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Gianreto Walther - One of the best experts on this subject based on the ideXlab platform.
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one century of vegetation change on isla persa a nunatak in the bernina massif in the swiss alps
Journal of Vegetation Science, 2008Co-Authors: Pascal Vittoz, Jeanne Bodin, Stefan Ungricht, Conradin A Burga, Gianreto WaltherAbstract:Abstract Question: How did the vascular plant species composition of a nunatak in the alpine vegetation belt change over a time span of 100 years? Location: A 5.6-ha nunatak, Isla Persa in the Swiss Alps, that remained ice-free during the last maximum glacier advance in the 1850s and is today partly covered with climactic alpine grassland and dwarf heath shrubs. Methods: Floristic inventories in 1906, 1927, 1972, 1995, 2003 and 2004 and a comparative analysis of the species composition over the period 1906–2004. Results: 31 species that were not recorded in the first inventory were found in the following surveys. However, among them only six were common by 2004. Generally, the new species prefer warmer conditions than those previously present and most newcomers are associated with montane or sub-alpine grasslands and woodlands. In particular, the observed increase of Vaccinium myrtillus and the arrival of shrub and tree species further substantiate a trend towards vegetation composition of the lower altit...
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One century of vegetation change on Isla Persa, a nunatak in the Bernina massif in the Swiss Alps
Journal of Vegetation Science, 2007Co-Authors: Pascal Vittoz, Jeanne Bodin, Stefan Ungricht, Conradin A Burga, Gianreto WaltherAbstract:Question: How did the vascular plant species composition of a nunatak in the alpine vegetation belt change over a time span of one century? Location: A 0.056-km2 nunatak, Isla Persa in the Swiss Alps, that remained ice free during the last maximum glacier advance in the 1850s and is today partly covered with climactic alpine grassland and dwarf heath shrubs. Methods: Floristic inventories in 1906, 1927, 1972, 1995, 2003 and 2004 and a comparative analysis of the species composition over the period 1906–2004. Results: Thirty-one species that were not recorded in the first inventory were found in the following surveys. However, among them only six were common by 2004. On average, the new species prefer warmer conditions than those previously present and most newcomers are associated with montane or subalpine grasslands and woodlands. In particular, the observed increase of Vaccinium myrtillus and the arrival of shrub and tree species further substantiate a trend towards vegetation composition of the lower altitudinal belt. Ferns represented 24% of the newcomers, probably due to the high dispersal ability of their lightweight spores. The observed species enrichment was globally small compared to previously inventoried summits. Conclusion: Floristic change strongly suggests warmer climatic conditions as the main factor contributing to species compositional change. The relative stability of species richness may be explained by several factors: the isolation of the nunatak and the difficulties for plants to reach the site, the colder local climate, a limited available species pool and interactions of established alpine plants with newly immigrating taxa. Supplementary data collected at about the same altitude would be necessary to better understand the influence of climate change on alpine grasslands.
Katarina Hedlund - One of the best experts on this subject based on the ideXlab platform.
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Corridor or drift fence? The role of medial moraines for fly dispersal over glacier
Polar Biology, 2013Co-Authors: Maria Ingimarsdottir, Jörgen Ripa, Katarina HedlundAbstract:Corridors are often considered to promote dispersal between habitat patches. In this paper, we study whether or not corridors induce colonisation of Nunataks (ice-free areas in glacier surroundings) by promoting dispersal from lowland to the Nunataks. On outlet glaciers, debris originating from Nunataks forms the so-called medial moraines that stretch from the Nunataks down-glacier to the lowland, forming corridors of debris on the glacier. Aerial dispersal was determined with yellow sticky traps on the moraines, bare glacier and glacier foreland. Dipterans were sampled in pitfall traps on the Nunataks. Flying insects that were present on the vegetated glacier foreland belonged to five orders, that is, Diptera, Hemiptera, Hymenoptera, Lepidoptera and Trichoptera. On the glacier and medial moraines, however, mainly dipterans were present, with the majority of individuals found on the moraines. Hoverflies (Syrphidae) were abundant on the moraines and on the edges of Nunataks close to the moraines, but were not present on the vegetated foreland. The origin of the hoverflies is thus not the Nunataks and not the lowland. Rather, they are brought in by air currents towards the glacier, where they aggregate on a land type where they have a chance of survival, although it is not habitable. Thus, we conclude that the medial moraines do not function as regular corridors but as drift fences that direct the dispersal towards the adjacent land types, that is, the Nunataks and the glacier foreland.
