, plant species richness was best described by total soil N:P ratio (positive relation) in one site and the relative abundance of unpalatable species (negative relation) and soil N:P ratio (positive relation) in a second site. In the third site, species richness was not significantly related to any measured variable. Vegetation diversity (Simpson's D) was negatively related to the relative abundance of unpalatable species in one site and positively related to pH in another site. The results suggest that no single factor can explain plant species richness and diversity in montane pastures. At very high densities unpalatable species can have adverse effects but soil nutrient status appears to be a more general determinant of plant species richness. Conservation efforts should give priority to the prevention of intensification of these pastures
    Investigation of a rotifer (Brachionus calyciflorus) - green alga (Scenedesmus pectinatus) interaction under non- and nutrient-limited conditions
    Lürling, M.F.L.L.W. - \ 2006
    Annales de Limnologie : international journal of limnology 42 (2006)1. - ISSN 0003-4088 - p. 9 - 17.
    colony formation - life-history - food quality - morphological-changes - nutritional quality - varying quality - daphnia growth - zooplankton - limitation - phytoplankton
    Two-day life cycle tests with the rotifer Brachiomus calyciflorus were run to study the nutritional quality effects to rotifers of Scenedesmus pectinatus grown under non-limiting nitrogen limiting and phosphorus limiting conditions and the feedback of the rotifers oil the Food algae. Under nutrient-limited conditions of its algal food Brachionus production was depressed, animals produced fewer eggs and were smaller sized. Clearance rates of Brachionus offered non-nutrient-limited and nutrient-limited Food were similar. The number of cells per colony was similar for S. pectinatus Under nitrogen limited and phosphorus limited conditions both in the absence and presence of Brochionus. Cell volumes phosphorus limited S. pectinatus were larger than those of nitrogen limited cells. The most dramatic response of the food alga S. pectinatus was observed in non-nutrient-limited conditions: a strong, size enlargement occurred only in file presence of Brachionus. This was caused by a higher share of eight-celled colonies and larger individual Cell volumes in the Presence of rotifers than in their absence. S. pectinatus might gain an advantage of becoming larger in moving out of the feeding window of its enemy, but nutrient limited conditions might undermine the effectiveness of such reaction.
    Competition between two grass species with and without grazing over a productivity gradient
    Kuijper, D.P.J. ; Dubbeld, J. ; Bakker, J.P. - \ 2005
    Plant Ecology 179 (2005)2. - ISSN 1385-0237 - p. 237 - 246.
    salt-marsh - plant competition - vegetation succession - mixture experiments - biomass allocation - nutrient - limitation - herbivory - patterns - nitrogen
    Soil nutrient-level and herbivory are predicted to have opposing effects on the allocation pattern of the competitive dominant plant species. Lower stem and higher leaf allocation are favoured when plants are grazed, whereas a higher stem allocation is favoured at high nutrient levels. Grazing by hares and geese can prevent invasion of the tall Elymus athericus, into short vegetation of Festuca rubra, at unproductive stages of salt-marsh succession but not at more productive stages. We hypothesise that the negative effect of herbivory on Elymus decreases due to increasing soil nitrogen levels and shifts the competitive balance towards this species. We tested how simulated grazing and nitrogen availability affected the competitive balance between adult plants of both grass species in a greenhouse experiment. Elymus had a higher above-ground biomass production, invested relatively more in stem and root tissue and had a larger shoot length than Festuca. The above-ground relative yield of Elymus in mixtures of both species increased with increasing nitrogen levels. This indicates that Elymus was the superior competitor at high soil fertility. Although clipping removed relatively more biomass from Elymus than from Festuca and exceeded the observed biomass removal in field conditions, it did not change the competitive balance between both species. Decreasing effects of herbivory due to increasing nitrogen levels are not a likely explanation for the invasion of Elymus in productive marshes. The results suggest that once Elymus has established it can easily invade vegetation dominated by Festuca irrespective of grazing by herbivores such as hares and geese. Herbivory by small herbivores may mainly retard the invasion of this plant by influencing establishment itself.
