Effect of experimental nitrogen load on methane and nitrous oxide fluxes on ombrotrophic boreal peatland

Methane (CH₄) and nitrous oxide (N₂O) dynamics were studied in a boreal Sphagnum fuscum pine bog receiving annually (from 1991 to 1996) 30 or 100 kg NH₄NO₃-N ha^–1. The gas emissions were measured during the last three growing seasons of the experiment. Nitrogen treatment did not affect the CH₄ fluxes in the microsites where S. fuscum and S. angustifolium dominated. However, addition of 100 kg NH₄NO₃-N ha^–1 yr^–1 increased the CH₄ emission from those microsites dominated by S. fuscum. This increase was associated with the increase in coverage of cotton grass (Eriophorum vaginatum) induced by the nitrogen treatment. The differences in the CH₄ emissions were not related to the CH₄ oxidation and production potentials in the peat profiles. The N₂O fluxes were negligible from all microsites. Only minor short-term increases occurred after the nitrogen addition.     

A Comparative Study on the Cleavage of Stereoisomeric Uridylyl (3',5')Uridines [D,D-, D,L- and L,D-UPU] by Acid,Base and Metal Ion Catalysts

Stereoisomeric uridylyl(3',5')uridines D,L-UpU andL,D-UpU were synthesised. Their cleavage was followed in thepresence of acid, base and metal ion catalysts to studywhether the stereochemistry affects the inherent reactivity ofthe internucleosidic phosphodiester bond, and whether the lowmolecular weight catalysts can distinguish between thesubstrates. The rate constants obtained were compared to thoseof D,D-UpU. The comparison shows that the stability of thephosphodiester bond does not depend on the stereochemistry ofthe sugar rings. In contrast slight reactivity differences areobserved in the presence of metal ion catalysts, whichsuggests that selective cleavage of stereoisomeric substrateseven by small molecular weight chemical catalysts may bepossible.     

Combined UV and Liquid Scintillation Detection in HPLC. Formation and Depurination of Substitution Inert Pt(II) Complexes of Purine Nucleosides

Abstract

Combined UV- and liquid scintillation-HPLC has been applied to study the complexing of purine nucleosides with Pt(II)-diamine ions, and the effect of the complex formation on the acidic depurination.     

Patch area, population density and the scaling of migration rates: the resource concentration hypothesis revisited

Empirical research has for a long time observed that animal densities may both increase and decrease with patch size, and these variable responses have been difficult to explain using the current theoretical framework. The most influential hypothesis, the resource concentration hypothesis, predicts only positive density–area relations, as a consequence of different emigration and immigration rates in small and large patches, and empirical deviations have inspired a flurry of alternative explanations. In this paper, we use realistic rules for the relationship between patch size and migration rates and show a wider predictive range for density–area relations than previously believed. Comparisons with published data suggest that observed density–area relations may easily fit in a framework based on a minimum set of behavioural and population processes. This does not imply that other mechanisms are unimportant, but merely that their quantitative importance can only be evaluated relative to patch geometry and local growth.     

Spatiotemporal Effects of Supplementary Feeding of Wild Boar (Sus scrofa) on Artificial Ground Nest Depredation

Supplementary feeding of ungulates, being widely used in game management, may have unwanted consequences. Its role in agricultural damage is well-studied, but few studies have considered the potential for the practice to attract ground nest predators. Our goal was to identify the factors influencing ground nest predation in the vicinity of year-round supplementary feeding sites for wild boar and to characterise their spatiotemporal scope. We conducted two separate artificial ground nest experiments in five different hunting districts in south-eastern Estonia. The quantity of food provided and distance of a nest from the feeding site were the most important factors determining predation risk. Larger quantities of food resulted in higher predation risk, while predation risk responded in a non-linear fashion to distance from the feeding site. Although predation risk eventually decreases if supplementary feeding is ceased for at least four years, recently abandoned feeding sites still pose a high predation risk.     

