Adaptive radiations (ARs) frequently show remarkable repeatability where single lineages undergo multiple independent episodes of AR in distant places and long-separate time points. Genetic variation generated through hybridization between distantly related lineages can promote AR. This mechanism, however, requires rare coincidence in space and time between a hybridization event and opening of ecological opportunity, because hybridization generates large genetic variation only locally and it will persist only for a short period. Hence, hybridization seems unlikely to explain recurrent AR in the same lineage. Contrary to these expectations, our evolutionary computer simulations demonstrate that admixture variation can geographically spread and persist for long periods if the hybrid population becomes separated into isolated sub-lineages. Subsequent secondary hybridization of some of these can reestablish genetic polymorphisms from the ancestral hybridization in places far from the birthplace of the hybrid clade and long after the ancestral hybridization event. Consequently, simulations revealed conditions where exceptional genetic variation, once generated through a rare hybridization event, can facilitate multiple ARs exploiting ecological opportunities available at distant points in time and space.

Temporal genetic variation was studied within the cyclic parthenogenetic <i>Daphnia galeata-cucullata</i> species complex in Lake Tjeukemeer (The Netherlands). During three successive years, three allozyme loci were studied in order to compare the level of genetic variation in <i>D. galeata</i> (G), <i>D. cucullata</i> (C) and their interspecific hybrid (C × G). This data set was used to investigate: whether C × G hybrids are regularly produced by the parental species and to what extent backcrossing takes place in this species complex. G and C × G were the most abundant taxa, whereas C was only abundant in late summer and autumn. Genetic diversity was highest in C, lowest in G, and intermediate in C × G. <i>pgm</i> and <i>pgi</i> allele frequencies of C × G were not intermediate to those of the parental species but were more similar to G than to C. In addition, almost no significant deviations from Hardy-Weinberg were observed. An UPGMA analysis of Nei's genetic distances showed that C × G hybrids are more closely related to G (difference <0.04), than to C (difference 0.30). My data suggest, in accordance with other studies, that C × G hybrids are probably still formed by the parental species, though not necessarily every year. Furthermore, my data suggest that backcrossing occurred frequently, and led to introgression of C alleles into G.

The Activated Sludge Model No. 2d (ASM2d) presents a model for biological phosphorus removal with simultaneous nitrification-denitrification in activated sludge systems. ASM2d is based on ASM2 and is expanded to include the denitrifying activity of the phosphorus accumulating organisms (PAOs). This extension of ASM2 allows for improved modeling of the processes, especially with respect to the dynamics of nitrate and phosphate.

We studied population extinction of the locally abundant fen plant <I>Swertia perennis</I> in Switzerland and used up to 127-year old herbarium records to relocate 63 sites that had once hosted this species. We recorded current site characteristics and related them to the absence or abundance of populations. Fifty-four sites (86%) were still traditionally used (extensively mown or grazed). Fifteen populations (24%) had gone extinct. Extinction was more likely at lower altitude, in the peripheral distribution range of <I>S. perennis</I> (58% peripheral, 9% central populations extinct). on the smallest fens (75% extinct on fens < 400 m²) and on fens with intensified land use. However, even on traditionally managed wetlands 18.5% of the populations had gone extinct. Moreover, 40% of all remaining populations were smaller than 250 flowering plants. We conclude that both intensified agricultural practice and habitat fragmentation contributed to local extinction of <I>S. perennis</I>. Small populations, especially, may not be able to persist in the long term.

We assessed the effects of habitat fragmentation on the demography of the locally abundant, long-lived fen plant <I>Swertia perennis</I> L., by examining population structure, components of fitness and herbivory of 17 populations in Switzerland. We distinguished between large MAIN, small, barely isolated NEAR and small, geographically isolated DISTANT habitat islands. Large isolation distance of small sites significantly affected the transition from sub-adult to adult age states: the mean population density was reduced by 30%, the density of vegetative adults by 60% and the density of reproductive adults by 78% on DISTANT compared with NEAR islands. Seedling survivorship decreased significantly from MAIN to NEAR to DISTANT islands. Moreover, several vegetative components of fitness were significantly reduced on DISTANT islands, i.e. the length and number of leaves and the stern height. Finally, leaf herbivory was highest on small NEAR islands. Our results indicate that population viability of <I>S. perennis</I> is reduced on small, isolated fens, possibly because of arrested individual adult growth due to inbreeding. In contrast, environmental influences such as higher productivity through increased nutrient influx on small sites may be responsible for changed plant-herbivore interactions.

