[Show abstract][Hide abstract] ABSTRACT: Trichocyst-enriched fractions were isolated from the marine dinophyte Prorocentrum micans. Transmission electron microscopy revealed that most of the trichocysts were discharged and had elongated to long filaments. Some trichocysts were still condensed. Fragments of discharged trichocysts measured up to 20 μm in length and 260 nm in width, those still condensed measured up to 1 μm in width and 16 μm in length. A distinct banding pattern with a transversal periodicity of approximately 16-18 nm and a periodic longitudinal striation of 3-4 nm could be measured along the trichocyst filaments. At higher magnifications, a fragile, alveolated, net-like organisation became obvious which resembled the one shown for the trichocysts of ciliates. When trichocyst-enriched fractions were treated with sodium dodecyl sulfate and centrifuged subsequently, no trichocysts were registered any longer in the sodium dodecyl sulfate-insoluble fraction by electron microscopy. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of trichocyst-enriched fractions and of the SDS-soluble fractions revealed a protein banding pattern which was dominated by polypeptides of 50-30, 12.5, and approximately 8.5 kDa. The polypeptide banding pattern deviated significantly from those registered for ejectisomes of cryptophytes and of the prasinophyte Pyramimonas grossii, for the Reb polypeptides which constitute the R-bodies of Caedibacter taeniospiralis, and also from the banding pattern of trichocysts of Paramecium. An antiserum directed against trichocysts of Paramecium did not cross-react with the polypeptides present in the trichocyst-enriched fraction of Prorocentrum micans.
[Show abstract][Hide abstract] ABSTRACT: Disentangling the mechanisms that maintain the stability of communities and ecosystem properties has become a major research focus in ecology in the face of anthropogenic environmental change. Dispersal plays a pivotal role in maintaining diversity in spatially subdivided communities, but only a few experiments have simultaneously investigated how dispersal and environmental fluctuation affect community dynamics and ecosystem stability. We performed an experimental study using marine phytoplankton species as model organisms to test these mechanisms in a metacommunity context. We established three levels of dispersal and exposed the phytoplankton to fluctuating light levels, where fluctuations were either spatially asynchronous or synchronous across patches of the metacommunity. Dispersal had no effect on diversity and ecosystem function (biomass), while light fluctuations affected both evenness and community biomass. The temporal variability of community biomass was reduced by fluctuating light and temporal beta diversity was influenced interactively by dispersal and fluctuation, whereas spatial variability in community biomass and beta diversity were barely affected by treatments. Along the establishing gradient of species richness and dominance, community biomass increased but temporal variability of biomass decreased, thus highest stability was associated with species-rich but highly uneven communities and less influenced by compensatory dynamics. In conclusion, both specific traits (dominance) and diversity (richness) affected the stability of metacommunities under fluctuating conditions.
[Show abstract][Hide abstract] ABSTRACT: A recurrent question in meta-analyses is the validity of including both field and laboratory studies in a single analysis, given the differences in characteristics such as the duration or size of these experiments. In particular, are field studies consistently more variable, longer in duration, or do they differ from laboratory studies in other important ways? We examined these questions using an unusually large and comprehensive data set on grazing effects on benthic microalgae, consisting of 865 experiments including both field and lab studies and using marine, lotic or lentic communities of small benthic primary producers. We found there was greater variation in field than laboratory studies, but that this difference explained only 0.5% of the variance in the coefficient of variation. Field studies were longer, on average, than laboratory studies, but experiments in the two systems did not differ consistently in other ecological or design parameters. Thus, the common assumption that field studies have higher variances than laboratory studies, while true, explained only a tiny proportion of the heterogeneity in variation. Therefore, perhaps surprisingly, any conclusions from research syntheses would be unlikely to be affected by consistent differences in variance (or other parameters we examined) between the laboratory and field studies.
