Alien vs. Native—Influence of Fallow Deer (Dama dama) Introduction on the Native Roe Deer (Capreolus capreolus) Population

Abstract

Fallow deer is one of the most widespread alien mammals in Europe. We documented the response of the roe deer population shortly after the fallow deer was introduced to a hunting ground in central Poland. Mean roe density dropped from 17.6 ind./100 ha to 10.5 ind./100 ha after the alien species was introduced. In the reference area, where fallow deer was absent, the roe deer density did not change in the analogue study period. At both study sites, mean roe deer productivity before fallow deer introduction was similar (1.6 juv./female). However, in the first study area, the productivity dropped to 1.4, while in the reference study area, it slightly increased to 1.75. The presence of fallow deer influenced roe deer space use negatively, i.e., the number of pellet groups of roe deer decreased with an increase in the number of fallow deer feces. Overall, the introduction of the fallow deer was successful and the population grew quickly. Yet, the economic impact of its introduction was far from satisfactory. At the same time, its negative influence on the roe deer was apparent. This shows that the fallow deer is an alien species threatening local biodiversity.