Petri Nummi works as a university lecturer at the University of Helsinki in the Department of Forest Sciences. Beaver and its effects on other wildlife was the starting point of his research. During recent times, the theme has widened, and now many ecosystem and biodiversity aspects are studied in the beaver engineering framework. His other main study theme is duck population dynamics. He has been collecting long-term data on duck populations, their breeding success and food resources in Evo, southern Finland for 30 years.