[Show abstract][Hide abstract] ABSTRACT: Ecosystem functioning is affected by horizontal (within trophic groups) and vertical (across trophic levels) biodiversity. Theory predicts that the effects of vertical biodiversity depend on consumer specialization. In a microcosm experiment, we investigated ciliate consumer diversity and specialization effects on algal prey biovolume, evenness and composition, and on ciliate biovolume production. The experimental data was complemented by a process-based model further analyzing the ecological mechanisms behind the observed diversity effects. Overall, increasing consumer diversity had no significant effect on prey biovolume or evenness. However, consumer specialization affected the prey community. Specialist consumers showed a stronger negative impact on prey biovolume and evenness than generalists. The model confirmed that this pattern was mainly driven by a single specialist with a high per capita grazing rate, consuming the two most productive prey species. When these were suppressed, the prey assemblage became dominated by a less productive species, consequently decreasing prey biovolume and evenness. Consumer diversity increased consumer biovolume, which was stronger for generalists than for specialists and highest in mixed combinations, indicating that consumer functional diversity, i.e. more diverse feeding strategies, increased resource use efficiency. Overall, our results indicate that consumer diversity effects on prey and consumers strongly depend on species-specific growth and grazing rates, which may be at least equally important as consumer specialization in driving consumer diversity effects across trophic levels.
[Show abstract][Hide abstract] ABSTRACT: Studies of experimental grassland communities have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change. Here we analyse diversity-stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems.
[Show abstract][Hide abstract] ABSTRACT: Freshwater biodiversity loss potentially disrupts ecosystem services related to water quality and may negatively impact ecosystem functioning and temporal community turnover. We analysed a data set containing phytoplankton and zooplankton community data from 131 lakes through 9 years in an agricultural region to test predictions that plankton communities with low biodiversity are less efficient in their use of limiting resources and display greater community turnover (measured as community dissimilarity). Phytoplankton resource use efficiency (RUE = biomass per unit resource) was negatively related to phytoplankton evenness (measured as Pielou's evenness), whereas zooplankton RUE was positively related to phytoplankton evenness. Phytoplankton and zooplankton RUE were high and low, respectively, when Cyanobacteria, especially Microcystis sp., dominated. Phytoplankton communities displayed slower community turnover rates when dominated by few genera. Our findings, which counter findings of many terrestrial studies, suggest that Cyanobacteria dominance may play important roles in ecosystem functioning and community turnover in nutrient-enriched lakes.
[Show abstract][Hide abstract] ABSTRACT: Ejectisome fragments were isolated from the prasinophyte Pyramimonas grossii and subjected to different treatments, i.e. Percoll density gradient centrifugation, incubation at pH 2.5 or at pH 10.8, or incubation in 6 M guanidine hydrochloride. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that Percoll density gradient centrifugation did not improve the purity of the ejectisome fragment-enriched fractions. The ejectisome fragments withstood pH 2.5 and pH 10.8 treatment, and no loosely bound polypeptides became detached. The disintegration of ejectisome fragments was achieved in 6 M guanidine hydrochloride, and reassembly into filamentous, ejectisome-like structures occurred after dialysis against distilled water. Fractions enriched either in ejectisome fragments or in reconstituted ejectisome-like structures were dominated by three polypeptides with relative molecular weights of approximately 12.5-19 kDa and two additional polypeptides of 23 and 26 kDa. A polyclonal antiserum directed against an ejectisome fragment-enriched fraction weakly cross-reacted with these polypeptides, and no significant immuno-labelling of ejectisome fragments was registered. A positive immuno-label was achieved using immunoglobulin (IgG) fractions which were gained by selectively incubating nitrocellulose stripes of these polypeptides with the antiserum.
[Show abstract][Hide abstract] ABSTRACT: Ökologische Stöchiometrie (ecological stoichiometry, ES) hat sich in den letzten beiden Jahrzehnten zu einer der grundlegenden Theorien der Umweltwissenschaften und der Biologie entwickelt. Durch den Vergleich von elementarer Zusammensetzung von Organismen und ihren Ressourcenansprüchen mit der relativen Verfügbarkeit der Ressourcen sagt ES Prozesse auf allen Organisationsebenen von subzellulären Strukturen bis hin zu Ökosystemen voraus. Allerdings wurde ES bisher selten angewandt um den Zusammenhang zwischen Biodiversität und Ökosystemfunktion zu verstehen, obwohl ES ideal dazu geeignet wäre, da es sowohl Vorhersagen zu Prozessen macht, die Biodiversität beeinflussen, als auch zu Materieflüssen und–transformationen, auf denen wichtige Ökosystemfunktionen basieren. In diesem Artikel untersuchen wir den Zusammenhang dieser beiden Forschungsfelder und zeigen zukünftige Forschungsfelder anhand von drei Themen auf: i) die stöchiometrische Aspekte der Treiber des Biodiversitätswandels, ii) stöchiometrische Grundlagen des Zusammenhangs zwischen Biodiversität und Produktivität, iii) potentielle Interaktionen zwischen Biodiversität und Stöchiometrie im Nahrungsnetzkontext.
