The research group Theoretical Ecology constitutes the theoretical counterpart of the research group Population Biology, with which it forms a coherent research unit. The main focus of the Theoretical Ecology is the modeling of biological systems, in particular biological populations and communities.

Mathematical models form an important tool to extrapolate the consequences of individual traits and aspects of individual life history to the dynamics of populations and communities. These model predictions reveal how mechanisms and interactions at the level of the individual organism translate into emergent phenomena at the population level. The predictions can subsequently be tested by comparison with data on population changes in actual populations in natural or manipulated (or otherwise disturbed) situations. In this way it is possible to assess to what extent processes generated by individuals explain the observed population dynamics.

Typically, populations exhibit structures of various kinds, either physiological (developmental phase, age, size, feeding state), spatial, genetic or social. These structures may influence the interactions between individuals within the same population/species (intraspecific competition, mating, cannibalism) or from other populations/species (interspecific competition, predation). A key research question addressed by the Theoretical Ecology group is how a particular type of population structure emerges as a consequence of individual life history and individual interactions and in turn how this population structure affects dynamics and processes at the individual level.

In its studies the research group focuses on physiological population structure, in particular population size structure, as well as on spatial or social population structure. Research mostly, but not exclusively, focuses on two different types of systems, both involving simple networks of interactions between different species in a food web:

1. freshwater fish in Scandinavian lakes are studied to develop theory on the role of size-structured interactions (size-dependent foraging, ontogenetic diet and habitat shifts, juvenile bottlenecks, cannibalism, dominance reversals) for population and community dynamics
2. pathogens of humans, cattle and arthropods are looked at in order to gain insight into evolutionary dynamics and the impact of spatial and social structure (parasite-induced host behaviour, multiple infection, virulence, kinship).

These systems differ in experimental accessibility, spatial scale and time scale of the dynamical processes, both offering different possibilities for studying the role of population structure.

The research projects have practical implications for strategies for prudent population exploitation (wildlife and fishery management) as well as strategies to counter the emergence of new diseases and evolutionary changes in disease severity (epidemiology and virulence management).