National and landscape parks and reserves on the boundaries between Poland, Ukraine and Slowakia in Eastern Carpathians create favourable conditions for naturalisation based, amongst others, on active protection. Increasing biodiversity is one of the forms of this process. Introduction of a suitable biotic factor triggers natural processes supporting naturalisation. The European beaver originally living in northeast Poland is such a factor in the Bieszczady Mts. The author deals with reasons for this action, describes the inhabitation and behaviour of the beaver in the new environment.
Pathomorphological Changesin the Small Intestine and Liver of the European Beaver (Castor fiber L. 1758): a case study.The aim of thestudy was to examine and describe the morphology and patomorphology of small intestine and liver of European beaver (Castor fiber). In natural environment beavers are in constant contact with various both internal and external parasites. Histological analysis revealed the pathological changes within the digestive track and liver indicating long-term inflammation. It was hypothesized that the observed inflammation was caused by the parasites not related to beavers so far.