    Sources and delivery of carbon, nitrogen, and phosphorus to the coastal zone: An overview of global Nutrient Export from Watersheds (NEWS) models and their application
    Seitzinger, S.P. ; Harrison, J.A. ; Dumont, E.L. ; Beusen, A.H.W. ; Bouwman, A.F. - \ 2005
    Global Biogeochemical Cycles 19 (2005). - ISSN 0886-6236 - p. GB4S01 - GB4S01.
    marine ecosystems - drainage network - river estuary - world rivers - human impact - limitation - eutrophication - plankton - systems - inputs
    An overview of the first spatially explicit, multielement (N, P, and C), multiform (dissolved inorganic: DIN, DIP; dissolved organic: DOC, DON, DOP; and particulate: POC, PN, PP) predictive model system of river nutrient export from watersheds (Global Nutrient Export from Watersheds (NEWS)) is presented. NEWS models estimate export from 5761 watersheds globally as a function of land use, nutrient inputs, hydrology, and other factors; regional and global scale patterns as of 1995 are presented here. Watershed sources and their relative magnitudes differ by element and form. For example, anthropogenic sources dominate the export of DIN and DIP at the global scale, although their anthropogenic sources differ significantly (diffuse and point, respectively). Natural sources dominate DON and DOP export globally, although diffuse anthropogenic sources dominate in several regions in Asia, Europe and N. America. "Hot spots" where yield (kg km-2 yr-1) is high for several elements and forms were identified, including parts of Indonesia, Japan, southern Asia, and Central America, due to anthropogenic N and P inputs in some regions and high water runoff in others. NEWS models provide a tool to examine past, current and future river export of nutrients, and how humans might impact element ratios and forms, and thereby affect estuaries and coastal seas.
    Assessing the relative importance of dispersal in plant communities using an ecoinformatics approach
    Ozinga, W.A. ; Hennekens, S.M. ; Schaminée, J.H.J. ; Bekker, R.M. ; Prinzing, A. ; Bonn, S. ; Poschlod, P. ; Tackenberg, O. ; Thompson, K. ; Bakker, J.P. ; Groenendael, J.M. van - \ 2005
    Folia Geobotanica 40 (2005). - ISSN 1211-9520 - p. 53 - 67.
    species-pool hypothesis - seed size - calcareous grassland - diversity - richness - vegetation - competition - limitation - landscape - habitats
    Increased insight into the factors that determine the importance of dispersal limitation on species richness and species composition is of paramount importance for conservation and restoration ecology. One way to explore the importance of dispersal limitation is to use seed-sowing experiments, but these do not enable the screening of large sets of species and habitats. In the present paper we present a complementary approach based on comparing small plots with larger regions with regard to species composition and distribution of functional traits. We developed a GIS tool based on ecological and geographical criteria to quantify species pools at various spatial scales. In this GIS tool, containing floristic, large databases, phytosociological and functional information are exploited. Our premise is that differences in the nature of the species in local and regional species pools with regard to functional traits can give important clues to the processes at work in the assembly of communities. We illustrate the approach with a case study for mesotrophic hay meadows (Calthion palustris). We tested the effects of differences in frequency in the local Habitat Species Pool and differences in dispersal and persistence traits of species on local species composition. Our results show that both species pool effects and functional traits affect the probability of occurrence in small plots. Species with a high propagule weight have, given the frequency in the Local Habitat Species Pool, a lower probability of occurrence in small plots. The probability of local occurrence, however, is increased by the ability to form a persistent soil seed bank and by adult longevity. This provides support for the view that the degree of dispersal limitation is dependent on the degree of spatial isolation of the focal site relative to source populations and moreover that species inherently differ in the degree to which dispersal limitation is a limiting factor for local occurrence.
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