Stoichiometry of endothermy: shifting the quest from nitrogen to carbon.

For many animals, notably herbivores, plants are often an inadequate food source given the low content of protein and high content of C-rich material. This conception is mainly based on studies on ectotherms. The validity of this conception for endotherms is unclear given their much higher carbon requirements for maintenance energy metabolism than ectotherms.

The consequences of climate-driven stop-over sites changes on migration schedules and fitness of Arctic geese.

1. How climatic changes affect migratory birds remains difficult to predict because birds use multiple sites in a highly interdependent manner. A better understanding of how conditions along the flyway affect migration and ultimately fitness is of paramount interest.

Adaptation of the fungal parasite Zygorhizidium planktonicum during 200 generations of growth on homogeneous and heterogeneous populations of its host, the diatom Asterionella formosa.

We followed adaptation of the chytrid parasite Zygorhizidium planktonicum during 200 generations of growth on its host, the freshwater diatom Asterionella formosa, in a serial passage experiment. Evolution of parasite fitness was assessed both on a homogenous and heterogeneous host population, consisting of respectively a single new and ten different new host strains. These 10 host strains were genetically different and also varied in their initial susceptibility to the parasite.

Avian herbivory: an experiment, a field test, and an allometric comparison with mammals.

Mechanistic studies on herbivore functional responses have largely taken place in mammals; very little has been done in herbivorous birds so far. Here we aim to fill that gap by experimentally quantifying the (short-term) functional response of a large avian herbivore, the Bewick's Swan (Cygnus columbianus bewickii). We explicitly distinguish between encounter-limited and handling-limited foraging by analyzing the results in the framework of the models of D.

Induced defenses in herbivores and plants differentially modulate a trophic cascade.

Inducible defenses are dynamic traits that modulate the strength of both plant-herbivore and herbivore-carnivore interactions. Surprisingly few studies have considered the relative contributions of induced plant and herbivore defenses to the overall balance of bottom-up and top-down control. Here we compare trophic cascade strengths using replicated two-level and three-level plankton communities in which we systematically varied the presence or absence of induced defenses at the plant and/or herbivore levels.

Population dynamics and diversity of viruses, bacteria and phytoplankton in a shallow eutrophic lake.

We have studied the temporal variation in viral abundances and community assemblage in the eutrophic Lake Loosdrecht through epifluorescence microscopy and pulsed field gel electrophoresis (PFGE). The virioplankton community was a dynamic component of the aquatic community, with abundances ranging between 5.5 x 10(7) and 1.

Goose-mediated nutrient enrichment and planktonic grazer control in Arctic freshwater ponds.

A dramatic increase in the breeding population of geese has occurred over the past few decades at Svalbard. This may strongly impact the fragile ecosystems of the Arctic tundra because many of the ultra-oligotrophic freshwater systems experience enrichment from goose feces. We surveyed 21 shallow tundra ponds along a gradient of nutrient enrichment based on exposure to geese.

The parasitic chytrid, Zygorhizidium, facilitates the growth of the cladoceran zooplankter, Daphnia, in cultures of the inedible alga, Asterionella.

In food-web studies, parasites are often ignored owing to their insignificant biomass. We provide evidence that parasites may affect trophic transfer in aquatic food webs. Many phytoplankton species are susceptible to parasitic fungi (chytrids).

Short-term foraging costs and long-term fueling rates in central-place foraging swans revealed by giving-up exploitation times.

Foragers tend to exploit patches to a lesser extent farther away from their central place. This has been interpreted as a response to increased risk of predation or increased metabolic costs of prey delivery. Here we show that migratory Bewick's swans (Cygnus columbianus bewickii), though not incurring greater predation risks farther out or delivering food to a central place, also feed for shorter periods at patches farther away from their roost.

Hampered foraging and migratory performance in swans infected with low-pathogenic avian influenza A virus.