Animals have evolved a number of ways to protect themselves from the harmful effects of ultraviolet-B (UV-B) radiation, but little is known about the relative importance of different mechanisms protecting amphibian embryos from UV-B radiation. Using enzymatic removal of gelatinous coats (jelly envelope) surrounding the eggs of <I>Rana temporaria</I>, we tested the hypothesis that the jelly envelope acts as a sunscreen that protects embryos from harmful effects of UV-B radiation. We conducted two independent factorial laboratory experiments employing three different UV-B (no UV-B, normal, and enhanced) levels and jelly removal (control, modified, and completely removed) treatments. We found no UV-B X jelly removal treatment interactions in survival rates or in frequency of abnormal individuals, suggesting that jelly removal did not increase susceptibility of embryos to UV-B radiation. These results support the contention that the jelly envelope is not the most important means of protecting <i>R. temporaria</I> embryos from UV-B radiation. Other factors (e.g., melanin pigments, other sunscreen compounds, effective DNA-repair mechanisms) must be responsible for the high UV-B radiation tolerance of embryos.

Domestic water use is generally the most important component of urban water consumption. In this paper, the relatively new technique of artificial neural network (ANN) is proposed to model and forecast the water demand in urban areas. Results indicate that the WDF-ANN (water demand forecast using artificial neural network) model offers an effective way to formulate domestic water demand in Weinan City in China. The model evaluation shows that the correlation coefficients are more than 90% both for the training data and the testing data.

Effects of free-air carbon dioxide enrichment (FACE, 60 Pa pCO₂) on plant growth as compared with ambient pCO₂ (36 Pa) were studied in swards of <em>Lolium perenne</em> L. (perennial ryegrass) at two levels of N fertilization (14 and 56 g m⁻² a⁻¹) from 1993 to 2002. The objectives were to determine how plant growth responded to the availability of C and N in the long term and how the supply of N to the plant from the two sources of N in the soil, soil organic matter (SOM) and mineral fertilizer, varied over time. In three field experiments, ¹⁵N-labelled fertilizer was used to distinguish the sources of available N.<br/> In 1993, harvestable biomass under elevated pCO₂ was 7% higher than under ambient pCO₂. This relative pCO₂ response increased to 32% in 2002 at high N, but remained low at low N. Between 1993 and 2002, the proportions and amounts of N in harvestable biomass derived from SOM (excluding remobilized fertilizer) were, at high N, increasingly higher at elevated pCO₂ than at ambient pCO₂. Two factorial experiments confirmed that at high N, but not at low N, a higher proportion of N in harvestable biomass was derived from soil (including remobilized fertilizer) following 7 and 9 years of elevated pCO₂, when compared with ambient pCO₂.<br/> It is suggested that N availability in the soil initially limited the pCO₂ response of harvestable biomass. At high N, the limitation of plant growth decreased over time as a result of the stimulated mobilization of N from soil, especially from SOM. Consequently, harvestable biomass increasingly responded to elevated pCO₂. The underlying mechanisms which contributed to the increased mobilization of N from SOM under elevated pCO₂ are discussed. This study demonstrated that there are feedback mechanisms in the soil which are only revealed during long-term field experiments. Such investigations are thus, a prerequisite for understanding the responses of ecosystems to elevated pCO₂ and N supply.

