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Hvammstangi, Iceland

Demars B.O.L.,Macaulay Institute | Russell Manson J.,Pomona College | Olafsson J.S.,Institute of Freshwater Fisheries | Gislason G.M.,University of Iceland | And 7 more authors.
Freshwater Biology

1. It is becoming increasingly clear that fresh waters play a major role in the global C cycle. Stream ecosystem respiration (ER) and gross primary productivity (GPP) exert a significant control on organic carbon fluxes in fluvial networks. However, little is known about how climate change will influence these fluxes. 2. Here, we used a 'natural experiment' to demonstrate the role of temperature and nutrient cycling in whole-system metabolism (ER, GPP and net ecosystem production - NEP), in naturally heated geothermal (5-25°C) Icelandic streams. 3. We calculated ER and GPP with a new, more accurate method, which enabled us to take into account the additional uncertainties owing to stream spatial heterogeneity in oxygen concentrations within a reach. ER ranged 1-25gCm-2day-1 and GPP 1-10gCm-2day-1. The median uncertainties (based on 1 SD) in ER and GPP were 50% and 20%, respectively. 4. Despite extremely low water nutrient concentrations, high metabolic rates in the warm streams were supported by fast cycling rates of nutrients, as revealed from inorganic nutrient (N, P) addition experiments. 5. ER exceeded GPP in all streams (with average GPP/ER=0.6) and was more strongly related to temperature than GPP, resulting in elevated negative NEP with warming. We show that, as a first approximation based on summer investigations, global stream carbon emission to the atmosphere would nearly double from 0.12PgCyear-1 at 13°C to 0.21 (0.15-0.33) PgCyear-1 with a 5°C warming. 6. Compared to previous studies from natural systems (including terrestrial ecosystems), the temperature dependence of stream metabolism was not confounded by latitude or altitude, seasonality, light and nutrient availability, water chemistry, space availability (water transient storage), and water availability. 7. Consequently, stream nutrient processing is likely to increase with warming, protecting downstream ecosystems (rivers, estuaries, coastal marine systems) during the summer low flows from nutrient enrichment, but at the cost of increased CO2 flux back to the atmosphere. © 2011 Blackwell Publishing Ltd. Source

Granquist S.M.,Institute of Freshwater Fisheries | Thorhallsdottir A.G.,Agricultural University of Iceland | Sigurjonsdottir H.,University of Iceland
Applied Animal Behaviour Science

Earlier research indicates that stallions may supress interactions of their harem members, leading to less stable hierarchies and friendship bonds in harems compared to non-stallion groups. In this paper, the effect of the presense of a stallion on the social behaviour of mares was studied by comparing six harems containing stallions to four mixed sex groups not containing stallions. Both temporary and permanent harems were studied, giving the possibility to investigate the effect of group stability on social interactions.A significant linear hierarchy was found in all non-stallion groups that were used for comparison, while the hierarchies were only found to be linear in three of the six harems containing stallions (Landaus h', p<0.05). Aggression rate was lower (t-test, p<0.05) and fewer friendship bonds (G-test, p<0.0001) were found within the harems, compared to the groups without stallions. Stallions seldom intervene directly in interactions between harem members. Thus, our results give support to the hypothesis that stallions may suppress interactions of harem members, but in a more indirect way than with direct interference. In addition, our results give support for earlier findings that aggression rate may be affected by group stability. We found a higher aggression rate in the temporary harems compared to the permanent harems (Kruskal-Wallis, p<0.05) and in the temporary non-stallion group compared to the permanent non-stallion group. The results have significance for further research on social structure of mammals, and may be applied in management of domestic animals. © 2012 Elsevier B.V. Source

Kristjansson B.K.,Holar University College | Malmquist H.J.,Natural History Museum of Kopavogur | Ingimarsson F.,Natural History Museum of Kopavogur | Antonsson T.,Institute of Freshwater Fisheries | And 2 more authors.
Biological Journal of the Linnean Society

