Biotic interactions between species determine an ecosystem’s structure and function. These interactions may result from the direct impact of one species on another, or indirect effects on a third species mediated by interactions between two other species. The direction of these interactions that often regulate biological communities may be described by top-down (the impact of a trophic level on a lower trophic level) or bottom-up (the impact of a trophic level on a higher trophic level). Changes in the direction of these regulations or changes in a species’ density (e.g. a change in prey density causing a change in prey consumption as described by a functional response function) partly contribute to ecosystem dynamics. For instance, the boreal ecosystem is dynamic with conspicuous cycles in its standing biomass. The most obvious biomass cycles in this system in Fennoscandia is observed in the regular 3-4 year cycles of vole populations. Voles are therefore often attributed a driving force governing the dynamics of the boreal forest ecosystem. And indeed; voles are likely to have profound effects on the boreal ecosystem. This research project aims to give insight into the mechanisms shaping the dynamics of the ecological community in the boreal forest.
Background and approach
In this research project, Hedmark University College is building a highly prestigious scientific network by linking Scandinavian ecological environments with the distinguished Canadian group working on the boreal forest ecosystem of Kluane National Park, one of the most well-studied ecosystems in North America. This network is the foundation for the present project where we will study the role of vole multiannual population cycles on the boreal forest ecosystem dynamics. We will manipulate vole cycles in large scale natural experimental plots (16 km2). Treatment groups will consist of 3 levels: (1) low non-cyclic vole densities; (2) high non-cyclic vole densities; and (3) controls, where vole populations are expected to fluctuate naturally. This is the first time a dynamic phenomenon such as vole cycles is manipulated at such a large spatial scale. The large scale manipulation gives a unique opportunity to resolve questions related to a natural food web at the landscape level, including the response of wide-ranging predators such as mustelids, fox and owls. Our approach will resolve how the conspicuous vole cycles may be a driver of the boreal forest ecosystem dynamics and whether temporal heterogeneity enhances species diversity similar to how spatial heterogeneity does. This project will also improve our understanding of how the Fennoscandian boreal forest ecosystem will react towards changes in vole cyclicity. Cyclicity is expected to diminish through global warming, but the consequences of this dampening of vole cycles for the economically and ecologically important boreal forest ecosystem are unknown. The proposed project assembles a scientific network expected to reveal why the Fennoscandian and North American boreal forest ecosystem dynamics are so different. We will use ecosystem models, such as the Ecopath trophic mass-balance modelling framework, to compare the dynamics of these two continents’ boreal forests. Because we are manipulating ecosystem dynamics at broad scales and comparing these dynamics on different continents, our research will provide a base for a broader and more predictive evidence-based management. The project will also contribute to general questions in ecology - including what factors contribute to variation in community structure and function and their cascading effects on natural systems.
The overall aim of the present project is to give insight into the mechanisms shaping the dynamics of the ecological community in the boreal forest. More precisely, we aim to:
- Assess whether vole population cycles are a major driver of the boreal forest ecosystem. In particular we will study whether vole dynamics lead to alternative ecosystem (a) structures (food webs, species richness and diversity); and (b) functions:
- Herbivory and its subsequent effects on nutrient dynamics, and how the vegetation indirectly affects invertebrates, insect predators and large herbivores;
- Numerical and functional responses of specialist and generalist predators;
- Use results from point 1 to model the various food webs and reveal top-down, bottom-up, and indirect cascading effects;
- Explore the differences between the North American and Fennoscandian boreal forest ecosystem dynamics through comparative ecosystem modelling.
Harry P. Andreassen, project leader