It is increasingly acknowledged that migratory birds, notably waterfowl, play a critical role in the maintenance and spread of influenza A viruses. In order to elucidate the epidemiology of influenza A viruses in their natural hosts, a better understanding of the pathological effects in these hosts is required. Here we report on the feeding and migratory performance of wild migratory Bewick's swans (Cygnus columbianus bewickii Yarrell) naturally infected with low-pathogenic avian influenza (LPAI) A viruses of subtypes H6N2 and H6N8.

Critical threshold effects of benthiscape structure on stream herbivore movement.

In landscape ecology, substantial theoretical progress has been made in understanding how critical threshold levels of habitat loss may result in sudden changes in landscape connectivity to animal movement. Empirical evidence for such thresholds in real systems, however, remains scarce. Streambed landscapes provide a strong testing ground for studying critical thresholds because organisms are faced with substantial environmental heterogeneity while attempting to overcome the physical force of water.

Ciliates are the dominant grazers on pico- and nanoplankton in a shallow, naturally highly eutrophic lake.

Abundance and biomass of the microbial loop members [bacteria, heterotrophic nanoflagellates (HNF), and ciliates] were seasonally measured in the naturally eutrophic and shallow (2.8 mean depth) Lake Võrtsjärv, which has a large open surface area (average 270 km2) and highly turbid water (Secchi depth <1 m). Grazing rates (filter feeding rates) on 0.

Can overwintering versus diapausing strategy in Daphnia determine match-mismatch events in zooplankton-algae interactions?

Mismatches between predator and prey due to climate change have now been documented for a number of systems. Ultimately, a mismatch may have far-reaching consequences for ecosystem functioning as decoupling of trophic relationships results in trophic cascades. Here, we examine the potential for climate change induced mismatches between zooplankton and algae during spring succession, with a focus on Daphnia and its algal food.

Animal-plant-microbe interactions: direct and indirect effects of swan foraging behaviour modulate methane cycling in temperate shallow wetlands.

Wetlands are among the most important ecosystems on Earth both in terms of productivity and biodiversity, but also as a source of the greenhouse gas CH(4). Microbial processes catalyzing nutrient recycling and CH(4) production are controlled by sediment physico-chemistry, which is in turn affected by plant activity and the foraging behaviour of herbivores. We performed field and laboratory experiments to evaluate the direct effect of herbivores on soil microbial activity and their indirect effects as the consequence of reduced macrophyte density, using migratory Bewick's swans (Cygnus columbianus bewickii Yarrell) feeding on fennel pondweed (Potamogeton pectinatus L.

Effect of salinity on temporal and spatial dynamics of ammonia-oxidising bacteria from intertidal freshwater sediment.

Temporal and spatial dynamics within an ammonia-oxidising community from intertidal, freshwater sediments were studied in microcosms simulating flooding twice a day with fresh, brackish and marine waters. The microcosms had been filled with the upper 5 cm of intertidal freshwater sediment from the river Scheldt. Changes in community composition were examined by denaturing gradient gel electrophoresis of amplified DNA from the community.

New DGGE strategies for the analyses of methanotrophic microbial communities using different combinations of existing 16S rRNA-based primers.

Methane-oxidising microbial communities are studied intensively because of their importance for global methane cycling. A suite of molecular microbial techniques has been applied to the study of these communities. Denaturing gradient gel electrophoresis (DGGE) is a diversity screening tool combining high sample throughput with phylogenetic information of high resolution.

Contrasting microcystin production and cyanobacterial population dynamics in two Planktothrix-dominated freshwater lakes.

Microcystin concentrations in two Dutch lakes with an important Planktothrix component were related to the dynamics of cyanobacterial genotypes and biovolumes. Genotype composition was analysed by using denaturing gradient gel electrophoresis (DGGE) profiling of the intergenic transcribed spacer region of the rrn operon (rRNA-ITS), and biovolumes were measured by using microscopy. In Lake Tjeukemeer, microcystins were present throughout summer (maximum concentration 30 microg l(-1)) while cyanobacterial diversity was low and very constant.

Contribution analysis of body mass dynamics in Daphnia.