The common occurrence of parallel phenotypic patterns suggests that a strong relationship exists between ecological dynamics and micro-evolution. Comparative studies from a large number of populations under varying sets of ecological drivers could contribute to a better understanding of this relationship. We used data on morphology of arctic charr (Salvelinus alpinus) and ecological factors from 35 Icelandic lakes to test the hypothesis that morphological patterns among monomorphic charr populations from different lakes are related to interlake variation in ecological characteristics. There is extensive phenotypic diversity among populations of Icelandic charr, and populations are easily distinguished based on overall body morphology. The results obtained in the present study showed that the morphological diversity of charr was related to large-scale diversity in lake ecology. Variation in charr morphology was related to water origin (e.g. spring fed versus run-off), bedrock age, and fish community structure. The present study shows how various ecological factors can shape the biological diversity that we observe. © 2011 The Linnean Society of London. Source

Gudmundsdottir R.,University of Iceland | Gudmundsdottir R.,Norwegian University of Science and Technology | Olafsson J.S.,Institute of Freshwater Fisheries | Palsson S.,University of Iceland | And 2 more authors.
Freshwater Biology

1.Spring-fed streams, with temperatures ranging from 7.1 to 21.6°C, in an alpine geothermal area in SW Iceland were chosen to test hypotheses on the effects of nutrients and temperature on stream primary producers. Ammonium nitrate was dripped into the lower reaches of eight streams, with higher reaches being used as controls, during the summers of 2006 and 2007. Dry mass of larger primary producers, epilithic chlorophyll a and biovolumes of epilithic algae were measured. 2.Bryophyte communities were dominated by Fontinalis antipyretica, and biomass was greatest in the warmest streams. Jungermannia exsertifolia, a liverwort, was found in low densities in few samples from cold streams but this species was absent from the warmest streams. 3.Nutrient enrichment increased the biomass of bryophytes significantly in warm streams. No effects of the nutrient addition were detected on vascular plants. The biomass of larger filamentous algae (mainly Cladophora spp.) was significantly increased by nutrient enrichment in cold streams but reduced by nutrients in warm streams. Thalloid cyanobacteria (Nostoc spp.) were not affected by nutrients in cold streams but decreased with nutrient addition in warm streams. Epilithic algal chlorophyll a was increased by nutrients in all streams and to a greater extent in 2007 than in 2006. Nutrient addition did not affect the epilithic chlorophyll a differently in streams of different temperatures. 4.There were small differential effects of nutrients, influenced by pH and conductivity, on different epilithic algal groups. 5.As global temperatures increase, animal husbandry and perhaps crop agriculture are likely to increase in Iceland. Temperature will directly influence the stream communities, but its secondary effects, manifested through agricultural eutrophication, are likely to be much greater. © 2011 Blackwell Publishing Ltd. Source

Woodward G.,Queen Mary, University of London | Dybkjaer J.B.,University of Aarhus | Olafsson J.S.,Institute of Freshwater Fisheries | Gislason G.M.,University of Iceland | And 3 more authors.
Global Change Biology

The Earth is experiencing historically unprecedented rates of warming, with surface temperatures projected to increase by 3-5 °C globally, and up to 7.5 °C in high latitudes, within the next century. Knowledge of how this will affect biological systems is still largely restricted to the lower levels of organization (e.g. species range shifts), rather than at the community, food web or ecosystem level, where responses cannot be predicted from studying single species in isolation. Further, many correlational studies are confounded with time and/or space, whereas experiments have been mostly confined to laboratory microcosms that cannot capture the true complexity of natural ecosystems. We used a 'natural experiment' in an attempt to circumvent these shortcomings, by characterizing community structure and trophic interactions in 15 geothermal Icelandic streams ranging in temperature from 5 °C to 45 °C. Even modest temperature increases had dramatic effects across multiple levels of organization, from changes in the mean body size of the top predators, to unimodal responses of species populations, turnover in community composition, and lengthening of food chains. Our results reveal that the rates of warming predicted for the next century have serious implications for the structure and functioning of these fragile 'sentinel' ecosystems across multiple levels of organization. © 2009 Blackwell Publishing Ltd. Source

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