Changes in the composition of herbivore communities, regarding the identity of the herbivores and their relative abundance can influence the functioning of tundra ecosystems, so management of these natural rangelands needs to consider the combined effects of different herbivores. Iceland represents a unique situation with no native large mammalian herbivores but extensive grazing by domestic and introduced mammals (sheep and reindeer), ptarmigan and increasing populations of migratory avian herbivores (geese). WP3 will assess the effects of herbivore diversity on Icelandic ecosystems (WP3a) and model changes in herbivore diversity across Iceland to guide management of these rangelands (WP3b).
WP3a. Assessing the effects of herbivore diversity on Icelandic ecosystems
The first step in WP3a will be to map vertebrate herbivore diversity across Iceland. Abundance data of different herbivore species will be combined by calculating the herbivores’ metabolic biomass, an index that includes the animal’s body weight and its energy requirements. The metabolic biomass allows comparisons across species and provides a more meaningful measure of the grazing pressure of the whole herbivore assemblage from an ecosystem functioning perspective, as it takes into account the relative abundance of different species. Once herbivore diversity and abundance (as approximated by the herbivore metabolic biomass) have been mapped across Iceland, we will select field sites with contrasting grazing pressure to measure different ecosystem processes.
WP3a lead: Isabel C Barrio
WP3b. Quantifying changes in herbivore diversity across Iceland
Herbivore communities are likely to change over time, due to environmental changes or changes in management. For example, the numbers of migratory geese have greatly increased in Iceland during the last decades due to changes in the availability of food in their wintering areas. These changes in the composition of herbivore assemblages and the relative change in grazing pressure by different herbivore groups will determine the impacts they have on ecosystems, but the consequences of these widespread changes in herbivore communities for regional management remain to be explored. For example, what are the ecological implications of shifting from a sheep- to a sheep-goose-dominated system in Iceland?
WP3b lead: James Speed