Basic and Applied Ecology 01/2014; · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent climate warming is expected to affect phytoplankton biomass and diversity in marine ecosystems. Temperature can act directly on phytoplankton (e.g. rendering physiological processes) or indirectly due to changes in zooplankton grazing activity. We tested experimentally the impact of increased temperature on natural phytoplankton and zooplankton communities using indoor mesocosms and combined the results from different experimental years applying a meta-analytic approach. We divided our analysis into three bloom phases to define the strength of temperature and zooplankton impacts on phytoplankton in different stages of bloom development. Within the constraints of an experiment, our results suggest that increased temperature and zooplankton grazing have similar effects on phytoplankton diversity, which are most apparent in the post-bloom phase, when zooplankton abundances reach the highest values. Moreover, we observed changes in zooplankton composition in response to warming and initial conditions, which can additionally affect phytoplankton diversity, because changing feeding preferences of zooplankton can affect phytoplankton community structure. We conclude that phytoplankton diversity is indirectly affected by temperature in the post-bloom phase through changing zooplankton composition and grazing activities. Before and during the bloom, however, these effects seem to be overruled by temperature enhanced bottom-up processes such as phytoplankton nutrient uptake.
Journal of Sea Research 01/2014; 85:359–364. · 1.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Changes in plant diversity have consequences for higher trophic levels, e.g., higher plant diversity can enhance the reproduction and fitness of plant-associated insects. This response of higher trophic levels potentially depends on diversity-related changes in both resource quantity (abundance) and quality (nutritional content). The availability of elemental nutrients in plant resources is one aspect of nutritional quality, but has rarely been addressed as a pathway relating plant diversity to associated insects. Using the experimental plant diversity gradient of a large biodiversity grassland project, the Jena-Experiment, we analyzed the %C, %N and %P and the molar ratios of those elements (C:N, C:P and N:P) in a pollinating bee, Chelostoma distinctum, and an herbivorous grasshopper, Chorthippus parallelus, reared on plots of different plant diversity. Insects showed higher content of C, N and P (% dry mass), and lower C:N and C:P ratios than plants. C:N ratios were significantly higher in grasshoppers than in bees and higher in females than in males of both species. Increasing plant species richness increased the C:N ratio of male bees and female grasshoppers. In both groups, stoichiometry was positively related to plant stoichiometry (male bees: C:P and N:P; grasshoppers: C:N and N:P). Path analysis revealed that diversity-driven changes in plant elemental composition can have consequences for abundance and chemical composition of higher trophic levels, with different responses of the two functional groups.
Basic and Applied Ecology 01/2014; · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Es wird angenommen, dass funktionelle Pflanzenmerkmale verantwortlich sind für beobachtete Effekte von Pflanzendiversität auf Ökosystemfunktionen, wodurch sich der Fokus der Biodiversitätsforschung von der Betrachtung der Effekte von Pflanzenartenzahlen hin zu der Betrachtung von Pflanzenmerkmalen in einer Gemeinschaft erweitert hat. Die Berücksichtigung von funktionellen Pflanzenmerkmalen hilft möglichweise zu verstehen, wie der Verlust von Arten Ökosystemprozesse beeinflusst. Unseres Wissens wurde jedoch die funktionelle Ähnlichkeit verschiedener Pflanzenarten zueinander noch nie als Grundlage für ein Grasland-Biodiversitätsexperiment genutzt.
Wir präsentieren den theoretischen Hintergrund, das experimentelle Design und erste Ergebnisse eines sogenannten ‚Trait-Based Biodiversity Experiments’ (TBE), welches 2010 im Rahmen des Jena Experimentes etabliert wurde und bei welchem direkt die funktionelle Diversität von Pflanzeneigenschaften manipuliert wurde.