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Food web assembly in isolated habitats: A study from recently emerged Nunataks, Iceland
Basic and Applied Ecology, 2013Co-Authors: Maria Ingimarsdottir, Jörgen Ripa, Ólöf Birna Magnúsdóttir, Katarina HedlundAbstract:Allochthonous arthropods can sustain a local food web on seemingly barren land, but are nevertheless often neglected in studies of community assembly. In the present study, we investigated primary food web assembly on Nunataks (ice-free areas) in a retreating glacier in Iceland. Nunataks enable studies that take into account both the temporal factor of the assembly and the influx of allochthonous organisms. Arthropods were collected on sites of different age on five Nunataks younger than 70 years, as well as the youngest parts of one old nunatak. The youngest sites had no vegetation and were dominated by detritivores and predators along with allochthonous arthropods. The arthropod biomass, that was considered established, increased with vegetation cover and site age but also differed among Nunataks. To investigate whether or not the assembly of arthropods was consistent with the predictions of assembly rules, we tested whether, (1) the proportion of each trophic level changed non-randomly, (2) predator-prey ratio remained constant, and (3) larger species replaced smaller ones. We could only verify that proportions of trophic levels changed non-randomly. As assembly rules only apply for established organisms, it is possible that difficulties in determining whether e. g. generalist predators were established or not may affect the outcome of analyses of assembly rules. It is thus important to be aware that unintentional inclusion of allochthonous arthropods in models of community assembly may affect whether or not the community can be explained and predicted by assembly rules. (Less)
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primary assembly of soil communities disentangling the effect of dispersal and local environment
Oecologia, 2012Co-Authors: Maria Ingimarsdottir, Jörgen Ripa, Ólöf Birna Magnúsdóttir, Tancredi Caruso, Massimo Migliorini, Katarina HedlundAbstract:It has long been recognised that dispersal abilities and environmental factors are important in shaping invertebrate communities, but their relative importance for primary soil community assembly has not yet been disentangled. By studying soil communities along chronosequences on four recently emerged Nunataks (ice-free land in glacial areas) in Iceland, we replicated environmental conditions spatially at various geographical distances. This allowed us to determine the underlying factors of primary community assembly with the help of metacommunity theories that predict different levels of dispersal constraints and effects of the local environment. Comparing community assembly of the Nunataks with that of non-isolated deglaciated areas indicated that isolation of a few kilometres did not affect the colonisation of the soil invertebrates. When accounting for effects of geographical distances, soil age and plant richness explained a significant part of the variance observed in the distribution of the oribatid mites and collembola communities, respectively. Furthermore, null model analyses revealed less co-occurrence than expected by chance and also convergence in the body size ratio of co-occurring oribatids, which is consistent with species sorting. Geographical distances influenced species composition, indicating that the community is also assembled by dispersal, e.g. mass effect. When all the results are linked together, they demonstrate that local environmental factors are important in structuring the soil community assembly, but are accompanied with effects of dispersal that may “override” the visible effect of the local environment.
Gerald M. Schneeweiss - One of the best experts on this subject based on the ideXlab platform.