Whether interspecific hybridization is important as a mechanism that generates biological diversity is a matter of controversy. Whereas some authors focus on the potential of hybridization as a source of genetic variation, functional novelty and new species, others argue against any important role, because reduced fitness would typically render hybrids an evolutionary dead end. By drawing on recent developments in the genetics and ecology of hybridization and on principles of ecological speciation theory, I develop a concept that reconciles these views and adds a new twist to this debate. Because hybridization is common when populations invade new environments and potentially elevates rates of response to selection, it predisposes colonizing populations to rapid adaptive diversification under disruptive or divergent selection. I discuss predictions and suggest tests of this hybrid swarm theory of adaptive radiation and review published molecular phylogenies of adaptive radiations in light of the theory.

The research on commons dilemmas is characterized by innumerable published findings, each standing relatively isolated from the other. To date there is little integration of the findings under a unified concept. The present contribution aims to integrate already existing findings in a general dynamic model of cooperative behavior in resource crises by means of computer simulation. The model postulates that people base their decisions regarding resource use on both ecological and social information. Whether or not ecological or social information will dominate, however depends on people's social values, attributions, and their perceptions of the state of the resource. The advantage of the simulation method used is that successful integration of the findings can be shown explicitly, as the simulation then replicates the experimental data. With the model presented here, it is also possible to let variables work together whose interaction has not yet been investigated in real experiments. For instance, the simulation model allows us to hypothesize that people, in dependence upon their resource uncertainty and in dependency upon their attributions, utilize a resource completely differently if the resource is in an optimal or sub-optimal condition.

The evaluation of toxicological effects at the cellular and molecular levels in organisms are often used to determine sites subjected to contamination problems that pose a threat to the long-term survival of organisms. However, the integration of multiple measurements on the health status of organisms into a model for site discrimination is challenging. This study compares two discrimination methods which are based on rule inference: rough sets (RS) analysis and classification trees (CT) with classical multivariate discriminant analysis (DA). Site classification was attempted with six biomarkers of effects: metallothionein levels, lipid peroxidation, DNA damage, levels of lipophosphoproteins (i.e., vitellins), phagocytosis activity and haemocyte cell viability on clam (<I>Mya arenaria</I>) populations from the Saguenay River fjord (Quebec, Canada). Rule based methods have the advantage of complete independence from data distribution constraints in contrast to the classification methods from multivariate analysis that are more commonly used in ecotoxicology. Results show that RS and CT gave better classifications than DA because they do not require strong distributional assumptions. Moreover, RS provided classification rules that could identify the most important biomarker(s) for site discrimination. RS and CT were shown to be simple and efficient methods for classifying multivariable ecotoxicological data. This methodology would be especially useful when freedom from distributional assumptions is required.

Among various groups of fishes, a shift in peak wavelength sensitivity has been correlated with changes in their photic environments. The genus <I>Sebastes</I> is a radiation of marine fish species that inhabit a wide range of depths from intertidal to over 600 m. We examined 32 species of <I>Sebastes</I> for evidence of adaptive amino acid substitution at the rhodopsin gene. Fourteen amino acid positions were variable among these species. Maximum likelihood analyses identify several of these to be targets of positive selection. None of these correspond to previously identified critical amino acid sites, yet they may in fact be functionally important. The occurrence of independent parallel changes at certain amino acid positions reinforces this idea. Reconstruction of habitat depths of ancestral nodes in the phylogeny suggests that shallow habitats have been colonized independently in different lineages. The evolution of rhodopsin appears to be associated with changes in depth, with accelerated evolution in lineages that have had large changes in depth.

Repression of competition (RC) within social groups has been suggested as a key mechanism driving the evolution of cooperation, because it aligns the individual’s proximate interest with the interest of the group. Despite its enormous potential for explaining cooperation across all levels of biological organization, ranging from fair meiosis, to policing in insect societies, to sanctions in mutualistic interactions between species, there has been no direct experimental test of whether RC favours the spread of cooperators in a well-mixed population with cheats. To address this, we carried out an experimental evolution study to test the effect of RC upon a cooperative trait – the production of iron-scavenging siderophore molecules – in the bacterium <I>Pseudomonas aeruginosa</I>. We found that cooperation was favoured when competition between siderophore producers and nonsiderophore-producing cheats was repressed, but not in a treatment where competition between the two strains was permitted. We further show that RC altered the cost of cooperation, but did not affect the relatedness among interacting individuals. This confirms that RC <I>per se</I>, as opposed to increased relatedness, has driven the observed increase in bacterial cooperation.

