http://hdl.handle.net/1956/2465 Søk i kanalen søk http://bora.uib.no/simple-search http://hdl.handle.net/1956/2598 Tittel: Tracing recovery from acidification in the Western Norwegian nausta watershed <br/> <br/>Forfattere: Halvorsen, Godtfred A.; Heegaard, Einar; Fjellheim, Arne; Raddum, Gunnar G. <br/> <br/>Sammendrag: A novel method, redundancy analysis (RDA), has been used to examine whether chemical recovery from acidification in the western Norwegian Nausta watershed produces detectable recovery within the community structure of the macro-zoobenthos. The RDA results have been compared with measures of recovery based on the changes detected using highly specialized and regionally defined biological acidity indices. We found that the beginning of biological recovery in the Nausta watershed was recognizable during the period 1989–1998. Recovery occurred in the upper reaches and in the tributaries. The multivariate approach proved to complement the acidity indices approach, and much biological information can be gained by their combined use. The RDA method is conservative, i.e. does not overestimate biological recovery, and it is not geographically constrained as are the acidity indices. We also found that seasonal climatic factors strongly influence the benthic community, and may confound the detection of the biological recovery process. Tue, 29 Oct 2002 22:58:59 GMT http://hdl.handle.net/1956/2583 Tittel: Responses of tundra plants to experimental warming : meta-analysis of the international tundra experiment <br/> <br/>Forfattere: Arft, A. M.; Walker, M.D.; Gurevitch, J.; Alatalo, J. M.; Bret-Harte, M. S.; Dale, M.; Diemer, M.; Gugerli, F.; Henry, G. H. R.; Jones, M. H.; Hollister, R. D.; Jónsdóttir, I. S.; Laine, K.; Lévesque, E.; Marion, G. M.; Molau, U.; Mølgaard, P.; Nordenhäll, U.; Raszhivin, V.; Robinson, C. H.; Starr, G.; Stenström, A.; Stenström, M.; Totland, Ørjan; Turner, P. L.; Walker, L. J.; Webber, P. J.; Welker, J. M.; Wookey, P. A. <br/> <br/>Sammendrag: The International Tundra Experiment (ITEX) is a collaborative, multisite experiment using a common temperature manipulation to examine variability in species response across climatic and geographic gradients of tundra ecosystems. ITEX was designed specifically to examine variability in arctic and alpine species response to increased temperature. We compiled from one to four years of experimental data from 13 different ITEX sites and used meta-analysis to analyze responses of plant phenology, growth, and reproduction to experimental warming. Results indicate that key phenological events such as leaf bud burst and flowering occurred earlier in warmed plots throughout the study period; however, there was little impact on growth cessation at the end of the season. Quantitative measures of vegetative growth were greatest in warmed plots in the early years of the experiment, whereas reproductive effort and success increased in later years. A shift away from vegetative growth and toward reproductive effort and success in the fourth treatment year suggests a shift from the initial response to a secondary response. The change in vegetative response may be due to depletion of stored plant reserves, whereas the lag in reproductive response may be due to the formation of flower buds one to several seasons prior to flowering. Both vegetative and reproductive responses varied among life-forms; herbaceous forms had stronger and more consistent vegetative growth responses than did woody forms. The greater responsiveness of the herbaceous forms may be attributed to their more flexible morphology and to their relatively greater proportion of stored plant reserves. Finally, warmer, low arctic sites produced the strongest growth responses, but colder sites produced a greater reproductive response. Greater resource investment in vegetative growth may be a conservative strategy in the Low Arctic, where there is more competition for light, nutrients, or water, and there may be little opportunity for successful germination or seedling development. In contrast, in the High Arctic, heavy investment in producing seed under a higher temperature scenario may provide an opportunity for species to colonize patches of unvegetated ground. The observed differential response to warming suggests that the primary forces driving the response vary across climatic zones, functional groups, and through time. Thu, 29 Oct 1998 22:58:59 GMT http://hdl.handle.net/1956/2581 Tittel: What is the observed relationship