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An explicit test of Pleistocene survival in peripheral versus nunatak refugia in two high mountain plant species
Molecular ecology, 2019Co-Authors: Da Pan, Karl Hülber, Wolfgang Willner, Gerald M. SchneeweissAbstract:Pleistocene climate fluctuations had profound influence on the biogeographical history of many biota. As large areas in high mountain ranges were covered by glaciers, biota were forced either to peripheral refugia (and possibly beyond to lowland refugia) or to interior refugia (Nunataks). However, nunatak survival remains controversial as it relies solely on correlative genetic evidence. Here, we test hypotheses of glacial survival using two high alpine plant species (the insect-pollinated Pedicularis asplenifolia and wind-pollinated Carex fuliginosa) in the European Alps. Employing the iDDC (integrative Distributional, Demographic and Coalescent) approach, which couples species distribution modelling, spatial and temporal demographic simulation and Approximate Bayesian Computation, we explicitly test three hypotheses of glacial survival: (a) peripheral survival only, (b) nunatak survival only and (c) peripheral plus nunatak survival. In P. asplenifolia the peripheral plus nunatak survival hypothesis was supported by Bayes factors (BF> 100), whereas in C. fuliginosa the peripheral survival only hypothesis, although best supported, could not be unambiguously distinguished from the peripheral plus nunatak survival hypothesis (BF = 5.58). These results are consistent with current habitat preferences (P. asplenifolia extends to higher elevations) and the potential for genetic swamping (i.e., replacement of local genotypes via hybridization with immigrating genotypes [expected to be higher in the wind-pollinated C. fuliginosa]). Although the persistence of plants on Nunataks during glacial periods has been debated and studied over decades, this is one of the first studies to explicitly test the hypothesis instead of solely using correlative evidence.
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A re-appraisal of nunatak survival in arctic-alpine phylogeography.
Molecular ecology, 2011Co-Authors: Gerald M. Schneeweiss, Peter SchönswetterAbstract:A long standing and at times fervid debate in biogeography revolves around the question whether arctic and high alpine organisms survived Pleistocene ice ages on small island-like areas protruding above the ice-sheet, so-called Nunataks, or whether they did so in peripheral nonglaciated refugial areas. A common picture emerging from a plethora of molecular phylogeographic studies in the last decade is that both in the Arctic and in temperate mountain ranges such as the European Alps nunatak survival needs to be only rarely invoked to explain observed genetic patterns (for a rare example see Stehlik et al. 2002). As two studies in this issue show, depreciation of the nunatak hypothesis is, however, not warranted. In this issue of Molecular Ecology Westergaard et al. (2011) investigate genetic patterns of two arctic-alpine plant species distributed on both sides of the Atlantic exclusively in areas that were mostly covered by ice-sheets during Pleistocene glacial advances. In both species, amplified fragment length polymorphism (AFLP) data identified divergent and partly genetically diverse groups east and west of the Atlantic. This suggests, for the first time in Arctic plants, in situ survival on Nunataks. In an entirely different geographic setting and on a different geographic scale, Lohse et al. (2011, this issue) study the colonization of high alpine areas in the Orobian Alps, situated within and adjacent to a prominent peripheral refugial area (massif de refuge) in the Southern Alps of northern Italy, by dispersal-limited carabid ground beetles. Using explicit hypothesis testing and inference of ancestral locations in a Bayesian framework, stepwise colonization from two separate southern refugia is found to shape the genetic pattern of these beetles, but at the northern edge, populations survived at least parts of the last glaciation in situ on Nunataks.
Maria Ingimarsdottir - One of the best experts on this subject based on the ideXlab platform.
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Corridor or drift fence? The role of medial moraines for fly dispersal over glacier
Polar Biology, 2013Co-Authors: Maria Ingimarsdottir, Jörgen Ripa, Katarina HedlundAbstract:Corridors are often considered to promote dispersal between habitat patches. In this paper, we study whether or not corridors induce colonisation of Nunataks (ice-free areas in glacier surroundings) by promoting dispersal from lowland to the Nunataks. On outlet glaciers, debris originating from Nunataks forms the so-called medial moraines that stretch from the Nunataks down-glacier to the lowland, forming corridors of debris on the glacier. Aerial dispersal was determined with yellow sticky traps on the moraines, bare glacier and glacier foreland. Dipterans were sampled in pitfall traps on the Nunataks. Flying insects that were present on the vegetated glacier foreland belonged to five orders, that is, Diptera, Hemiptera, Hymenoptera, Lepidoptera and Trichoptera. On the glacier and medial moraines, however, mainly dipterans were present, with the majority of individuals found on the moraines. Hoverflies (Syrphidae) were abundant on the moraines and on the edges of Nunataks close to the moraines, but were not present on the vegetated foreland. The origin of the hoverflies is thus not the Nunataks and not the lowland. Rather, they are brought in by air currents towards the glacier, where they aggregate on a land type where they have a chance of survival, although it is not habitable. Thus, we conclude that the medial moraines do not function as regular corridors but as drift fences that direct the dispersal towards the adjacent land types, that is, the Nunataks and the glacier foreland.