Ecotoxicological effect studies often expose test organisms under optimal environmental conditions. However, organisms in their natural settings rarely experience optimal conditions. On the contrary, during most of their lifetime they are forced to cope with sub-optimal conditions and occasionally with severe environmental stress. Interactions between the effects of a natural stressor and a toxicant can sometimes result in greater effects than expected from either of the stress types alone. The aim of the present review is to provide a synthesis of existing knowledge on the interactions between effects of "natural" and chemical (anthropogenic) stressors. More than 150 studies were evaluated covering stressors including heat, cold, desiccation, oxygen depletion, pathogens and immunomodulatory factors combined with a variety of environmental pollutants. This evaluation revealed that synergistic interactions between the effects of various natural stressors and toxicants are not uncommon phenomena. Thus, synergistic interactions were reported in more than 50% of the available studies on these interactions. Antagonistic interactions were also detected, but in fewer cases. Interestingly, about 70% of the tested chemicals were found to compromise the immune system of humans as judged from studies on human cell lines. The challenge for future studies will therefore be to include aspects of combined stressors in effect and risk assessment of chemicals in the environment.

The factors controlling rates of contaminant reduction by magnetite (Fe<SUB>3</SUB>O<SUB>4</SUB>) are poorly understood. Here, we measured the reduction rates of three ArNO<SUB>2</SUB> compounds by magnetite particles ranging from highly oxidized (<I>x</I> = Fe<SUP>2+</SUP>/Fe<SUP>3+</SUP> = 0.31) to fully stoichiometric (<I>x</I> = 0.50). Rates of ArNO<SUB>2</SUB> reduction became almost 5 orders of magnitude faster as the particle stoichiometry increased from <I>x</I> = 0.31 to 0.50. To evaluate what was controlling the rate of ArNO<SUB>2</SUB> reduction, we measured apparent <SUP>15</SUP>N kinetic isotope effects (<SUP>15</SUP>N-AKIE) values for nitrobenzene and magnetite open-circuit potentials (<I>E</I><SUB>OCP</SUB>). <SUP>15</SUP>N-AKIE values were greater than unity for all magnetite stoichiometries investigated, indicating that mass transfer processes are not controlling the rate of ArNO<SUB>2</SUB> reduction by magnetite. <I>E</I><SUB>OCP</SUB> measurements showed that the <I>E</I><SUB>OCP</SUB> for magnetite was linearly related to the stoichiometry, with more stoichiometric magnetite having a lower potential. Based on these results, we propose that conceptual models that incorporate both redox and Fe<SUP>2+</SUP> diffusion processes, rather than those that rely solely on diffusion of Fe<SUP>2+</SUP>, are more appropriate for understanding contaminant reduction by magnetite. Our work indicates that particle stoichiometry should be considered when evaluating rates of contaminant reduction by magnetite.

Life history variation and genotype composition were studied in two species of the <I>Daphnia longispina</I> group: the relatively large <I>D. galeata</I> (1.4 mm) and the smaller <I>D. cucullata</I> (0.9 mm). Several multi-locus genotypes of these species were compared with genotypes of their interspecific hybrid, <I>D. cucullata</I> × <I>D. galeata</I>. Both species and the hybrid co-occur in the shallow eutrophic Tjeukemeer. For two successive years, laboratory life table experiments were conducted at three temperatures (12.5°, 17.5°, and 22.5°C) and two food levels (carbon concentrations 0.62 and 1.64 mg/mL) to study the mechanisms that permit coexistence of taxa in this <I>Daphnia</I> hybrid species complex. Three-way analyses of variance showed significant main effects (e.g., temperature, food level, taxon) for most reproductive traits (e.g., number of newborns, age at first reproduction, number of juvenile instars, intrinsic rate of increase) among the <I>Daphnia</I> taxa. For size-related traits (e.g., size at maturity and offspring size) only one main effect, taxon, was found. Hybrids were intermediate to the parental species with respect to size and maturity, offspring size, and number of newborns. For developmental traits (number of juvenile instars and age at maturity) the hybrids tended to have the lowest values for all conditions. The intrinsic rate of increase (<I>r</I>) of the hybrid did not differ significantly from that of <I>D. galeata</I>, but was significantly higher than that of <I>D. cucullata</I>. We argue that essentially <I>r</I> will reach higher values for the hybrids than for <I>D. galeata</I>, because of the strong influence of size-selective fish predation. Our results are discussed in reference to different theories about the maintenance of hybrid species complexes in nature.

