Karl Inne Ugland

Lognormal Distributions and the Concept of Community Equilibrium

The lognormal distribution of individuals among species fits many sets of ecological data remarkably well. Dispute exists however, as to whether this distribution is a mathematical artifact of large numbers or whether it has a biological meaning. In analysing general lognormal curves we argue that the characteristics discovered by Preston relating to the canonical lognormal are in fact merely mathematical properties of the whole family of lognormal curves. We develop a model that assumes that a community is composed of groups of species each differently adapted to a habitat. By integrating the distributions of these groups a lognormal distribution results if the community is in equilibrium. If the community is disturbed however, many species change their abundance and then species abundance curves show multiple maxima and no longer conform to a single lognormal curve.

Changes in the root-associated fungal communities along a primary succession gradient analysed by 454 pyrosequencing

We investigated changes in the root‐associated fungal communities associated with the ectomycorrhizal herb Bistorta vivipara along a primary succession gradient using 454 amplicon sequencing. Our main objective was to assess the degree of variation in fungal richness and community composition as vegetation cover increases along the chronosequence. Sixty root systems of B. vivipara were sampled in vegetation zones delimited by dated moraines in front of a retreating glacier in Norway. We extracted DNA from rinsed root systems, amplified the ITS1 region using fungal‐specific primers and analysed the amplicons using 454 sequencing. Between 437 and 5063 sequences were obtained from each root system. Clustering analyses using a 98.5% sequence similarity cut‐off yielded a total of 470 operational taxonomic units (OTUs), excluding singletons. Between eight and 41 fungal OTUs were detected within each root system. Already in the first stage of succession, a high fungal diversity was present in the B. vivipara root systems. Total number of OTUs increased significantly along the gradient towards climax vegetation, but the average number of OTUs per root system stayed unchanged. There was a high patchiness in distribution of fungal OTUs across root systems, indicating that stochastic processes to a large extent structure the fungal communities. However, time since deglaciation had impact on the fungal community structure, as a systematic shift in the community composition was observed along the chronosequence. Ectomycorrhizal basidiomycetes were the dominant fungi in the roots of B. vivipara, when it comes to both number of OTUs and number of sequences.

Predicting the effects of habitat homogenization on marine biodiversity.

Seafloor habitats throughout the worlds oceans are being homogenized by physical disturbance. Even though seafloor sediments are commonly considered to be simple and unstructured ecosystems, the negative impacts of habitat homogenization are widespread because resident organisms create much of their habitats structure. We combine the insight gained from remote sensing of seafloor habitats with recently developed analytical techniques to estimate species richness and assess the potential for change with habitat homogenization. Using habitat-dependent species-area relationships we show that realistic scenarios of habitat homogenization predict biodiversity losses when biogenic habitats in soft sediments are homogenized. We develop a simple model that highlights the degree to which the reductions in the number of species and functional diversity are related to the distribution across habitats of habitat-specific and generalist species. Our results suggest that, by using habitat-dependent species-area relationships, we can better predict variation in biodiversity across seafloor landscapes and contribute to improved management and conservation.

High diversity of root associated fungi in both alpine and arctic Dryas octopetala.

BackgroundDryas octopetala is a widespread dwarf shrub in alpine and arctic regions that forms ectomycorrhizal (ECM) symbiotic relationships with fungi. In this study we investigated the fungal communities associated with roots of D. octopetala in alpine sites in Norway and in the High Arctic on Svalbard, where we aimed to reveal whether the fungal diversity and species composition varied across the Alpine and Arctic regions. The internal transcribed spacer (ITS) region of nuclear ribosomal DNA was used to identify the fungal communities from bulk root samples obtained from 24 plants.ResultsA total of 137 operational taxonomic units (OTUs) were detected (using 97% similarity cut off during sequence clustering) and well-known ECM genera such as Cenococcum, Cortinarius, Hebeloma, Inocybe and Tomentella occurred frequently. There was no decrease in fungal diversity with increasing latitude. The overall spatial heterogeneity was high, but a weak geographical structuring of the composition of OTUs in the root systems was observed. Calculated species accumulation curves did not level off.ConclusionsThis study indicates that the diversity of fungi associated with D. octopetala does not decrease in high latitude arctic regions, which contrasts observations made in a wide spectrum of other organism groups. A high degree of patchiness was observed across root systems, but the fungal communities were nevertheless weakly spatially structured. Non-asymptotical species accumulation curves and the occurrence of a high number of singletons indicated that only a small fraction of the fungal diversity was detected.