between species richness and productivity? Comment <br/> <br/>Forfattere: Whittaker, Robert J.; Heegaard, Einar Tue, 29 Oct 2002 22:58:59 GMT http://hdl.handle.net/1956/2580 Tittel: Period lenght in cyclic animal populations <br/> <br/>Forfattere: Högstedt, Göran; Seldal, Tarald; Breistøl, Arild <br/> <br/>Sammendrag: Although cyclic animal dynamics have long been a focus of scientific interest, the variable cycle lengths are poorly understood. Based on a review of the literature, we suggest that period length in animals showing multiannual cycles is related to the life span of their food plant rather than to any trait of the animal, such as mass or fecundity. We envisage that this pattern is brought about by a prolonged mobilization of induced defenses in longer lived plants, which can better afford periods of low reproductive output than can short-lived plants. On the basis of this hypothesis we expect animals with similar diets to show similar cycle lengths, irrespective of taxonomy and size. A path analysis, on the vertebrate herbivores, shows that 92% of the variation in cycle length is explained by foodplant longevity and that body mass adds little to this. Fri, 29 Oct 2004 22:58:59 GMT http://hdl.handle.net/1956/2578 Tittel: Wind to insect pollination ratios and floral traits in five alpine Salix species <br/> <br/>Forfattere: Totland, Ørjan; Peeters, Liza <br/> <br/>Sammendrag: This study examines the ratio of wind to insect pollination of five alpine-arctic Salix species and possible correlations between plant traits and this ratio. The field work was done in an alpine area in southwest Norway, at an elevation of 1250 m. Female catkins were enclosed within mesh cloth to prevent insect visitation, and their fruit set was determined and compared with that of open-pollinated control catkins. Simultaneously, pollen production per anther, pollen dispersal, standing crop of nectar, flower length, number of flowers per catkin, and catkin length were measured. The amount of wind pollination of the species varied from 2 to 52%. All species spread pollen in the air. Nectar content, catkin length, flower number, and flower length showed a negative relationship with the percentage of wind pollination. Significant negative linear correlations between female catkin length and flower length and amount of wind pollination were detected. Pollen production per anther did not show any relationship to the pollination system. We suggest that the evolution to insect pollination in alpine Salix species may have resulted in a lengthening of anthers and pistils, and an increase in nectar production. Thu, 29 Oct 1998 22:58:59 GMT http://hdl.handle.net/1956/2571 Tittel: The rise and fall of forests <br/> <br/>Forfattere: Birks, Harry John Betteley; Birks, Hilary H. Wed, 29 Oct 2003 22:58:59 GMT http://hdl.handle.net/1956/2570 Tittel: Dispersal limitations matter for microbial morphospecies <br/> <br/>Forfattere: Telford, Richard J.; Vandvik, Vigdis; Birks, Harry John Betteley <br/> <br/>Sammendrag: In contrast with macroorganisms, whose geographical ranges are typically restricted, many microbial species appear to have cosmopolitan distributions. This observation has been explained as a consequence of ubiquitous dispersal caused by the enormous population sizes of microbial species. Recently, this "everything is everywhere, but, the environment selects" theory has been challenged by the detection of considerable regional genetic variability within microbial morphospecies. We demonstrate that, contrary to what is expected under ubiquitous dispersal, evidence of regional-scale metacommunity processes can be detected in microbial morphospecies. Our results imply that the microbial and macrobial world are structured by analogous processes. Sat, 29 Oct 2005 22:58:59 GMT http://hdl.handle.net/1956/2569 Tittel: Response to comment on “Dispersal limitations matter for microbial morphospecies” <br/> <br/>Forfattere: Telford, Richard J.; Vandvik, Vigdis; Birks, Harry John Betteley <br/> <br/>Sammendrag: Pither argues that the relationship we found between regional species-richness maxima and modal lake-pH is expected because both values are constrained by the regional pH range and therefore cannot be interpreted as a signal of regional metacommunity dynamics. However, the null model he uses sets inappropriate parameters, generating unrealistic simulated data. We confirm our previous conclusions using a more appropriate null model. Sun, 29 Oct 2006 22:58:59 GMT