Demographic crash associated with high parasite load in an experimental roe deer (Capreolus capreolus) population

Abstract

In March 2002, ten roe deer (Capreolus capreolus) were released in a partly wooded 14.2-ha enclosure to investigate the effect of high population density on vegetation cover and demographic parameters. However, in mid 2003, five animals died after rapid emaciation. Two other deer were killed to carry out further post-mortem examination. In addition to a general loss of body mass and injuries in males caused by the healthiest of them, we found a high level of parasitism. The remaining animals received anti-parasite treatment, and four other treated roe deer were added into the enclosure. All the deer were then captured and treated against parasites twice a year, the fawns being removed when first captured. Four years after the crash, the population seemed healthy: deaths no longer occurred; mean adult body mass reached 27.6 kg in March; females produced on average 1.6 fawns per year, with a mean body mass of 13.8 kg in October and 16.7 kg in March. Furthermore, undergrowth cover changed little since March 2004. These results suggest that outbursts of parasites may cause population crashes in high-density situations before the onset of nutritive stress and may explain certain cases of ‘abnormal’ (massive) mortality recorded in roe deer.