Aim Using six free-living deer species in Great Britain as a case study, we studied biogeographical relationships of ecologically related species composed of both native and introduced species.
Location Great Britain.
Methods We modelled the environmental favourability for the deer species using variables related with spatial location, climate, topography, human disturbances and habitat structure. Favourability values of each pair of native (naturalized)-introduced species were used to estimate the fuzzy overlap index (FOvI) as a measure of overall similarity between the environmental requirements for the species in Great Britain. The absolute local overlap values (FOvI-L) were also used to measure the degree to which a given location was favourable simultaneously for each pair of species. We assessed the trends of species favourability across a range defined by the absolute local overlap values and studied the shape of the obtained curves since they informs us about the favourability balance between the studied species.
Results Muntjac and Chinese water deer attained higher favourability values than native species in localities with intermediate values of FOvI-L (a reduced number in the study area), suggesting that if competitive relationships were established in these localities the introduced deer species may have some advantages over natives. Sika deer only achieved higher values than fallow deer in those localities clearly unfavourable for the naturalized species. Our analyses predicted that fallow deer will be less affected by the introduced deer species than native species.
Main conclusions We developed an approach based on the favourability function to describe biogeographical relationships between species, natives and introduced and to assess from a biogeographical perspective if introduced species could pose a competitive risk to natives. Although the results of present analyses do not conclusively demonstrate competitive exclusion, they provide directional hypotheses that can be tested in experimental field and laboratory studies.