A main recurrent theme of Atle Mysterud's research is foraging ecology, life history and population ecology of large mammals, in particular ungulates. Mysterud is interested in how foraging ecology affect life history, and the feedback of life history back on foraging ecology. More recent specific themes are linked to partial migration of deer, and how human harvesting affects populations both directly through mortality, but also by changing behavioural ecology of rut indirectly affecting demography and by selective harvesting specifically removing particular phenotypes. He has worked extensively with climate effects on ecosystems. Another major effort has been to run large scale experiments to study the whole suit of large herbivore grazing effects on ecosystems; from soil processes, plants, invertebrates, birds, small mammals and how changes in plant communities feedback on the herbivores. In recent years, Mysterud is focusing on ticks and tick-borne diseases, in particular Lyme disease. Initially, focus was on linking deer migration to ticks. Now, he is interested in how incidence of disease is dependent on the vertebrate host community, land use and climate.