Community and food web assembly on virgin habitat islands - The nunatak saga
Author
Summary, in English
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.
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.
Department/s
Publishing year
2012
Language
English
Document type
Dissertation
Publisher
Department of Biology, Lund University
Topic
- Ecology
Keywords
- allochthonous material
- arthropods
- community assembly
- corridor
- dispersal
- Iceland
- metacommunity
- nunataks
- primary succession
- stable isotopes.
Status
Published
Research group
- Soil Ecology
Supervisor
- Katarina Hedlund
- Jörgen Ripa
- Starri Heiðmarsson
ISBN/ISSN/Other
- ISBN: 978-91-7473-275-7
Defence date
30 March 2012
Defence time
09:30
Defence place
Blå hallen, Ecology building, Sölvegatan 37, Lund
Opponent
- Peter de Ruiter