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Food web assembly in isolated habitats: A study from recently emerged Nunataks, Iceland
Basic and Applied Ecology, 2013Co-Authors: Maria Ingimarsdottir, Jörgen Ripa, Ólöf Birna Magnúsdóttir, Katarina HedlundAbstract:Allochthonous arthropods can sustain a local food web on seemingly barren land, but are nevertheless often neglected in studies of community assembly. In the present study, we investigated primary food web assembly on Nunataks (ice-free areas) in a retreating glacier in Iceland. Nunataks enable studies that take into account both the temporal factor of the assembly and the influx of allochthonous organisms. Arthropods were collected on sites of different age on five Nunataks younger than 70 years, as well as the youngest parts of one old nunatak. The youngest sites had no vegetation and were dominated by detritivores and predators along with allochthonous arthropods. The arthropod biomass, that was considered established, increased with vegetation cover and site age but also differed among Nunataks. To investigate whether or not the assembly of arthropods was consistent with the predictions of assembly rules, we tested whether, (1) the proportion of each trophic level changed non-randomly, (2) predator-prey ratio remained constant, and (3) larger species replaced smaller ones. We could only verify that proportions of trophic levels changed non-randomly. As assembly rules only apply for established organisms, it is possible that difficulties in determining whether e. g. generalist predators were established or not may affect the outcome of analyses of assembly rules. It is thus important to be aware that unintentional inclusion of allochthonous arthropods in models of community assembly may affect whether or not the community can be explained and predicted by assembly rules. (Less)
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primary assembly of soil communities disentangling the effect of dispersal and local environment
Oecologia, 2012Co-Authors: Maria Ingimarsdottir, Jörgen Ripa, Ólöf Birna Magnúsdóttir, Tancredi Caruso, Massimo Migliorini, Katarina HedlundAbstract:It has long been recognised that dispersal abilities and environmental factors are important in shaping invertebrate communities, but their relative importance for primary soil community assembly has not yet been disentangled. By studying soil communities along chronosequences on four recently emerged Nunataks (ice-free land in glacial areas) in Iceland, we replicated environmental conditions spatially at various geographical distances. This allowed us to determine the underlying factors of primary community assembly with the help of metacommunity theories that predict different levels of dispersal constraints and effects of the local environment. Comparing community assembly of the Nunataks with that of non-isolated deglaciated areas indicated that isolation of a few kilometres did not affect the colonisation of the soil invertebrates. When accounting for effects of geographical distances, soil age and plant richness explained a significant part of the variance observed in the distribution of the oribatid mites and collembola communities, respectively. Furthermore, null model analyses revealed less co-occurrence than expected by chance and also convergence in the body size ratio of co-occurring oribatids, which is consistent with species sorting. Geographical distances influenced species composition, indicating that the community is also assembled by dispersal, e.g. mass effect. When all the results are linked together, they demonstrate that local environmental factors are important in structuring the soil community assembly, but are accompanied with effects of dispersal that may “override” the visible effect of the local environment.
