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- Cichon, M, et al.
(författare)
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Mass-dependent mass loss in breeding birds : getting the null hypothesis right
- 1999
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Ingår i: Oikos. - : JSTOR. - 0030-1299 .- 1600-0706. ; 87:1, s. 191-194
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Tidskriftsartikel (refereegranskat)abstract
- An assumption central to many tests of statistical association between two variables is the null expectation of zero association. Here, we draw attention to the fact that in many published tests of mass-dependent mass loss in breeding birds, this assumption has been violated. We show that a correct null hypothesis can be derived by using resampling methods, and analyse three data sets (two previously published) from passerine birds to illustrate the approach. Our results show, that under a correct null hypothesis, the biological interpretation of the previously published results is reversed-initially heavy birds do actually lose less mass (relative to their weight) than the initially light birds.
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| 2. |
- Olofsson, Johan, et al.
(författare)
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On the balance between positive and negative plant interactions in harsh environments
- 1999
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Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 86:3, s. 539-543
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Tidskriftsartikel (refereegranskat)abstract
- Positive interactions between plants typically occur where the presence of a species ameliorates the abiotic environment for another. However, there is also a potential for resource competition to act at the same time, which creates a situation where the net outcome is a balance between positive and negative interactions. We present data from a nine-year study in two extreme high alpine habitats that was designed to test whether the effects of established Ranunculus glacialis individuals on germination and growth of Oxyria, digyna are primarily positive or negative at the altitudinal limit of vascular plants. We show net effects ranging from neutral to negative, but no positive effects were detected. We also argue that close associations between plants in these harsh environments may both ameliorate and deteriorate the abiotic environment, and that experimental manipulations are necessary to tell the difference.
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| 3. |
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| 4. |
- Svensson, Bo, 1946-, et al.
(författare)
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Interdecadal changes in CO2 and CH4 fluxes of subarctic mire : Stordalen revisted after 20 years
- 1999
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Ingår i: Oikos. - : JSTOR. - 0030-1299 .- 1600-0706. ; 85:1, s. 22-30
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Tidskriftsartikel (refereegranskat)abstract
- The first subarctic wetland CO2 and CH4 flux measurements were made at Stordalen in the beginning of the 1970s in connection with the IBP study. A return to this area in 1994-95 offered a unique opportunity to study possible interdecadal changes in northern wetland CO2 and CH4 emissions. Measurements of CO2 and CH4 fluxes were carried out in similar habitats as those investigated in 1974. The mire distribution of wet minerotrophic areas relative to the elevated ombrotrophic areas had changed dramatically over the twenty years. There were no significant differences between the CH4-flux in 1974, 1994, and 1995. However, the CO2 fluxes were significantly higher in 1995 than in 1974. Since differences in climatic conditions gave no cause for such a change it suggests a possible increase in decomposition rate to be due to other factors. We suggest changes in vegetation composition, altered mineralization pathways and disintegration of permafrost as causes for the interdecadal increase in decomposition rates.
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| 5. |
- Eckstein, Rolf Lutz, et al.
(författare)
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Recycling of nitrogen among segments of Hylocomium splendens as compared with Polytrichum commune : Implications for clonal integration in an ectohydric bryophyte
- 1999
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Ingår i: OIKOS. - : Nordic Society Oikos. - 0030-1299. ; 86:1, s. 87-96
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Tidskriftsartikel (refereegranskat)abstract
- Physiological integration in clonal plants, which can be assumed to be dependent on vascular connections among ramets, is associated with several potential benefits, especially in nutrient-poor environments. However, some experimental evidence indicates that ectohydric bryophytes, i.e. species lacking specialised tissues for internal water conduction, also have physiologically integrated ramets. We tested this hypothesis by analysing nitrogen dynamics and tracing movements of a 15 N label among interconnected ramets of the ectohydric Hylocomium splendens over one season. The observed patterns were compared with translocation patterns in Polytrichum commune, an endohydric species that is known to show a high degree of clonal integration. Our aims were (1) to evaluate the degree of physiological integration among segments in H. splendens and (2) to study whether the pattern of 15 N movement obtained matched those depicted by changes in total nitrogen pool size. Current-year segments (G0) of both species were identified as strong sinks for nitrogen owing to their considerable increase in the 15 N pool during the season. In P. commune all other segments types showed a net loss of 15 N from June to September, which was probably due to autumn resorption of nitrogen to subterranean structures. In H. splendens one-year-old segments (G1) increased their 15 N pool, while older green segments (G2+) lost 50% of their initially absorbed 15 N. All the label lost from these source segments could be recovered in G0 and G1 segments. We suppose that most of the recycled nitrogen is provided by degeneration of three-year-old segments, which turn brown in parallel with the reallocation of nitrogen during the season. The high degree of physiological integration in H. splendens is discussed with respect to its life history and ecosystem nitrogen cycling.
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| 7. |
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| 8. |
- Olsson, M, et al.
(författare)
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Sperm choice and sperm competition: suggestions for field and laboratory studies
- 1999
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Ingår i: OIKOS. - : MUNKSGAARD INT PUBL LTD. - 0030-1299. ; 84:1, s. 172-175
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The recent explosion of research on sperm competition, and the emerging idea that females may control paternity of their offspring via "sperm choice", raise many methodological questions. One central issue is the role of inbreeding-induced mortality of of
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| 9. |
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| 10. |
- Tunlid, Anders
(författare)
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Molecular biology : A linkage between microbial ecology, general ecology and organismal biology
- 1999
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Ingår i: Oikos. - : JSTOR. - 0030-1299. ; 85:2, s. 177-189
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Tidskriftsartikel (refereegranskat)abstract
- The field of microbial ecology has been developing rapidly, largely owing to the introduction of new molecular methods for identifying individuals, species and populations of microorganisms in nature. In contrast to traditional methods, the new ones do not require the isolation and culture of organisms from the environment. With many of the new methods, genotypes and species of microorganisms can be identified by using 'marker' sequences of nucleic acids that can be related to those of other organisms by applying phylogenetic methods. Thus molecular techniques provide information on both the structure and evolutionary relationships of organisms in microbial communities. Methods are also available for analyzing gene expression and metabolic activities of microbial communities in situ. They make it possible to link microbial diversity to ecological processes and to bridge the gap between microbiology in the laboratory, microbial ecology and general ecology. The development of microbial ecology has been highly dependent on information obtained from studies of microorganisms in pure or mixed cultures. These studies have been focused on identifying genes, enzymes, metabolites, etc., involved in important microbial interactions and ecological processes, such as parasitism, symbiosis, decomposition and nitrogen transformation. Recently this 'organism-oriented' branch of microbial ecology has been strongly stimulated by the results obtained within the large genome projects. Large-scale sequencing and functional analyses of genes, transcripts, proteins and metabolic pathways are being carried out on a number of microorganisms, including the well-characterized 'model organisms' (such as Saccharomyces cerevisiae) as well as several species of substantial ecological importance. A major future challenge of 'post-genome' projects will be to decipher the relationships between genotypes and phenotypes, and to link molecular mechanisms to adaptive variation. These are also central problems in ecology. The strong connection between microbial ecology and molecular biology should inspire us to make further advances in these areas of ecology as well as to integrate general ecology more closely with organismal biology.
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