Organochlorine contaminants in a local marine food chain from Jarfjord, Northern Norway

Abstract Polychlorinated biphenyls (PCBs; 17 congeners), ΣDDT (p,p′-DDT, p,p′-DDD, p,p′-DDE and o,p′-DDD), chlordanes (oxychlordane and trans-nonachlor), hexachlorocyclohexanes (HCHs; α-, β- and γ-isomers) and hexachlorobenzene (HCB) have been determined in a local marine food chain including the lesser sandeel (Ammodytes marinus), cod (Gadus morhua), harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus), caught in Jarfjord, Northern Norway. The concentrations of the pollutants generally increased with trophic level. The highest biomagnification factor (36.9) was found for ΣDDT from sandeel to harbour seal. The compositional patterns of accumulated organochlorines also differed between the species. The proportions of highly chlorinated biphenyls, p,p′-DDE and oxychlordane increased with higher trophic level, while the proportions of mono-ortho substituted and meta–para unsubstituted PCB congeners, together with DDD decreased from fish to seal. The data suggest that the bioaccumulation mechanisms at lower trophic levels (fish) depend primarily on physicochemical factors, such as the water solubility and lipophilicity of the pollutants. At higher trophic levels (seals), the bioaccumulation mechanisms are primarily affected by biochemical factors, such as the metabolic capacity of the organisms. Prey preference may also influence the patterns of accumulated pollutants in the different species.

On the evolution of reproductive rates in microtine rodents

The purpose of this study was to evaluate the effects of various patterns of population dynamics on the evolution of reproductive rates of voles. Population sizes of both field voles (Microtus agrestis) and bank voles (Clethrionomys glareolus) show different degrees of fluctuation in different regions; the degree of cyclicity increases northwards. Animals caught in both optimal and suboptimal habitats in three regions of Sweden were examined regarding litter size and length of reproductive season. The litter size was greater in optimal than in suboptimal habitats during the increase phase of cyclic populations. The breeding season was shorter during the peak than during the increase phase. In both species, during low—density phase, the reproductive rate of overwintered females increased northwards. Young—of—the—year females of the field vole, but not of the bank vole, showed a decrease in the reproductive rate with distance northwards. These results were compared with predictions based on three hypotheses on the evolution of reproductive rates, emphasizing, respectively, (1) food supply, (2) the pattern of density fluctuations, and (3) a combination of both food supply and the pattern of fluctuation. Observed between—habitat differences in reproductive patterns could be explained by hypothesis. 1. However, hypothesis 2 could explain part of the remaining variation among regions. In addition, when data from optimal habitats in the present study were combined with similar data from the literature, a high correlation was found between litter size and degree of cyclicity, confirming the predictions of hypothesis 2.

ORGANOCHLORINE CONTAMINATION IN DEEP-SEA FISH FROM THE DAVIS STRAIT

Eight species of deep-sea fish caught at various depths off the west coast of Greenland exhibited low to moderate organochlorine (OC) contamination. Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane metabolites (DDTs) were the dominating organochlorines. Hepatic levels of sum-PCB (19 individual PCB congeners) ranged from 110 ng g−1 lipid weight in jelly wolf-fish (Anarhichas denticulatus) to 1156 ng g−1 in blue hake (Antimora rostrata). Sum-DDT (p,p′-DDE, o,p′-DDD, p,p′-DDD, multiplied by a factor (1.11), and p,p′-DDT) ranged from 70 ng g−1 in jelly wolf-fish to 1446 ng/g in blue hake. Sum-chlordanes (oxychlordone and trans-nonachlor) ranged from 28 ng g−1 in jelly wolf-fish to 309 ng g−1 in roughhead grenadier (Macrourus berglax). HCB (hexachlorobenzene) ranged from 3.6 ng g−1 in smalleyed rabbit-fish (Hydrolagus affinis) to 73 ng g−1 in tusk (Brosme brosme). Sum-HCH (hexachlorocyclohexanes α-HCH, β-HCH and γ-HCH) was of minor importance with levels ranging from 9.3 ng g−1 in Greenland halibut (Reinhardtius hippoglossoides) to 22 ng g−1 in tusk. The levels are lower than most of the corresponding published data from deepsea fish and probably reflect a moderately contaminated area. No simple relationship was found between organochlorine contamination and depth range of the investigated species.

