Spatial and temporal circumstances affecting the population growth of beavers

Understanding the spreading patterns of an invading or expanding species is necessary for ecological theory and conservation. The return of the Eurasian beaver throughout Europe is considered one of the biggest conservation success stories. In general, the process of the spreading beaver population has been described in detail, however several aspects regarding the principles of colonisation have not been mentioned. We propose that the process of colonisation should follow Skellam's model for the case of first occupation by a pioneer beaver during the establishment of population growth.We retrospectively reconstructed the continuous colonisation of Eurasian beavers in six catchments in Western Bohemia in the Czech Republic. The extracted data from published resources were analysed to reveal (in detail) the progress of the colonisation front, in addition to considering current population densities in the catchments. All of the catchments were settled from one possible source, but were reached by pioneer beavers regardless of the distance or the considered source of the spread. However, an increased distance from the source of spread delayed the start of rapid population growth. The barrier effect among the divides of the watershed was not substantial because beavers regularly crossed the divides. The progress of the colonisation front followed Skellam's diffusion model as densities spread from sites with higher values into areas with lower values. The model did not, however, accurately predict the pattern of the first pioneer occupancy.