Cell walls of five Gram-positive bacterial strains, including four coryneforms and a <I>Bacillus brevis</I> strain were isolated and subsequently chemically analysed. The wall contribution to the total cell mass is calculated from a comparison of D-Lactate concentrations in hydrolysates of whole cells and isolated walls. D-Lactate concentrations are measured enzymatically after purification of the samples with active carbon. The optimum condition for the quantitative elimination of D-lactate from the peptidoglycan appears to be at 120°C and 4 M HCl. The wall fraction for the cells of the coryneform bacteria are in the range of 26-32% and is about 75% for the <I>B. brevis</I> cells.<br/> The peptidoglycan fraction in the walls of the coryneform bacteria was found to be rather high and constitutes about 23 to 31% of the cell wall dry weight. The protein content of the cell wall dry weight is somewhat lower and in the range of 7 to 14%. The peptidoglycan in the wall of the <I>B. brevis</I> strain forms a thin layer and contributes only about 5% to the cell wall dry weight. The high amount of proteins in the <I>B. brevis</I> cell wall (> 56%) can be attributed to a so called S(urface)layer.

In small to mid-size streams, forested riparian zones can moderate water temperature, provide important sources of organic matter (leaf litter, woods, and tree roots), and strongly influence the growth of algae, mosses and macrophytes by the degree of canopy cover. Furthermore they reduce inputs of nutrients, other chemical substances, and sediments from agricultural uplands and stabilize stream banks. Therefore, the riparian forests are very important for the energy budget, the habitat complexity and the macroinvertebrate community of a stream system. The urban development and the intensive management of agricultural lands during the last forty years has led to losses or reductions of riparian forest zones. The consequences of these human activities for the aquatic communities require restoration and protection measures for the residual riparian strips.

Die Organisation kollektiver Aktionen kann mit Hilfe von Computersimulationen optimiert werden. Zu diesem Zweck wird in der vorliegenden Arbeit ein akteurzentrierter Ansatz verfolgt, in dessen Rahmen die individuelle Teilnahmeentscheidung eines Akteurs auf der Basis einer Erweiterung der Theorie des geplanten Verhaltens modelliert wird. In das Modell der individuellen Teilnahmeentscheidung gehen die Variablen Einstellung, Ertrag, subjektive soziale Norm und die wahrgenommene Handlungskontrolle bezüglich der Teilnahme ein. Durch den Einbezug dieser vier Variablen werden verschiedene sozialwissenschaftliche Theorien (Elaboration Likelihood Model; Theorie des geplanten Verhaltens; Rational Choice Theorie) integriert. Diese Theorien ermöglichen die Konzeption von Interaktionen zwischen den Individuen, wodurch der Effekt von Personen, die andere Personen für die Teilnahme an einer kollektiven Aktion anwerben, untersucht werden kann. Aus Simulationen einer Population mit 10.000 unterschiedlichen Individuen wird ermittelt, welchen Einfluss die Anwerbeform der motivierenden Personen, die Höhe der Beiträge der Teilnehmer zum Kollektivgut, die Größe des Kollektivguts und die Ausstattung der Aktivatoren (Überzeugungstraining oder Möglichkeit zu belohnen) auf die Effektivität kollektiver Aktionen hat. Die Simulationsergebnisse werden schliesslich zu umsetzbaren Empfehlungen für die Organisation kollektiver Aktionen zusammengefasst.

