| 1. |
- Chi, Celestine N., et al.
(författare)
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Reassessing a sparse energetic network within a single protein domain
- 2008
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 105:12, s. 4679-4684
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the molecular principles that govern allosteric communication is an important goal in protein science. One way allostery could be transmitted is via sparse energetic networks of residues, and one such evolutionary conserved network was identified in the PDZ domain family of proteins by multiple sequence alignment [Lockless SW, Ranganathan R (1999) Science 286:295-299]. We have reassessed the energetic coupling of these residues by double mutant cycles together with ligand binding and stability experiments and found that coupling is not a special property of the coevolved network of residues in PDZ domains. The observed coupling for ligand binding is better explained by a distance relationship, where residues close in space are more likely to couple than distal residues. Our study demonstrates that statistical coupling from sequence analysis is not necessarily a reporter of energetic coupling and allostery.
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| 2. |
- Löbel, Swantje, 1978-, et al.
(författare)
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Mating system, reproduction mode and diaspore size affect metacommunity diversity
- 2009
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 97:1, s. 176-185
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Tidskriftsartikel (refereegranskat)abstract
- 1. Metapopulation persistence and metacommunity diversity in patchy dynamic landscapes critically depend on efficient dispersal. Dispersal strategies could involve trade-offs that result in different species responses to habitat fragmentation, alteration in habitat quality and changes in landscape dynamics. 2. We studied spatial structuring in species richness of obligate epiphytic bryophytes in 135 deciduous forest patches in a largely coniferous landscape in Sweden. We tested the effects of forest patch size (0.01-15 ha), patch quality and present and historic connectivity (as revealed by air photographs) on species richness of species groups with different mating systems, reproduction modes and diaspore sizes. 3. Present connectivity to other deciduous forest patches had positive effects on richness of dioecious species with predominant asexual reproduction, whereas richness of monoecious species with predominant sexual reproduction was affected by historic connectivity only. The scale of spatial structuring in species richness increased with decreasing diaspore sizes. Forest patch quality affected richness of monoecious species reproducing sexually but not of dioecious species reproducing asexually. 4. Our results suggest shorter dispersal distances, but higher establishment rates, of large asexual diaspores than of small sexual ones. In monoecious species with sexual reproduction, it may take several decades from establishment to first spore production, and this may explain the strong effect of historic, but not present, forest patch connectivity on species richness of this group. This suggests a trade-off between dispersal distance and age at first reproduction, which may explain the parallel evolution of asexual reproduction and monoecism in species inhabiting patchy, transient habitats. 5. Synthesis. We conclude that dispersal success of metacommunity members is influenced both by species traits and habitat characteristics. In patch-tracking metacommunities, trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat patchiness and dynamics. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions may lead to distinct changes in metacommunity diversity: Species reproducing asexually may drastically decline with increasing distances among patches, whereas sexually reproducing species may decline with increasing patch dynamics.
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| 3. |
- Löbel, Swantje, 1978-
(författare)
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Metapopulation and metacommunity processes, dispersal strategies and life-history trade-offs in epiphytes
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to increase knowledge about metapopulation and metacommunity processes in patchy, dynamic landscapes, using epiphytic bryophytes as a model system. Host trees and deciduous forest stands in the coniferous landscape are patchy, temporal and undergo changes in habitat quality during succession. Epiphytes must track this dynamic habitat network for their long-term survival. Community patterns at different spatial scales were explored and linked to regional metapopulation processes and local population dynamics. Spatial structuring in species richness both at a local and regional scale indicated stronger dispersal limitation but lower sensitivity to habitat quality in species with large asexual than in species with small sexual diaspores. In sexually dispersed species, a strong rescue effect was indicated by a bimodal frequency distribution of the species and by increasing local abundance with increasing patch connectivity. Present connectivity to other deciduous forest patches had positive effects on richness of asexually dispersed species, whereas richness of sexually dispersed species was instead related to the landscape connectivity 30 years ago. A study of local growth and reproduction suggested that this is caused by delayed sexual, but not asexual, reproduction. Habitat conditions affected the production of sporophytes, but not of asexual diaspores. No differences in either growth rates or competitive abilities among species with different dispersal and life-history strategies were found. In vitro experiments showed that establishment is higher from large asexual diaspores than from small sexual. Establishment of all diaspore types was limited by pH. There were indications of trade-offs between high germination and protonemal growth rates, desiccation tolerance and a rapid development of shoots from protonema. The results indicated that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance (diaspore size) versus age at first reproduction, and dispersal distance versus sensitivity to habitat quality. Trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat turnover, connectivity and irregular water supply rather than by species interactions. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions can lead to distinct changes in metacommunity diversity: the results indicate that increasing distances among patches cause most harm to asexually dispersed species, whereas cuttings of forests of high age and quality as well as increasing patch dynamics are most harmful to sexually dispersed species.
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| 6. |
- Ringvall, Anna, et al.
(författare)
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Unrestricted guided transect sampling for surveying sparse species
- 2007
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Ingår i: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 37:12, s. 2575-2586
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Tidskriftsartikel (refereegranskat)abstract
- We present a modification of an earlier presented method using prior auxiliary information in the layout of survey strips. The idea is to imitate a skilled surveyor who purposively seeks the species of interest. Yet, the method “unrestricted guided transect sampling” (UGTS) is a probability sampling method. In comparison with a strip survey using no auxiliary information, UGTS gave 11%–64% lower standard errors for estimates of species population size in three simulated forest types. In a test in six stands where European aspen (Populus tremula L.) and an epiphytic moss (Orthotrichum speciosum Nees) had been mapped, UGTS gave a small improvement in some stands but considerably higher standard errors in other stands with kNN estimates of volume of deciduous trees derived from satellite images as covariate values. With covariates values simulated from aspen basal area, UGTS gave 8%–75% lower standard error than a strip survey using no auxiliary information. The study shows a gain in precision by using auxiliary information both in the design and in estimation when surveying sparse species but also that the correlation between the covariate and the variable of interest has to be relatively strong to make the method worthwhile.
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| 7. |
- Sandgren, Fredrik, 1967-, et al.
(författare)
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Towns and rural industrialisation in Sweden 1850-1890: A spatial statistical approach
- 2009
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Ingår i: Scandinavian Economic History Review. - London : Routledge. - 0358-5522 .- 1750-2837. ; 57:3, s. 229-251
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Tidskriftsartikel (refereegranskat)abstract
- Using a spatial statistical analysis we study the relation between rural industrial employment and distance to towns and access to communications in nineteenth century Sweden. Our results show that rural parishes with access to communicationshad a higher proportion of rural industrial workers than parishes without. In a region with few towns, the south-east of Sweden, parishes close to large towns had a higher proportion of industrial employees than distant parishes in1850, while no significant correlation was observed in 1890. In a region with arelatively dense urban system, Mälardalen, only in 1890 did parishes close to large towns show a higher proportion of rural industrial workers than did more distant parishes. However, the mean positive effect was negligible beyond 10 km. Thus, in the second half of the nineteenth century the immediate urban hinterland was industrialising prior to large scale urbanisation and urban industrialisation.
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