Mithilfe einer Hauptkomponentenanalyse wurden sechs Pflanzenmerkmale von 60 Graslandarten analysiert, die bedeutend für Ressourcenaufnahme und -nutzung sind. Dabei bildeten die Pflanzenarten, die entlang zweier unabhängiger Achsen angeordnet waren, Gradienten in ihrer funktionellen Ähnlichkeit, die als Basis für das Design des TBE dienten. Auf neu angelegten Versuchsflächen etablierten wir Pflanzengemeinschaften mit unterschiedlicher Pflanzenartenzahl, die sich in ihrer räumlichen und zeitlichen funktionellen Komplementarität unterscheiden. Das neuartige Design des TBE erlaubt es uns in Zukunft den relativen Einfluss von Selektions- und Komplementaritätseffekten auf Ökosystemprozesse zu bestimmen und ermöglicht die mechanistische Erforschung der Konsequenzen von vereinfachten Lebensgemeinschaften.
Basic and Applied Ecology 01/2014; · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Landscape connectivity can increase the capacity of communities to maintain their function when environments change by promoting the immigration of species or populations with adapted traits. However, high immigration may also restrict fine tuning of species compositions to local environmental conditions by homogenizing the community. Here we demonstrate that dispersal generates such a tradeoff between maximizing local biomass and the capacity of model periphyton metacommunities to recover after a simulated heat wave. In non-disturbed metacommunities, dispersal decreased the total biomass by preventing differentiation in species composition between the local patches making up the metacommunity. On the contrary, in metacommunities exposed to a realistic summer heat wave, dispersal promoted recovery by increasing the biomass of heat tolerant species in all local patches. Thus, the heat wave reorganized the species composition of the metacommunities and after an initial decrease in total biomass by 38.7%, dispersal fueled a full recovery of biomass in the restructured metacommunities. Although dispersal may decrease equilibrium biomass, our results highlight that connectivity is a key requirement for the response diversity that allows ecological communities to adapt to climate change through species sorting.
[Show abstract][Hide abstract] ABSTRACT: Human alterations to nutrient cycles1, 2 and herbivore communities3, 4, 5, 6, 7 are affecting global biodiversity dramatically2. Ecological theory predicts these changes should be strongly counteractive: nutrient addition drives plant species loss through intensified competition for light, whereas herbivores prevent competitive exclusion by increasing ground-level light, particularly in productive systems8, 9. Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory. This experiment, replicated in 40 grasslands on 6 continents, demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate. Nutrient addition consistently reduced local diversity through light limitation, and herbivory rescued diversity at sites where it alleviated light limitation. Thus, species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light.
[Show abstract][Hide abstract] ABSTRACT: Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally-replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance varied most among regions (subcontinents), whereas cover was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds mono-dominance with invasion resistance. Monitoring species' relative abundance will more rapidly advance our understanding of invasions. This article is protected by copyright. All rights reserved.
Global Change Biology 08/2013; · 6.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The linkages between biological communities and ecosystem function remain poorly understood along gradients of human-induced stressors. We examined how resource provisioning (nutrient recycling), mediated by native freshwater mussels, influences the structure and function of benthic communities by combining observational data and a field experiment. We compared the following: (1) elemental and community composition (algal pigments and macroinvertebates) on live mussel shells and on nearby rocks across a gradient of catchment agriculture and (2) experimental colonisation of benthic communities on live vs. sham shells controlling for initial community composition and colonisation duration. We show that in near pristine systems, nutrient heterogeneity mediated by mussels relates to greater biodiversity of communities, which supports the notion that resource heterogeneity can foster biological diversity. However, with increased nutrients from the catchment, the relevance of mussel-provisioned nutrients was nearly eliminated. While species can persist in disturbed systems, their functional relevance may be diminished or lost.
[Show abstract][Hide abstract] ABSTRACT: In their seminal paper, Goldman et al. suggested that phytoplankton close to maximum growth rate attains a
restricted optimal N: P ratio close to the Redfield ratio of molar N: P 5 16. Recently, the presence of such a
global attractor for optimal phytoplankton stoichiometry has been questioned in models and empirical analyses.