This paper is based on an extensive review of soil fertility in the literature of soil science, agronomy and ethnic studies. The spectrum of scientific opinions on soil fertility was visualized in mind-maps, definition types were analyzed, and problems within the conceptual approach towards soil fertility were shown.<br/> Differently oriented concepts were divided between the terms of soil fertility and soil quality. Soil fertility is not applicable as a technical term in natural sciences as it describes a definite, but dispositional (concealed), soil feature; therefore, it is not fully operationalizable for the natural sciences.<br/> Soil quality denotes undefined and interchangeable sets of appreciated soil attributes and functionalities, which are assigned by value judgements. It is a tool that integrates different soil state variables and functions in order to evaluate the capacity of a soil to do what it is expected (i.e. function) or to assess the sustainability of current land-use practices.<br/> The phenomenon of soil fertility appears to the consciousness as an autonomous counter-instance with its own mental and material qualities, referred to in traditional cultic cultivation. The main features of cultic cultivation of soil fertility are the uniting of the four elements, the religio towards the spiritual side of nature, the sacrificial, and the eros.<br/> A reevaluation of the soil fertility phenomenon in modern terms would be an innovative and forward-looking research program. Practical and scientific work on soil fertility should rediscover and revive the feeling for, and apperception of, the phenomenon of soil fertility in its mental and material aspects.

In this paper we present a new global multimedia fate model that considers the influence of temperature on the environmental transport, degradation, and partitioning of persistent organic pollutants. The model consists of a variable number of latitudinal zones with specific annual temperature courses; each zone contains soil, oceanic surface water, and tropospheric air. The chemicals' degradation rates and Henry's law constants (<I>H</I>) are implemented as functions of temperature and the concentrations in the soil, water, and air compartments of each latitudinal zone are calculated as functions of time. The resulting temporal and spatial concentration patterns are characterized by persistence and spatial range. Model calculations are carried out for tetrachloromethane, α-hexachlorocyclohexane (α-HCH), and mirex, and the specific distribution patterns of these three chemicals are discussed. The model results show that the soil and water concentrations of the polar zones are strongly sensitive to changes of the latitudinal gradient of <I>H</I> and of washout ratios, adsorption to aerosol particles, and deposition rates.

Three types of epidermal cultures of fish were used for toxicological investigations, a primary cell culture and a tissue culture prepared from the rainbow trout <i>Oncorhynchus mykiss</i> Walbaum and the cell line EPC, derived from a skin tumour of the carp <i>Cyprinus carpio</i> L. Two studies were carried out to compare the different culture systems. In the first cultures were incubated with nonylphenol and in the second set of experiments the cell cultures were exposed to a wastewater sample containing low concentrations of nonylphenol (NP). Both cell cultures were similarly sensitive to nonylphenol with respect to the endpoints cell viability (LC₅₀ (24 h) 47.1 μM NP (primary cell culture) and 44.2 μM NP (EPC)) values and apoptotic rate (significantly increased apoptotic rate after exposure to 50 μM NP for 24 h, <i>p</i> < 0.001 (primary cell culture), <i>p</i> = 0.008 (EPC)). The explant culture was slightly less sensitive (increased apoptotic rate after exposure to 50 μM NP for 24 h, but not significant: <i>p</i> = 0.385), which could be due to the capabilities of a differentiated tissue, providing more protective repair mechanisms, compared with single cells. All cultures revealed a concentration–response relationship for the endpoint apoptotic rate after the application of nonylphenol for 24 h. After wastewater exposure, a significant decrease in the apoptotic rate was measured in the primary cell culture (dilution wastewater : medium 1:1:<i>p</i> = 0.018; dilution wastewater : medium 1:2:<i>p</i> = 0.003), whereas the cell line EPC did not reveal any effects. Our results show that the endpoint apoptotic rate is more sensitive than the parameter cell viability for detecting adverse effects of a wastewater sample.

