Indirect effects of rodents on arthropods in a Scandinavian boreal forest

Abstract

Rodents in boreal forest are an important component of food webs. Their role as drivers of the boreal forest ecosystem is debated. As herbivores they affect plant communities and alter qualities of plants. Consequently availability of food resources for other herbivorous species is altered. In my thesis I studied whether rodents indirectly influence communities of arthropods via plant resources. It is assumed that phytophagous arthropods respond to changes in plant resources by different feeding behaviour that further affects higher trophic levels including predators and parasites. I swept the arthropods in 96 plots at six localities in a boreal forest in Eastern Norway with different rodent densities in the months of June and August in 2014. I assessed abundance of arthropod orders and biomass of arthropod feeding guilds in relation to observed rodent populations. I found rodents were important for arthropod communities in the month of June, but not in August. All feeding guilds and orders Diptera and Collembola were correlated negatively, while orders Hemiptera, Thysanoptera and Opiliones were correlated positively with rodent density. I assume the relations I found are not necessarily the result of indirect interactions only, but potentially also of direct predation of rodents on arthropods, or the combination of both direct and indirect interactions. The influence of rodents seems to depend on vegetation type creating differently functioning systems. In addition, I briefly discuss the effects of environmental and habitat factors which were used to explain variance in the arthropods living in different conditions.