Sharing space with a larger relative : examining interspecific effects of fallow deer on roe deer performance

Sammanfattning: Interspecific competition of some form is a part of life for most species across the world. For some species it can be part of their evolutionary history over many thousands of years, while for others it is a more recent experience, as is the case of roe deer (Capreolus capreolus) and fallow deer (Dama dama), in Scandinavia. In Sweden the number of fallow deer have shown a strong increase in the last 30 years, bringing more attention to the potential competition between the two related species. This study aimed to compare two areas, Bogesund and Koberg, which have contrasting densities of fallow deer, and to examine if indices of roe deer fitness differ between the two. Bogesund having no resident fallow deer and being an area with much prior research on roe deer. Koberg being an area divided into two by a wildlife fenced road and housing contrasting densities of fallow deer after a deliberate reduction of the population in one of the areas (north) while keeping it more constant in the other (south). This creates a good opportunity for comparative studies between high and low fallow deer density populations. The data used came primarily from hunting statistics at the two study areas, starting in the same year (2006). Physiological indices believed to be relevant and related to fitness were used to examine potential signs of reduced fitness in the roe deer population. The indices were fawn body mass, female ovulation rate and male antler length. The results showed a clear effect of study area in the expected direction, in three out of four possible model selection procedures, namely a potentially negative effect of high fallow deer density on roe deer in two of the investigated fitness traits (fawn body mass and ovulation rate). However, the pattern was reversed when regarding the antler length between study areas (Koberg and Bogesund). But this trait differed between the two contrasting (high/south vs low/north) areas in Koberg, where male antler length was greater in the area with low fallow deer density. The unexpected and reversed result between Koberg and Bogesund antler length is discussed in terms of genetics, non-random sampling and effects of supplemental winter feeding during the time when antlers are growing and still in velvet. This study suggests that there is an interspecific competition relationship between the two deer species and that this could have a negative impact on roe deer fitness, with possible management implication in areas where both species occur. Overall, I believe further studies are required to be able to gain better insight into the field of deer management but that this study functions to illustrate the interspecific competitive relationship between roe deer and fallow deer.