As the chemical composition of phytoplankton is of major importance for our understanding of global elemental cycles and biogeochemical transformations, we assembled 55 data sets of phytoplankton growth rate and biomass N: P ratios in a meta-analysis testing (1) whether phytoplankton N: P converges at high growth rates, (2) whether N: P ratios scale with growth rate, and (3) whether the optimal N: P ratios achieved at highest growth rates reflect organism traits or environmental conditions. Across systems and species, phytoplankton N: P decreased with increasing growth rate and at the same time showed decreasing variance, i.e., fast-growing phytoplankton is more P rich and has a more confined elemental composition. Optimal N: P increased with increasing N: P of available nutrients, i.e., with increasing P limitation. Other differences were rare, except cyanobacteria showed higher optimal N: P than diatoms. Understanding the role of phytoplankton in biogeochemical transformation requires modeling approaches that are stoichiometrically flexible to reflect the dynamics of growth and nutrient supply in primary producers.
Limnology and oceanography 05/2013; 58:2076-2088. · 3.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The nutrition of animal consumers is an important regulator of ecological processes due to its effects on their physiology, life-history and behaviour. Understanding the ecological effects of poor nutrition depends on correctly diagnosing the nature and strength of nutritional limitation. Despite the need to assess nutritional limitation, current approaches to delineating nutritional constraints can be non-specific and imprecise. Here, we consider the need and potential to develop new complementary approaches to the study of nutritional constraints on animal consumers by studying and using a suite of established and emerging biochemical and molecular responses. These nutritional indicators include gene expression, transcript regulators, protein profiling and activity, and gross biochemical and elemental composition. The potential applications of nutritional indicators to ecological studies are highlighted to demonstrate the value that this approach would have to future studies in community and ecosystem ecology.
[Show abstract][Hide abstract] ABSTRACT: Plant growth can be limited by resource acquisition and defence against consumers, leading to contrasting trade-off possibilities. The competition-defence hypothesis posits a trade-off between competitive ability and defence against enemies (e.g. herbivores and pathogens). The growth-defence hypothesis suggests that strong competitors for nutrients are also defended against enemies, at a cost to growth rate. We tested these hypotheses using observations of 706 plant populations of over 500 species before and following identical fertilisation and fencing treatments at 39 grassland sites worldwide. Strong positive covariance in species responses to both treatments provided support for a growth-defence trade-off: populations that increased with the removal of nutrient limitation (poor competitors) also increased following removal of consumers. This result held globally across 4 years within plant life-history groups and within the majority of individual sites. Thus, a growth-defence trade-off appears to be the norm, and mechanisms maintaining grassland biodiversity may operate within this constraint.
[Show abstract][Hide abstract] ABSTRACT: In the course of the biodiversity-ecosystem functioning debate, the issue of multifunctionality of species communities has recently become a major focus. Elemental stoichiometry is related to a variety of processes reflecting multiple plant responses to the biotic and abiotic environment. It can thus be expected that the diversity of a plant assemblage alters community level plant tissue chemistry. We explored elemental stoichiometry in aboveground plant tissue (ratios of carbon, nitrogen, phosphorus, and potassium) and its relationship to plant diversity in a 5-year study in a large grassland biodiversity experiment (Jena Experiment). Species richness and functional group richness affected community stoichiometry, especially by increasing C:P and N:P ratios. The primacy of either species or functional group richness effects depended on the sequence of testing these terms, indicating that both aspects of richness were congruent and complementary to expected strong effects of legume presence and grass presence on plant chemical composition. Legumes and grasses had antagonistic effects on C:N (-27.7% in the presence of legumes, +32.7% in the presence of grasses). In addition to diversity effects on mean ratios, higher species richness consistently decreased the variance of chemical composition for all elemental ratios. The diversity effects on plant stoichiometry has several non-exclusive explanations: The reduction in variance can reflect a statistical averaging effect of species with different chemical composition or a optimization of nutrient uptake at high diversity, leading to converging ratios at high diversity. The shifts in mean ratios potentially reflect higher allocation to stem tissue as plants grew taller at higher richness. By showing a first link between plant diversity and stoichiometry in a multiyear experiment, our results indicate that losing plant species from grassland ecosystems will lead to less reliable chemical composition of forage for herbivorous consumers and belowground litter input.
PLoS ONE 01/2013; 8(3):e58179. · 3.73 Impact Factor