Top-down and bottom-up effects in a Fennoscandian tundra community
The objective of this thesis was to investigate the effects of mammalian grazers, such as microtine rodents and reindeer, (top-down effects) and nutrient availability (bottom- up effects) on the plant community of a tundra heath. I conducted a large-scale fertilization experiment and studied the imp...
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Umeå universitet, Institutionen för ekologi, miljö och geovetenskap
2001
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ftumeauniv:oai:DiVA.org:umu-96883 2023-10-09T21:51:28+02:00 Top-down and bottom-up effects in a Fennoscandian tundra community Grellmann, Doris 2001 application/pdf http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-96883 eng eng Umeå universitet, Institutionen för ekologi, miljö och geovetenskap Umeå : Umeå Universitet http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-96883 urn:isbn:91-7305-032-6 info:eu-repo/semantics/openAccess consumer-resource interactions exclosures food web dynamics grey-sided voles lemmings NPK-fertilization plant defences reindeer soil microbes vertebrate grazing Ecology Ekologi Earth and Related Environmental Sciences Geovetenskap och miljövetenskap Doctoral thesis, comprehensive summary info:eu-repo/semantics/doctoralThesis text 2001 ftumeauniv 2023-09-22T13:48:15Z The objective of this thesis was to investigate the effects of mammalian grazers, such as microtine rodents and reindeer, (top-down effects) and nutrient availability (bottom- up effects) on the plant community of a tundra heath. I conducted a large-scale fertilization experiment and studied the impact of grazers using exclosures. I measured the effects of fertilization and grazing on soil microbial activity and nutrient cycling. I investigated the responses to fertilization of the invertebrate community, I studied the effects on the quality of bilberry as food for mammalian herbivores, and I looked at how concentrations of nutrients and carbon-based secondary defences against herbivory fluctuated between seasons in unfertilized and fertilized treatments. The results of my thesis show that the plant community investigated is exposed to a strong top-down control by mammalian herbivores. On the fertilized and grazed areas the aboveground biomass of the vascular plant community did not increase compared to unfertilized areas. However, the productivity of the plant community was clearly nutrient- limited. During the eight years of the experiment, on the fertilized areas plant biomass was significantly increased inside the herbivore exclosures In my study mammalian herbivores at comparatively low densities and grazing outside the growing season were sufficient to control the biomass of a heterogeneous plant community. Microtine rodents (Norwegian lemmings and grey-sided voles) preferred the fertilized areas for overwintering. The food plant quality of bilberry for grey-sided voles was improved on the fertilized areas throughout the year. Grazing decreased the nitrogen storage in the aboveground plant biomass. Reindeer and rodents had also important indirect effects on the plant community by decelerating soil nutrient cycling and soil microbial activity. This effect may be accelerated by the impact of herbivore on plant species composition. Graminoids, which contained the highest nitrogen concentrations in their ... Doctoral or Postdoctoral Thesis Fennoscandian Tundra Umeå University: Publications (DiVA) |
institution |
Open Polar |
collection |
Umeå University: Publications (DiVA) |
op_collection_id |
ftumeauniv |
language |
English |
topic |
consumer-resource interactions exclosures food web dynamics grey-sided voles lemmings NPK-fertilization plant defences reindeer soil microbes vertebrate grazing Ecology Ekologi Earth and Related Environmental Sciences Geovetenskap och miljövetenskap |
spellingShingle |
consumer-resource interactions exclosures food web dynamics grey-sided voles lemmings NPK-fertilization plant defences reindeer soil microbes vertebrate grazing Ecology Ekologi Earth and Related Environmental Sciences Geovetenskap och miljövetenskap Grellmann, Doris Top-down and bottom-up effects in a Fennoscandian tundra community |
topic_facet |
consumer-resource interactions exclosures food web dynamics grey-sided voles lemmings NPK-fertilization plant defences reindeer soil microbes vertebrate grazing Ecology Ekologi Earth and Related Environmental Sciences Geovetenskap och miljövetenskap |
description |
The objective of this thesis was to investigate the effects of mammalian grazers, such as microtine rodents and reindeer, (top-down effects) and nutrient availability (bottom- up effects) on the plant community of a tundra heath. I conducted a large-scale fertilization experiment and studied the impact of grazers using exclosures. I measured the effects of fertilization and grazing on soil microbial activity and nutrient cycling. I investigated the responses to fertilization of the invertebrate community, I studied the effects on the quality of bilberry as food for mammalian herbivores, and I looked at how concentrations of nutrients and carbon-based secondary defences against herbivory fluctuated between seasons in unfertilized and fertilized treatments. The results of my thesis show that the plant community investigated is exposed to a strong top-down control by mammalian herbivores. On the fertilized and grazed areas the aboveground biomass of the vascular plant community did not increase compared to unfertilized areas. However, the productivity of the plant community was clearly nutrient- limited. During the eight years of the experiment, on the fertilized areas plant biomass was significantly increased inside the herbivore exclosures In my study mammalian herbivores at comparatively low densities and grazing outside the growing season were sufficient to control the biomass of a heterogeneous plant community. Microtine rodents (Norwegian lemmings and grey-sided voles) preferred the fertilized areas for overwintering. The food plant quality of bilberry for grey-sided voles was improved on the fertilized areas throughout the year. Grazing decreased the nitrogen storage in the aboveground plant biomass. Reindeer and rodents had also important indirect effects on the plant community by decelerating soil nutrient cycling and soil microbial activity. This effect may be accelerated by the impact of herbivore on plant species composition. Graminoids, which contained the highest nitrogen concentrations in their ... |
format |
Doctoral or Postdoctoral Thesis |
author |
Grellmann, Doris |
author_facet |
Grellmann, Doris |
author_sort |
Grellmann, Doris |
title |
Top-down and bottom-up effects in a Fennoscandian tundra community |
title_short |
Top-down and bottom-up effects in a Fennoscandian tundra community |
title_full |
Top-down and bottom-up effects in a Fennoscandian tundra community |
title_fullStr |
Top-down and bottom-up effects in a Fennoscandian tundra community |
title_full_unstemmed |
Top-down and bottom-up effects in a Fennoscandian tundra community |
title_sort |
top-down and bottom-up effects in a fennoscandian tundra community |
publisher |
Umeå universitet, Institutionen för ekologi, miljö och geovetenskap |
publishDate |
2001 |
url |
http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-96883 |
genre |
Fennoscandian Tundra |
genre_facet |
Fennoscandian Tundra |
op_relation |
http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-96883 urn:isbn:91-7305-032-6 |
op_rights |
info:eu-repo/semantics/openAccess |
_version_ |
1779314577448632320 |