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Community and food web assembly on virgin habitat islands - The nunatak saga
2012Co-Authors: Maria IngimarsdottirAbstract:The classical view of primary community assembly is that colonisation by plants is essential before invertebrates can establish. It has been recognised, however, that invertebrates can establish before plants, and that they may be important in the first steps of community assembly. Plant succession is well studied but assembly of invertebrates and how their dispersal abilities affect the community assembly has, so far, gained less attention. The thesis adresses the questions: Does isolation decrease the rate of community assembly? Do invertebrates use corridors to direct their dispersal? What are the food resources of predators on new land? Is the assembly of communities more controlled by dispersal or the environment? Communities were studied along chronosequences on recently emerged Nunataks (ice-free land in glacial areas) in Iceland. Each nunatak has a community assembly that starts with long distance dispersal from other terrestrial environments. This allowed a study on both local community and food web assembly, and on the effect of geographical isolation on this process. To determine ways of dispersal, invertebrates were collected on the glacier, lowland and on medial moraines. Medial moraines form corridors of debris on the glacier that stretch from the Nunataks to the lowland. They directed the dispersal of flies that were moving over the glacier, to the Nunataks and down to the lowland. When the rate of the community assembly on the Nunataks was compared with that of non-isolated areas, no difference was observed. This indicates that isolation is not restricting the rate of community assembly, at least not of the first colonisers. Environmental gradients thus have a strong effect on the assembly of communities, compared to dispersal constraints. However, dispersal may restrict the colonisation of larger invertebrates, which are not as widespread on the Nunataks. The first colonisers are small invertebrate predators and detritivores and when plants start to establish, more trophic groups can be added to the food webs, like herbivores and their predators. More invertebrates arrived at the Nunataks than established and these may make up an important part of the food web, especially where primary productivity is lacking. By using the technique of stable isotopes, it was shown that early colonising predators feed on prey that is of a geographically distant origin. Perhaps, some of the predators are of a distant origin themselves. This thesis shows that dispersal abilities of many invertebrates is large and isolated areas are therefore not always as isolated as we may think.
Jeanne Bodin - One of the best experts on this subject based on the ideXlab platform.
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one century of vegetation change on isla persa a nunatak in the bernina massif in the swiss alps
Journal of Vegetation Science, 2008Co-Authors: Pascal Vittoz, Jeanne Bodin, Stefan Ungricht, Conradin A Burga, Gianreto WaltherAbstract:Abstract Question: How did the vascular plant species composition of a nunatak in the alpine vegetation belt change over a time span of 100 years? Location: A 5.6-ha nunatak, Isla Persa in the Swiss Alps, that remained ice-free during the last maximum glacier advance in the 1850s and is today partly covered with climactic alpine grassland and dwarf heath shrubs. Methods: Floristic inventories in 1906, 1927, 1972, 1995, 2003 and 2004 and a comparative analysis of the species composition over the period 1906–2004. Results: 31 species that were not recorded in the first inventory were found in the following surveys. However, among them only six were common by 2004. Generally, the new species prefer warmer conditions than those previously present and most newcomers are associated with montane or sub-alpine grasslands and woodlands. In particular, the observed increase of Vaccinium myrtillus and the arrival of shrub and tree species further substantiate a trend towards vegetation composition of the lower altit...
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One century of vegetation change on Isla Persa, a nunatak in the Bernina massif in the Swiss Alps
Journal of Vegetation Science, 2007Co-Authors: Pascal Vittoz, Jeanne Bodin, Stefan Ungricht, Conradin A Burga, Gianreto WaltherAbstract:Question: How did the vascular plant species composition of a nunatak in the alpine vegetation belt change over a time span of one century? Location: A 0.056-km2 nunatak, Isla Persa in the Swiss Alps, that remained ice free during the last maximum glacier advance in the 1850s and is today partly covered with climactic alpine grassland and dwarf heath shrubs. Methods: Floristic inventories in 1906, 1927, 1972, 1995, 2003 and 2004 and a comparative analysis of the species composition over the period 1906–2004. Results: Thirty-one species that were not recorded in the first inventory were found in the following surveys. However, among them only six were common by 2004. On average, the new species prefer warmer conditions than those previously present and most newcomers are associated with montane or subalpine grasslands and woodlands. In particular, the observed increase of Vaccinium myrtillus and the arrival of shrub and tree species further substantiate a trend towards vegetation composition of the lower altitudinal belt. Ferns represented 24% of the newcomers, probably due to the high dispersal ability of their lightweight spores. The observed species enrichment was globally small compared to previously inventoried summits. Conclusion: Floristic change strongly suggests warmer climatic conditions as the main factor contributing to species compositional change. The relative stability of species richness may be explained by several factors: the isolation of the nunatak and the difficulties for plants to reach the site, the colder local climate, a limited available species pool and interactions of established alpine plants with newly immigrating taxa. Supplementary data collected at about the same altitude would be necessary to better understand the influence of climate change on alpine grasslands.