Fatty acid composition in blubber, heart and brain from phocid seals

The fatty acid composition of phocid seals was investigated in order to map the possible stratification of fatty acids in the depot fat and to detect possible differences between different tissues and between the four species grey seal (Halichoerus grypus), harbour seal (Phoca vitulina), ringed seal (Phoca hispida) and harp seal (Phoca groenlandica). We used a chemometric method in this analysis: the fatty acids were determined by gas chromatography, and the relative amounts of fatty acids were treated by principal component analysis. Analysis of the depot fat in the four species indicates that the fatty acid composition of the blubber varies along a gradient from the epidermis. We are able to distinguish between three distinct vertical layers. With increasing depth from the epidermis, the amount of saturated and long-chained monounsaturated fatty acids in the blubber fat increased, while the amount of short-chained monounsaturated fatty acids decreased. The four seal species exhibited differences in fatty acid composition in the outermost layer of the blubber. In contrast, the middle and inner layers did not show differences between species. We also analysed the fatty acid composition of heart and brain tissue from harp seals. The three tissues had distinctly different profiles.

Accuracy of age estimates in spring spawning herring (Clupea harengus L.) reared under different prey densities

This study shows that the otolith microstructure provides useful information for age determination of herring larvae with normal growth. However, the experiments also reveal the importance of being cautious when aging young and/or slow growing larvae. Limited resolution of the light microscope, causing several increments to be invisible, is considered to be the main reason for the low accuracy found in slow growing larvae. Limited resolution of the light microscope may also explain why the accuracy is so dependent on the otolith growth when it is less than 0.8 μm/day. It is concluded that the average increment width of the otolith provides useful information to identify larvae in danger of receiving highly biased age estimates.

Mercury and selenium in arctic and coastal seals off the coast of Norway

Mercury and selenium concentrations (wet weight) have been determined in samples of liver, kidney and brain of grey seal (Halichoerus grypus), harbour seal (Phoca vitulina), harp seal (Phoca groenlandica) and ringed seal (Phoca hispida) caught along the Norwegian coast, 114 individuals in all. Significant differences have been found in mercury contamination between the 4 species caught in the same coastal area, Jarfjord, located at the north-east of the Norwegian coast close to the Russian border. Very low hepatic mercury levels were found in the arctic species, ringed and harp seals, ranging from 0.20 to 0.67 and 0.04 to 1.0 microg g(-1), respectively, while in the coastal seal species the concentrations were 10 to 40 times higher. The corresponding ranges were 0.7 to 48.3 microg g(-1) in grey seals and 0.2 to 19.0 microg g(-1) in harbour seals. The median values were 13.5 and 0.7 microg g(-1), respectively. The highest levels were found in grey seals, indicating that particularly the stock frequenting the waters of the north-east coast of Norway and north-west coast of Russia had received a substantial mercury exposure. Fifty-five percent of these grey seals from Jarfjord had hepatic mercury levels above 10 microg g(-1) and 21% had levels above 20 microg g(-1). By a one-way analysis of covariance, sex and age were found to explain 28 and 30%, respectively, of the total variability in the mercury concentration in grey seal from Jarfjord. Significant differences in mercury concentrations were also found between stocks of harbour seals caught at different sites along the Norwegian coast, and decreasing concentration from the south to the north-east coast of Norway was revealed. The renal mercury levels in the arctic seals ranged from 0.08 to 0.45 microg g(-1), and about five times higher levels were found in grey seals and harbour seals. The mercury levels in the brain ranged from the detection level (0.01 microg g(-1)) to about 0.1 microg g(-1). The hepatic selenium levels in the arctic seal species ranged from 0.8 to 3.7 microg g(-1). The corresponding ranges in grey seals and harbour seals were 1.0 to 23.3 microg g(-1). The renal selenium levels were lower, and the levels in the brain were below the detection level (0.01 microg g(-1)). The mercury/selenium ratio was close to unity for mercury concentrations greater than 15 microg g(-1), and a nonlinear, concave relationship was found between the ratio of the hepatic mol concentrations of mercury and selenium and the hepatic mol concentrations of mercury.