Most environments periodically impose severe stress that may cause high mortality and alter population structure, for example, by removing sick and old individuals. We examined how anoxic conditions and starvation of the host affect virulence of two closely related trematode parasites, <I>Rhipidocotyle campanula</I> and <I>R. fennica</I>. These parasites differ by prevalence of infection and by exploitation rate of individual hosts (freshwater clam, <I>Anodonta piscinalis</I>). Infection by <I>R. campanula</I> is rare (<5% prevalence of infection) and destroys on average 90% of the gonad tissue of the individual host. Infection by <I>R. fennica</I> is more common (20–60% prevalence of infection) and leads to on average 30% gonad destruction. In the end, both infections lead to host infertility. We predicted that <I>R. campanula</I> induces higher host mortality than <I>R. fennica</I> under host stress. In two laboratory experiments, we exposed naturally-infected and uninfected clams to anoxia and to starvation. Anoxia occasionally takes place during winter in eutrophic lakes, while some degree of starvation should occur seasonally. We found that mortality rate of clams was much higher under anoxia than under starvation, and that infection increased mortality rate under both types of host stress. As predicted, <I>R. campanula</I> induced higher host mortality than <I>R. fennica</I>. Host survival was population-specific, suggesting that clams of different origins carried different amount of energy reserves. Severe environmental perturbation may remove <I>R. campanula</I> infected individuals from the host population, but recolonization from the fish host is likely to prevent extinction of the parasite suprapopulation. The observed high host mortality induced by <I>R. campanula</I> may be one ecological explanation for the consistently lower prevalence of infection of <I>R. campanula</I> when compared to <I>R. fennica</I>.

The behavior, morphology and response to stimuli in biological systems are dictated by the interactions between their components. These interactions, as we observe them now, are therefore shaped by genetic variations and selective pressure. Similar to what has been achieved by comparing genome structures and protein sequences, we hope to obtain valuable information about systems' evolution by comparing the organization of interaction networks and by analyzing their variation and conservation. Equally, significantly we can learn whether and how to extend the network information obtained experimentally in well-characterized model systems to different organisms. We conclude from our analysis that, despite the recent completion of several high throughput experiments aimed at the description of complete interactomes, the available interaction information is not yet of sufficient coverage and quality to draw any biologically meaningful conclusion from the comparison of different interactomes. Thus, the transfer of network information obtained from simple organism to evolutionary distant species should be carried out and considered with caution. By using smaller higher-confidence datasets, a larger fraction of interactions is shown to be conserved; this suggests that with the development of more accurate experimental and informatic approaches, we will soon be in the position to study the network evolution.

The effects of elevated pCO₂ on net ecosystem CO₂ exchange were investigated in managed Lolium perenne (perennial ryegrass) and Trifolium repens (white clover) monocultures that had been exposed continuously to elevated pCO₂ (60 Pa) for nine growing seasons using Free Air CO₂ Enrichment (FACE) technology. Two levels of nitrogen (N) fertilization were applied. Midday net ecosystem CO₂ exchange (mNEE) and night-time ecosystem respiration (NER) were measured in three growing seasons using an open-flow chamber system. The annual net ecosystem carbon (C) input resulting from the net CO₂ fluxes was estimated for one growing season. In both monocultures and at both levels of N supply, elevated pCO₂ stimulated mNEE by up to 32%, the exact amount depending on intercepted PAR The response of mNEE to elevated pCO₂ was larger than that of harvestable biomass. Elevated pCO₂ increased NER by up to 39% in both species at both levels of N supply. NER, which was affected by mNEE of the preceding day, was higher in T. repens than in L. perenne. High N increased NER compared to low N supply. According to treatment, the annual net ecosystem C input ranged between 210 and 631 g C m^-2 year ^-1 and was not significantly affected by the level of pCO₂. Low N supply led to a higher net C input than high N supply. We demonstrated that at the ecosystem level, there was a long-term stimulation in the net C assimilation during daytime by elevated pCO₂. However, because NER was also stimulated, net ecosystem C input was not significantly increased at elevated pCO₂. The annual net ecosystem C input was primarily affected by the amount of N supplied.