The replication of kinetoplast DNA networks in Crithidia fasciculata

Kinetoplast DNA from the mitochondria of Crithidia is in the form of a two-dimensional network of thousands of minicircles each containing about 2.5 kb, and a small number of maxicircles each containing about 40 kb. Fractionation of kinetoplast DNA by equilibrium centrifugation in a CsCl-propidium dilodide gradient resolves it into three types of networks. Form I networks band at high density and contain minicircles which are covalently closed; form II networks band at low density and contain minicircles which are nicked or gapped; and replicating networks band at intermediate density and contain some minicircles of each type. Form I networks contain about 5000 minicircles; form II networks contain about 11,000; and replicating networks contain an intermediate number. When cells are pulse-labeled with ³H-thymidine, radioactivity in mitochondrial DNA is preferentially incorporated into replicating networks, but after a chase it appears first in form II networks and finally in form I. Examination of replicating networks by electron microscopy in the presence of ethidium bromide reveals that minicircles in the central region of the network are twisted and therefore covalently closed, whereas those in the peripheral region are not twisted and therefore must be nicked or gapped. The pulse-label is incorporated into the nicked or gapped minicircles of the replicating networks. These results indicate that replication of form I networks begins in peripheral minicircles and that progeny minicircles remain nicked or gapped. As replication proceeds, the size of the network increases, and the peripheral zone of nicked or gapped minicircles enlarges. Finally, when all minicircles have replicated, the network, now form II, is double the size of form I and contains only nicked or gapped minicircles. The final step in replication presumably includes both the cleavage of the network into two form I species and the covalent closure of all the minicircles.     

Temperature dependence of predation depends on the relative performance of predators and prey

The temperature dependence of predation rates is a key issue for understanding and predicting the responses of ecosystems to climate change. Using a simple mechanistic model, we demonstrate that differences in the relative performances of predator and prey can cause strong threshold effects in the temperature dependence of attack rates. Empirical data on the attack rate of northern pike (Esox lucius) feeding on brown trout (Salmo trutta) confirm this result. Attack rates fell sharply below a threshold temperature of +11°C, which corresponded to a shift in relative performance of pike and brown trout with respect to maximum attack and escape swimming speeds. The average attack speed of pike was an order of magnitude lower than the escape speed of brown trout at 5°C, but approximately equal at temperatures above 11°C. Thresholds in the temperature dependence of ecological rates can create tipping points in the responses of ecosystems to increasing temperatures. Thus, identifying thresholds is crucial when predicting future effects of climate warming.     

Standing genetic diversity and selection at functional gene loci are associated with differential invasion success in two non‐native fish species

Invasive species are expected to experience a unique combination of high genetic drift due to demographic factors while also experiencing strong selective pressures. The paradigm that reduced genetic diversity should limit the evolutionary potential of invasive species, and thus, their potential for range expansion has received little empirical support, possibly due to the choice of genetic markers. Our goal was to test for effects of genetic drift and selection at functional genetic markers as they relate to the invasion success of two paired invasive goby species, one widespread (successful) and one with limited range expansion (less successful). We genotyped fish using two marker types: single nucleotide polymorphisms (SNPs) in known‐function, protein‐coding genes and microsatellites to contrast the effects of neutral genetic processes. We identified reduced allelic variation in the invaded range for the less successful tubenose goby. SNPs putatively under selection were responsible for the observed differences in population structure between marker types for round goby (successful) but not tubenose goby (less successful). A higher proportion of functional loci experienced divergent selection for round goby, suggesting increased evolutionary potential in invaded ranges may be associated with round goby's greater invasion success. Genes involved in thermal tolerance were divergent for round goby populations but not tubenose goby, consistent with the hypothesis that invasion success for fish in temperate regions is influenced by capacity for thermal tolerance. Our results highlight the need to incorporate functional genetic markers in studies to better assess evolutionary potential for the improved conservation and management of species.     

Physiological and autonomic stress responses after prolonged sleep restriction and subsequent recovery sleep in healthy young men

Sleep and Biological Rhythms - Sleep restriction is increasingly common and associated with the development of health problems. We investigated how the neuroendocrine stress systems respond to...