Abstract
Distribution patterns of species are affected by resource availability, dispersal, disturbance and population dynamics. The smaller population size and range of the native Eurasian beaver (Castor fiber) compared to the non-native North American beaver (Castor canadensis) in Finland raise questions on reasons for the slower range expansion of the native species. We compared the population growth rates and the spread of both species from their release sites. We also studied the factors possibly affecting the spread of the Eurasian beaver in South western Finland in more detail. We found that the North American beaver has spread longer distances than the Eurasian beaver, but we did not find evidence for movement barriers constraining the expansion rate of the native species. Lack of high-quality habitats does not seem to constrain the expansion to nearby areas either. Despite this, the Eurasian beaver population has grown to a high density close to its reintroduction site, and it has started to spread to novel areas only recently. We conclude that the expansion of the native beaver in Finland seems to be controlled by factors other than those related to barriers for movement: movement behavior and population dynamics, which require further investigation.
Highlights
Distribution patterns of species are largely affected by resource availability, dispersal, disturbance and population dynamics (Guisan and Thuiller 2005)
The distance which the beavers spread per year from the release site to the furthest observation point, i.e. the maximum spread rate, was on average 2.8 km per year along shoreline for the Eurasian beaver, and 6.9 km per year for the North American beaver
The sizes of the main drainage basins within the whole range did not differ between the North American beaver and the Eurasian beaver
Summary
Distribution patterns of species are largely affected by resource availability, dispersal, disturbance and population dynamics (Guisan and Thuiller 2005). Natural and anthropogenic barriers, e.g. mountains, large water bodies, dams and roads, may prevent dispersal (Shephard et al 2008; Hapeman et al 2011; Bracken et al 2015; Machado et al 2018). Natural Resources Institute Finland Luke, Itäinen Pitkäkatu 4 A, 20520 Turku, Finland location of the introduction site and the size of the founder population largely determine the present distribution and population size (Stephens and Sutherland 1999). In newly formed populations, the rate of spread may decrease due to problems related to a small population size, such as difficulty in finding mates at low densities (Allee 1931; Stephens and Sutherland 1999). Populations can become clumped due to an aggregation of resources and high-quality habitats or due to conspecific attraction (Stephens and Sutherland 1999)
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