The concept of body mass dynamics can be viewed as part of life history theory, but its potential has remained largely untapped due to a lack of analytical methodology. We therefore propose a method, called contribution analysis, which enables us to decompose a change in body mass into contributions associated with variations in individual egg mass, clutch size, and standard somatic mass (somatic mass adjusted to body length). The advantage of contribution analysis is that various contributions are expressed in the same units (units of mass) and show the amount of resources committed to changes in the individual traits, while the traits themselves are measured in different units and thus incomparable on their own.

Molecular characterization of cyanobacterial diversity in a shallow eutrophic lake.

We have studied the diversity of pelagic cyanobacteria in Lake Loosdrecht, The Netherlands, through recovery and analysis of small subunit ribosomal RNA gene sequences from lake samples and cyanobacterial isolates. We used an adapted protocol for specific amplification of cyanobacterial rDNA for denaturing gradient gel electrophoresis (DGGE) analysis. This protocol enabled direct comparison of cyanobacterial community profiles with overall bacterial profiles.

Assimilation and depuration of microcystin-LR by the zebra mussel, Dreissena polymorpha.

Zebra mussels (Dreissena polymorpha) are an important component of the foodweb of shallow lakes in the Netherlands, amongst others in Lake IJsselmeer, an international important wetland. Large numbers of ducks feed on these mussels in autumn and winter. The mussels are filter feeders and are exposed to high densities of cyanobacteria in summer and autumn.

Analysis of structural and physiological profiles to assess the effects of Cu on biofilm microbial communities.

We investigated the effects of copper on the structure and physiology of freshwater biofilm microbial communities. For this purpose, biofilms that were grown during 4 weeks in a shallow, slightly polluted ditch were exposed, in aquaria in our laboratory, to a range of copper concentrations (0, 1, 3, and 10 microM). Denaturing gradient gel electrophoresis (DGGE) revealed changes in the bacterial community in all aquaria.

Toxic and nontoxic microcystis colonies in natural populations can be differentiated on the basis of rRNA gene internal transcribed spacer diversity.

Assessing and predicting bloom dynamics and toxin production by Microcystis requires analysis of toxic and nontoxic Microcystis genotypes in natural communities. We show that genetic differentiation of Microcystis colonies based on rRNA internal transcribed spacer (ITS) sequences provides an adequate basis for recognition of microcystin producers. Consequently, ecological studies of toxic and nontoxic cyanobacteria are now possible through studies of rRNA ITS genotypic diversity in isolated cultures or colonies and in natural communities.

Basal metabolic rate, food intake, and body mass in cold- and warm-acclimated Garden Warblers.

We address the question of whether physiological flexibility in relation to climate is a general feature of the metabolic properties of birds. We tested this hypothesis in hand-raised Garden Warblers (Sylvia borin), long-distance migrants, which normally do not experience great temperature differences between summer and winter. We maintained two groups of birds under cold and warm conditions for 5 months, during which their body mass and food intake were monitored.

A simple remedy against artifactual double bands in denaturing gradient gel electrophoresis.

Denaturant gradient gel electrophoresis (DGGE) is a widely used method for mutation analysis and for studies of microbial diversity. Particular combinations of target gene fragments and primers may give rise to erroneous DGGE profiles. We report on a very straightforward means to eliminate the artifactual 'double bands' that can be encountered in several applications.

Detecting the phosphate status of phytoplankton by enzyme-labelled fluorescence and flow cytometry.

The novel phosphatase substrate, ELF-97 phosphate, yields intensely green fluorescent precipitates of ELF-97 alcohol (ELFA) upon enzymatic dephosphorylation, and thereby traces phosphatase activity back to its producer. In this study, we show that ELFA fluorescence is a useful tool in flow cytometric analysis of natural phytoplankton populations. Presence of endogenous fluorescent pigments allowed flow cytometric distinction of clusters in the phytoplankton community in Lake Loosdrecht (The Netherlands): Eukaryotes (diatoms and green algae), chlorophyll a and b containing but phycobilin-less cyanobacteria (Prochlorothrix hollandica), and phycocyanin-containing cyanobacteria (predominantly Limnothrix sp.